Someone asked me why their car's front brakes always seem to need
replacing long before the rear brakes do.

I started to give him the old "inertial weight transfer to the front
while braking" reply and then found that it really wasn't making total
sense to me.

Providing you don't drive and brake like a madman neither the front or
rear tires are doing much skidding on the pavement so it's likely all
four are all making the same number of revolutions while braking. So, if
the brake pad areas and the piston diameters were all equal front and
rear I'd expect the pad wear rate to also be equal.

It's been too long since I've done a DIY brake job and I never stopped
to study the relative sizes of drums, shoes, pads and pistons back when
I used to do that stuff on all our family jalopies.

Answers please?

Jeff

--
Jeffry Wisnia
(W1BSV + Brass Rat '57 EE)
The speed of light is 1.8*10^12 furlongs per fortnight.

Jeff Wisnia wrote:

Someone asked me why their car's front brakes always seem to need
replacing long before the rear brakes do.

I started to give him the old "inertial weight transfer to the front
while braking" reply and then found that it really wasn't making total
sense to me.

Providing you don't drive and brake like a madman neither the front or
rear tires are doing much skidding on the pavement so it's likely all
four are all making the same number of revolutions while braking. So, if
the brake pad areas and the piston diameters were all equal front and
rear I'd expect the pad wear rate to also be equal.

It's been too long since I've done a DIY brake job and I never stopped
to study the relative sizes of drums, shoes, pads and pistons back when
I used to do that stuff on all our family jalopies.

The braking system is designed to give the
front brakes more authority than the rear.
The increased pressure and heat causes them
to wear out faster.

And that goes back to the weight transfer
issue. The front brakes get more authority
because they can use it without breaking
traction.

"Jim Stewart" wrote in message
news
Jeff Wisnia wrote:

Someone asked me why their car's front brakes always seem to need
replacing long before the rear brakes do.

I started to give him the old "inertial weight transfer to the front
while braking" reply and then found that it really wasn't making total
sense to me.

Providing you don't drive and brake like a madman neither the front or
rear tires are doing much skidding on the pavement so it's likely all
four are all making the same number of revolutions while braking. So, if
the brake pad areas and the piston diameters were all equal front and
rear I'd expect the pad wear rate to also be equal.

It's been too long since I've done a DIY brake job and I never stopped to
study the relative sizes of drums, shoes, pads and pistons back when I
used to do that stuff on all our family jalopies.

The braking system is designed to give the
front brakes more authority than the rear.
The increased pressure and heat causes them
to wear out faster.

And that goes back to the weight transfer
issue. The front brakes get more authority
because they can use it without breaking
traction.

I seem to remember something called a "proportioning valve", between front
and rear brakes.
--
DT

"DrollTroll" wrote in message
...

"Jim Stewart" wrote in message
news
Jeff Wisnia wrote:

Someone asked me why their car's front brakes always seem to need
replacing long before the rear brakes do.

I started to give him the old "inertial weight transfer to the front
while braking" reply and then found that it really wasn't making total
sense to me.

Providing you don't drive and brake like a madman neither the front or
rear tires are doing much skidding on the pavement so it's likely all
four are all making the same number of revolutions while braking. So, if
the brake pad areas and the piston diameters were all equal front and
rear I'd expect the pad wear rate to also be equal.

It's been too long since I've done a DIY brake job and I never stopped
to study the relative sizes of drums, shoes, pads and pistons back when
I used to do that stuff on all our family jalopies.

The braking system is designed to give the
front brakes more authority than the rear.
The increased pressure and heat causes them
to wear out faster.

And that goes back to the weight transfer
issue. The front brakes get more authority
because they can use it without breaking
traction.

I seem to remember something called a "proportioning valve", between front
and rear brakes.

That's correct and some are adjustable. On those units it is necessary to
balance the system after changing out the master cylinder.


JC

Jeff Wisnia writes:

Someone asked me why their car's front brakes always seem to need
replacing long before the rear brakes do.

I started to give him the old "inertial weight transfer to the front
while braking" reply and then found that it really wasn't making total
sense to me.

Providing you don't drive and brake like a madman neither the front or
rear tires are doing much skidding on the pavement so it's likely all
four are all making the same number of revolutions while braking. So,
if the brake pad areas and the piston diameters were all equal front
and rear I'd expect the pad wear rate to also be equal.

With most cars its even more than just inertial transfer -- there's a
lot more weight on the fronts than the rears *before* you put the
brakes on.

If you the areas, piston diameters, and line pressures were equal
you'd lock up the rears before you were applying full force to the
fronts. The brake proportioning (however the manufacturer goes about
it) really does make the fronts exert more force than the rears.

The corollary I've never been able to figure out is why they don't use
smaller brakes and more pressure in the rear, so they'd all wear out
at the same time (well, as a matter of fact most vehicles I've had
apart have had larger fronts than rears. But not by enough to make up
for the difference in how hard the fronts have to work).

Joe Pfeiffer wrote:

The corollary I've never been able to figure out is why they don't use
smaller brakes and more pressure in the rear, so they'd all wear out
at the same time (well, as a matter of fact most vehicles I've had
apart have had larger fronts than rears. But not by enough to make up
for the difference in how hard the fronts have to work).

My guess is safety.

Joe Pfeiffer wrote:

The corollary I've never been able to figure out is why they don't use
smaller brakes and more pressure in the rear, so they'd all wear out
at the same time (well, as a matter of fact most vehicles I've had
apart have had larger fronts than rears. But not by enough to make up
for the difference in how hard the fronts have to work).


I've replaced the front pads once on my car with 160,000 miles, still waiting for rears to
give it up. Changed front pads at 121,000.

Wes
--
"Additionally as a security officer, I carry a gun to protect
government officials but my life isn't worth protecting at home
in their eyes." Dick Anthony Heller

"Jim Stewart" wrote in message
.. .
Joe Pfeiffer wrote:

The corollary I've never been able to figure out is why they don't use
smaller brakes and more pressure in the rear, so they'd all wear out
at the same time (well, as a matter of fact most vehicles I've had
apart have had larger fronts than rears. But not by enough to make up
for the difference in how hard the fronts have to work).

My guess is safety.

It isn't safety, it's standardisation to lower costs.

JC

"Joe Pfeiffer" wrote in message
...
Jeff Wisnia writes:

Someone asked me why their car's front brakes always seem to need
replacing long before the rear brakes do.

I started to give him the old "inertial weight transfer to the front
while braking" reply and then found that it really wasn't making total
sense to me.

Providing you don't drive and brake like a madman neither the front or
rear tires are doing much skidding on the pavement so it's likely all
four are all making the same number of revolutions while braking. So,
if the brake pad areas and the piston diameters were all equal front
and rear I'd expect the pad wear rate to also be equal.

With most cars its even more than just inertial transfer -- there's a
lot more weight on the fronts than the rears *before* you put the
brakes on.

If you the areas, piston diameters, and line pressures were equal
you'd lock up the rears before you were applying full force to the
fronts. The brake proportioning (however the manufacturer goes about
it) really does make the fronts exert more force than the rears.

The corollary I've never been able to figure out is why they don't use
smaller brakes and more pressure in the rear, so they'd all wear out
at the same time (well, as a matter of fact most vehicles I've had
apart have had larger fronts than rears. But not by enough to make up
for the difference in how hard the fronts have to work).

Why would you want them to all wear out at the same time? That wouldn't be
safe or save money.

John R. Carroll wrote:
"Jim Stewart" wrote in message
.. .
Joe Pfeiffer wrote:

The corollary I've never been able to figure out is why they don't use
smaller brakes and more pressure in the rear, so they'd all wear out
at the same time (well, as a matter of fact most vehicles I've had
apart have had larger fronts than rears. But not by enough to make up
for the difference in how hard the fronts have to work).
My guess is safety.

It isn't safety, it's standardisation to lower costs.

Standardization of what? Every car I've ever
seen that had 4w disk brakes had bigger ones
on the front.

"John R. Carroll" wrote in message

"DrollTroll" wrote in message
...

I seem to remember something called a "proportioning valve",
between front and rear brakes.

That's correct and some are adjustable. On those units it is
necessary to balance the system after changing out the master
cylinder.

But aren't the front and rear independent systems, with separate reservoirs
and all? It sounds like this valve is a single point of failure common to
both systems.


--

Reply in group, but if emailing add one more
zero, and remove the last word.

Tom Del Rosso wrote:
"John R. Carroll" wrote in message

"DrollTroll" wrote in message
...
I seem to remember something called a "proportioning valve",
between front and rear brakes.
That's correct and some are adjustable. On those units it is
necessary to balance the system after changing out the master
cylinder.

But aren't the front and rear independent systems, with separate reservoirs
and all? It sounds like this valve is a single point of failure common to
both systems.

Most cars have two independent systems,
right front/left rear and left front/right rear.

Jeff Wisnia writes:

I started to give him the old "inertial weight transfer to the front
while braking" reply and then found that it really wasn't making total
sense to me.

When you step on the brakes, you are thrown forward.
So is the car. There is more weight on the front wheels than on the rear.

On Oct 17, 12:07*pm, Jeff Wisnia wrote:
Someone asked me why their car's front brakes always seem to need
replacing long before the rear brakes do.

At rest, or at moderate speeds, the front and rear tires
bear the same load (that's why you use the same, or
nearly the same, tire pressures front and rear).

When braking, the nonrotation of the car means the torque (by
the wheel/road friction) and countertorque (by imbalance of
front wheel/rear wheel load force) are equal. That
means the front wheels bear more load during the braking
of forward motion than at rest.

Since the front wheels bear more load during braking,
they can safely apply more friction force (and are sized and
proportionally engaged to do so). Higher friction force means
more wear on the front brake parts than on the rear.

Phrases like 'throws weight forward' are suggestive of
the car center-of-mass shifting with respect to the wheelbase.
That doesn't happen. Compression of the front springs
(the hood dips when you brake) is easy to see happening,
and should indicate (to folk who don't do force diagrams)
the front-tire-load situation.

On Fri, 17 Oct 2008 17:21:21 -0700, the infamous Jim Stewart
scrawled the following:

John R. Carroll wrote:
"Jim Stewart" wrote in message
.. .
Joe Pfeiffer wrote:

The corollary I've never been able to figure out is why they don't use
smaller brakes and more pressure in the rear, so they'd all wear out
at the same time (well, as a matter of fact most vehicles I've had
apart have had larger fronts than rears. But not by enough to make up
for the difference in how hard the fronts have to work).
My guess is safety.

It isn't safety, it's standardisation to lower costs.

Standardization of what? Every car I've ever
seen that had 4w disk brakes had bigger ones
on the front.

80-90% of the stopping power comes from the front brakes.

--
"Politics is the art of looking for trouble, finding it whether it
exists or not, diagnosing it incorrectly, and applying the wrong
remedy." -- Ernest Benn

On Fri, 17 Oct 2008 17:47:37 -0700, the infamous Jim Stewart
scrawled the following:

Tom Del Rosso wrote:
"John R. Carroll" wrote in message

"DrollTroll" wrote in message
...
I seem to remember something called a "proportioning valve",
between front and rear brakes.
That's correct and some are adjustable. On those units it is
necessary to balance the system after changing out the master
cylinder.

But aren't the front and rear independent systems, with separate reservoirs
and all? It sounds like this valve is a single point of failure common to
both systems.

Most cars have two independent systems,
right front/left rear and left front/right rear.

Are you nuts, Jim? That would put a car in a spin in seconds flat if
one reservoir were dry. I believe that all the cars I ever worked on
up through the 90s had separate circuits for front and rear. I see no
reason they'd change that. It's a real safety issue.

If you know of crossed systems, please post a link. I gotta see this.

--
"Politics is the art of looking for trouble, finding it whether it
exists or not, diagnosing it incorrectly, and applying the wrong
remedy." -- Ernest Benn

"ATP*" writes:

"Joe Pfeiffer" wrote in message
...

The corollary I've never been able to figure out is why they don't use
smaller brakes and more pressure in the rear, so they'd all wear out
at the same time (well, as a matter of fact most vehicles I've had
apart have had larger fronts than rears. But not by enough to make up
for the difference in how hard the fronts have to work).

Why would you want them to all wear out at the same time? That wouldn't be
safe or save money.

Well, "roughly" the same time (and you get a lot of notice from when
the wear strip first starts dragging until your brakes are unsafe).
Putting bigger rear brakes on than necessary costs weight and costs
the manufacturer money.

Jim Stewart writes:

Tom Del Rosso wrote:
"John R. Carroll" wrote in message

"DrollTroll" wrote in message
...
I seem to remember something called a "proportioning valve",
between front and rear brakes.
That's correct and some are adjustable. On those units it is
necessary to balance the system after changing out the master
cylinder.

But aren't the front and rear independent systems, with separate reservoirs
and all? It sounds like this valve is a single point of failure common to
both systems.

Most cars have two independent systems,
right front/left rear and left front/right rear.

All (modern) cars have two independent systems; a very few are like
you say while the vast majority are a front system and a rear system.

"Jim Stewart" wrote in message
.. .
John R. Carroll wrote:
"Jim Stewart" wrote in message
.. .
Joe Pfeiffer wrote:

The corollary I've never been able to figure out is why they don't use
smaller brakes and more pressure in the rear, so they'd all wear out
at the same time (well, as a matter of fact most vehicles I've had
apart have had larger fronts than rears. But not by enough to make up
for the difference in how hard the fronts have to work).
My guess is safety.

It isn't safety, it's standardisation to lower costs.

Standardization of what? Every car I've ever
seen that had 4w disk brakes had bigger ones
on the front.

Emergency brake systems are typically in the rear rotor housing so they'll
be different in order to make room.
To have the same area the rear rotors would necessarily require a bigger OD
and a different caliper.

JC

Larry Jaques writes:

On Fri, 17 Oct 2008 17:47:37 -0700, the infamous Jim Stewart
scrawled the following:

Most cars have two independent systems,
right front/left rear and left front/right rear.

Are you nuts, Jim? That would put a car in a spin in seconds flat if
one reservoir were dry. I believe that all the cars I ever worked on
up through the 90s had separate circuits for front and rear. I see no
reason they'd change that. It's a real safety issue.

If you know of crossed systems, please post a link. I gotta see this.

googling for diagonal split brake turns up enough hits describing it
as the other alternative to front-rear split (see
http://books.google.com/books?id=U4T...m=12&ct=result)
that *somebody* must have done it. My never-reliable memory is that
Volvo has used it; googling for "volvo diagonal split brakes" turns up
lots of allusions to this (see
http://web.ukonline.co.uk/james.sumner/740.html) and to their
triangular split brake system, but nothing that's really as concrete
as I'd like.

On Oct 18, 11:57 am, Larry Jaques
wrote:
On Fri, 17 Oct 2008 17:47:37 -0700, the infamous Jim Stewart
scrawled the following:



Tom Del Rosso wrote:
"John R. Carroll" wrote in message

"DrollTroll" wrote in message
...
I seem to remember something called a "proportioning valve",
between front and rear brakes.
That's correct and some are adjustable. On those units it is
necessary to balance the system after changing out the master
cylinder.

But aren't the front and rear independent systems, with separate reservoirs
and all? It sounds like this valve is a single point of failure common to
both systems.

Most cars have two independent systems,
right front/left rear and left front/right rear.

Are you nuts, Jim? That would put a car in a spin in seconds flat if
one reservoir were dry. I believe that all the cars I ever worked on
up through the 90s had separate circuits for front and rear. I see no
reason they'd change that. It's a real safety issue.

If you know of crossed systems, please post a link. I gotta see this.

--
"Politics is the art of looking for trouble, finding it whether it
exists or not, diagnosing it incorrectly, and applying the wrong
remedy." -- Ernest Benn

FYI - Alfa Romeo in the early 70's did, the 1750GTV and the 2000GTV
from staring at the engine bay - also had a separate booster on each
set. Why? - no idea, really. Probably a good idea at the time -

Andrew VK3BFA.

"John R. Carroll" writes:

"Jim Stewart" wrote in message
.. .
John R. Carroll wrote:
"Jim Stewart" wrote in message
.. .
Joe Pfeiffer wrote:

The corollary I've never been able to figure out is why they don't use
smaller brakes and more pressure in the rear, so they'd all wear out
at the same time (well, as a matter of fact most vehicles I've had
apart have had larger fronts than rears. But not by enough to make up
for the difference in how hard the fronts have to work).
My guess is safety.

It isn't safety, it's standardisation to lower costs.

Standardization of what? Every car I've ever
seen that had 4w disk brakes had bigger ones
on the front.

Emergency brake systems are typically in the rear rotor housing so they'll
be different in order to make room.
To have the same area the rear rotors would necessarily require a bigger OD
and a different caliper.

There's a couple of flaws with this. First, I don't think I've ever
seen the same calipers on the fronts and rears. Second, my comment
above doesn't imply they should have the same area, it implies the
rears (which already have less area than the fronts) should be smaller
yet.

On Fri, 17 Oct 2008 21:14:38 -0600, Joe Pfeiffer
wrote:

Larry Jaques writes:

On Fri, 17 Oct 2008 17:47:37 -0700, the infamous Jim Stewart
scrawled the following:

Most cars have two independent systems,
right front/left rear and left front/right rear.

Are you nuts, Jim? That would put a car in a spin in seconds flat if
one reservoir were dry. I believe that all the cars I ever worked on
up through the 90s had separate circuits for front and rear. I see no
reason they'd change that. It's a real safety issue.

If you know of crossed systems, please post a link. I gotta see this.

googling for diagonal split brake turns up enough hits describing it
as the other alternative to front-rear split (see
http://books.google.com/books?id=U4T...m=12&ct=result)
that *somebody* must have done it. My never-reliable memory is that
Volvo has used it; googling for "volvo diagonal split brakes" turns up
lots of allusions to this (see
http://web.ukonline.co.uk/james.sumner/740.html) and to their
triangular split brake system, but nothing that's really as concrete
as I'd like.
========
My 74 SAAB EMS had the diagional split brake set-up. Worked fine
for the 11 years I had the car.

http://www.saabpedia.org/pmwiki.php?...aabInnovations
see 1963

http://www.saabcentral.com/features/..._aero_t16s.php
see about 2/3 down


Unka' George [George McDuffee]
-------------------------------------------
He that will not apply new remedies,
must expect new evils:
for Time is the greatest innovator: and
if Time, of course, alter things to the worse,
and wisdom and counsel shall not alter them to the better,
what shall be the end?

Francis Bacon (1561-1626), English philosopher, essayist, statesman.
Essays, "Of Innovations" (1597-1625).

Joe Pfeiffer wrote:

There's a couple of flaws with this. First, I don't think I've ever
seen the same calipers on the fronts and rears. Second, my comment
above doesn't imply they should have the same area, it implies the
rears (which already have less area than the fronts) should be smaller
yet.

Nah, The front ones need to be even larger so they don't wear out as fast! ;-)

Seriously, you do NOT want all to wear out at the same time. In these tough economic
times some will have difficulty getting ONE set of brakes repaired at the time. If both
the front and rear wore out at the same time they'd be tempted to, or would actually,
drive around with no brakes at all, except the resistance created by metal scraping metal
which would result in even more expense later -- along with many accidents, some fatal.

....Then YOUR uninsured motorists premium would go up! :-8

Al

"Joe Pfeiffer" wrote in message
...
"John R. Carroll" writes:

"Jim Stewart" wrote in message
.. .
John R. Carroll wrote:
"Jim Stewart" wrote in message
.. .
Joe Pfeiffer wrote:

The corollary I've never been able to figure out is why they don't
use
smaller brakes and more pressure in the rear, so they'd all wear out
at the same time (well, as a matter of fact most vehicles I've had
apart have had larger fronts than rears. But not by enough to make
up
for the difference in how hard the fronts have to work).
My guess is safety.

It isn't safety, it's standardisation to lower costs.

Standardization of what? Every car I've ever
seen that had 4w disk brakes had bigger ones
on the front.

Emergency brake systems are typically in the rear rotor housing so
they'll
be different in order to make room.
To have the same area the rear rotors would necessarily require a bigger
OD
and a different caliper.

There's a couple of flaws with this. First, I don't think I've ever
seen the same calipers on the fronts and rears. Second, my comment
above doesn't imply they should have the same area, it implies the
rears (which already have less area than the fronts) should be smaller
yet.

Well, in the context of this thread it's fair to state the following.

First, the front brakes primarily stop a vehicle because that's where most
of the weight is in a vehicle with the engine in the front.

Second, manufacturers like to standardize this sort of stuff to the extent
possible. I've got 13.5 inch diameter front rotors and 12 inch rears but
when delivered, the car had twelve incher's all the way around. The
principal difference between calipers was what got machined as far as
porting and mounts between the front and rear calipers, any wheel could go
in any position in a pinch.
The tires are directional in this case and so are the wheels (ventilation)
but the offset is the same.

Anyway, if you want rotors that last essentially forever, have them
Cryogenically treated. In ordinary use, you won't be able to wear them out
and it isn't all that expensive. Cross drilling or grooving in advance will
add tremendously to pas life and if you by carbon fiber/metalic pads and put
them on cross drilled and cold cryo'd rotors you will have done you last
break job. The only thing to watch out for is heat dissapation. Use DOT 7
fluid IIRC. There is a place in Indianapolis that does a set of rotors for
$75.00, or they did. Price might be more today. Carbon fiber/metalic pads
take and make a lot more heat than other systems and you can end up cooking
things unintentionally, like brake fluid and hoses. In extreme cases, you
can cook the bearing grease.
I'll find the cold cryo info if anyone wants it.
Dumb name that, cold cryo. Of course it's cold - it's cryogenic FCS.

Anyway, this is something I do to stabilize the materials we build LOX
manifolds, as well as chamber flanges of rocket motors made from stainless
steel. Works on vehicle brake rotors as well - maybe better.


JC

In article ,
F. George McDuffee wrote:

On Fri, 17 Oct 2008 21:14:38 -0600, Joe Pfeiffer
wrote:

Larry Jaques writes:

On Fri, 17 Oct 2008 17:47:37 -0700, the infamous Jim Stewart
scrawled the following:

Most cars have two independent systems,
right front/left rear and left front/right rear.

Are you nuts, Jim? That would put a car in a spin in seconds flat if
one reservoir were dry. I believe that all the cars I ever worked on
up through the 90s had separate circuits for front and rear. I see no
reason they'd change that. It's a real safety issue.

If you know of crossed systems, please post a link. I gotta see this.

googling for diagonal split brake turns up enough hits describing it
as the other alternative to front-rear split (see
http://books.google.com/books?id=U4T...9&dq=diag ona
l+split+brake&source=web&ots=MULRSuTJwj&sig=BY1Rd STvdfe91cLfXdeszfqwFW4&hl=en
&sa=X&oi=book_result&resnum=12&ct=result)
that *somebody* must have done it. My never-reliable memory is that
Volvo has used it; googling for "volvo diagonal split brakes" turns up
lots of allusions to this (see
http://web.ukonline.co.uk/james.sumner/740.html) and to their
triangular split brake system, but nothing that's really as concrete
as I'd like.
========
My 74 SAAB EMS had the diagional split brake set-up. Worked fine
for the 11 years I had the car.

http://www.saabpedia.org/pmwiki.php?...aabInnovations
see 1963

http://www.saabcentral.com/features/..._aero_t16s.php
see about 2/3 down

I've had Volvos since the 1970s. They all had dual brake systems. Each
system did both front wheels plus one back wheel. The front calipers
had two sets of pistons, one set per system. The manual claimed that
one could achieve 60% of the normal stopping power even if one system
had leaked dry. I never had the opportunity to test this, but it seems
plausible to me, and I never read or heard anything to the contrary.

Joe Gwinn

On Fri, 17 Oct 2008 23:05:17 -0500, the infamous F. George McDuffee
scrawled the following:

On Fri, 17 Oct 2008 21:14:38 -0600, Joe Pfeiffer
wrote:

Larry Jaques writes:

On Fri, 17 Oct 2008 17:47:37 -0700, the infamous Jim Stewart
scrawled the following:

Most cars have two independent systems,
right front/left rear and left front/right rear.

Are you nuts, Jim? That would put a car in a spin in seconds flat if
one reservoir were dry. I believe that all the cars I ever worked on
up through the 90s had separate circuits for front and rear. I see no
reason they'd change that. It's a real safety issue.

If you know of crossed systems, please post a link. I gotta see this.

googling for diagonal split brake turns up enough hits describing it
as the other alternative to front-rear split (see
http://books.google.com/books?id=U4T...m=12&ct=result)
that *somebody* must have done it. My never-reliable memory is that
Volvo has used it; googling for "volvo diagonal split brakes" turns up
lots of allusions to this (see
http://web.ukonline.co.uk/james.sumner/740.html) and to their
triangular split brake system, but nothing that's really as concrete
as I'd like.
========
My 74 SAAB EMS had the diagional split brake set-up. Worked fine
for the 11 years I had the car.

Yabbut, luckily, you never had half a master cylinder fail.


http://www.saabpedia.org/pmwiki.php?...aabInnovations
see 1963

http://www.saabcentral.com/features/..._aero_t16s.php
see about 2/3 down

Hmm, interesting. I guess I missed seeing them because I worked
primarily on domestic and Japanese vehicles.

I see that it was pretty much a 4-wheel disc/Swedish (and 1 Italican)
thing in the 60s through 80s. I'm guessing that the 4-wheel disc
feature is what made it possible, but I sure wouldn't want to test it.

--
"Politics is the art of looking for trouble, finding it whether it
exists or not, diagnosing it incorrectly, and applying the wrong
remedy." -- Ernest Benn

Joe Pfeiffer wrote:

googling for diagonal split brake turns up enough hits describing it
as the other alternative to front-rear split


I think my dad's plymouth duster had such a set up.

Wes
--
"Additionally as a security officer, I carry a gun to protect
government officials but my life isn't worth protecting at home
in their eyes." Dick Anthony Heller

Larry Jaques wrote:
On Fri, 17 Oct 2008 17:47:37 -0700, the infamous Jim Stewart
scrawled the following:

Most cars have two independent systems,
right front/left rear and left front/right rear.


Are you nuts, Jim? That would put a car in a spin in seconds flat if
one reservoir were dry. I believe that all the cars I ever worked on
up through the 90s had separate circuits for front and rear. I see no
reason they'd change that. It's a real safety issue.

If you know of crossed systems, please post a link. I gotta see this.


No. He's right. At least the SAAB s were the first ones with the
diagonal braking system in the Late 50s or early 60s, I believe.
At that time I was driving a SAAB 850 GT and so was following
the foreign car "developments" quite closely.
...lew...

In article , John R. Carroll
wrote:

"Joe Pfeiffer" wrote in message
...
"John R. Carroll" writes:

"Jim Stewart" wrote in message
.. .
John R. Carroll wrote:
"Jim Stewart" wrote in message
.. .
Joe Pfeiffer wrote:

The corollary I've never been able to figure out is why they don't
use
smaller brakes and more pressure in the rear, so they'd all wear out
at the same time (well, as a matter of fact most vehicles I've had
apart have had larger fronts than rears. But not by enough to make
up
for the difference in how hard the fronts have to work).
My guess is safety.

It isn't safety, it's standardisation to lower costs.

Standardization of what? Every car I've ever
seen that had 4w disk brakes had bigger ones
on the front.

Emergency brake systems are typically in the rear rotor housing so
they'll
be different in order to make room.
To have the same area the rear rotors would necessarily require a bigger
OD
and a different caliper.

There's a couple of flaws with this. First, I don't think I've ever
seen the same calipers on the fronts and rears. Second, my comment
above doesn't imply they should have the same area, it implies the
rears (which already have less area than the fronts) should be smaller
yet.

Well, in the context of this thread it's fair to state the following.

First, the front brakes primarily stop a vehicle because that's where most
of the weight is in a vehicle with the engine in the front.

Second, manufacturers like to standardize this sort of stuff to the extent
possible. I've got 13.5 inch diameter front rotors and 12 inch rears but
when delivered, the car had twelve incher's all the way around. The
principal difference between calipers was what got machined as far as
porting and mounts between the front and rear calipers, any wheel could go
in any position in a pinch.
The tires are directional in this case and so are the wheels (ventilation)
but the offset is the same.

Anyway, if you want rotors that last essentially forever, have them
Cryogenically treated. In ordinary use, you won't be able to wear them out
and it isn't all that expensive. Cross drilling or grooving in advance will
add tremendously to pas life and if you by carbon fiber/metalic pads and put
them on cross drilled and cold cryo'd rotors you will have done you last
break job. The only thing to watch out for is heat dissapation. Use DOT 7
fluid IIRC. There is a place in Indianapolis that does a set of rotors for
$75.00, or they did. Price might be more today. Carbon fiber/metalic pads
take and make a lot more heat than other systems and you can end up cooking
things unintentionally, like brake fluid and hoses. In extreme cases, you
can cook the bearing grease.
I'll find the cold cryo info if anyone wants it.
Dumb name that, cold cryo. Of course it's cold - it's cryogenic FCS.

Anyway, this is something I do to stabilize the materials we build LOX
manifolds, as well as chamber flanges of rocket motors made from stainless
steel. Works on vehicle brake rotors as well - maybe better.


JC


THIS is why I read this newsgroup! Fascinating info... thanks, John!
-j

On Oct 17, 7:43*pm, whit3rd wrote:
On Oct 17, 12:07*pm, Jeff Wisnia wrote:

Someone asked me why their car's front brakes always seem to need
replacing long before the rear brakes do.

At rest, or at moderate speeds, the front and rear tires
bear the same load (that's why you use the same, or
nearly the same, tire pressures front and rear).

When braking, the nonrotation of the car means the torque (by
the wheel/road friction) and countertorque (by imbalance of
front wheel/rear wheel load force) are equal. *That
means the front wheels bear more load during the braking
of forward motion than at rest.

Since the front wheels bear more load during braking,
they can safely apply more friction force (and are sized and
proportionally engaged to do so). *Higher friction force means
more wear on the front brake parts than on the rear.

Phrases like 'throws weight forward' are suggestive of
the car center-of-mass shifting with respect to the wheelbase.
That doesn't happen. * Compression of the front springs
(the hood dips when you brake) is easy to see happening,
and should indicate (to folk who don't do force diagrams)
the front-tire-load situation.

The front wheels need bigger brakes for two, maybe three
reasons: 1. The front is often heavier. 2. The rear end tends to get a
bit light as the car rotates around the center of mass as the braking
forces are applied. 3. You DON'T want the rear end breaking loose. In
the days before ABS, rear brakes that were as strong as the front
could cause the rear wheels to lock up, and if you've ever done the
park-brake-skid thing, you'll know that once the rear wheels are
locked you might as well have a skid plate back there. There's no
particular direction the wheels will want to go, and so the car will
try to swap ends. Dangerous. Much better to make the rear brakes
weaker than to risk breakaway.

Dan

In article ,
Larry Jaques wrote:
:On Fri, 17 Oct 2008 17:47:37 -0700, the infamous Jim Stewart
scrawled the following:
:
:
:Most cars have two independent systems,
:right front/left rear and left front/right rear.
:
:Are you nuts, Jim? That would put a car in a spin in seconds flat if
ne reservoir were dry. I believe that all the cars I ever worked on
:up through the 90s had separate circuits for front and rear. I see no
:reason they'd change that. It's a real safety issue.
:
:If you know of crossed systems, please post a link. I gotta see this.

Without ABS, if you lost the front brakes you'd almost certainly lock up
the rear wheels in a desperate effort to stop with 70% of your braking
power lost, and that would be very likely to put you in a spin too.
That was the reasoning behind dual-diagonal split. My Saab had it back
in the 60's, and I believe the Fiat I owned back around that same time
did too.

Of course the Saab was so spin-prone anyway that a little extra didn't
matter much. A friend of mine once told me, "Everybody I've known who
owned a Saab has done a 180 in it." Yes, I'm in that category too, even
without a brake failure.

--
Bob Nichols AT comcast.net I am "RNichols42"

Robert Nichols wrote:

Of course the Saab was so spin-prone anyway that a little extra didn't
matter much. A friend of mine once told me, "Everybody I've known who
owned a Saab has done a 180 in it." Yes, I'm in that category too, even
without a brake failure.

I drove my GT850 for quite a few years in central PA with lots of
snow and ice and never did any. Now I did do one on ice in my
Citroen ID 19. :-)
...lew...

On Sat, 18 Oct 2008 18:46:59 -0500 (CDT), Robert Nichols wrote:
Larry Jaques wrote:
:On Fri, 17 Oct 2008 17:47:37 Jim Stewart scrawled the following:

:Most cars have two independent systems,
:right front/left rear and left front/right rear.
:
:Are you nuts, Jim? That would put a car in a spin in seconds flat if
ne reservoir were dry. I believe that all the cars I ever worked on
:up through the 90s had separate circuits for front and rear. I see no
:reason they'd change that. It's a real safety issue.
:
:If you know of crossed systems, please post a link. I gotta see this.

Seconded! Cites, please.

It's theoretically possible to make a cross-split, but also
technically difficult - you need either two residual valves for rear
drums, or four wheel discs that parking brakes are a nightmare on. Or
a parking brake system totally separate from the service brakes.

And theoretically very unstable on system half-failure - I'd rather
stomp on the pedal and get nothing than a guaranteed spin.

Without ABS, if you lost the front brakes you'd almost certainly lock up
the rear wheels in a desperate effort to stop with 70% of your braking
power lost, and that would be very likely to put you in a spin too.
That was the reasoning behind dual-diagonal split. My Saab had it back
in the 60's, and I believe the Fiat I owned back around that same time
did too.

Of course the Saab was so spin-prone anyway that a little extra didn't
matter much. A friend of mine once told me, "Everybody I've known who
owned a Saab has done a 180 in it." Yes, I'm in that category too, even
without a brake failure.

You SAAB owners must be cursed, or just not paying attention - I put
100K on a 61 Corvair that owns the "Tail-Happy Award" for the USA (The
Porsche 911 is a lock for Europe), and while I had it partly to mostly
sideways several times and caught it, I never once went all the way
around.

Most cars will give you a bit of advance warning that the stiction
is going away if you know to listen and feel for it.

-- Bruce --

On Sun, 19 Oct 2008 13:28:33 -0700, Bruce L. Bergman
wrote:

On Sat, 18 Oct 2008 18:46:59 -0500 (CDT), Robert Nichols wrote:
Larry Jaques wrote:
:On Fri, 17 Oct 2008 17:47:37 Jim Stewart scrawled the following:

:Most cars have two independent systems,
:right front/left rear and left front/right rear.
:
:Are you nuts, Jim? That would put a car in a spin in seconds flat if
ne reservoir were dry. I believe that all the cars I ever worked on
:up through the 90s had separate circuits for front and rear. I see no
:reason they'd change that. It's a real safety issue.
:
:If you know of crossed systems, please post a link. I gotta see this.

Seconded! Cites, please.

It's theoretically possible to make a cross-split, but also
technically difficult - you need either two residual valves for rear
drums, or four wheel discs that parking brakes are a nightmare on. Or
a parking brake system totally separate from the service brakes.

And theoretically very unstable on system half-failure - I'd rather
stomp on the pedal and get nothing than a guaranteed spin.

Without ABS, if you lost the front brakes you'd almost certainly lock up
the rear wheels in a desperate effort to stop with 70% of your braking
power lost, and that would be very likely to put you in a spin too.
That was the reasoning behind dual-diagonal split. My Saab had it back
in the 60's, and I believe the Fiat I owned back around that same time
did too.

Of course the Saab was so spin-prone anyway that a little extra didn't
matter much. A friend of mine once told me, "Everybody I've known who
owned a Saab has done a 180 in it." Yes, I'm in that category too, even
without a brake failure.

You SAAB owners must be cursed, or just not paying attention - I put
100K on a 61 Corvair that owns the "Tail-Happy Award" for the USA (The
Porsche 911 is a lock for Europe), and while I had it partly to mostly
sideways several times and caught it, I never once went all the way
around.

Most cars will give you a bit of advance warning that the stiction
is going away if you know to listen and feel for it.

-- Bruce --
==========
Most of the problem seemed to be on slick surfaces with the front
wheel drive.

With a rear wheel drive when things get a little goosey on slick
surfaces, you generally let up on the gas, and the engine drag on
the rear wheels helps things straighten out. With a front wheel
drive, the engine drag is on the front wheels and nothing on the
rear so the car wants to swap ends even more. When you get used
to this and learn to feather the throttle so there is just a
*SLIGHT* pull on the front, things are much better.

Another problem with many new SAAB owners is that they expected
some sort of super snow car. While better than most, SAABs would
still spin on glare or black ice. Even with studded snow tires
you can still spin, but you will be going faster than anything
else on the road when you do it. [File under the category "so
soon old, too late smart."]

Wish I still had my 74 EMS, but the front U-joints cost more to
replace [after c.200k miles] than the entire car was worth [and
it was about a 5 hour drive to the nearest dealer].


Unka' George [George McDuffee]
-------------------------------------------
He that will not apply new remedies,
must expect new evils:
for Time is the greatest innovator: and
if Time, of course, alter things to the worse,
and wisdom and counsel shall not alter them to the better,
what shall be the end?

Francis Bacon (1561-1626), English philosopher, essayist, statesman.
Essays, "Of Innovations" (1597-1625).

On Fri, 17 Oct 2008 23:05:17 -0500, the infamous F. George McDuffee
scrawled the following:

On Fri, 17 Oct 2008 21:14:38 -0600, Joe Pfeiffer
wrote:

Larry Jaques writes:

On Fri, 17 Oct 2008 17:47:37 -0700, the infamous Jim Stewart
scrawled the following:

Most cars have two independent systems,
right front/left rear and left front/right rear.

Are you nuts, Jim? That would put a car in a spin in seconds flat if
one reservoir were dry. I believe that all the cars I ever worked on
up through the 90s had separate circuits for front and rear. I see no
reason they'd change that. It's a real safety issue.

If you know of crossed systems, please post a link. I gotta see this.

googling for diagonal split brake turns up enough hits describing it
as the other alternative to front-rear split (see
http://books.google.com/books?id=U4T...m=12&ct=result)
that *somebody* must have done it. My never-reliable memory is that
Volvo has used it; googling for "volvo diagonal split brakes" turns up
lots of allusions to this (see
http://web.ukonline.co.uk/james.sumner/740.html) and to their
triangular split brake system, but nothing that's really as concrete
as I'd like.
========
My 74 SAAB EMS had the diagional split brake set-up. Worked fine
for the 11 years I had the car.

Yabbut, luckily, you never had half a master cylinder fail.


http://www.saabpedia.org/pmwiki.php?...aabInnovations
see 1963

http://www.saabcentral.com/features/..._aero_t16s.php
see about 2/3 down

Hmm, interesting. I guess I missed seeing them because I worked
primarily on domestic and Japanese vehicles.

I see that it was pretty much a 4-wheel disc/Swedish (and 1 Italican)
thing in the 60s through 80s. I'm guessing that the 4-wheel disc
feature is what made it possible, but I sure wouldn't want to test it.
As I understand it, the lines and a proportioning valve are plumbed
into the system. As a safety measure, there is also a "check valve"
plumbed into the system so that if a brake line blows open, the check
ball goes to that particular side, blocking the flow of fluid to those
lines - - - and incorporated into the design is "crossed" plumbing so
that even with a blown line, you will have braking on right front/left
rear or left front/right rear until you get repairs made. Sometimes
when bleeding a system, the check ball will move to the "side" and
turn on a brake light on the dash, and fixing it involved bleeding a
bit of fluid from the other side to "center" the ball.
Ken.

After reading a bit on triangular brake systems (two hydraulic
systems; both systems go to both front wheels and one system goes to
each rear) I find myself wondering if there have been auto
manufacturers that have used duplicate hydraulic systems, both running
to all four wheels.