Hello and sorry for the possibly OT post.

I have a 1995 (M) Vauxhall Corsa Merrit (1.2) and have been experiencing
some problems with the brakes, specifically the front right. My dad used
to be a mechanic and can help me with this so I'm not going into this
completely blind!

When we got the car a few years ago it required new pads so we fitted
them. We found the caliper was of the sliding type (standardish on
new Vauxhalls so I understand) and 'slides' on a axel with a screw
thread on on one end. Being Vauxhall it needs a 7mm hex key (a size
not usually found in a tool kit), someone had damaged the caliper bolt
having taken a pair of mole-grips to it instead of using the correct
hex piece.

We replaced the pads/springs anyway and put it back together, a few
months ago the front right started making a grinding noise and upon
further inspection a little while later we found the pad had cut a
groove into the disks. We replaced the pads and disks (both sides) as
explained in the Haynes manual... It still made a grinding noise so
we thought it could be the damaged caliper guide bolts (not allowing the
caliper to fully 'open').

We aquired and fitted new bolts but alas it's still grinding and upon
further inspectin we caan see the brake pad is 'toeing in' on one side
to the disk for no apparent reason. The noise seems to happen once per
rotation... Given theses are new disks we are guessing they shouldn't be
warped and were hoping some other people may have some ideas?

Thanks in advance.

P.S. The grinding noise could also be described as a rubbing/binding
noise.

--
Regards,
Aaron.

Hello and sorry for the possibly OT post.

Try uk.rec.cars.maintenance

On Sun, 14 Aug 2005 21:23:39 GMT, Aaron
wrote:

The noise seems to happen once per rotation...

Then whatever else is wrong with the pads & calipers, your disks are
warped. This can happen by poor fitting, by over-torquing wheel bolts,
by poor run-in, or simply by buying poor quality disks.

I wouldn't want to work on disks without a dial gauge and magnetic stand
(not too expensive from Draper or eBay). Although they usually do go
together without problems, you ought to check runout anyway.

What's the pad wear like ? The usual indication of caliper slide
problems is when either one pad wears before the other, or when they
wear tapered.

7mm Allens are easily available - Sykes-Pickavant and people do them,
specifically labelled as brake caliper wrenches - I think it was Ford
who started using them for this first. I have one I bought 15 years ago
and I think that's the only thing I've ever had cause to use it on.

Andy Dingley wrote:
Then whatever else is wrong with the pads & calipers, your disks are
warped. This can happen by poor fitting, by over-torquing wheel bolts,
by poor run-in, or simply by buying poor quality disks.

It could be a combination of all of these factors :I.

I wouldn't want to work on disks without a dial gauge and magnetic stand
(not too expensive from Draper or eBay). Although they usually do go
together without problems, you ought to check runout anyway.

We have these I think but whether they were used or not is another
matter (I didn't do them), the most I ever done on a car is the
electronics.

What's the pad wear like ? The usual indication of caliper slide
problems is when either one pad wears before the other, or when they
wear tapered.

I may take the wheel off tommorow and have a look.

7mm Allens are easily available - Sykes-Pickavant and people do them,
specifically labelled as brake caliper wrenches - I think it was Ford
who started using them for this first. I have one I bought 15 years ago
and I think that's the only thing I've ever had cause to use it on.

Indeed, a quick trip to Halfords got us one.

--
Regards,
Aaron.

"Aaron" wrote in message
. uk...
Hello and sorry for the possibly OT post.

I have a 1995 (M) Vauxhall Corsa Merrit (1.2) and have been experiencing
some problems with the brakes, specifically the front right. My dad used
to be a mechanic and can help me with this so I'm not going into this
completely blind!

When we got the car a few years ago it required new pads so we fitted
them. We found the caliper was of the sliding type (standardish on
new Vauxhalls so I understand) and 'slides' on a axel with a screw
thread on on one end. Being Vauxhall it needs a 7mm hex key (a size
not usually found in a tool kit), someone had damaged the caliper bolt
having taken a pair of mole-grips to it instead of using the correct
hex piece.

We replaced the pads/springs anyway and put it back together, a few
months ago the front right started making a grinding noise and upon
further inspection a little while later we found the pad had cut a
groove into the disks. We replaced the pads and disks (both sides) as
explained in the Haynes manual... It still made a grinding noise so
we thought it could be the damaged caliper guide bolts (not allowing the
caliper to fully 'open').

We aquired and fitted new bolts but alas it's still grinding and upon
further inspectin we caan see the brake pad is 'toeing in' on one side
to the disk for no apparent reason. The noise seems to happen once per
rotation... Given theses are new disks we are guessing they shouldn't be
warped and were hoping some other people may have some ideas?

Thanks in advance.

P.S. The grinding noise could also be described as a rubbing/binding
noise.

One possible explanation for 'toeing in' of a brake pad ( i.e. it wears
asymmetrically
and develops a taper from one side to another ) is that you have dual brake
pistons/cylinders
for each brake caliper, and one of them is siezed. Typically, the seized
piston will move the
brake pad against the brake disk when the brake is applied, but it will not
retract
sufficiently again, even the tiny amount that is needed to free it from the
disk, when you remove
your foot from the brake.

The end resut is premature wear on one end of the pad, leading to a tapered
appearance,
usually accompanied with lots of brake dust coating your alloys, increased
petrol consumption,
and a squeak coming from that wheel, best heard with the window down.

The symptoms you have described are slightly different to this explanation
as you mention
a grinding noise and a groove cut into the disk ( possible if the taper on
the brake pad
becomes severe, I suppose ). Anyway, that's my theory on what might be
happening. To fix
it you need to undo the calipers from the wheel, then using a piece of wood
to equalise the brake pistons' movement, apply the brake pedal until the
pistons pop out ( under no circumstances
remove the brake caliper completely from the car then attempt to prise the
pistons out as
they will probably be in very tight - let the hydraulics do it for you ).
Then clean/replace pistons/seals
as appropriate.

Andy.

andrewpreece wrote:
"Aaron" wrote in message
. uk...

Hello and sorry for the possibly OT post.

I have a 1995 (M) Vauxhall Corsa Merrit (1.2) and have been experiencing
some problems with the brakes, specifically the front right. My dad used
to be a mechanic and can help me with this so I'm not going into this
completely blind!

When we got the car a few years ago it required new pads so we fitted
them. We found the caliper was of the sliding type (standardish on
new Vauxhalls so I understand) and 'slides' on a axel with a screw
thread on on one end. Being Vauxhall it needs a 7mm hex key (a size
not usually found in a tool kit), someone had damaged the caliper bolt
having taken a pair of mole-grips to it instead of using the correct
hex piece.

We replaced the pads/springs anyway and put it back together, a few
months ago the front right started making a grinding noise and upon
further inspection a little while later we found the pad had cut a
groove into the disks. We replaced the pads and disks (both sides) as
explained in the Haynes manual... It still made a grinding noise so
we thought it could be the damaged caliper guide bolts (not allowing the
caliper to fully 'open').

We aquired and fitted new bolts but alas it's still grinding and upon
further inspectin we caan see the brake pad is 'toeing in' on one side
to the disk for no apparent reason. The noise seems to happen once per
rotation... Given theses are new disks we are guessing they shouldn't be
warped and were hoping some other people may have some ideas?

Thanks in advance.

P.S. The grinding noise could also be described as a rubbing/binding
noise.


One possible explanation for 'toeing in' of a brake pad ( i.e. it wears
asymmetrically
and develops a taper from one side to another ) is that you have dual brake
pistons/cylinders
for each brake caliper, and one of them is siezed. Typically, the seized
piston will move the
brake pad against the brake disk when the brake is applied, but it will not
retract
sufficiently again, even the tiny amount that is needed to free it from the
disk, when you remove
your foot from the brake.

The end resut is premature wear on one end of the pad, leading to a tapered
appearance,
usually accompanied with lots of brake dust coating your alloys, increased
petrol consumption,
and a squeak coming from that wheel, best heard with the window down.

The symptoms you have described are slightly different to this explanation
as you mention
a grinding noise and a groove cut into the disk ( possible if the taper on
the brake pad
becomes severe, I suppose ). Anyway, that's my theory on what might be
happening. To fix
it you need to undo the calipers from the wheel, then using a piece of wood
to equalise the brake pistons' movement, apply the brake pedal until the
pistons pop out ( under no circumstances
remove the brake caliper completely from the car then attempt to prise the
pistons out as
they will probably be in very tight - let the hydraulics do it for you ).
Then clean/replace pistons/seals
as appropriate.

Andy.



Sounds plausable and I think I remebered my dad mumbling about cleaning
the piston and re-doing the seals. Maybe we'll give it a go.

Thanks.

--
Regards,
Aaron.

In article ,
Aaron wrote:
Being Vauxhall it needs a 7mm hex key (a size
not usually found in a tool kit), someone had damaged the caliper bolt
having taken a pair of mole-grips to it instead of using the correct
hex piece.

A standard allen key is unlikely to be long enough anyway to undo the pin.
Eurocarparts sell the correct tool for a couple of quid - other cars use
the same brakes.

But it's better to buy a set to fit a 3/8 drive socket set - Halfords do
them. That will also give you the one for the discs, as well as other
things round the car.

--
*I'm not being rude. You're just insignificant

Dave Plowman London SW
To e-mail, change noise into sound.

In article ,
Andy Dingley wrote:
Then whatever else is wrong with the pads & calipers, your disks are
warped. This can happen by poor fitting, by over-torquing wheel bolts,
by poor run-in, or simply by buying poor quality disks.

I wouldn't want to work on disks without a dial gauge and magnetic stand
(not too expensive from Draper or eBay). Although they usually do go
together without problems, you ought to check runout anyway.

I've never found the need. You have to make sure the mating surfaces are
clean on assembly, though. And I'm not convinced that uneven tightening
could cause a solid flat lump bearing against another solid flat lump to
warp. Or at least not before the wheel fell off. ;-)

IMHO, the likely cause of warping is stopping fast from high speed and
keeping the brakes applied when you stop, causing uneven cooling.

What's the pad wear like ? The usual indication of caliper slide
problems is when either one pad wears before the other, or when they
wear tapered.

7mm Allens are easily available - Sykes-Pickavant and people do them,
specifically labelled as brake caliper wrenches - I think it was Ford
who started using them for this first. I have one I bought 15 years ago
and I think that's the only thing I've ever had cause to use it on.

Think I first saw this on a BMW.

--
*My designated driver drove me to drink

Dave Plowman London SW
To e-mail, change noise into sound.

In article ,
andrewpreece wrote:
One possible explanation for 'toeing in' of a brake pad ( i.e. it wears
asymmetrically and develops a taper from one side to another ) is that
you have dual brake pistons/cylinders for each brake caliper, and one of
them is siezed. Typically, the seized piston will move the brake pad
against the brake disk when the brake is applied, but it will not
retract sufficiently again, even the tiny amount that is needed to free
it from the disk, when you remove your foot from the brake.

I'm sure they exist, but my largish BMW has single pistons both front and
rear. Makes for a very simple system. My old SD1 has four per caliper. ;-)

--
*I want it all and I want it delivered

Dave Plowman London SW
To e-mail, change noise into sound.

On Mon, 15 Aug 2005 09:47:08 +0100, "Dave Plowman (News)"
wrote:

My old SD1 has four per caliper. ;-)

Although they usually have an average of 3 1/2 in service at any one
time.

In article ,
Andy Dingley wrote:
My old SD1 has four per caliper. ;-)

Although they usually have an average of 3 1/2 in service at any one
time.

Heh heh. Rebuilt them recently with 'new' pistons and seals. Although the
pistons weren't new, but reclaimed from several ordinary four pot types -
mine has the twin circuit vented discs, so the calipers are very expensive
on exchange. It seems very strange to me the pistons are chrome plated for
such an arduous position - especially since there's no dust cover. But I
got a seal kit from my local factors, and the bores were fine.

The main problem with the SD1 brakes is those rear drum self adjusters
which have a mind of their own.

--
*Whatever kind of look you were going for, you missed.

Dave Plowman London SW
To e-mail, change noise into sound.

Dave Plowman (News) wrote:
In article ,
Aaron wrote:

Being Vauxhall it needs a 7mm hex key (a size
not usually found in a tool kit), someone had damaged the caliper bolt
having taken a pair of mole-grips to it instead of using the correct
hex piece.


A standard allen key is unlikely to be long enough anyway to undo the pin.
Eurocarparts sell the correct tool for a couple of quid - other cars use
the same brakes.

But it's better to buy a set to fit a 3/8 drive socket set - Halfords do
them. That will also give you the one for the discs, as well as other
things round the car.


This is what we have, we used such a tool to remove the bolts and we
discovered the damage on them.

--
Regards,
Aaron.

In article , "Dave Plowman (News)"
says...
In article ,
Andy Dingley wrote:
My old SD1 has four per caliper. ;-)

Although they usually have an average of 3 1/2 in service at any one
time.

Heh heh. Rebuilt them recently with 'new' pistons and seals. Although the
pistons weren't new, but reclaimed from several ordinary four pot types -
mine has the twin circuit vented discs, so the calipers are very expensive
on exchange. It seems very strange to me the pistons are chrome plated for
such an arduous position

Why? Chrome is hard and corrosion resistant.

"Rob Morley" wrote in message
t...
In article , "Dave Plowman (News)"
says...
In article ,
Andy Dingley wrote:
My old SD1 has four per caliper. ;-)

Although they usually have an average of 3 1/2 in service at any one
time.

Heh heh. Rebuilt them recently with 'new' pistons and seals. Although the
pistons weren't new, but reclaimed from several ordinary four pot types -
mine has the twin circuit vented discs, so the calipers are very
expensive
on exchange. It seems very strange to me the pistons are chrome plated
for
such an arduous position

Why? Chrome is hard and corrosion resistant.

As soon as a stone hits, the chrome chips and the steel below rusts
(likewise if the ground to size chrome has a speck of steel showing), if the
pistons were good stainless then they would never need replacement.

mrcheerful

In article ,
Rob Morley wrote:
Heh heh. Rebuilt them recently with 'new' pistons and seals. Although
the pistons weren't new, but reclaimed from several ordinary four pot
types - mine has the twin circuit vented discs, so the calipers are
very expensive on exchange. It seems very strange to me the pistons
are chrome plated for such an arduous position

Why? Chrome is hard and corrosion resistant.

But they had all corroded which is why they needed replacing. ;-)

--
*I'd kill for a Nobel Peace Prize *

Dave Plowman London SW
To e-mail, change noise into sound.

On Tue, 16 Aug 2005 01:42:46 +0100, Rob Morley
wrote:

Why? Chrome is hard and corrosion resistant.

Resistant, not rust proof. Look at any of these calipers and you're
guaranteed at least one piston with rust pitting through the chrome.
Road salt is a harsh environment.

Stainless pistons are much more rust resistant, however they're softer
and more likely to develop scoring.