On Sat, 8 Jun 2013 18:07:13 -0700, "PrecisionmachinisT"
wrote:


"Ed Huntress" wrote in message
.. .
On Sat, 08 Jun 2013 14:56:23 -0500, Ignoramus20041
wrote:

On 2013-06-08, Bob Engelhardt wrote:
On 6/8/2013 12:05 AM, Ignoramus29060 wrote:

... I just replaced the rear brake pads for the
first time in my pick-up truck, at 88,000 miles. The front brake pads
were less than half [worn] and did not need replacing.
...

That's interesting: on every vehicle that I (or my wife) have ever had,
the front brakes wear 2 or 3 times as fast as the back. 'Cause that's
where the weight is - especially on stopping, with the inertial weight
transfer. Do you generally have a lot of weight in the back?

Not really. It is a pick-up, most weight is in front. Actually what
you said does not make sense.

In most vehicles, front brakes wear far faster than rear brakes. And
it's because the weight shifts to the front upon braking. It applies
even to rear-engined cars.


Brakes not bear any vehicle weight; that is what axle bearings are for.

Brake wear is due solely to torque, which is going to identical on all four
wheels until one of them locks up.

Shows how much you know about vehicles and brakes.

You are PARTLY right- but mostly wrong.
The amount of weight on the wheels affects the amount of friction
between tire and road. If you put the same amount of stopping power on
the rear wheels as the front, when the weight distribution is 60/40
front /back, you will be backing into things or hitting things with
your rear quarter panels on a regular basis as the rear end will be
sliding around uncontrollably. That's why trucks had load sensing
proportioning valves to cut the pressure to the rear wheels when they
unloaded LONG before anti-lock brakes were common.

This is also why, for instance, drum brake vehicles had wider shoes on
the front than the back, and MUCH larger cyls on the front than the
rear - Example - 1971 Dodge Dart with drum brakes - 9 inch diameter
front and rear, front shoes 2.25" wide, rear shoes 2 inches wide,
front cyls 1 inch diameter, rear cyls 0.8125" diameter
On a '68 or '69 Ford Falcon V8 with drum brakes, 10 inch drums, 2,25
inch wide front linings, 1.75 rear, and 1.125" front cyl and .906 rear
in 68, and .875 in '69 ( due to rear brake lockup problems)

On a '68 or '69 Mustang with 390 V8, 10 inch diameter brakes, 2.5"
wide front shoes, 1.5" wide rear shoes, 1.094" diameter front cyls and
..813" diameter rears

This is to reduce the amount of braking torque the rear wheels can
develop so they do not break the rear tires loose from the road before
the front ones, due to reduced friction between the tires and the road
due to reduced weight.