Rear Brake WearDear Ole Mechanic;

I just got my '95 Chevy ton pickup out of the shop after a front-end brake job.  It dawned on me that I have had three sets of front disc-brake pads replaced, but the rear drum-brake linings have never been replaced.  I called the shop where I had the work done and asked them if they had done the rear brakes.  They said "No," because the rear brake shoes had almost half of the lining left.  Is there something wrong with the front brakes that has caused them to wear out much faster than the rear ones?  Or is there something wrong with the rear ones causing them to not wear?  What is going on?  By the way my Son’s '95 half-ton pickup has gone thru four sets of front brake pads and one set of rear shoes in the same mileage.  Can you explain what is going on?

BW
 

Dear BW;

First, let me address the wear difference between your ton and your Son’s half-ton truck.  Your ton truck has MUCH larger brakes to deal with the larger load capacity that comes with the ton rating.  Your truck, if it has the heavy-duty options, can have a GVWR (Gross Vehicle Weight Rating) of as much as 8,600 pounds.  That means that the truck and any load in it should not exceed 8,600 pounds.  The GVWR of your Son’s half-ton can be as low as 4,200 pounds, so it has much smaller brakes.  Also your truck is probably geared lower so it can handle more load and weight.  Your Son’s half ton is geared higher for better fuel economy.  That means that when you back off the gas pedal in your truck, you get more engine braking, which means less wear on your brakes when compared to the half ton’s brakes.

You are also dealing with two different drivers, which means that you can take two identical trucks and get different brake-life (and gas mileage) with the different drivers, even though they drive the same number of miles.  In short, trying to compare you and your ton truck to your Son and his half-ton is like trying to compare apples to bananas, even if he is a chip off the old block.

Front BrakesNow to your three sets of front brakes.  Big advances have been made in disc-brake technology, because when they first came out their wear was all over the place.  Some manufactures were having ten sets of front pads wear out before the rear drum-brakes needed new shoes.  And the pads wore out fast, too.  Other manufacturers were only wearing out two front sets for each rear.  The biggest problems were with pickup trucks, as there could be very little weight on the rear (unloaded) and then a lot of weight on the rear (loaded).  To keep the rear wheels from locking up when unloaded or not doing their share of the braking when loaded was a big problem and all different sorts of load-sensing devices were tried.  The best solution was to set up the front brakes to do most of the work under light braking.  Of course, they then wear out faster.  A proportioning-valve is the answer, because when more pressure is applied to the brake pedal, more braking is done by the rear brakes.  It also helps keep the rear brakes from locking up under light-to-normal braking.  If you are one of those drivers that take it easy when braking, the proportioning-valve may not even let the rear brakes apply.  The entire stop is accomplished by the front brakes.  However, during one of those “what the - - - OH CRAP!” stops, the rear brakes will come into play.  But even during one of those stops, the weight-transfer is to the front, your mail slides foreward off the seat, the front brakes must do at least 2/3 of the stopping --and they wear out faster.  The proportioning-valve is fixed and cannot be adjusted, which is a good thing because one set for even wear during normal braking would cause the rear ones to lock up in a panic stop.  That is when a pickup may swap ends.  Not good.  The best answer, so far, has been antilock brakes.  While I am not an advocate of electronic controls, this is one area where I feel that actual progress for safety has been made for us average drivers, because not all of us are trained race drivers.

Your experience with brake wear is not abnormal, nor is your Son’s experience either.  With today’s traffic and speeds, brakes are one thing that I do not make jokes about and I make sure that my vehicle’s brakes are in good condition.  It is a lot cheaper than repairing a damaged vehicle.

Herr Professor Nuzanbolts