'98 K-1500 ext cab

[zr sled head]

My trusty old truck has been the most reliable / lowest cost to operate vehicle I've ever owned but I must say it's also got the worst brakes ever made short of maybe a Chevette. IMHO it's main problem lies in the fact the rear brakes only energise one shoe when moving forward and the rear shoe when moving in reverse which leaves the front brakes stuck doing the bulk of the stopping.

Has anyone come up with a way to covert the rear to Bendix style brakes? I'm sure it would also need to involve an adjustable prop valve but hey what a small price to pay for decent braking power.

 

ANY IDEAS??

 

Thanks

Rick

[Garage Mechanic's Companion]

You are refering to converting your rear brakes from leading-trailing shoe to duo-servo.

 

The thing that you have to keep in mind is your tire is what is doing the stopping. Uping the torque output of your rear brakes may not work if you cannot transfer the torque to the ground. Remember, running empty, (which probably most of us do most of the time), there is less weight on your rear axle than on the front, and under hard braking, much of that weight transfers to the front axle.

 

Duo-Servo brakes have fallen out of favour in passenger vehicles, due to their hyper sensitivity to changes in brake lining friction (which controls the amount of amplifiction in brake torque output due to self-energization). This leads to a large swing in potential torque output. Friction modifiers can vary from lining charateristics between OEM & replacement shoes to the amount of humidity that is in the air. Remember the GM X-car fiasco, that was caused by making just such a change in rear brake design.

 

Changing the rear proportioning should not be an issue, as our trucks are fitted with DRP (Dynamic Rear Proportioning), which is a very sensitive ABS algorithym that is enabled whenever the slightest amount of rear slip is encounter, sort of like torque management in reverse.

 

I was also disappointed in the braking capability of the brakes on my '96. Just this week, I realised that my caliper slide pins had siezed, and ate the inner brake pads. I unsiezed the pins and installed a set of good quality brake pads.

 

When shopping for brake pads, you can glean some indication of the lining performance level by looking at the edge code. There is a two letter designator for the hot and cold friction coefficient embeded in this code. This code is ussually an EE or an FF (the Monroe linings I just installed were FF's). The higher the letter of the alphabet, the higher the friction coefficient. HH is the highest friction rating available and this is typically only used on motorcycles & race applications, as pad life is usually very short and perfromance in freezing temperatures can be greatly reduced.

 

After my brake job, the performance is greatly improved, but you are correct, there is room for improvement. I have never changed the rear shoes or hardware, that is the next stop on my brake odyssey.

 

As far as brake mod's go, I would concentrate principly on the front brakes, unless you do run your truck at GVWR a significant amount of time.

 

Hope this helps,

 

Derek

[zr sled head]

I've got tons of front brakes using ceramic pads but can't keep it from destroying rotors. I've now gone away from Raybestos SSD rear shoes to their cheapy standard riveted shoes which so far is far better than the trucks ever been. OH and I've also dropped the rear wheel cylinder diameter by 1/32 to help energize the shoes earlier.

[Garage Mechanic's Companion]

You have actually gone the wrong direction with the rear brakes as far as torque output goes.

 

Reducing the rear wheel cylinder size will give you the impression that the brakes are actuating sooner, but what it has done is reduced the volume of fluid required to actuate the cylinder, which results in a higher, firmer pedal.

 

What this also does is reduces the piston area of the cylinder, which results in a lower net force output, which actually reduces the torque output. It is the same old story, tuning brakes is like tuning engines: you can't only change one thing. To make this work, you will have to increase the friction rating of your shoes or something. Of course doing this will affect the sensitivity of the brake, life, fade characteristics, etc, etc, ...

 

If a higher, firmer pedal is what you are after, you would be better off reducing the expansion rate of you brake system by installing stainless braided brake hoses. And reverting to the stock wheel cylinder bore.

 

I really can't comment on the the ceramic brake pads (I have no experience with them), other than your short rotor life really is not surprising. Once again, you only changed one thing. Does Ratbestos make brake rotors? I think that they do, they are probably designed to work with those brake pads.

 

Cheers,

 

Derek

[zr sled head]

UPDATE..............I've now driven it about 1,000 miles since the new cyls / shoes and rotors, everything is seated in nicely and I can tell you 100% for sure it is not only the best feeling pedal it's ever had but it now stops the best it ever has. There is no doubt it now has far more rear brakes going both forwards and in reverse, you can feel it plus the truck no longer does it's tell tail nose dive under moderate to firm braking, in reverse it now drops the back end down and for the first time is actually activating the self adjusters and bringing the pedal back up.

It still doesnt' stop anywhere close to my old 1/2 tons of yester year but it's well within reason.

My thanks to the field rep from Raybestos for his insight into this issue.

 

Rick