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Rear Brakes 88 Comanche Chief


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I bought and began to install new parking brake cables on my 88 Comanche Chief.

 

I couldn't believe what I found when I removed the right rear brake drum. The linings for the brake shoes were completely destroyed and separated from the metal. All that was left was a pile of small broken pieces laying in the bottom of the drum, and everything was soaked with a black, grimy, brake fluid based, pile of ....s***.

 

I knew that I had a problem, but I never expected this. The only indication of a problem was a loss of fluid in the front master cylinder reservoir, and a low brake pedal that had to be pumped a couple of times to make a full pedal....never a complete loss of brakes, and no warning light.

 

I've got a theory about what caused this (other than the brake maintenance that I've neglected), and I'd like some opinions.

 

After reading about the brakes on this Comanche I found out that this truck was equipped with "The Load Proportioning Valve" on the rear suspension.

 

While I was under the truck I found this valve but the linkage to the rear axle was missing.The lever on the valve was pointing straight down.From the was I understand it, The rear wheels were getting a increased dose of pressure from the Master cylinder because the valve (in error) sensed a heavy load in the bed...

 

I think that the wheel cylinder on the right rear wheel had been leaking for some time and had softened the lamination of the brake shoe to the metal.The right rear shoes suddenly failed and broke into hundreds of small pieces which remained inside the drum.

 

At that point, the wheel cylinder over extended and leaked more brake fluid into the drum. The over extension was the result of there being no liners on the steel shoes which caused the cylinders to extend out at least 1/4" further than they ever had.

 

There were no score marks on the drum so the bare brake shoe never got pushed out far enough to make contact. There was no noise (none that I heard) coming from the right rear brake.

 

The brakes have never been great since I've owned this truck, but I thought it was just the nature of the beast.

 

I've ordered new brake shoes, wheel cylinders and brake hardware. I plan to rebuild both sides of the rear brakes.....then move to the front. I don't get my parts until Thursday, but I soaked the brake line fittings with PB blaster, and the brake lines broke loose easily from the wheel cylinders, so at least that was some luck.

 

I measured the drums and they apparently haven't ever been resurfaced so I'm gonna get both of them cleaned up. They measure 10" ID and the stamping in the drum says 10.060"  so I believe that means that the drums can be turned to a max of 10.060" ID.  I gonna take as little metal off as I can to get the surfaces in good condition.

 

For anyone who's looking for brake parts, I bought all of the rear brake parts, rebuild kits and new pads for the front calipers and a new serpentine drive belt for this truck for less than $70 delivered. All quality parts...AC Delco, Bendix, Goodyear, Morse and Raybestos from RockAuto.com. They all ship from the same warehouse which is a big savings on freight if you deal with them.

 

I made a few pictures that I intend to post if I can reduce their size (in Pix).

 

Any comments?

thanks

steve

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Does anybody know (or will measure) how long the linkage for that Height Sensing valve is supposed to be.

I plan to make one if I can find the correct center to center dimensions between the mounting pins.

Stock Truck with no lift.

 

thanks

steve

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I don't know why the dark lines appeared in my post unless it was because I edited my post in A Word Program and then copied and pasted it to the forum.

Sorry about that.

I don't know how to fix it.

 

steve

I took the liberty of editing out the color background codes. Dunno what you did, but ... DON'T DO IT AGAIN!

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Does anybody know (or will measure) how long the linkage for that Height Sensing valve is supposed to be.

I plan to make one if I can find the correct center to center dimensions between the mounting pins.

Stock Truck with no lift. thanks steve

 

Here's one way you can make a new linkage arm for the load sensing valve:

 

http://comancheclub.com/topic/16955-adjustable-mj-load-sensing-valve/?hl=adjustable

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Well the Comanche Chief is back on the road with new rear brakes and parking brake cables.

I took extra time to clean all of the rust off the pieces that I re-used and paint them black enamel.

I also cleaned and painted the backing plate.

 

I learned one thing and I've read somewhere else on this forum about a problem with the brake shoes pushing themselves out of position and not wanting to stay seated properly when re-installing the brake drum.

 

I had this problem and the fix for the problem was to finish the installation of the (new) parking brake cable before installing the drums.

 

The spring on the new cable is fully extended and can push the parking brake lever back too far (inside the drum where cable attaches) . 

This prevents the lever from fitting into the indentation that's formed in the backing plate just for this lever, and prevents the rear shoe from fitting in proper position.

I attached both new rear parking cables to the adjuster (main cable) beside the gas tank and tightened the cables just enough to allow the brake shoes to set properly.

The shoes then sat as they should and I was able to rock (knock by hand) the brake shoe assembly from side to side and check for proper movement.

 

I didn't tighten the cables enough to cause movement of the shoes because I had not as yet adjusted the brakes.

Just enough to allow the shoes to sit properly and still be able to slide the drums on and off freely.

 

I then gravity bled the new wheel cylinders, adjusted the brake shoe by hand until I had a small amount of resistance when installing the drums,  then did a final adjustment thru the hole in the backplate with a "brake spoon" (a screw driver will work.)

You want a slight drag on the new rear shoes when the brakes are correctly adjusted.

The "auto adjuster" will do the rest.

 

Then I adjusted the parking brake cables until I could push the pedal in the cabin almost to the bottom.....maybe 5 clicks from bottom.

 

I've now got what I wanted when this all started.....a parking brake.

O yeah, I also have rear brakes too, for the first time in ?????

What a difference....and all it cost was some work and <$100 for parts and fluids.

 

steve

 

I've posted some pics.

 

 

 

 

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