1986 Comanche Break Replacement

Hello everyone,

I have recently inherited a 1986 Jeep Comanche for my 16th birthday, but it has a few problems.

The main problem is the breaking system. The calipers, break pads, shoe, and wheel cylinders, all need to be replaced.

I have a marginal amount of experience repairing vehicles, but this is the first time I have done much work with breaks. So all in all, I came to ask the experienced. Is there any particular obstacles should I look out for? Should I replace all 4 breaks or will just 2 work. What kind of break pads and calipers would you recommend, are their any tips and tricks I should know, and how long is it going to take. (My gut thought says first time about 6 hours) Any other advice is greatly appreciate.

I'm trying to do the world a favor, get another Comanche on the road.

Thanks everyone.

First, it's "brakes," not "breaks."

The MJ system is fairly simple, except for the rear height-sensing proportioning valve. For a truck that old, you should be replacing as much as possible. If the front rotors and rear drums aren't too bad they can be turned by a brake shop or automotive machine shop to clean up the surface. Any shop that does this work will know how to measure the parts. Rotors cannot be turned to less than a minimum thickness or they aren't safe, and drums can't be turned to more than a maximum inside diameter or they aren't safe. If the shop can clean them up within the allowable tolerances, you'll have to buy new drums or rotors.

For calipers, take the old ones to your favorite parts store and trade them in for rebuilt units. Wheel cylinders are not very expensive, so just buy new. For the drums, you should also buy a small parts kit -- that will include new hold-down springs, return springs, basically everything you'll need to rejuvenate the brakes.

Best approach on the drums is to do one side at a time, so the other side is there as a reference. Just remember that they are mirror image.

I think you are optimistic on your time estimate. Obviously, we haven't seen the vehicle so we don't know how much rust you have to deal with. If it's your first brake job, you need to work carefully, so don't try to rush it.

There is a special bleeding procedure for the MJ due to the height-sensing proportioning valve over the rear axle. I've posted it on here a couple of times and other people have since posted links to the description. Be sure to follow it, it is important.

Would you post the link to the special bleeding procedure for the MJ please sir?

My special procedure is to bypass that load valve and plug off the extra line at the front. But that's just me!

Would you post the link to the special bleeding procedure for the MJ please sir?

I'm sorry, I do not have it bookmarked. I would have to search for it the same way you do. It's there. Perhaps someone else has a bookmark to it.

After bleeding the brake calipers and cylinders the rear brake by-pass line must also be bled.

 

Open a front caliper bleed fitting and depress the brake pedal to the floor. This will shuttle the by-pass differential valve and allow fluid to flow through the by-pass line. The brake warning light on the instrument panel will illuminate when the ignition key is in the ON position. This signals the shuttling of the valve.

 

Re-Bleed the rear brake cylinders with the front caliper bleed fitting open.

 

After re-bleeding the rear brake cylinders the entire system must be bled again.

 

Bleed the brake calipers and cylinders in the following sequence:

 

1st -- Right rear

 

2nd -- Left rear

 

3rd -- Right front

 

4th -- Left front

And I hate to be ''that guy'' but I have bled the brakes numerous times in my MJ with a rear prop valve without any problems just following the usual bleed procedure, RR, RL, FR, FL (I didn't know of the other bleed procedure before now). I did however use a vacuum bleeder, maybe this allowed the air to be sucked out of the prop valve area since the system was not under pressure?

What exactly does that rear proportioning valve do?

Limits the pressure to the rear drum brakes based on the amount of load in the bed of the truck.

Is the valve really that important? Or can it be removed?

Would you post the link to the special bleeding procedure for the MJ please sir?

uh, I just pushed the pedal a few times, and they stiffened right up.

The rear valve limits the rear brakes when there is no load so you don't lock up and skid. I have mine bypassed and went to larger wheel cyls, so I do get rear lockup in the rain sometimes. Next step would be a smaller bore rear cyl to keep the lockup under control.

Hello everyone,

I have recently inherited a 1986 Jeep Comanche for my 16th birthday, but it has a few problems.

Happy birthday! Wish I'd been able to start out with something nice as an MJ when I turned 16 - - - Anyway, Have a reputable shop look at your brake lines - Most your age & many a lot older have never experienced sudden loss of brakes - Usually no warning - It isn't good - - All to common on older vehicles after rebuild/replace of calipers/cylinders/master cylinder & such - - - - - Ask for LOADED rebuilt calipers if you go that way - means ready to bolt on in most cases - ask anyway JIC

:thumbsup:

Some additional info for you. There are two widths of rear brake shoes. I made an assumption and got the wrong ones the first time. If your MJ is 2 wheel drive, your front rotors are different from the 4wd ones. The 2wd ones are one piece units with the wheel bearings pressed into them vs. a unit bearing and separate rotor for the 4wd ones. As mentioned before, rust can be an issue. When I bought my 86, it had poor rear brakes. All the adjusting mechanisms were siezed solid, so the shoes barely touched the drums. Once I replaced all the hardware and the shoes, I started to bleed the system. As soon as I started to get some pressure in there, it blew a line. It broke up beside the fuel tank at the worst possible location. I had to do the load sensing valve bypass and fortunately the other line held pressure.

I have 4 wheel drive and it leaking out of the wheel cylinder . Also my load sensing thing isn't even hooked up

I have 4 wheel drive and it leaking out of the wheel cylinder . Also my load sensing thing isn't even hooked up

So if it's leaking from a wheel cylinder ... you replace the wheel cylinder.