Hi,
Was wondering if someone could help? I replaced both rear wheel brake cylinders, brake shoes and hardware and bled the 4 wheels, but I get fading pedal travel when 1st applying the brakes on the road test. I cleaned the internal surfaces and components with brake cleaner and made sure the adjustment screw and mechanism were working properly. My emergency brake hasn't worked for a long time and it appears the linkage in both wheels is frozen up and a linkage component has been removed to render the e-brake useless. No problem, I just thought I would mention this, but I don't think it has any bearing on the problem. I have a hunch it may be the master cylinder. 1986 (non-turbo) truck is old plenty of rust basically a beater but great for fishing, hunting and getting off the beaten path.

Prior to the brake job I noticed the rear brakes would lock up if I applied them with urgency. Later I had a rear driver's side wheel cylinder fail and I had total brake failure. I thought the master cylinder was a 2 circuit MC that would prevent total brake loss? Looking at it, it appears to have 2 circuits, or at least 2 lines exiting the MC side. My guess is that the 2 internal pistons seals are not functioning and they have come in contact with each other and are acting like one single piston essentially making it a one circuit system.

I have tried bleeding the system a couple times with no success. I have since read on a thread that there is a load sensoring pressure valve in between the rear 2 wheels where the left and right brake lines split and it has a bleeder valve on it. I will try and bleed it there but am skeptical it will fix the problem. I have also read it is possible the 1-way vacuum valve supplying the power assist can fail and brake fluid can enter the engine and burn off. But I don't see any significant brake fluid loss. I assume this would signify a MC sealing problem as well as a inline valve failure.

After replacing rear brake shoes I adjusted the rear brake adjusting screw so that the drum just barely installs with slight drag. I did this with the drum off adjusting a little at a time, putting the drum on/off until I felt little tolerance between the brake shoes and the drums. I saw a slot access from the backing plate to turn the toothed adjusting wheel, but did not use it as it seemed easier to just adjust with the drum off until it fit snugly. Is there another adjustment needed after installing the drums using this slotted hole?

So how do I troubleshoot my problem? My plan is to bleed the LPSV. If I still have the problem, how do I determine if I need a new MC or if it's something else? Does the fact that I had total brake failure after a rear wheel cylinder leak signify 100% that my MC seals are failing? Any help troubleshooting would be appreciated as I hate the trial and error approach. Thanks!

 

So what are the results? I am in the same boat as you. I have bled and adjusted accordingly and still nothing. I'm going to assume the MC is the cause, but I'd like to hear your findings first before I start throwing parts at the problem.

 

Falling pedal is usually MC... or a leak..

 

my rear brakes dont work at all because of the T fitting on the rear axle..
its clogged or something..i have fluid going to it..but no fluid coming out..lol

 

And you should be able to see a leak (also, for the pedal to fall you need to leak a lot, and the reservoir will drop pretty quickly.)

A reman brake master cylinder at Autozone around here is only $45; your time is worth something (and your life?). So replace it.

DO get yourself a set of metric flare nut wrenches. Otherwise, you'll round off the flare nuts for sure, and then once you get them off with a vise grips you'll have to rebuild the brake lines. In fact, you might want to go long and get a really good flare nut wrench (Mac tools, etc.) This is the only tool where I can really see the difference between the $15 set and the $200 set.

"Generally" brakes that need to be bled lead to a "spongy" pedal. A sinking pedal is usually the master cylinder.

 

Well I replaced the MC reasoning that it is certainly the original and it is 23+ years old and since I had total brake failure from 1 wheel cylinder leaking it probably wasn't functioning on 2 circuits like the initial safety design intended. I also replaced both rear wheel cylinders and put on new brake shoes and hardware. Drum surfaces were marginal (should have resurfaced but not enough material to turn down). Re-used drums. Rationale was only 30% braking takes place on the rear wheels and front pads should wear out twice before I should have to mess with the rear shoes again. When and if I still own the vehicle I will replace the drums and replace the frozen parking brake linkages.

I bled the brakes with a plastic tube attached to each bleeder and got ALL the air out. Started with RR, LR, RF, LF lastly lpsv valve. Lpsv was very rusted but after thorough blast w/WD40 I could make out that the bleeder is configured a bit different. It has a separate bolt adj for tightening/loosening next to the zirk. All bleeders bled okay. Had to be careful the tubing is tightly affixed to the zirks. RR was the longest. Got a ton of air and dirty fluid bled out. Bled a good pint of fluid out of all 5 locations. After getting the air out of the RR, most of the others had little air but took awhile to bleed the dirty fluid out. When opening the bleeder valves I had to be careful not to open to far (letting air in around the threads) and not quite enough (very little fluid movement).

When I finished I still wasn't satisfied after road test. Keep in mind my parking brake is useless and locked up. I almost decided to replace the PB linkage but in the end did not. The reason is adjusting the rear brakes is easier if the PB is functional. Instead I had to manually adjust the rear brake shoes with the drum on via access through the back slot. This is a must as you will not get the proper clearance simply sliding the drum over the brake shoes. I had to find a super short flat blade screw driver and adjusted the star screw blindly facing the drum from the lug nut side and reaching around the drum to the slot. Hopefully you remember where the adjustment screw wheel is prior to putting the drum back on. If not trial and error or pop off the drum and peek. I tried to look in from under the vehicle with a flashlight...no dice, no way you can see anything as the slot is located on the upper side of the drum. Once you find it (adjustment wheel) you know it, adjusting upwards pushes the shoes outward. I think I read there is only suppose to be 0.6 mm of clearance (about the thickness of a thick piece of cardboard). Pretty tight. That is why they have to be adjusted after the drum is installed.

After that I road tested. I drove in reverse and hit the brakes a few times hoping to activate the automatic adjusting rear brake mechanism. Not sure if it worked but I did experience much improved braking.

One question I had after finishing was regarding the MC bench bleeding. The instructions said to push the plunger of the MC in 3/4-1" repeatedly until all air is remd and it should stiffen and you can only push it in 1/8". Well that's a joke. I got all the air out but the plunger kept engaging 3/4-1". I called the parts store where I purchased and they assured me it was okay so I installed it. Now, while I got good braking I can push the pedal hard and it will bottom out under pressure. Wasn't sure if that was good so I ran by the local Midas for a free brake inspection. He said he's installed 100s of MC and they don't stiffen, and he also reassured me if you push hard enough on any brake pedal it will go to the floor. He ran out and tested mine and said it was good. He said as long as it doesnt fall to the floor Im okay. So I guess I'm done with the brakes. Pedal seems a little softer than previous but perhaps it is my pedal travel now rather than fading. Will have to look in the book as to what the factory specs are but you are suppose to be able to adjust the pedal travel after installing the MC.

Anyway I'm up and running. Now I need shocks and add a leaf. Then 2 new rear tires. I have heard 31 x 10.5s are best for stock 15" rims with no lift. probably can go 32 or 33 as long as I keep the width no wider than 10.5. Midas was going to charge me $591 for the brake job and that didnt include a MC. I got by with $65 for the MC and another $65 for wheel cylinders, hardware, fluid, grease, brake cleaner and shoes. $130 total. Saved at least $500 so I can now afford tires and shocks with what I saved.

 

its nice to see things worked out..

 

Scope,
You are correct a 10mm flarenut wrench is worth every penny. However, being impatient and having one wheel cylinder brake line that didnt want to cooperate, I was able to forgo the 10mm open end wrench for a pair of vice grips! Gotta love vice grips as they did the trick. I didn't round the hex head, but you know when it's not going to turn w/o rounding, so i went directly to the vice grips since I didnt have a flare nut wrench.

Just wanted to add that it's important to use brake cleaner and grease. My thinking is if I'm going to get into it spend the extra little bit of money and time and do it right. Brake cleaner leaves no residue to gum up your brakes. I had major cleaning to do on the inside of the drums and all over the backing plates as brake fluid mixed with road grime and brake shoe dust to create a thick coating of sludge. Used a wire brush on the backing plates taking special care to remove all debris and rust from inside the drum cavity. Also be careful not to breathe any of the particulate. That's another reason to apply the brake cleaner liberally soaking everything.

Also the hardware kit included the rubber plugs for the adjustment slot as well as rubber caps for the bleeders. Good idea as I frequently back up into water loading a boat and if not there the water just flows in. Previously none of the rubber plugs were present. Pay for the new hardware as 2 of my return springs broke removing the drums; probably from rapping on the drums with a 1 pound sledge to remove plus they were all rusted.

 

Forgot to mention: After removal and draining the MC had a sludge in the bottom that looked just like fine mud. I'm sure that couldn't be good for the seals and components in the system. So even if it was functioning I would have had to rebuild it. This is also why I had to bleed a pint of fluid through the system to get the dirt out.

All and all it was pretty basic and if I had to do it again could do it in half the time as is usually the case. Rusty components always prove interesting when repairing.

Anyone recommend one shock absorber manufacturer over another?

 

Gman.... I have one word of advice for you.



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