No rear brakes

[rage987]

I have been searching the forum without luck...

Have new pads all around, new master cylinder (bench bled), new rear brake cylinders, new rear brake lines (short ones from the split), new booster, bleed the entire system multiple times, driven the car, then bleed the brakes again, tightened up the rear shoes without solving this problem.

The brake pedal is very hard until I start the car, then with the car started it feels somewhat soft. Driving and stopping hard only locks up the front brakes (even on gravel). Driving and stopping using only the e-brake, works fine.

Is it possible I have a bad master cylinder, did a bad bench bleed, or?

Thanks

 

[Superhereaux]

The brake pedal is very hard until I start the car, then with the car started it feels somewhat soft.

this is normal, most cars will do it (no vacuum to the booster and all)


get the car up on jack stands. get the car into gear and let it roll, then apply the brakes. easiest way to check 'em


keep in mind the front discs are more powerfu and apply harder than the rear drums so on gravel it makes sense that the fronts would lock up first. the rear drums might also be glazed over so they wont grab as hard. why are you trying to lock em up any way?

 

[rage987]

Thanks for the response.

Yes, I understand the booster, but the pedal appears to be too "light", ie. when stopping there is nearly zero resistance in the pedal and no braking in the first portion of the pedal movement. It feels like air, but I have run bottle after bottle of fluid through the system, and no air comes out. (which makes me think master cylinder trouble)

I have done the jack stand test and yes, the rear brakes apply fine. These are nearly new pads and turned drums, so they should not be glazed yet.

If I do the gravel test with another vehicle (equipped with similar brakes), it appears to brake in a uniform fashion, while my car lurches forward with the back of the car coming way up, as if the front brakes are apply nearly 100% force... at normal driving speeds with normal braking this effect is much more apparent and sudden stops it feels dangerous because the front of the car dives down and the back comes way up. None of my other vehicles brake in this fashion.

It appears that the back brakes are fully functional (verified visually and with the jack stand test), but just do not apply enough force when under load.

Any more ideas?

 

[Dr_EluSivE]

could be a stuck rear Proportioning valve, but that would be pretty unsual.. They are so simple i cant see one going bad. But you could gut it and install a manual valve.. you just have to make sure you set it correctly.

Dr.

 

[Red_LX]

I was having problems with the rear brakes on my mustang sticking at low speeds (if I was going slow on a wet road, the rears would actually lock up). I redid them with new shoes and springs and all that junk, and after that they never worked for ****. If I set the parking brake, it would adjust the shoes out sofar that they would drag like crazy and I'd have to actually pull the drum and back the shoes off manually. I don't know what was wrong with them.

 

[rage987]

Thanks, I will check it out

 

[RustBucket]

You say that the pedal is "light" for the first part of travel. If you pump the pedal does it stiffen up? Try pumping the pedal. If it does in fact firm up, hold it and see if you can feel it bleed down. If it bleeds down and you see no fluid leaks anywhere, you've got a bad master cylinder.

Did it ever got any better after all the times you bled the brakes? Maybe for a day or two?

 

[rage987]

No, the bleeding does not seem to improve anything, I will test the pedal like you suggested and post the results.

 

[rage987]

I tried pumping it (with engine running) and it does not appear to significantly stiffen up pedal feel, or have any significant bleed down.
Should this be quite obvious to the layman?

 

[RustBucket]

Well, it wouldn't be the first defective reman master cylinder I've seen. If that's not the problem, then I think I'll have to side with Dr. Elusive on this and point at the proportioning valve.

I don't know if it still holds true, but those valves used to be a safety device as well. They were able to tell if there was a pressure loss on either the front or the rear systems and block them off so you could get home without either sucking air in to the rest of the system or draining the reservoir dry due to a leak. They were supposed to be self-resetting. Once they saw proper pressure on the blocked off line, they'd pop back in place, the brake light would go out and you'd be all set.

 

[rage987]

Thanks guys, I guess I will see what happens with some new parts

 

[rd]

try bench bleeding the mc again, or jack up the rear of the car to get the mc level, while installed and bleed.

I did this to the Capri and it improved the brakes back to normal.

 

[rage987]

Jacked up the rear end today to make the mc level and bleed everything again (longest to shortest), pumped alot of nice clean air free fluid through the system and no change, if anything it feels a bit worse and more dangerous now.

 

[Stinger]

I have had two different 87-93 Mustangs and neither one of them had rear brakes that worked...they didn't even work a little bit. Jack the car up, apply the brakes...tires keep on rolling.

I tried to track down the problem and never had any luck...I'm convinced the lines are corroded or rusted shut somewhere between the prop valve and the end of the steel brake line at the rear. If I unhook the rear brake line...no fluid comes out.

 

[RustBucket]

Hey Stinger, have you checked for fluid coming out of the rear brake section of the prop valve?

 

[rage987]

I get fluid out of mine, not a lot though... Took apart the prop valve today, seems to be in good shape... re-bled the master cylinder and brakes and nothing changed.
Finally gave in and bought a "new" (non reman) master cylinder, bench bled and installed, bled the entire system again and the brakes seem to feel better.

The rear brake fluid still has lots of very very tiny bubbles in it, I cannot seem to bleed them out and finally ran out of time and energy tonight, may give it another go tomorrow.
Any ideas on the bubbles, or just bleed the *#%$ out of it?

 

[Stinger]

Yes, I get fluid out of the prop valve...

 

[rage987]

Rigged up a homebrew power bleeder today. Didn't get enough air out to make a difference. The rears didn't seem to flow as much as I think they should... I guess the next step is to get a pressure gauge and see if they are within specs.

 

[white1989]

Sounds like a check valve issue.

 

[rage987]

Are you refering to the vacuum valve on the booster?