[Taper]

Hi...I'm pretty new to Cougars and no doubt this question has been posed before...but I would really appreciate some help. I have a shop manual and followed it, but still have problems. After replacing the master cylinder, both front calipers, and both rear wheel cylinders, I still haver very weak brakes. I bench bled the MC, bled the entire system 3 times and yet when I apply the brakes hard, the rears lock up. It is as if there are no front brakes at all. The warning light stays lit even after trying to re-balance the system as per the shop manual. My question is this: Does the dist. block and proportioning valve stay stuck occasionally and require replacing? The book says it is not servacible. No leaks in the system, anywhere. Brakes pump up firm and hold fine while sitting still, but when driving.....no fronts or very little. My proportioning valve does not have the O-ring I have read about. Would this cause my condition?

Please help.....

 

[bowl]

Did you adjust the rear brake shoes? adjust them til they drag pretty hard then back it off til they just BARELY rub. tap the brake peddel a few times and recheck, the tire should rotate freeley and you can still hear a slight "shh" sound of the shoes. that will give you less peddle travel by decreesing the distance the shoes have to move before contacting the drum.

cheers,
rich

 

[Taper]

Hi Rich...thanks for the reply. To answer your question, yes. I did adjust the back shoes exactly like you described. I am not an expert brake guy, but after installing all new hydraulic components (except the distribution block and the proportioning valve) I am inclined to think they are at fault. The light stays lit, and I have tried to re-balance the valve by creating a imbalance of the OPPOSITE side of the system....just like the book suggests. This did not help...so I was wondering if the valve is permanently stuck in one direction and will not re-center...thereby causing little or no front brakes. Also, the O-ring I have read about is missing...and was wondering if this causes anything?
Any other things I might try???
Mike

 

[dark7068]

well, the light staying lit is a sign of air leak in the system, and when you get hard pedal when the cars at idle, and no pedal when cruizing, you could have a faulty booster or a small vacuumm leak somewhere. Run the car in reverse and set the automatic adjusters by slamming on the brakes, hopefully that works. Brakes are definately nothing to play with if they arent working properly, take it to a shop if your unsure. Good luck.

Rick

 

[Taper]

Hi...thanks again for the replies you guys...keep them coming.
I also changed out the brake vacuum booster for a rebuilt one from Adavance Auto parts store ( local auto parts supplier) Perhaps I am not explaining the situation properly. The rear brakes seem to work fine. Its the fronts that are almost non existant. That is why I am inclined to think that the proportioning valve and/or distribution block is faulty. These are the only parts not replaced. I do have pedal when driving...it just takes almost all of the pedal travel to get the brakes to engage....and when they do engage...it appears as if ONLY the rear brakes are applying. There is NO fluid leaks anywhere!!! I bench bled the master cylinder, and all the wheels at least 3 times now. I cannot see how air is in the system anywhere.
Thanks again guys...PLEASE KEEP THE REPLIES COMING!!!

 

[Ray]

OK heres a stupid question. Did ya manage to put the RS caliper on left and vice versa cause if ya did you'll never get the air outta the frts. Two the prop valves do stick but its not a prop valve at all its a metering block with a sliding piston that completes grnd so dash lite lites. Take the metering block out open each end and the switch in center out center the pin inside. Its trick but can be done also tedious.Prop valve is the tubed bit on 68/9 that has RESIDUAL valve inside. 67s have Residual at rear diff and 70s incorporate into master cylinder any residual needed.

 

[Taper]

Thanks RAY........I appreciate your reply. This maybe what I had done. How embarrassed I will bhe if this is the case.
As far as #2 goes....you suggest to take the metering block and manually center it? Will try it out.
Do I need the o-ring on the prop valve? It is partially missing/deteriorated. I assume this is to hold the residual pressure in?

Mike

 

[Cougar Bill]

O-Ring

The O-ring is basically a dust/vent cover. The center spool get corroded and sticks. This could be why the light won't go out. I rebuild them using square cut O-rings. Clean up using #0000 steel wool and use spray cleaner on the whole thing before reassembly. The rear pressure residual valve (pro.valve) can be rebuilt the same way. The trick is getting the thing apart w/ out damaging something. Use drifts to drive out the spool valves.

On another note, you say you replaced the booster. The rod between the master cyl and booster has a adjustable tip. I suggest checking the distance, as shown in the service manual. I made a "gauge" from the book. I find a 1/2 to 3/4 turn out (longer) after the guage setting give the best results.

I suspect the master cyl is not activating fully ( enough fluid movement) the front calipers. Adjusting this will give the pedal a harder feel. Don't go too far out, or the brakes won't release.

Hope this helps, Cougar Bill

 

[Taper]

Thanks Cougar Bill....I really appreciate the help.
Guys...my expertise is in construction. Hence the name "taper" I have a drywall company. Any wall related questions you have.....please email me. I would gladly return the favor.
Same goes for anyone out there who took the time to write a reply. Very nice of you guys.....

Mike

 

[greggieatthebat]

Mike-
Dumb question, but are you sure your front lines are clear? If there is a blockage in your lines, you could be negating the work of the prop valve/metering block. This would more likely happen to only one side and cause pulling left or right, but maybe it's possible to block both lines? Or maybe the blockage is at the master, so the fronts aren't getting any fluid pressure? If the brake pedal is depressed, do you observe the calipers moving at all?

I'm just trying to brainstorm, and I'm having flashbacks of the masking tape stuck into my fuel line to "keep the line clear". Took ~100 psi to blow it out.

Don't forget to tell us what your problem was once you find it!

 

[Taper]

Greggieatthebat....thanks for any insight to this matter you can muster up...no matter how trivial or "dumb" you might think it to be. To answer your question....the lines appear to be free of blockage. My calipers at the fronts bleed when cracked...and move when brakes applied. I bought a master cylinder/booster valve combo..and it came pre assembled (MC attached to booster) and I assumed it to be ok. After taking the MC off the booster, I went to put ot back on and didnt even realize it at the time...but I had to use the two nuts to pull the MC tight to the booster. That implies that the rod was out of adjustment and too long. Ray brought this to my attention (thanks again Ray) He thinks that the p[iston in the MC is not returning back all the way and therefore all the travel is not being utilized. Here in KC we are getting ready for a winter storm, and I have not had a chance to take the MC back off and adjust the rog lenght. Once I do, I'll post the results. I feel it is either that, or the prop valve/metering block is off center...causing my light to stay on and not allowing fluid to flow to the fronts properly.
Thanks guys......I appreciate the help.
Mike

 

[itow]

Who needs brakes, thats what guide rails and walls are for!!!
JUST KIDDING! I think they have you on the right track now. Good luck and like Greggieatthebat said let us know what you find out is wrong...
Scott