Getting Disc Brakes to Retract

[Don Coatney]

Do not do both. I suggest you first remove the residual valve in the master cylinder.

 

[Joe Flanagan]

That's all it is, just that little disc at the back of the cylinder (marked "valve assembly" in the diagram)?

Edited June 2, 2014 by Joe Flanagan

[Jeff Balazs]

Joe;

It appears that I may have spoken out of turn. I did not attempt to use an original M/C so my comments are probably not valid to your situation.

What ever you end up doing make sure you do some panic stop testing under safe conditions. This should be done early on. Any time brakes are being modified it is important to make certain that you have a proper balance between the front and the rear.

 

Jeff

[Joe Flanagan]

OK, thanks Jeff. I will be sure to test the brakes thoroughly once I get it going.

[Joe Flanagan]

I just opened up the master cylinder and found what looks like the residual valve. But there was also a rubber washer that fell out once I took the rear cap off the cylinder and I'm not sure where it goes. From the imprints on the rubber, it looks like it goes where it is positioned in this picture. Can anyone tell me if this is correct? The diagram doesn't show this washer. It's probably part of what is called the "assembly." Sure looks like this is where it went:

 

 

If I remove the residual valve, I assume this washer gets removed, too, correct?

Edited June 2, 2014 by Joe Flanagan

[casper50]

Joe I have an original mcrebuild kit.  I'll look in about 90 min when I get home and see if the valve has that rubber attached.

[nonstop]

If I'm not mistaken, I left the washer in there when I took it out - if for nothing else it kept that much more tension on the spring. The big thing is just getting that valve removed.

[Joe Flanagan]

That's what I figured. I see no harm in leaving it there. 

[casper50]

Joe the washer is separate from the valve.

[casper50]

instructions are hard to see clearly even in person

 

[Joe Flanagan]

Thanks, everyone. Looks like it stays.

[Joe Flanagan]

Removing the stock residual valve seems to have done the trick. The front rotors turn freely after stepping on the brake pedal. I also disassembled and cleaned the calipers. The pedal returns much more easily, too, though at times it seems to hang up very slightly. I have yet to bleed the system but will be doing that this weekend. I had a couple of leaking fittings that I had a really tough time fixing. I was wondering if the fact that I had two residual pressure valves in place might have had something to do with that. I'd step on the pedal and it would build up a lot of pressure and just stay there. I'm wondering if the prolonged pressure might have made those fittings more prone to leaking. 

[Don Coatney]

Doubtful on the excess pressure causing leaks. The system is designed to take a lot more pressure than normal driving. Glad you fixed the problem.

[RobertKB]

If it leaks, tighten it. If it sitll leaks tighten some more. If it still leaks tighten some more. If it sitll leaks something is defective. Should not leak just sitting there. Think of the PSI when braking hard and a viable system has no leaks.

[Joe Flanagan]

I had to re-do a couple of flared ends. One connection wouldn't stop leaking no matter how much I tightened it, so that one's a project. Only leaks under pressure and a small leak at that, but I have to fix it.

[nonstop]

What is that one going into? I ask because I had a leaking line that turned out to be the brass fitting instead - it had a small crack in it.

[Joe Flanagan]

It goes into a brass fitting. It was an original T junction. I re-did the flare end but it still leaked. Then I replaced the T with a new one. Still leaked. Re-did the flare again and tightened it up. It was good for a long time, leaked a few drops yesterday when the front brakes were locked up and under pressure, then hasn't leaked again since (even when pumping the pedal). 

[Joe Flanagan]

This problem is back. Today I bled the brakes and all went well until I realized that the fronts have locked up again. If I crack the bleeder valves open, they free up, but applying the brakes makes them lock up. You may remember from earlier posts that I disassembled and cleaned the calipers. Now I have replaced them just so I could eliminate them as a cause of the problem. I've got more pressure in the system than I ever did before, which was not the case last weekend, when I got the front rotors to move freely. Also, as you may recall, I removed the stock residual valve from the MC. I still have the inline valves installed, 2 lbs.to the front and 10 lbs. to the rear. I have confirmed that the return port is not blocked. One thing I have not ruled out is the hoses, which someone mentioned may have started deteriorating inside and which may be acting as one-way check valves. I plan to replace those, but they look great on the outside. They did sit for 12 years with no fluid in them. They were new then. I had to stop the bleeding process when I realized I never really fixed the leaking fitting at the T-joint. So next step is to replace the hoses in the front and get a new T-joint and then see what happens. Any other suggestions?

[Jeff Balazs]

Joe;

I think you may find that the 2# residual valves are causing the problem. Remove them and it should solve the problem. This sounds just like what I found when I put my brake system together......and the solution was to remove these valves. It is amazing how much force this 2#'s can exert.

 

There is however one other thing you can check on. It is just possible that you don't have the brake pedal adjustment set correctly. If there is not enough free play at the pedal this can prevent the M/C from fully releasing pressure on the brakes. I don't know about the cars but on my truck with a different M/C mounted.......this adjustment is fairly fussy. Literally a 1/4 turn one direction or the other from the right spot and it either causes the brakes to drag or has too much free play.

 

Hope this helps.

Jeff

[Joe Flanagan]

Thanks, Jeff. If I were to remove the inline residual valve, I would have no residual pressure at all on the front brakes because I removed the stock valve from the master cylinder. Will check the pedal adjustment.

[Don Coatney]

I had a pedal adjustment issue (as in not enough free play) when I installed my dual chambered Master Cylinder resulting in the same issue you are having. Suggest you check that first.

[Joe Flanagan]

Pedal adjustment was something I completely overlooked in this process. I just went and checked it and there is zero freeplay in the pedal. Interesting that 1/8 to 1/4 inch freeplay, as required in the manual, would make that much difference. I haven't adjusted the push rod yet but will do so tomorrow and report back.

Thanks. 

[Young Ed]

Pedal adjustment was something I completely overlooked in this process. I just went and checked it and there is zero freeplay in the pedal. Interesting that 1/8 to 1/4 inch freeplay, as required in the manual, would make that much difference. I haven't adjusted the push rod yet but will do so tomorrow and report back.

Thanks. 

 

DING DING DING we have a winner. I bet you'll be problem free after that. I believe the freeplay is what allows the MC to retract enough to unblock the relieve port

Edited June 9, 2014 by Young Ed

[Jeff Balazs]

Joe;

That sounds like it is going to be the solution. When you have it set right you should be able to release the parking brake and roll the car by pushing it. There will be a bit of drag at the discs but you should be able to roll the car.

 

Jeff

[Joe Flanagan]

It turns out that adjusting the pedal freeplay solved the problem. But while trying to repair a persistent leak, the plot got more complicated. 

I had a leak at the fitting where the brake line goes into the 2 lb. residual valve to the front brakes. While disassembling the connection, the innards of the residual valve came out: one small spring, a rubber object with a very complicated shape, and the brass fitting that goes in the end. This happened when I pulled the brake line away from the valve. 

Since I didn't know how they all went together, I considered disassembling the 10 lb. valve to the rear, but this was difficult and I stopped before I made matters worse. Research didn't turn up any answers on how the pieces went together.

So I studied it, took a guess, and reassembled it. A neighbor and I bled the brakes. The pedal feels good, plenty of pressure, but the fronts are locked up. The rears turn freely. I'm assuming I put the valve back together wrong and have a new one on order.

Just to see what would happen, I increased the pedal freeplay but that had no effect.

Recall that I did remove the stock residual valve from the master cylinder. Also, an observation that may shed some light on the problem: As of yesterday evening, the front brakes were locked up tight. This morning they are free. I depressed the pedal once and they are locked up again. So it seems that pressure is relieved somehow over time. I'd be curious to get your ideas on what's happening here. Thanks.