Vette Master Cylinder

[XJ Chief]

Okay, I've checked just about everything there is to check now. Wheel cylinders are good, lines are good. Only thing left IS the master. Here's what I'm thinking...

I think the push rod needs to be lenthened. I think the front cylinder is being compressed and getting great pressure to the front (rear wheels) piston but the push rod is stopped before it can push the rear (front wheels) piston. Lengthening the push rod would allow the front and back to both be pressurized.



This is a simple system, there really isn't anything else left to trouble shoot so this week I'll adjust the pushrod and see if that's it. Other than that, there's nothing left to do except go back to the original system or keep trying other master cylinders until I find one that works.

[robsgp]

Sure sounds like 3 of us are having the same thing. I did some more adjusting this weekend. Pedal feels better and truck seems to stop better. I looked in the adjustment slots and turned until all had about 1/4" of threads showing. Also had my son pump and cracked the front bleeders again. More than a trickle like I had before but it's not shooting out. I also pulled the LR wheel and drum because I saw a drop of fluid down the backing plate. I think it was coming from where the line attaches to the wheel cylinder so I put another crank on it. Unfortunately I only get a few hours a week to fiddle with my truck.

[WetCJ]

Not sure I'm following your thinking here, the front piston is supposed to be moved by the pressure created in front of the back piston (the area shown in your brackets) not a mechanical connection. Yes the mechanical connection is there but should only come into play if there is a pressure loss in the rear. Usually you can feel when this is occuring, does it feel like the pedal goes part way then you feel the contact with the front piston? Or am I missing your point?
I've fought some brake systems in the past so I can understand your frustration. That said let me offer some thoughts I've had in reading these posts the last couple days-
Brake adjustment can make a big difference in how smoothly the bleeding process goes. If you have any doubts adjust the brakes out all the way tight while bleeding to eliminate that possibility. Back off later.
I was originally taught to bleed a new master cylinder by plugging both outlets with my finger tips while someone else slowly stepped on the pedal. Hold them tightly closed so no air can get back in when the pedal is released. When you have fluid pushing past your finger for the complete stroke, hook that line back up. Messy yes, but you know for sure that you are creating pressure. Might be worth a try.
One other thought, if your lines happen to be same size, switch them on the master cylinder just to see if your problem switches ends also. If yes, master cylinder issue.
Just my thoughts, Good Luck, Todd

[Fastfrankie]

Lengthening the pushrod won't do a thing. I lengthened mine and about a half inch and at that point it was pushing the piston into the bore. Forget lengthening it unless you plan on doing some serious fabricating and moving the entire brake pedal assembly back a little to compensate for the longer pushrod.
I went back to a stock pushrod because lengthening it would create more problems.
It won't be too long before I go back to the stock m/c either.
As far as bleeding the fronts to get the pedal to go to the floor - I couldn't get it to happen. Couldn't get a stream if I tried and I tried everything! I even cracked both bleeders on one side and tried that. I even tried to experiment and removed the stinking drums to just see if "an adjustment" problem was occuring - by allowing the drums on all fours to expand without restriction, an din theory allowing the piston to "travel" more and push out m ore fluid.

Nope....adjusting your drums in my humble opinion and almost 20 years of working on cars has nothing to do with how successful bleeding your brakes will be.

I've bled tons of wheel cylinders and the pedal always goes to the floor or drops when cracking the bleeders. I couldn't get the pedal to drop no matter what I tried. Something is wrong...

[XJ Chief]

Success! At least for now. I pressure bled the system from the brake line out of the master and after pushing a whole lot of brake fluid through the system I coaxed out all the air. I then reconnected the line and reverse pressure bled the system from the furthest point and the brakes are now working. What a PITA this has been. If I still have brakes and no fluid leaks next time I drive I will be satisfied that it is %100 done.

[Fastfrankie]

You have more willpower than me. I returned the vette master about three hours ago, got my money back and will be installing the Wagner single resevior m/c Thursday or Friday evening.
I don't own a pressure bleeder...how were you able to pressure bleed each line separately off the master cylinder? Is there some sort of adaptor?
When I bled those brakes, I had my old man pump them manually so much, that night he could barely walk! I've never had to use a pressure bleeder so far with anything...well I am glad you found success.
Just for kicks, can you do me a small favor? Now that everything is working, have someone get in your truck and pump up the brakes and you go and crack a front bleeder. Let me know if the pedal drops to the floor and you get a steady stream of fluid...that will be a good test!

[robsgp]

Since installing m/c and wheel clyinders I'm on my 4th bottle of brake fluid. When it was up on jack stands the front wheels do lock up. I haven't pulled a front drum to see if there's been any shoe wear but after my last drive all 4 drums felt slightly warm. I'll have to ride the brakes a little more next time but am thinking maybe I'm getting closer.

I was wondering if this trouble has anything to do with the different size lines? Wouldn't the same volume of fluid have less pressure in a larger line? Or would the lines from the distribution block out to the fronts equalize that? At the m/c the one to the fronts is 1/4 and 3/16 to the back if i recall. I don't know if the m/c ports are the same size but I know the threads are different.

[DAVEJ]

Just a comment on brake bleeding procedures. Pumping the brake is not the proper way to bleed them,(according to my tech school instructer,many years ago).The "proper way" is ,open bleeder,push down pedal,close bleeder,release pedal ,repeat,repeat,etc. My son was working on his friends truc and couldnt get brakes by pumping and opening bleeder,told him to try my way,said it wouldn't work. Well after about 30 seqeunces of the proper way ,they had brakes. Dad-one ,Junior-0. Supposedly pumping can cause too many bubbles in the fluid.

[XJ Chief]

You have more willpower than me. I returned the vette master about three hours ago, got my money back and will be installing the Wagner single resevior m/c Thursday or Friday evening.
I don't own a pressure bleeder...how were you able to pressure bleed each line separately off the master cylinder? Is there some sort of adaptor?
When I bled those brakes, I had my old man pump them manually so much, that night he could barely walk! I've never had to use a pressure bleeder so far with anything...well I am glad you found success.
Just for kicks, can you do me a small favor? Now that everything is working, have someone get in your truck and pump up the brakes and you go and crack a front bleeder. Let me know if the pedal drops to the floor and you get a steady stream of fluid...that will be a good test!

I'll give it a shot next time I pull the truck out. As for the pressure bleeder, just make one. I used a pump sprayer and some 1/4 ID line. Not that fancy and only cost 20 something dollars. I was going to make a super cool one but I didn't feel like tracking down a master cylinder cover and drilling a hole in it. Mine is really just the pump spayer and the 1/4 ID line. It fit nicely over the 1/4 OD brake line. That's the reason I had to reverse bleed it after clearing the line, when I reattached it to the master I'm sure a little air got back in while I reconnected it.

Here's a link to where I got the idea:
http://www.bmw-m.net/TechProc/bleeder.htm

[amphi]

This might explain why the (pump, push-hold, open-bleeder, close-bleeder, pump again) method is not working.

Year's back, I had a similar problem with the brakes on my Amphicar. I simply could not get all of the air out of the system using the normal pump hold method. I went thru many jugs of fluid and many hours if frustration.

Finally got it purged of air by putting a container with fluid at each wheel with a hose from each bleeder -- did the slow pump and release keeping the master cylinder full. The brakes have been fine now for years.

Here is what was going on!!

With pressure applied to the pedal and a bleeder opened it would go to the floor as expected. After closing the bleeder and then releasing the pedal the piston in the master cylinder would return to the normal at-rest position supposedly refilling with fluid. However that was not happening. The rear cup on the master cylinder piston was drawing outside air on each quick long return stroke introducing more air each time. Maybe if I had released the pedal more slowly it would have filled with fluid and not air but I don't really know because I solved the problem as mentioned above.

This could very likely explain the reason for some of the problems mentioned in this thread since the front brakes are plumbed to the rear cavity on the dual cylinder. The rear piston, where push the rod is, has a cup exposed to atmosphere. However this doesn't explain why in one case above where the pedal did not go to the floor. I don't get that one.

The normal (pump, push-hold, open-bleeder, close-bleeder, pump again) method might work if the brake pedal is release very very slowly after closing a bleeder.