another brake issue

[cheyenne10]

I guess we can spend a lot of time on brakes, the single most important part of truck!! Truck is 71 C20 2 wheeler with PDB.

I installed a new/rebuilt booster, prop valve and master cyl. I bench bled the master and installed the rest. I now go to bleed standard sequence and I keep checking master and front reservior is overflowing (brake fluid on my new parts,..........sob, sob) Anyway continue to struggle with this and same thing over and over. Front calipers have bleeder ontop of caliper so hard to get to and getting messy under there too. Doesn't seem to have volume of fluid expected coming our of bleeders in front. Work and work on it and end up calling it a night. Take for drive and all feels well. I am still uncomfortable with what I saw. Very dirty fluid coming out and strange symptom where front reservior seems fuller than when filled.

Is fluid passing from front to backc reserviors?
What have I done wrong? I opened the bleeder on prop valve 1st and then did all 4 brakes twice.

Is there special sequence for prop valve and master cyl. bleeding on truck? I will need to eventaully get to rebuild all brakes at wheels, just hoping to get it driveable for next 2 weeks.

[cheyenne10]

Just drove it to work (a couple of miles with about 6 stops). Worked ok but I would expect fronts to grab firmer with new pieces.

Any help on overflowing master cylinder?

[cheyenne10]

Still worried about overflowing master. I remove fluid down to exceptabel level, use brakes a little and open up and fluid spills out. Whats up with that?

[BobbyK]

It's poss the seal inbetween the two resovoirs(on the piston) has gone bad.

When you depress the pedal fluid is going to the calipers but also bleeding past the seal on the piston into the other resovoir.

They're are plenty of guys who have had problems with rebuilt M/C's right out the box.

[Fred T]

Talk to the store where you bought the m/c. Sounds like they should replace it for you.

[Longhorn Man]

Are your rear shoes adjusted properly?
I have no idea why, or if it is even related, but when my rear shoes were way out of adjustment, the rear resivour would go low and the front over filled.
no idea why or how...but i know it stopped when I replaced the shoes and had them adjusted properly.

[cheyenne10]

Rear shoes have lots of pad and adjusted correctly (star wheels/self adjusters work good!!)

Still having front reservoir overfilling and maybe slight leak at back of master near booster. This sounds like faulty master but system should still work well shouldn't it?)

Back to bleeding, do I have to keep the switch on the front of the proportioning valve depressed to bleed system? (read this somewhere that ther was a tool to keep button depressed during bleeding)

Also bleeders on front calipers are on top of caliper. This makes it tough to bleed into attached hose. I left the hose off the 1st time but big mess. Is there a better bleeder kit to use for 1 man operation?

Last question for now. How much free travel should I have in pedal before I should feel resistance after bleeding is done?

As usual I appriciate all advise.

[cheyenne10]

Please help with suggestions. I'm without driver right now.

[MOTHERTRUCKERS]

If the master is leaking at the booster it is a bad master cylinder, when we get rebuilt master cylinders we pull them apart and run a brake cylinder hone through them and check for bore pits before installing them. I would bet you have some scratches, deep pits or its been rebuilt so many times its over the bore limit, take it apart and check it for scratches,bad o-rings etc.

[cheyenne10]

Ed;

thank you for help. I didn't understand that rebuilts might have problem. I guess it makes sense because they take cores in when they sell replacement units and probably production line the rebuilds. Would this type of defect also cause the fluid to get from the back reservoir into the front one? I fill up both with correct amounts, use it a little and then front is over flowing and back one is way down.

[MOTHERTRUCKERS]

Yes if there are scratches,bore pits or non sealing 0 rings.