no rear brakes (1978 cj7)

[ksouthw80]

I just installed a new mastercylinder(bench bled), a new proportioning valve, and all new premade brake lines and I have no rear brakes. There is very little fluid to the rear, almost residual. The pedal stiffens up somewhat. Is it possible it needs to be pressure bled? Maybe a bad Pvalve? I have cracked all the lines in an attempt to release any hyd lock. The pvalve does push fluid once built up, then no fluid seems to leave the master cyl. ? ? ?

 

[IOPort51]

I just installed a new mastercylinder(bench bled), a new proportioning valve, and all new premade brake lines and I have no rear brakes. There is very little fluid to the rear, almost residual. The pedal stiffens up somewhat. Is it possible it needs to be pressure bled? Maybe a bad Pvalve? I have cracked all the lines in an attempt to release any hyd lock. The pvalve does push fluid once built up, then no fluid seems to leave the master cyl. ? ? ?

some time ago I replaced a MC and it had short hoses that you ran from the fitting holes back to the reservoir and hand pumped fluid to fill it. The last MC I did had plugs in the fittings and the procedure was to hand pump until it built pressure, no pumping fluid at all.

I actually had to go back and read the instructions to find that the accepted procedure had changed.

If you look at the MC piston/spring arraignment you can see how one end must pump up before the other receives any fluid at all.

I also had a heck of a time getting all the air out of the system. I had to make a plate to set on the top of the reservoir with a vacuum fitting on it to pull air from the top of the system in addition to pulling it down through the wheel calipers.

 

[ksouthw80]

I just read in a chiltons book that the pvalve fwd valve stem, the part with the dust cover has to be held in.. I've never heard that before. Guess I'll try that too.

 

[IOPort51]

I hate working on anything that involves a tubing wrench and a creeper.

 

[ksouthw80]

I know right, I'm a mechanic for a living and I will say putting those new lines in was a pain.Of course every one of the fittings were completely rounded.But everything is back in to factory specs, line clamps and all. This is the only thing keeping me from driving it , or so I think. I do need to order an extended rear brake hose, but I want to drive it TODAY.

 

[BusaDave9]

There is very little fluid to the rear, almost residual.

So you pedal is firm or somewhat firm. When you open the bleeder valve on the rear cylinder do you get good flow when the pedal is pushed?

No rear brakes or just not as much as there should be? With the rear jacked up and someone pressing on the brake can the rear tire be rotated?

 

[ksouthw80]

There is no fluid to the rear. but there is fluid past the pvalve. Its like it doesnt have enough (pressure?) to fill the rear lines. I'm going to try to bleed them with a hose and a container filled with fluid from the rear cylinders. I've never had to do it this way but maybe will work. All lines are new. The pedal is relatively firm.

 

[IOPort51]

If and/or when that does not work, put the plugs that came in the MC back in and pump till hard. hook the lines back up and do the hose in a jar thing.

 

[ksouthw80]

Ok I finally got fluid to the rear by pumping for hours. Test drive went well... Thanks for all the input, I"m glad this part of the project is DONE!