Got a bit of a problem. Can't get the rear brakes to bleed!

Tried using a pressure bleeder and pushing from the rear back to the MC but all it would do is build pressure and blow the bleeder hose off the bleeder valve. Never got any fluid into the wheel cylinder.

Pumped up the pedal and tried to bleed the old fashioned way but can't get any fluid to the rear bleeders on either side. Cracked a line at the wheel cylinder and it would leak out but can't get anything through the wheel cylinder!

Master cylinder is new dual chamber, new booster, new lines, new metric discs on front (bled fine), everything but the wheel cylinders (I know, why keep one old part but they looked great and were working fine when I switched to the power boster and new MC) is brand new. Why would the brakes work before and now not let fluid through?!?!?

Ideas?

Thanks,
SPark

PS, got it running, sounds great but I really would like to drive it again before it starts snowing around here!

 

I might not be reading everythnig correctly...are you saying you pump up the pedal, then while you have pressure on the pedal, your helper cracks the bleeder?

If so, does your pedal fall to the floor?

 

A pressure bleeder is meant for pushing fluid from the master to the wheels.

Your bleeding problem sounds like you have plugged bleeder screws. Remove the nipples, take a drill bit that fits inside and remove the debris. Be sure to clean the tiny hole in the side also. This is a common problem on vehicles which don't have the little rubber caps.

 

I had similiar problem on my 56F600 and the brake hose had crap in it. New hose on and --no more problem.....Bill

 

With some makes the books say that if you have a residual valve in line, in order to bleed the rear brakes you have to open the rear valve (on the residual) and hold it open with a "c-clip" or other clip of some kind. The rear is usually adjusted for less pressure and I think by pressure bleeding or pumping the peddle the rear valve will close and not allow correct fluid flow....?
Sorry for the generic terminolgy, but check with the master cyl. mfg. and see how they reccoment bleeding the system.
good luck, Ed

 

You don't have a under the floor brake system so you don't need a residual valve. The correct master cylinder and proportioning valve for a front disc and back drums looks like what you should have. I would crack the rear line at the master cylinder and using compressed air check front to rear line, then check flex line, then the cylinder bleeder to see where the blockage is located. If you run your front to back lines on the drivers side, bleed RH rear first,then LH rear. Bleeder valves do get clogged. Have a great day, chuck

 

When she pumps it up (wife is actually trying her best to help with this) and I crack the RR bleeder, nothing comes out and the pedal doesn't move at all. The bleeder is clean and I can blow through it. Same when I tried the LR bleeder. Nothing.

The line will leak if I crack it where it enters the wheel cylinder.

I have a pressure/vacuum bleeding system. it can be used either way. I tried the vacuum method and got nothing. I could not pull any fluid through the bleeder screw. I switched it to pressure and couldn't send pressure back towards the MC. I put enough pressure against it that I blew the rubber line off the pump (nice mess to clean up).

I have rebuilt many, many sets of drum breaks in the last 35 years and have never come up against this one.

Starting to use my plumber's words. Wife went in the house. Arrggghhhh!

SPark

 

You didn't say how many miles since rear cylinders were rebuilt. Some times they are original since they work until they leak. With all new everything I would have opened them to check for corrosion. Dot 3 and 4 is bad about moisture and pitting the inside of cylinders. Corrision may be clogging the inside of the bleed hole, especially if it is facing downward and you say the cylinder input shows fluid. After all is found I would go to dot 5 fluid, better for heat and no moisture. Have a great day,chuck

 

Hey Chuck, When I wrote "residual" I meant "proportioning"...it was a long day and no more brain cells left.
But I still think the issue is in the proportioning valve, its either adjusted too much or the valve needs to be cliped open for bleeding???

Spark, Did the fronts bleed O.K. ???

 

Fronts bleed fine. Used the vacuum pump and it pulled fluid fine, Then pumped/bleed just to be sure. Perfect.

I'm beginning to expect the wheel cylinders have some problems. Brakes worked fine when I took it apart a couple months ago but who knows. Looking for wheel cylinders today.

Here's a link that shows a pic of the booster.MC/combo valve I am using. No proportioning valve other than the combo valve. Like I said, fluid is getting back to the wheel cylinders, just not through them.

https://www.ford-trucks.com/user_gal...163156&width=0

 

So does it leak if you take the bleeder screws right out of the cylinder?

 

LM14, combo valve is the same as proportioning/ metering valve. I have never seen a factory valve be adjustable. After market/hotrod valves do adjust. That is why we buy a master cylinders and combo valves for our installation. Either a disc/disc or a drum/drum or disc/drum installation requires a matching m/c and combo valve. Just because everything is new doesn't mean it can't be clogged, have production faults, bent during running chassis line installation. Troubleshoot all parts of the circuit or system before throwing parts at it. Half the fun of building trucks is learning by your mistakes and making new friends helping you. Have a great day,chuck

 

If you have fluid at the wheel cylinders, but none at the bleeder, then the rest of the system is obviously working. No problems with prop valve, or m/c. It leaves you with the only part left, and that is the wheel cylinders. remove them and inspect them for blockage in the inlet port, make sure they are getting fluid in them. The piston may be stuck as well, pull them down, and check them out, or go with the idea of replacing them.

 

The MC/Boster/Combo valve was custom made for this disc/drum combination.

I am just stumped on why I can't get anything to go through either rear wheel cylinder when it all worked fine before removal. That's what has me stumped.

Took the MC back off the boster, bench bled it again (no air after the first push) and put it back on.

Still can't draw fluid through or push it back through the wheel cylinders! Going to crack each joint between the wheel cylinder and the MC one at a time and work backwards and try to get fluid at each joint.

Keep looking, I guess.

SPark

 

Fresh update. I can break the bleeders at each rear wheel and push fluid through the bleeder from left to right. Each bleeder is working. I can't get a pedal to bleed the rears. The fronts bleed fine but I don't get anything out the rears. No signs of fluid at the rears (as many as 15 to 20 times doing the pumping and bleeding routine). Still nothing out the rears.

Starting to suspect the combo valve? I can get fluid out the MC to the line going to the combo valve and at one point I had fluid past the combo valve but not going to the rear.

What would be the signs of an improper combo valve?

Is it possible the pushrod between the boster and MC is too short and not getting a full stroke to the MC?

SPark