Bleeding Brakes

[Monark192]

Here we go again - after learning from you helpful folks that persistance is the key when bleeding brakes and getting the job done on the now sold '75, I thought I could manage it the next time around on the '74.5. Well, it aint working. The master is brand new, installed and full of fluid. I tried and tried to get the rear blakes to bleed with no luck I moved to the fronts in search of a little acomplishment and joy, I can hapily pump fluid out of each caliper. Back to the rears, I even tried removing the brake line from the cylinder to make sure there isn't a blockage downstream. Still nothing. I understand (I think) that is is a dual line system but am confused as to how the master will only pump to the fronts. Is there a trick to getting it going??

Sorry for the long ramble (but I do feel a little better for it /bcforum/images/%%GRAEMLIN_URL%%/crazy.gif)

 

[Keoke]

HI your problem is in the Master Cylinder. Since it is new I would return it for a replacement. However, make sure you have the correct free play in the clutch pedal.--Fwiw--Keoke

 

[Bruce74B]

Or might it be a clog or a pinch UPline from the rear brakes... in the rear brake line somewhere? Disconnect the line where is goes over the axle and see if you have hydraulics there. Then work your way back to the MC and see if it pumps fluid out into the line.

Bruce

 

[jlaird]

I would suspect a line problem as well and would do as Bruce suggests. One step at a time.

 

[ecurie_ecosse]

I would suspect a line problem as well and would do as Bruce suggests. One step at a time.

As they say "one step at a time." It's a beastly job and there are no short cuts. /bcforum/images/%%GRAEMLIN_URL%%/eek.gif

Stuart.

 

[DrEntropy]

Yes! Look to the flex-line at the diff. Loosen it at the chassis side and push the pedal a few times... I bet you'll get fluid. The flex-line can swell internally and not allow fluid to get to the rear cylinders. Cheap fix.

Other possibility is the hydraulic "switch" on the left inner wing: made to bias pressure to the working side of the system in case of failure. But check the flex hose first!

 

[Steve_S]

The rear pipes are often crushed from careless flatbed operators.

 

[PeterC]

Did you check that the shuttle is centered in the PWDA? Remove switch, re-center shuttle, install switch. You "should" be OK.

Peter C.

 

[Monark192]

I have removed the brake line where it exits the master cylinder to remove all possible downstream blockages. Still nothing comes out. Can the new cylinder be bad like this?

 

[PeterC]

Hmmm.... I don't have one in front of me, but is the pushrod adjustable? Is it adjusted too tight, no freeplay? Maybe the port isn't opening. And, yes, unfortunately new cylinders can be bad.

Peter

 

[DrEntropy]

It's ~possible~ the front section of the M/C is airlocked (i.e. not hauling fluid into it due to air blocking it), bench bleeding it prior to installation would relieve this. But it really sounds as if the M/C was pre FUBAR'd. Rarely will a M/C *not* pump thru both chambers after the second pedal stroke.

Pushrod on this'n isn't adjustable, IIRC.

 

[Bumble_Bee]

I just replaced my M.C. and all of the wheel cylinders as well as the brake shoes and all of the lines. It was very frustrating for sure to get all of the air out. But out of frustration and thought I did this. I adjusted the brake shoes all the way out so the wheels would not turn, THEN I bled the system. My theory is that there is more pressure to the cylinders when there is not movement in the wheel cylinders and therefore more fluid flow to the bleeders. I did this along with the tube to the baby food jar of fluid and a 1/2 hour later viola!!! Make sure to go to each wheel and re-adjust the brake shoes. It worked great for me! Larry

 

[DrEntropy]

Setting the shoes to correct adjustment then pulling the handbrake will do the same thing, FYI.