Master cylinder bleed

dweymer · dweymer's Garage

What's the best way to bleed the brake MC on a '74?

Steve Marshall · 11-06-2005, 06:17 PM

Power Bleeder.

dweymer · dweymer's Garage

I'm using that, and still have a major bubble, almost no pressure to the pedal.

DByers · 11-07-2005, 05:59 AM

Don, Just had to go through his process myself on my 71. The old fashioned way is the only method that really works. If you are getting no pedal then the trick is to use the power bleeder to build pressure in the system. Say about 20psi. This will get the brake system the pressure it needs for the pedal to start working since the air is not allowing pressure to build the oild fashioned way. Then go around to each caliper starting with the closest and bleed the old fashioned way, with the PB still in place. Do this more then several times per cylinder and keep the pressure in the PB up. Once you get pedal, start removing PSI from the PB in 5PSI increments while going around to the calipers again bleeding the old fashioned way. Took Ingo, my freind Lara and myself about 45 minutes doing it this way. One on the pedal, one at the caliper being bled and one for the PB. Came across this purely method by accident when trying to remove air from my brakes.
Good luck,
Dan

RallyJon · 11-07-2005, 06:18 AM

Dan, you're saying you pump the pedal with the PB attached and pressurized?

Can you leave the valves open or do you still close them in between pedal strokes?

dweymer · dweymer's Garage

man I need speed bleeders....thanks Dan, will try it later today.

DByers · 11-07-2005, 08:07 AM

Quote:

Dan, you're saying you pump the pedal with the PB attached and pressurized?

Yes. What I found was that with a total loss of pedal do to air in the lines you could not build enough pressure by using just the pedal method. If you used just the power bleeder, you would never actuate the master cylinder and are just moving fluid and the air can still ge trapped. By using the PB to pressurize the system you are able to use the pedal to move the brake fluid thru the MBC and lines. By doing the 3 pump on the pedal and then opening the (any 1) caliper at the top of the 4th stroke and closing by the bottom (the old fashioned bleed) you are able to start removing the air in the MBC and lines easier. Once you start to get firm pedal, or any pedal, you can start to reduce the PSI from the PB. Like I said, we just happened on this by accident. We were unable to get any pedal in my 71 and the PB was not removing the air at all. By using the PB/Pedal method we were able to remove all the air quickly.
Note #1 - I filled the PB with fluid (cheap stuff as you will go through alot!) so I wouldnt have to just deal with keeping the reservoir full with fluid.
Note #2 - this is a 2 person job and speed bleeders should not be used. You need to build pressure with the pedal and the speed bleeders will not allow that when open. The fluid will just flow when the pedal is pressed as they are designed to do. You must use the open at the top of pedal stroke and close at bottom to build pressure and remove the air. Speedbleeders work fine when the air is already removed and you are just changing fluid.
Note #3 - this is just my experience and I could be FOS.

Hope that makes more sense.

dweymer · dweymer's Garage

Nope, Dan you are FOS...

Kidding, it did not work though. I need another quart of fluid. I am stumped on this one. The fluid is not leaking past the seals either, it is like the line from the resevoir to the MC is vapor locked.

DByers · 11-09-2005, 12:31 PM

Don, did you use speed bleeders? Hopefully you had a spare set of hands to open and close the bleed valves at the calipers while you worked the pedal. The last thing you could do is bleed the MBC while its installed by opening the lines at the MBC while working the pedal.
Your problem sounds exactly like mine.
It took the better part of 45 minutes for 3 of us to do my brakes. Before that it took me the better part of 3 weeks by myself to get nowhere. Its a process for sure. I went threw many a hammer and verbage before mine started to work.

Either way I am FOS.

dweymer · dweymer's Garage

no speedbleeders, me and the wife. I need more fluid, so will try again tommorrow. Wife on the pedal, you know brake fluid burns a little on the skin....

DByers · 11-14-2005, 04:13 PM

Don, any update on this problem?

dweymer · dweymer's Garage

Nope, I am changing the rear t-bars, and bushings, so I figure I'll leave it as is so I can just do the whole thing after that. I will probably start with that today, so maybe a week until the brakes again. I'll update it again. It seems I am losing pressure/fluid from the soft lines at the resevoir, so I'll change those too.