[spoor]

I just replaced my Master cylinder and I can’t get the air out of the rear system. We spent all weekend pumping and did not make any progress. Where is the air?? Proportioning Valve? In the rear brake cylinders? Will a Pressure Bleed Help this situation? We were going to Sebring this week for the Historics, take advantage of the track touring hours, but with no brakes ... we might have to take the family SUV....aahhahaahh....HELP

I have read a few of the Brake Post, but no one seems to have a true mechanics fix, just luck it seems.

Is there a Mechanics hotline that can educate me on what to check for?


Thank you all!

 

[65Sprint]

Did you bench prime the master cylinder before installing it? There is some discussion here. How did you determine that only the rear brake lines have air in them? You may indeed just see bubbles in the bleed line at the rear wheels but if your pedal is very spongy or goes to the floor, I suspect you have air in other locations as well. Without being overly aggressive with the brake pedal, bleed in order of decreasing distance to the master cylinder (passenger side rear, driver side rear, passenger side front, driver side front). Typically, I cannot get a perfect "pedal" on the initial bleed. I get very close and then drive the car for a day or two and bleed again.

 

[spoor]

When the front calipers are closed I have half pedal, open front and pedal drops. We bled the MS on the car with all 4 calipers open and 4 hoses running back to the MS. No air in any of the lines when bleeding. And used your above wheel bleed system starting with driver side rear. Currently pedal drops about 4 to 5 inches with minimal stopping power....not drivable. No leaks either. This afternoon I was going to take off the rear line, plug it at the MS. And see if the pedal improves. I think this might tell me that the air is in portioning valve or jammed rear calipers?

 

[jcslocum]

OK you have air in the rear section becasue you didn't bench bleed the master. Because the lines are so long, Every time you pump it, you move the air, then you bleed and stop, The air moves back towards the master as air will do.

You need to do a full on vacuum bleed (you can make your own with a coffee can and use your shop vac) not a little tinny mity vac or pressure bleed to chase that air out. If you can find a big syringe, you can also reverse bleed it and force the air back up to the master. The local hardware store might have something you can use.

Good luck!!!

 

[MNVXer]

You can "bench bleed" the master cylinder (MC) attached to the car.

Fill with fluid, have a helper push on the brake pedal as such:

With all three brake lines removed from the MC have the helper SLOWLY push and hold down the pedal all the way. Put your fingers over the three holes (where the brake lines attach) on the master cylinder so that it is air tight. Once you are holding the holes closed, have the helper release the pedal. do this about five times, keeping an eye on the fluid level. Catch the fluid that comes out with many towels, as it can remove paint easily.

Once you finally release, re attach the brake lines and bleed normally - do rear passenger side first, then rear driver's side, then front passenger side, then front driver's side.

If this doesn't work check:

1- is the rear rubber line intact? It runs from the rear axle to the chassis and is about 18" long IIRC.
2- Are the fittings tight at the proportioning valve above the rear axle?
3- If you removed and re-installed the calipers is the bleed screw on the calipers on the top as it should be?
4- Is your master cylinder the culprit? Maybe leaking air past its seals.

 

[spoor]

Thanks - Great info.... Rear Caliper bleed screws are on the bottom - we must have installed them on wrong sides...right? Didn't think that was possible.

Rear Rubber line is wat started this, clogged, so we replaced with new and re-built the rear calipers and new master cylinder. Car had been sitting for 10 years or so.

Thanks again!

 

[MNVXer]

I don't have any images of when I did my brakes about a month ago, but here is a good shot of a rear caliper. Note the bleed screw is on top. If the bleed screw is not at the top - the calipers can't be bled with gravity, due to there being an air-pocket inside the caliper. Check your front calipers too - look at their bleeder screw orientation to double check.

 

[spoor]

Absolutely - Problem SOlvEdeD....

Fronts Bleed screws are up, backs are down...wasted a whole weekend, but looking at the bright side - worked up the muscles in my legs.

Thanks!!!

 

[spoor]

Thanks everyone, yes had the rear calipers on wrong sides, bled the brakes in 20 min and good to go, off to Sebring for track touring tomorrow....

 

[Stevew]

Spoor,

Congrats for fessing up! I would have made up some BS story or just let the thread die .

Best wishes.