richeyb

I installed a new master cylinder, wheel cylinders, ran about 3qts of brake fluid through and bleed until all air bubbles had disappeared. 72 Cutlass with Drum, drum brakes

Took a test drive...
1. No brake pedal pressure went almost to floor to stop... several forward and back stops ——car stop good
Possible boost failure, wrong linkage, more air in line or need to manually adjust brake tighter or all the above?

2. Checking fluid after drive... front bowl down about 3/8” but back bowl over flowing

What could cause front bowl to lose fluid? And back to gain ???

Any suggestions?

This is one of three threads I’ve posted on my three month brake saga🤪

oldcutlass

It possibly could be a bad seal in the master cylinder allowing fluid to flow within the chambers. Did it do this before you changed it?

Sugar Bear

I've never seen or heard of those symptoms; but, I agree with oldcutlass.

zeeke

Not sure what your degree of knowledge is so I'll just state the obvious, apologies if you've done all this? Pull the booster line and see if you draw from the vacuum, you should get a whooshing sound from air rushing in, if not it's probably shot. Run the car a few minutes and try it again. Did you bench bleed the master? Not sure what would cause the fluid to shift. When you bled the system did you start with the furthest point first? Definitely adjust brakes. I saw something similar years ago in my friends 72 Cutlass Supreme, changed everything but the portioning valve. Never got to the bottom of it. Lack of patience as a young buck.

It could also be a defective master out of the box. It's more common than not these days.

Sometimes air lays up high in the lines so years ago I purchased a cheap KD power bleeder unit to push fluid through the breaks. I used a Branick plate for the top. The KD unit looks like a pump sprayer. I've seen them for about $90. The plate I haven't priced in years. If you have any interest in that set up you could try a company call Tool Discounters. I use it on multiple vehicles to flush the fluid as needed throughout the years. Only drawback is I have DOT3 in that unit and the newer cars are DOT4. Pump it to about 7 lbs and open the bleeder key. I made up a bottle with a vacuum line going into a drilled hole in the cap to minimize the mess. It also shows you when clean fluid is hitting the wheel cylinders.

Let us know how you make out.

Fun71

This is about the only thing that would result in fluid loss in one reservoir and fluid gain in the other one. Once again, "new" doesn't always mean "good".

richeyb

Thank you all for responding... 4 out of 4 are guessing bad master cylinder transferring fluid and I had that feeling but just hated to pull it and start over, especially if someone had a different idea. But I think I need to take it back..

I'll be running some test on the booster and looking for vacuum leaks.
And yes I've bench bled and will do that again with the new one...


Hope to get to it again this weekend..

Happy Easter everyone and hope the bad weather stays out of Grandbury, my sister lives there too Oldcutlass

richeyb

Another question —- how level should the bowls of the master cylinder set? Is there a standard or specification?

oldcutlass

Are you taking fluid level or the master cylinder itself? I keep the fluid level about 1/16th of an inch below the top. As far as the physical level of the MC, its at an angle based on the booster mounting.

Fun71

The master cylinder will have a fairly obvious tilt with the front much higher than the rear. Dunno why they are set up like that.

richeyb

Ok thanks, it just had an obvious tilt and while I’m messing with it was just curious....not too many old cutlass cars around town to compare

oldcutlass

The tilt is for the booster to clear the BBO valve cover, the angle is a straight line for the actuator rod to connect to the lower hole on the brake pedal. If there were manual brakes then the master cylinder sits level and the actuator rod connects to the upper hole on the brake pedal. If you want to compare, most chassis items are identical to a Chevelle or any other A body of the same year.

richeyb

Thanks Oldcutlass. That makes sense to me, I’ve got a real education on brakes in the past three months. I think I’m about there. Went with a new Master cylinder and booster, would hope after bleeding everything again I’ll be on th road! Appreciate everyone’s help!

oldcutlass

We've all had our daunting first time, once you understand how it all works it's actually fairly simple.