al714

Hello to all

I have a 72 cutlass supreme , I recently swapped out a master cylinder since old one was leaking. Bought a new one from summit . Everything was fine for about a week and I noticed my car would shake during idle. I checked the hoses and they were good , but noticed that air was getting sucked in from bottom of master cylinder . To make sure it was the master cylinder I put a piece a tape on the bottom and it stopped taking in air.. Is the master cylinder faulty or is it something else ? Thanks for the help in advance

tru-blue 442

Are you sure it isn't the vaccume booster?
It could be a bad diaphram. How are the brakes?

al714

No I checked that .. The brakes are good. The sucking is coming from a hole underneath the m/c

tru-blue 442

That is a new one on me.
Sounds like something screwy
going on for sure.

Maybe someone on the board has
come across this before and will
chime in soon for you. Good luck.
I will be watching your thread because
I would like to know as well.

oldcutlass

There is really no way vacuum should be coming from the vent hole at the bottom of the master cylinder.

al714

I googled like crazy and found someone with a similar problem a couple of years ago. He solved his problem with a new pushrod boot. Sounds about right? And where can I buy that. Looked around and most places don't really sell olds stuff

nsnarsk65cutlass

What hole on bottom of master cylinder post some pictures.

MDchanic

I didn't post anything here last night because I couldn't think of anything nice to say.

There is no hole on the bottom of the master cylinder. Period.

There is no way for the master cylinder to suck in air, unless it's empty. Period

I have no idea what's going on with your car, but whatever it is it's not what you are telling us.

- Eric

joe_padavano

The only possible relationship between the M/C and the vacuum problem is that you somehow damaged or didn't properly install the rubber seal between the M/C and the booster. The leak is at this seal. Also verify that the sealing face on the back of the replacement M/C isn't damaged or dirty. As Eric noted, there is no possible way for air to be "sucked in" through the M/C.

al714

After taking the m/c off I noticed that the seal was damaged. So that's the culprit , here's a pic of the hole I mention on the m/c . Most got confused thinking it was right under or in the middle . It's more toward the booster

Thanks for the help

MDchanic

Don't think I've ever seen a hole there.

Glad you got it figured out!

- Eric

al714

I'm having a hard time finding this piece . The piece that goes between the master cylinder and booster. Anybody knows a site where they sell it?

joe_padavano

This one should be close:

http://www.westcoastcorvette.com/p-6...FYOk4AodnhsASg

al714

Thanks!!

TripDeuces

That hole allows air to equalize on each side of the rubber diaphragm as it collapses and extends. It's the gasket that's leaking allowing vacuum to act on that hole, which you've already figured out.

al714

Thanks for the explanation , I was wondering what that hole was for