replaced brake Master Cylinder, but need rubber seal between MC and booster (72 GMC)

[centuryhouse]

I spent over $1000 on brakes today

At the end of it all, my brakes felt far worse than they did when I wen to the shop to begin with.

The engine is revving higher than normal and running rough, instead of low and smooth like it was before taking it in. And pushing really hard on the brake pedal is required to stop the car now.

There is a rubber seal between the MC and the booster, which they tore when removing it. Air is hissing from there, like a leak.

How can I find a replacement?

(72 GMC c15 2wd, 305 engine, TH350 trans.

Parts replaced today: New front rotors, new pads, greased calipers, repacked bearings, new drums, new shoes & hardware kits, new wheel cylinders, new brake line, replaced axle seal, new master cylinder, flushed refilled & bled brake system, new emergency brake cable system.

[LockDoc]

Originally Posted by centuryhouse

I spent over $1000 on brakes today

At the end of it all, my brakes felt far worse than they did when I wen to the shop to begin with.

The engine is revving higher than normal and running rough, instead of low and smooth like it was before taking it in. And pushing really hard on the brake pedal is required to stop the car now.

There is a rubber seal between the MC and the booster, which they tore when removing it. Air is hissing from there, like a leak.

How can I find a replacement?

(72 GMC c15 2wd, 305 engine, TH350 trans.

Parts replaced today: New front rotors, new pads, greased calipers, repacked bearings, new drums, new shoes & hardware kits, new wheel cylinders, new brake line, replaced axle seal, new master cylinder, flushed refilled & bled brake system, new emergency brake cable system.

Sounds like the diaphram in the booster may be bad & leaking.... I don't think that seal being torn would make it leak vacuum. You definitely have a vacuum leak somewhere.

LockDoc

[old Chevy guy]

X's2 the booster is bad or the connection going to it. High erratic idle and hard to push pedal are brake booster for sure ,been there done that. Try and track down where the hiss is coming from. Could be something they did while replacing the master.

[centuryhouse]

Originally Posted by old Chevy guy

X's2 the booster is bad or the connection going to it. High erratic idle and hard to push pedal are brake booster for sure ,been there done that. Try and track down where the hiss is coming from. Could be something they did while replacing the master.

Did you guys see in my post where I said they replaced the master cylinder, but didn't replace the seal that goes between it and the booster?

The seal is torn and has a hole in it but they stuck it back in place, because they didn't have a new one and the parts stores can't seem to find the part.

The booster worked 100% with no vacuum leak when I drove it into the shop yesterday.

My problem that I am posting about, is that I can't figure out where to buy that part - the rubber grommet / seal that goes between the MC and booster. Unless you guys think the seal can't cause a vacuum leak. But it makes no sense to me that a 100% working booster would coincidentally stop working the same afternoon they replaced the rest of the stuff.

[dozerbill72]

A place called Docrebuilds has that seal, but what every you do, do NOT tell them it's for a truck. I told them that is what I was working on and they refused to sell it to me. In fact they sent a nasty e-mail to me saying I was a dumb a$$. Mine had a part # on it that was the same as their part number but that didn't matter to them. They sell Corvette parts so I guess that gives them the right. I ended up junk yarding mine. Good luck.

Bill

[LockDoc]

Originally Posted by centuryhouse

Did you guys see in my post where I said they replaced the master cylinder, but didn't replace the seal that goes between it and the booster?

The seal is torn and has a hole in it but they stuck it back in place, because they didn't have a new one and the parts stores can't seem to find the part.

The booster worked 100% with no vacuum leak when I drove it into the shop yesterday.

My problem that I am posting about, is that I can't figure out where to buy that part - the rubber grommet / seal that goes between the MC and booster. Unless you guys think the seal can't cause a vacuum leak. But it makes no sense to me that a 100% working booster would coincidentally stop working the same afternoon they replaced the rest of the stuff.

Yes, I saw what you posted about the seal but as I stated in my previous post I don't think that seal would create a vacuum leak. The booster should be a sealed unit. If you find that I am wrong I hope you will add that info to the thread.... By the same token if I am right that info would be useful to others also.

LockDoc

[Racer382D]

Check first to make sure that your vacuum line is installed correctly from the booster to the manifold. The gasket you are speaking of is not causing the issue you are describing.

[centuryhouse]

The sound of the leak is coming from the exact spot the seal is - which is where the MC meets the booster.

The line from the booster is fine, plugged in well and no leaking.

As to the idea that the seal can't be the source of the leak - my question is why would a seal exist, if it isn't sealing anything?

And again, a booster that works 100% until they tear the seal makes me think that the thing that changed is what is wrong. If I find out that isn't the case, I'll certainly post here.

[Racer382D]

That is a dust seal to keep debris out of the booster which is a sealed unit..... It would not leak even if the master isn't bolted to it.... It sounds like they may have ruined your booster.

[dozerbill72]

The seal between the booster and master cylinder is more than a dust seal. I had the exact same problem on mine about 3 months ago after replacing the master cylinder. If you look at the location of the seal it is on the vacuum side of the booster. Boosterdeweyexchange may also provide that seal. After searching for a replacement for mine I found it's a fairly common problem

[Racer382D]

It's not supposed to be, if it is leaking vacuum there it means the booster is bad.

[RichardJ]

Forget the seal. I've seen boosters like this one, with a notch to let the fluid from a bad, leaking master, drain out so it doesn't puddle in front of the booster.

A much bigger error than a missing seal would be a failure to check and adjust the booster pin length.



If a gasket between the MC and booster corrected a vacuum leak, You've got a bad booster.

[Racer382D]

Originally Posted by RichardJ

Forget the seal. I've seen boosters like this one, with a notch to let the fluid from a bad, leaking master, drain out so it doesn't puddle in front of the booster.

A much bigger error than a missing seal would be a failure to check and adjust the booster pin length.



If a gasket between the MC and booster corrected a vacuum leak, You've got a bad booster.

There you go!! ^^ exactly what I was saying.... In more detail lol

[jsera]

Unbolt the master and put some rtv on it and let it dry. If it persists replace the booster.

[Racer382D]

I repeat.... The mc does not deal vacuum!!!!

[jsera]

Originally Posted by Racer382D

I repeat.... The mc does not deal vacuum!!!!

I agree but the rtv seal would settle the argument

[Racer382D]

Originally Posted by jsera

I agree but the rtv seal would settle the argument

NO IT WOULDNT! it would band aid the issue of a bad booster. THERE IS NO ARGUMENT!!

[The Rocknrod]

Here is a post from another forum that shows the seal. Not required.
https://www.corvetteforum.com/forums...post1602295807
And the part: https://www.corvettecentral.com/c3-6...-gasket-192306

[BigBird05]

Plug the vacuum line going to the brake booster and see if the engine runs normal.