Brake Master cylinder leaking again?

JR47

MEMBER
1999 PONTIAC GRAND PRIX
3.8L
V6
2WD
AUTOMATIC
299,248 MILES

I replaced the brake master cylinder about a year ago with a new one, but recently discovered it had leaked fluid again in the same spot as last time where it connects to the brake booster. I have read that a failed pushrod seal can cause vacuum to pull fluid past the secondary seal in the master cylinder. Could this be what's causing the leak and how would you go about testing the booster to see if it needs replacement as well? Not sure how old the booster is but do know it's the same one that's been in the car since I bought it 11 years ago and the leak isn't a continuous leak it just appears to have leaked some fluid and stopped.

5 Replies

JACOBANDNICKOLAS

MECHANIC
109,724 POSTS

Hi,

I believe the push rod seal they refer to is on the master cylinder and not the booster. Have you ever experienced a hard pedal or anything out of the ordinary?

As far as the rear seal leaking on the MC, that is the only place it will leak from unless you have a loose steel brake hose. By chance, was the MC a remanufactured part or was it a new one?

Let me know. Also, often times the master cylinder is a lifetime replacement component. Is that the case with the one you have?

Let me know.

Joe

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Saturday, November 26th, 2022 AT 11:39 PM

JR47

MEMBER
100 POSTS

Never experienced a hard pedal at all with the car or anything else that would be considered out of the ordinary and the part was listed as new on the company website. It also states it has a limited lifetime warranty but unsure if I have the receipt still.

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Sunday, November 27th, 2022 AT 2:54 AM

JACOBANDNICKOLAS

MECHANIC
109,724 POSTS

Hi,

What was the name of the manufacturer? If you purchased it online, some of the items are poorly manufactured. If it is leaking at the rear,

If it is leaking from the rear, the only thing you can do is fix or replace it. The cause in this case wouldn't be related to the push rod. I wish I had a better answer.

I don't know if you need it, but here is a link that explains in general how one is replaced:

https://www.2carpros.com/articles/how-to-replace-a-brake-master-cylinder

Also, if you want to repair/rebuild the one you have, I attached the directions below specific to this vehicle. If you look at the exploded view, at the rear of the primary piston there is a seal (number 8 in the picture). That is what has failed.

Let me know if this helps or if you have other questions.

Take care,

Joe

See pics below.

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Sunday, November 27th, 2022 AT 5:52 PM

JR47

MEMBER
100 POSTS

It's the brake best select brand, I bought online and picked up in store from O'Reilly's auto and I'm just going to replace it.

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Sunday, November 27th, 2022 AT 7:04 PM

JACOBANDNICKOLAS

MECHANIC
109,724 POSTS

Hi,

I would do the same thing. You can rebuild them, but by the time you get the parts and tue time into things, it's not worth the effort.

When you get one, make sure it is a good brand. I use a lot of Dorman parts at the shop. I don't work for them and trying to sell their products. I've just had good luck with them over the years.

I attached a pic below.

Let me know how things work out for you.

Joe

See pic below.

Image (Click to make bigger)