Brake Booster Check Valve

James Wallace · 04-21-2016, 11:41 AM

I have an 88 944S that is well sorted and bone stock except for a few suspension changes. This car literally consumes the brake booster check valve at every track day. The plastic looks as if it's dried cracked mud when I remove the pieces. It's so routine I keep a spare in the glove box. Last one went 350 miles before cracking up, which of course screws the idle, soots the plugs, and makes for leg press braking.

Anyone experience anything similar? I'm thinking exhaust gas or big heat getting in there somehow but it's a fresh and well sorted motor and I am not sure where or what to look for. Thanks and have a great day.

v2rocket_aka944 · 04-21-2016, 01:54 PM

That's crazy, never heard of that before.
As far as I know, the one on my car is original from 1984.

Excessive oil fumes maybe??

djnolan · djnolan's Garage

There must be something hooked up wrong!

dgcantrell · dgcantrell's Garage

I'm thinking the same thing. There should be no hot gasses getting to it as it is under vacuum all the time and connected to the intake. It should be connected to the bottom of the intake directly under the pulley for the throttle cable. If it's connected to anything other than directly to the intake, it's connected wrong.

Yeah, somebody painted the intake some goofy purple color. I'll be remedying that at some point.

djnolan · djnolan's Garage

Another theory is the master cylinder is leaking brake fluid and it is getting sucked through the check valve and dissolving the plastic. Master cylinders have been know to leak out the back when old. There would be a telltale stain down the booster. This is a potential safety issue, too.

Can you post a picture of exactly what you are talking about?

James Wallace · 04-25-2016, 07:12 PM

Quote:

Originally Posted by djnolan

Another theory is the master cylinder is leaking brake fluid and it is getting sucked through the check valve and dissolving the plastic. Master cylinders have been know to leak out the back when old. There would be a telltale stain down the booster. This is a potential safety issue, too.

Can you post a picture of exactly what you are talking about?

Thanks, pretty sure you nailed it based on the appearance of the booster below the MC, there is paint missing shaped in an upside down V. That would definitely eat up some plastic. I'll update the post after getting a chance to go over the MC and Booster on the table. Thanks again.