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You might want to check the calipers. On my '88 I had a problem where pits in the caliper pistons were causing them to stick. Once that happens the system heats and locks up. I have not really read closely enough to know if this could be your issue, but might be worth a look.
Today I removed the master cylinder and found that there's about 1 mm of push between it and the brake booster (see pic). This means that the MC is not getting fully into rest position. So likely with a bit of heat expansion the problem occurs. But the pin on the brake booster protrudes just a tiny amount - the same amount that my old brake booster's pin protrudes that's not in the car. So it's not the brake pedal extending the push rod (plus, I checked the 158 mm spec.). The folks who did the MC rebuild say they use the same snap ring, so that distance couldn't be shorter.
So I can:
Shave down the booster pin. I don't know how I'll get in there to do so and I don't like grinding something down that's expensive. Plus it's nice and rounded now.
Drill out the master cylinder receiver. Same concerns as above.
Make a gasket between the two with 2mm rubber.
Your ideas??
When I did all this the first time getting the 13 mm inner bolt between the Bb and the MC was easy because the engine was out. This is NOT easy with the engine in.
Before you drill, grind or make any other permanent mods.... keep in mind the average washer is about 1.5mm. I'd try that first on the bolts with an oring on the MC bore to seal out dust to test the theory.
If your booster is dimensionally holding the brakes on, it's bad (and a common problem.)
I'd certainly not start grinding or modifying anything. It's the braking system, after all!
A rebuilt booster, at 928 International, is $395.
Semi-retired, as of Feb 1, 2023.
The days of free technical advice are over.
Free consultations will no longer be available.
Will still be in the shop, isolated and exclusively working on project cars, developmental work and products, engines and transmissions.
Have fun with your 928's people!
This is a rebuilt booster from 928 International. The person at White Post said there was no way the push rod receiver got shortened. I’m thinking the washer / gasket route.
I’m waiting on a rebuild from Roger my final testing with the Mc front and rear feed into the reserve shows it is cycling correctly apparently. After I reconnected the front and rear lines and check with the system connected the lockup appears. What I did find when the Master C clip came off second returned repair, apparently some brake fluid ended up in the booster. I know it from that because fluid is clean and about a tablespoon. I have removed what I found but now concerned it will damage my Booster fail down the road.
I’m waiting on a rebuild from Roger my final testing with the Mc front and rear feed into the reserve shows it is cycling correctly apparently. After I reconnected the front and rear lines and check with the system connected the lockup appears. What I did find when the Master C clip came off second returned repair, apparently some brake fluid ended up in the booster. I know it from that because fluid is clean and about a tablespoon. I have removed what I found but now concerned it will damage my Booster fail down the road.
Flush out the area brake fluid came in contact with using some water, let it sit for a few min and then dry it with air. Brake fluid is hydroscopic so it will absorb and be somewhat deactivated by water. Then hope for the best.
Last edited by icsamerica; 02-24-2023 at 02:44 PM.
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Does it have the "Do It Yourself" manual transmission, or the superior "Fully Equipped by Porsche" Automatic Transmission? George Layton March 2014
928 Owners are ".....a secret sect of quietly assured Porsche pragmatists who in near anonymity appreciate the prodigious, easy going prowess of the 928."
I'm not a parts expert, like you,
but clearly Porsche still had them 6 years later.
And instead of coming in a Porsche box, they came in an Ate box, with an "Ate Classic" sticker on them.
And I'm lucky enough to have the correct part, in multiples.
We all had plenty until the stock ran out. I sold my last one about two years ago.
I am also pretty certain that the 86.5 to 95 Master will work on at least the S3 cars - we will find out soon.
Some good news - Porsche are now showing a possible SS to a new number - when that will happen is anyone's guess.
02-21-2023, 07:13 PM
George Layton March 2014