I can't tell you guys how thrilled I am to be back in the drivers seat of my 928, after a year of trying to figure out what was wrong with my brakes.

Recap: Calipers had been rebuilt, flex lines replaced, part of the system drained in the process. Upon filling and bleeding the system, pedal travel was 2" longer and pressure point was soft. No amount of pressure or reverse bleeding, new master cylinder, or other changes fixed this problem.

About three weeks before Sharktoberfest, Bill Ball recommended I take it to a specialist. I had already spoken with Marvin Weitz from The RennShop in Santa Clara. I knew Marvin, because he resolved a tricky ignition issue on my car a few years earlier, and subsequently worked for two Porsche dealerships before starting his own shop.

I trust Marvin, because he puts a lot of emphasis on proper diagnostics before starting any repair work - more like a good MD, but specialized in Porsches (a "Porschologist"). His great communications and squeaky clean shop perfectly fits that picture.

So, Bill and I took the car to The RennShop. Marvin went through the whole car in detail. He then put together a treatment plan for healing all its little ailments (of which there were not very many).

For the brakes, he recommended to replace the bias valve, and vacuum bleed the system 2-3 times, to eliminate all potential air pockets.

Before, during, and after the process, Marvin patiently educated me about the reasons for, as well as the steps, and limitations of the procedures he suggested. If he was a medical doctor, people would say he has great "bedside manners"...

When I picked-up the car, it felt like it had woken up from the dead - the brakes suddenly responded like never before! At least I really don't remember ever having had such great brake performance.

Marvin mentioned he got some large bubbles when bleeding the master cylinder, and suggested I come back after a few hundred miles for one more vacuum bleed.

I feel my baby was in great hands with Marvin, and highly recommend him to anyone in the area who needs work done on his 928.

He is a great "Porschologist" with great shark-side manners, and works out of a nice, clean clinic.

The RennShop Inc.
1423 Laurelwood Road
Santa Clara, CA 95054
Phone: 408-727-0911
Email: therennshop@gmail.com
www.therennshop.com

 

I'm glad to hear you finally have a good resolution to the brake problem Nicole.

Thanks for the info on RennShop.

 

Nice Nicole! Glad your back in the saddle again.

Funny, I never thought of the bias valve as being a problem although I did have a similar problem in a late 90's VW. Good info for the rest of us.

 

Interesting... The bias valve itself should not have caused the spongy-ness, unless it was a collection point for air. Nevertheless, I am SOOOOOOO happy for you. I know you were just about ready to give up on it, but now you're ready to hit the raods again in your wonderful 928.

 

Nicole it would be interesting to know what the inside of the bias valve looked like, I have removed more than a few and nearly every one was corroded in some way.
Glad you got your ride going,

 

Congrats Nicole!

So glad to hear this issue is put to bed, and great hear a solid recommendation for this shop. -Ed

 

Congrats on getting your shark back on the road.

Out of curiosity, how much he charged for the "surgery"?

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1979 Euro

 

SWEET! What are brakes for anyways?

 

Would it be possible for a bad bias valve to be the cause of a hard pedal/weak brake issue on an 81'? The booster seems to check out as good.

 

Andrew: I should add that we are not 100% sure, if the valve or the bubble that came out of the master cylinder were the culprit.

What I can say is that brake performance was pretty weak, and either the fronts or rears did not get enough pressure. The new valve and vacuum bleeding made all the difference.

 

You can pretty much count on it being the air in the system.

 

Nicole, I too am glad you got it resolved.

Vacuum bleed huh? Very interesting that multiple prior attempts at bleeding didn't get all the bubbles out.

 

Nicole-- can you expand a bit on the vacuum bleeding process? Like where he applied vacuum and how much? This kind of thing needs to be in our collective arsenal, maybe with a few tools/hoses/connectors in a ziplok bag.

 

VERY interesting that the bias valve caused the bubbles, which in turn made a soft-low pedal.....

 

I wish other people changed one part at a time. Then I'd learn more.

(I'm too busy to do that myself.)

Sounds to me like trapped air.

Nicole: How were you bleeding it previously?