bwoodry

I just today finished replacing my master cylinder. The symptom...the brake pedal went to the floor and bounced back with a quick jab at the pedal I was able to regain pedal pressure. then if would brake fine for awhile then suddenly lose the pedal. We pulled the master cylinder to check for fluid between it and the brake boost assembly and fluid was present indicating bad seals.

The master cylinder is not cheap but I got one overnight from Vertex and all is well..


Car has 130k so seems reasonable that mine failed..


Good luck

Bob

Tom W

Try the master cylinder first. Then try the ABS - get a salvaged unit for about $400 instead of a new one.

Randy 1

I called Pelican directly, they didn't appear to have it on their website.

Per the other posts here, the intermediate cost solution may be to try and replace the master cylinder.

Randy 1

I'll try a thorough brake bleed first, and then the master cylinder.

I'm hoping (praying) it's simply a function of the MC seal drying out due to the low miles (my car has around 12,500 on it now).

I have a C4S, and while I'm accustomed to the brake booster light coming on, there have been two occassions where the ABS light came on, and stayed on, but went out again after about 2 minutes of driving.

Out of interest, why would a failing ABS controller cause this symptom? I'm not familiar with the purpose/mechanics of the part. Can anyone enlighten me?

Finally, where does one find salvaged parts, aside from dealing with LA Porsche Dismantelers? I could easily stomach $400, $1800 before labor is an exorbitant fix!!

Mike J

The MC seals can't dry out...they are in contact with brake fluid. But if the fluid sits for long periods (like they would with your mileage) you can get corrosion on the inside barrel of the cylinder. Then you then pump the brakes, the seals slide past this corrosion and start to lose the ability to seal properly. This will cause the pedal to sink to the floor slowly underpressure.

Cheers,

Mike

Randy 1

Sonofa...!!!!!

Well, Otto jokingly tells me to just live with it, because after some inspection it appears to be the ABS pump.

As the pedal does not sink right to the floor boards (it retains firmness about halfway through the pedal's travel), it doesn't appear to be the MC. There is no leakage around the nipples of the calipers. There's a fellow with the Bosch system to pull the fault codes.

Looks like I'm stuck with what appears to be a replacement of the ABS. Sheeee-it. Anyone else have any bright ideas? Or a low-cost provider of said ABS pump?

JPS

This raises a Q too...if all is good, should you be able to get the pedal to the floor at all? I mean, if I stand on my pedal, it will sort of begrudgingly hit the stop...but not in a "no fluid" way, you know? Or should the pressure be so tight that the pedal won't even go all the way down?

Randy 1

In reference to your question, JPS, I'm not sure I could ever get the pedal even three quarters through it's travel before this issue reared its head. The pressure was such that I don't think I ever hit the stop under pressure. That's compared to the current situation where constant but relatively light pressure will eventually get the pedal to sink to the pedal stop.

geolab

Hi, I am really lost is it the ABS controller or ABS pump guys are talking about????
ABS controller is electronic, does it impact on the pedal range? I do not think so, and I think it is oil related, so either or:

CHECK WITH THE GURUS HERE,
THEN, go to ebay
enter porsche ABS*
then on the right of the search input bar, click on advanced options.
In the advanced options, stroll 'Items in the USA' and choose Around the world.

In the results, there is a used ABS Pump at $110 buy-it-now and a used ABS controller at
also $110 buy-it-now.
Make sure you choose the right part numbers that apply to your car.
No affiliation of course

George A

Does it go soft after a turn? If so, you might want to check your wheel bearings. I chased the same problem for over a year, replacing everything. It only got corrected once my bearing (and hub) broke and I replaced them.

George

Randy 1

Geolab,

Thanks a million! I see both.

I understand it is the mechanical part, which I think is the pump. I have a 1996 C4S, and I'm unclear on what the part number is. Are there different parts for AWD cars vs. RWD?

geolab

Yes , the part number for the 4WD is 993.355.955.50 and or 0265 217 006 BOSCH cross reference.

Randy 1

Wonderful. The quick response is so very much appreciated!

Out of interest, for the layman, what's the best resource for finding these part numbers?

Edward

Hi George,
Could you elaborate? I just don't get what you're saying. TIA!

Edward

George A

Edward,

My soft brake pedal was due to an imperfect bearing/hub at the rear. This caused the pistons in the caliper to be pushed back ever so slightly, which in turn gave me a soft pedal. If I pumped the brakes, I would get the stiff pedal back, but only until put a little stress on the hub/bearing. Does that makes sense?

George