Crystal Cranks

Thanks for the input Steve, re checked the battery connection as it was a while since I had done it, nice and shiny
Got the replacement abs relay (R34) today and fitted it but no joy. The replacement (ebay used) also rattles when shook, can someone confirm if this is normal.
From reading MANY posts on ABS problems here I think the ABS hydraulic unit is the culprit as it solved the problem for some with the same symptoms as me.

Indycam

How about taking the top off of your old relay for a look see ?

There is a 964 C2 abs pump on ebay for $99.99 .
390254825241

rbauhart

I track an RS America and just had my first ABS problems on the track.

On the track, well into a session, my ABS warning light came on and the beeper went off under heavy braking. The brake pedal felt soft and it took much longer to scrub speed than usual. This was the first time that this had happened to me. The beeper stopped and the warning light remained on, so I came into the pits. After turning the vehicle off and then on again, the warning light was off.

During my next session the brakes felt soft, and it didn't happen immediately, but further into that session, the same thing happened. this happened about 5 or 6 times again that day.

Any thoughts? I am guessing that I had probably overheated both the fluid and the ABS pump, causing the ABS to shut down, and my pedal to remain soft. I run Motul RBF, so this must have been quite hot. I am just surprised as it has never happened to me in the past, and I was driving no differently than I usually do.

If it isn't due to overheating, I am not sure what the problem. I think I will be trying to add some cooling ducts to my front brakes, and running Castrol SRF fluid, and then hopefully the problem will subside.

Any thoughts on other possible causes and solutions?

Thanks,

Roland

Crystal Cranks

Thanks Indycam, have one already on the way.... which brings up my next question, is there anything on top of the standard brake bleeding procedure that needs to be done on a C2 when replacing the abs hydraulic unit.

Indycam

I think you need to lock up the brakes over and over to do the complete bleeding . To get the air out of the abs pump assembly .
And then if you replace all the fluid in the brake system it would make sense to replace the brake fluid in the clutch system at the same time because any moisture in the old fluid will get right into the new fluid .

Crystal Cranks

Update - RESULT! . Fitted new ABS hydraulic unit (pump) and now have ABS working for the first time since I have owned the car.

And the best bit ......... Ebay $75.00 labour $0.00

How much would this fix cost at an OPC?

Indycam

Hot dang !

Gregg-K

Congrats, Crystal Cranks great that you wrestled this to the ground !

So as to tidy up this thread for future ABS sufferers, could you please summarize what you found about your questions at the start of this thread ... like how the C2 ABS is supposed to operate... whether the pump is supposed to run when ignition comes on, etc.

THanks,
.. Gregg

C24FUN

That's awesome! What a great feeling to solve a tricky problem, especially without spending a fortune.

And it proves the mantra of the classic Porsche owner: "ebay is your friend"

Jim

Crystal Cranks

I'll have to check but I don't recall hearing anything extra on start up.
What i have learnt is that the abs relay does rattle. and if you have no abs and no warning light after checking the usual suspects (relays/wheel sensors etc.) there is a good chance the fault is with the abs pump.

.............................. oh and the abs pump is also referred to as the abs hydraulic unit.

Indycam

Did you ever take the cover off of the abs relay to see why it rattles ?

Crystal Cranks

Yes, there is a rectangular piece that insulates the circuit board from the cover that is not attached to anything.