Crystal Cranks

How can you tell you have a bad abs Pump on a C2, how can you test it, should you hear it run on start up?

Indycam

I think the abs pump only runs the abs kicks in .
I have never thought about testing it , can it be powered up and run ?

C24FUN

Uh, as far as I know ABS pumps were only equipped on C4's???

C2's have a more standard vacuum based system.

Jim

Indycam

The C4 has a pump that the C2 does not , but the C2 and the C4 have "ABS" Anti lock Brake System .
That ABS is a pump on the floor of the front trunk .

C24FUN

No, there is no pump in a C2, just a pressure distribution box in the front trunk (behind the battery) attached to the vacuum assist which is under the car near the steering rack.

Jim

Indycam

http://porsche964.com/wordpress/wp-c...overviewR1.pdf
page 11-12-13

It shows photos of the abs pump installed in a C2 .

http://shop.ebay.com/?_from=R40&_trk...All-Categories
EBay has a few 964 C2 abs pumps .

C24FUN

OK, to be specific, the 964 bible (Adrian Streather's book) says the C2 has vacuum assist brakes. The only non-4WD 964s with the high pressure hydraulic pump installed were the Turbos, the 92-93 C2 Turbo-looks, and the Carrera RS's.

Cheers!

Jim

Indycam

We are not talking about the pdas pump that is found only in the C4 .
We are not talking about the C2s vacuum assist .
We are talking about the "abs Pump on a C2".

I have given you a link to the info you need .
It is by Adrian Streather , did you read it ?

C24FUN

Sorry for the confusion guys, misinterpreted the question!

As for running the return pump in the ABS hydraulic unit, according to the schematics, pin 9 on the hydraulic unit shows as being directly connected to the internal motor. If I were trying to confirm operation of the motor I would hook up a voltmeter to pin 9 and check to see when it got voltage and what the voltage was (+12V I assume). This maybe only when the ABS was active I suppose, so it might be a challenge to measure! You could then disconnect the hydraulic unit connector and apply voltage to pin 9 (while grounding the unit properly) to see if there were any signs of life. (I would have some qualms with this procedure unless I had more detailed info on the operational characteristics of the pump in the hydraulic unit).

Of course, all this assumes that there is some problem with the ABS that points to the return pump as a possible fault point, which may not be the case (any further info Crystal Cranks?). A more likely failure point on the ABS is the control unit itself or the crazy way they have the power for the system wired directly to the positive post of the battery where it tends to get loose or corroded over time causing intermittent ABS operation (search "ABS Woes" in this forum).

Anyway, sorry again for the misdirection. Hope this is of some help.

Cheers!

Jim

Crystal Cranks

I am talking about the unit behind the battery I have always referred to this as the abs pump, I am aware of the differences between the c2 and c4
I do not have any warning lights, the abs will work the first time after start up but will fail on the second test (locked wheels)and will not work again.
Have tested wheel sensors and battery connection/grounds,pins on the control unit look ok

Indycam

If you turn off the car , then the abs works again ?
If so that sounds like an electrical / electronic problem .
If you pull a relay and reseat it while the car is running , will the abs work again ?
If you put your abs computer in another C2 does that car have your problem ?

Crystal Cranks

Just to clarify, this problem was in the car when I got it (3 years ago) the symptoms then were as I said, ABS would work first test after start but then fail (no warning lights). but lately this has got worse as it does not work at all most of the time but it does work occasionally as I have felt it in the pedal a couple of times, still no warning lights.

When it does work the pulsing in the pedal feels weaker than in a modern car, what should the pedal feel like?

I'm thinking the fault is more mechanical as there is no warning lights, I have an ABS relay ordered as it's the easiest/cheapest thing to change. My relay rattles when I shake it, is this normal?

Crystal Cranks

If you pull a relay and reseat it while the car is running , will the abs work again ? No
If you put your abs computer in another C2 does that car have your problem Do not have an other C2 close by to test , don't like the idea of pulling somebody's car apart.

Indycam

The computer will not "see" every problem , it will not turn on a light for every problem .

I don't think a rattle is normal .

boxsey911

You're right, a modern car's ABS pulses rapidly and feels like a ratchet under your foot. The 964 ABS is a lot more agricultural....you can almost count each pulse as it comes on and off.

I know you've already said that you've checked battery connections but have you pulled the tail lead from the positive terminal that goes to the ABS controller and given it a polish up with emery paper?