Captain_Slow

Joel -
I had thought about this last night after reading something Mrmerlin posted in a thread about ABS light coming on. That thread had nothing about brake dragging, but it can't hurt to try (or even re-seat it).

Since I really don't know how long the fluid has been aging in the pump/valves, I will do a change and proper cycling of the pump, then bleed again to flush out all the old fluid.

Getting to the bottom of this could take awhile.

fraggle

The abs harness wiring, especially in the back, tends to deteriorate. I rebuilt mine in the rear but haven't touched the front. I would suspect the sensors and wiring before the relay, but pulling the fuse, as you have, should at least isolate the system and "prove" is has to do with abs, which is nice to have, but nonessential.

John Speake

You changed the ABS relay in the CE panel, but there are two more ABS relays, inside the back of the ABS unit, under the fender inner cover. These are Bosch relays and can be easily and cheaply bought from a Bosch agent.

Captain_Slow

John - I haven't changed any relays yet. But now that you mention it, the relays on the unit inside the fender are the ones I recall Stan describing. He said they were easy to test removed from the ABS unit. But he didn't describe how to test them.

John Speake

OK Jon, I misread your comments. The two relays in the back of the ABS are Bosch 0332 002 176 (a large single pole relay) and Bosch 0332 205 003 (a smaller relay with a single pole changeover set of contacts.)

These both have 12v coils, so easy enough to test. Energise coil, measure contacts with multi meter on ohms. For the small relay test energised and non energised contacts.

I paid about 35 USD for the larger relay and about 25 for the smaller one. The relay in the CE panel I have only been able to source from Porsche and it cost about 160 USD..... Roger probably has them at a better price. Its Porsche P/N is 928 615 124 03.

Captain_Slow

Does testing the relays involve both continuity checks and applying 12V and listening for a click? I don't know which pins to check or where to apply the voltage. I'm getting the necessary "tools" together. I can pull the 12V battery from my lawn tractor for a 12V source.

I still need to inspect the wiring carefully. The ABS light is very intermittent (meaning it happens often for a period of weeks, then is gone for several weeks). Often it and the warning light will flash briefly (neither staying on). I'm suspecting either chaffed ABS wires or poor sensor connection.

Interestingly, lifting the car definitely seems to influence the ABS light behavior. Over the winter I put new wheels and tires on the car, and again noticed the ABS light seldom came on. The light went away for the longest period (almost a month) after the car was on stands for 3 weeks in June. I have an idea why this might be so, but no point in describing it here until I've attempted to confirm it.

For now I've pulled the ABS fuse and will start inspecting the wires, sensor connections, and try the wheel spin tests with the car lifted (will put the fuse back in, of course). The ABS worked just fine a week or two ago when I was locking up the wheels on a gravel road. Worked impressively well, with the distinctive ABS shudder.

Captain_Slow

Sorry John...I was typing while you are responding
Thanks!

Rob Edwards

Pics for posterity:





Relays 928 618 930 00/01 ('87 and '88-'95) and 928 618 931 00/01/02 ('87/'88/'89-95)

Captain_Slow

Rob - Thanks for adding the pictures. Very helpful.

Fraggle - I forgot to mention earlier that my rear wiring harnesses are both ratty looking. The outer casing is falling apart. The wires all look good at a glance, but who knows there could be one or more chaffed wires back there. I notice the bundle of ABS wires going to each wheel appear to be twisted around a nylon stress cord that is as tight as a guitar string when the car is on stands and wheels hanging down. The wires, however, are slack and kind of spreading apart without the casing holding them in a bundle.