..and I bet he didn't even have a brake light to warn you!

 

Many thanks to tdiquattro for the write up & ABS pump info.

Mine had the same symptoms of no ABS but the pump would run when 12V was applied to it. Even after running the pump a few times the ABS still did not work.

I purchased a used Merc unit off Ebay & on stripping it found it to look like new. Being a lazy sort of person I did not really want to remove my ABS unless absolutley necessary. Luckily the Merc unit came with the plug & a short length of wiring loom so I decided to make a rig to test as much of the ABS as possible. I wired up four switches, 1 to power the pump (with indicator bulb), one to power the solenoids (with indicator bulb), 1 to operate the ABS "block" solenoid for 1 channel and 1 to work the ABS "return" solenoid for 1 channel.

I started with front right. The pump powered up & the bulb lit to show that the relay had pulled in and the solenoid relay pulled in. Neither "block" or "return" had any effect on the brake pedal although the solenoids could be heard engaging. Tried front left & the noise from the pump changed slightly. "block" & "return" both seemed to work as expected. Switched back to front right & it also now worked correctly. Road tested & ABS now working!!! Looks like as well as running the pump the valves needed to be moved to get it to unstick.

My car is already "internet enabled" to run the fuel pump. After having 2 pumps rust solid over the winter (ethanol attracts water into the fuel) I now wire the car up using a "Z Wave" relay to run the pump once a week for 10 mins to keep the water & fuel mixed, problem solved. Looks like I shall have to do something similar with the ABS pump!

 

That is a great way to test the ABS actuation - esp given the the difficulty in getting the Bosch 2-LED tester - I don't spose you have any diagrams or schematics for the test rig you built?

loving the idea of internet enabled ABS unit.

 

Hi alexjc4
Electronics is not my forte so no schematic but I shall try and explain what I did. The usual disclaimers apply. If you bust your ABS or set your car on fire do not blame me.
I stripped back the loom on the spare Merc plug and connected all the wires to a 30amp chock block. Crocodile clips on flying leads connected straight to the battery for 12v & 0v. To be safe an appropriate fuse should be fitted.

Using the Porsche wiring diagram for the appropriate model year (93) pin numbers on the ABS unit.
1. Solenoid valve front left *
2. Valve relay. Connect through switch to 0v to turn on valve relay & power valves
3. Solenoid valve front right *
4. Valve relay output. Connect through 12v bulb to 0v. Shows when valve relay is on.
5. Solenoid valve rear *
6. Supply for valves. Connect to 12v.
7. ABS warning lamp. Not used
8. Spare
9. Pump relay output. Connect through 12v bulb to 0v. Shows when pump relay is on.
10. Supply for relays. Connect to 12v.
11. Pump relay. Connect through switch to 0v to turn on pump relay & power pump
12. Supply for pump . Connect to 12v.

*The inner working of the ABS unit (especially the solenoid valves) were a bit of a mystery to me but Adrian Streather’s description in his book clarified matters by stating that a current of 2amps worked the “block” valve and that a current of over 5amps worked the “return” valve. I guessed that connecting straight to 12v would work one valve & through an appropriate resistor would work the other. With the spare Merc ABS it was safe to experiment. A bit of schoolboy physics and I calculated that a 4.7ohm/25watt resistor should be about right. A direct 12v connection to pin 1 produced a nice click and through the resistor a different click.

I hope that the above makes sense. Originally I was just trying to confirm that the problem was with the pump before removing the ABS unit. It turned out that I was very lucky & managed to unstick whatever was stuck! Also I now have an easy way to exercise the ABS & a way to test it without having to drive on the road and brake like a maniac.

 

On finding my ABS wasn't working a couple of years back I also did a test of the pump /relays direct from the battery. The pump seemed fine after several runs and indeed the ABS then functioned properly. Happy days.
I was surprised when we found the ABS wasn't working a couple of weeks ago, but after stripping the pump motor and finding seized pistons I think the only long term option is to open the ABS unit and clean / lube the internals.
It does seem odd that the Merc units all seem in good condition internally. It would seem the heat in the engine bay must help the build up of moisture inside the ABS unit which the Porsche unit does not get being stuck in the bottom of the boot.

 

I agree that clean/lubricate is the proper long term solution. However I have learnt over the years that lack of use is usually the cause of stuck/rusted/seized items. It must be years since my ABS cut in with normal road driving & not being used over the winter can only make matters worse. Just as I seem to have cured my rusting fuel pump problem I shall now try to regularly exercise the ABS & see if long term it keeps working.

 

The Bosch tester ABS 2-LED as mentioned in the Streather book is nowhere to be found !!!
not even on EBay.de which stocks zillion 911 parts.
How can I get one ?

p.s. page 409 of the Streather Bible contains an error....front left pins 4 and 5, 5 is not used
should be 6 !!!!

 

Stay tuned............we should have beta test results within the next two weeks.
Hang in there,
Michael

 

I'm very interested in buying the tester currently in Beta.


Any indication on the price?

 

Just want to let folks know that Ninemeister have the Bosch ABS tester. I'll post photos of the kit when I next have the chance.

 

Can't believe I missed this thread and I also have a new ABS C2 tester on order. Nice to know someone figured out a low cost repair procedure for the pump. I can't recall my ABS braking system as activating. Do you hear it and feel it in the brake peddle?

 

Next time you are driving on wet roads...get on them and give your abs system a workout...

 

I would be interested to hear what lubes people use for this.
Thanks

 

Can anyone explain the following brake issues ;: when testing the ABS it doesn't work on the rear axle , while the front is working fine. This being a race car i can switch off the ABS but even then the rear wheels lock up first while there seems to be little presure on the front brakes . can the ABS problem cause this or is there another cause for my problem ??

 

Yes, an issue with the ABS system could result in what you have observed. Our cars have a 3 channel ABS system, with one channel allocated to the rear wheels. If there is an issue in this channel, then the rear wheels will not have the proper ABS function. The system can be fully exercised in the garage with the car on stands.

Good luck,
Michael, (cajonfan)