Need ABS Info from Supplement Manual

After a year and a half, I’m still having issues with my car’s ABS and its currently preventing me from driving the car. I’ve come to accept the fact that the only way I’m ever going to get this fixed is to become the world’s foremost expert on the Girling ABS system of the earlier cars. With that said, I’m hoping I get lucky and someone can help me with some info I need. I have several repair manuals for these cars, but I do not have the Supplemental Model Information files that were previously sold on CD-ROM, and I know they contain a few items that are unique. In Figure 24, it shows the readings of the Inputs/Outputs circuits for the ABS ECU, which I have. Does it also offer a listing of Input/Output circuit readings for the ABS modulator/pump? I’m going out of my mind feverishly studying electrical diagrams for this car, but it may be in vain if I can’t get this info.

Brett,

No - only the ABS ECU inputs/outputs

Thank you for checking Bryan. Guess I’ll just need to spend some more time with the electrical diagrams. If worse comes to worse, I may have to ask if someone can take a few electrical readings from their working ABS system.

Brett …

Exactly what are the issues you’re having with you '89 ?

I’ve had 2 problems with an “Anti-Lock Failure” light on my '89 in the past.

!st problem solved by replacing ABS ECU in the trunk.

2nd problem solved by reflowing solder joints on the ABS over voltage relay also in the trunk.

As I’m sure you know the ABS wheel sensors are another potential problem. You can easily clean the sensors
and then check the sensor wires at the ECU for correct resistance.

Grooveman, this is going back to the issue I’ve been having ever since getting my car back on the road, but its gotten worse. Its really two issues that I think can be remedied with the same fix… if I could figure out what that fix is. The first issue is I am having a constant ABS failure indicated on my dash. Secondly, I cannot bleed the rear brakes as no fluid will come out.

For the first issue, I have literally replaced every part of the ABS system. I have replaced the ABS ECU, the ABS modulator/pump, all three relays in the system, and replaced all four wheel sensors with brand new ones. Still, I get the ABS failure warning and nothing happens at my modulator/pump when the car is started or running.

For the second issue, its become increasingly difficult to bleed my rear brakes, an now its not happening at all. I’ve pinpointed the problem to, you guessed it, the ABS modulator/pump. Brake fluid flows to it, but will not come out the exiting ports. My trick I figured out last year also no longer works. Also, I’ve tried to bleed them utilizing a helper pressing the brake pedal while I work the bleeder valves, using a hand operated vacuum pump, and using a compressor operated vacuum pump.

I’m almost at my wit’s end. I’ve resorted to studying the electrical diagrams for the ABS system thinking there has to be a bad signal or shorted wire somewhere, but I’m having a lot of difficulty trying to figure out what the readings should be in a properly working ABS system. If you have any ideas or think I’ve missed something, I’m certainly open to suggestions. At this point, I’ll try anything!

Brett …

Here’s an excellent video on ABS modulators. While not specific to your car they all work fundamentally the same.

I don’t understand why you aren’t getting fluid to the rear brakes. Even if the ABS modulator fails you SHOULD have normal braking. If you have fluid going into the modulator but nothing coming out then you have definitely narrowed down your problem.

Thanks for the suggestions Grooveman. The video you posted does a great job of showing how the ABS pump works in a general sense, but does not get into the specifics I need to diagnose my issue. I’m at the point of going through my system wire by wire. Also, the design of the pumps on the earlier systems are significantly different than the one in the video and I’m not able to disassemble it to fiddle with the internals like he does.

I should also mention that I don’t know why the fluid won’t flow through the ABS pump either. I can only make an educated guess that possibly the internal pump valving for the rear brakes is in the closed position and won’t let the fluid pass. I’ve been trying to find a way to use a 12V power source to essentially jump the unit started so that I can at least get the fluid through it for me to bleed the rear brakes, but no luck thus far.

Brett …

Hmm … so you can’t get the unit apart.

You said that you’ve replaced the ABS modulator so it seems a bit of a coincidence that you would be having the same problem if it’s an internal mechanical failure.

I’ve never had my unit out of the car (one of the very few things that I haven’t) so I’d be really interested in it’s innards. Is it riveted together? Generally what man has assembled man can tear apart.

I agree with what you say. I think its unlikely to be an internal mechanical failure. The only reason I’d be interested in getting it apart is to be able to understand the electrical components of it more clearly.

Realistically, I probably could get it apart if I was really intent on doing so, but since I have no idea how difficult it would be or what I should expect to see, I’m hesitant to do so because I may never get it back together again correctly! I installed a NOS unit on my car shortly after this issue arose, so I’ve been messing with my original spare for the bench testing I’ve been doing.