pkjense

I have an 88 951 with the brembo big reds up front, blacks in back. I have never been able to get a good pedal feel. There is a 5/33 bias installed at the master cylinder. I have always had a sneaking suspision... and when I checked the ABS unit there is also the stock bias mounted there. I suspect that may be the issue so will remove it. Because of the way the lines are set up, I will probably relocate the 5/33 to the "lower" location.

Or...

While I am in there should I just remove the ABS? I never liked and it generally fails after the first time it activates (tire size issues?). The car does street and DE events. I can find very little documentation on the web from people who have done this. I thik there are a couple of routes to go.
1) I could bridge the rear line with a straight through connector, and T the fronts much as the rear is T'd at the back. This is easy, has little line modifications, and it would be simple to reconnect the ABS if I needed to for resale.
2) I noticed on the master that there is a blocked off port, opposite and identical to the front brake line connection point. Could I use that port to go direct to the driver's side front brake, and use the front feed to the ABS to connect to the passenger side brake? Anybody do this? I could then simply bypass the ABS for the rear with a straight through connector. I'd have to fabricate some lines, but this seems like a good solution, and IMHO would be better as there would be two separate feeds for the front (bigger) brakes.

Once that is done I can get around the idiot light issues.

Opinions, experiences?

Van

On my '88 turbo S, there was only a proportioning valve at the ABS pump - not the master cylinder.

However, I had a great pedal feel with that.

Things to check: flexible brake lines, firewall cracks, bleeding with a pressure bleeder.

pkjense

Things to check? That is all taken care of. Two P valves cannot be good though. I should probably just get rid of the old one, bleed and be done. But I am in there now, and I sooo hate (primitive) ABS kicking in and going chugga chugga, when I am trying to threshold brake. If it was consistant I could live with it.

Oddjob

Should not be a prop valve on the MC on an ABS car; should only be one mounted on the ABS pump.

Most that track/race 944/951s with and without ABS, do feel the ABS system (although outdated) does function fine. If yours is performing inconsistently, first get rid of the extra bias valve to see if that helps. If problems still exist w/ the ABS function, then start trouble shooting other aspects of the system.

pkjense

Thanks, I'll give it a shot; it is the easy route for now. And i am sure it will help my pedal feel issue, everything else has ben well covered. I'd just like to get most of this out of the way while waiting for Lindsey to finish building my engine. But, if the ABS still fails, once I am back on the road, I can always disable it until I get get aroud to it...

Oddjob

Pull the ABS fuse, and the system will/should function like a non-abs setup (but will have warning lights on the dash). If there are braking problems w/ the fuse pulled (imbalance, inconsistent pedal effort, etc), then might have a problem w/ the pump unit, or other problem w/ the standard components (MC, bleeding, calipers, etc).

Cris Brady

I agree with the others. I race and my 89 has ABS. I'm a good threshold braker and in the dry I rarely ever engage it. My main issue with it is some events can trigger the warning mode, drastically reducing your braking power, such as going over the rumble strips in the bus stop at the Glen. That's why I put in a Reset button that cycles the system and it's a non-event now.

So if you are having issues I'd be looking elsewhere. The suggestion to pull the ABS fuse is good and could help you track it down.

pkjense

reset would be great! how do i goo about doing that?

Cris Brady

There's a bunch on threads here on how to do it. I did it several years ago and what I remember is you need to splice a lead going to the abs relay and route it to a button that either takes the lead to ground or interrupts it, I don't remember. I picked up the lead out of the bottom of the main fuse box and routed it to my console area. I originally used a push button but now I just use a regular toggle switch to match the rest of my switches on the panel. You just need a momentary switch to reset it. When it goes into warning mode with the big red ! on my instrument panel, I just reach down and flip it up, wait a beat and flip it down. Don't even have to think about it when racing.