Need advice for an odd braking issue...likely with the ABS. Track Weekend Tomorrow.

[MemphisRob]

ok... I could use some guidance.

1.) I have an issue where my brakes work fine except as I come to a stop... only at very low speed (like sub 15mph) the pedal goes a bit soft. It feels like the rear brake pistons back off the rotors.

2.) I thought the issue had something to do with the brake booster so I found a whole assembly on eBay for $100 that is the brake booster, master cylinder, and pedal travel sensor.... and replaced the whole damn thing. But it didn't fix it.

3.) I had some pretty heat glazed rotors and I just replaced those with new ones and some newish pads... that didn't fix it.

4.) Just last night after I bedded in the new pads and rotors... I stopped for a while to chat with some buddies that are going to Barber this weekend. When I started the car back up my ABS and ASC lights lit up (as they have before on track on occassion)... and then the soft pedal issue was completely absent.

So, the issue is clearly something to do with the ABS system. I checked Bimmerforums and below are the likely reasons for the ABS/ASC light to come on. But I am in a weird spot where when the ABS/ASC lights pop on, my (arguably) more serious issue of the soft pedal goes away.

1. A faulty wheel speed sensor
2. A bad ABS relay
3. A bad pedal travel sensor
4. A stuck/clogged solenoid valve
5. A faulty ABS pump motor
6. A bad brake light switch

What should I do next to further narrow down the issue? Although the cost of the new booster assembly wasn't too bad at $100... it took me all day to swap it out and I don't want to continue to chase my tail.

Also, what is the easiest way to defeat the ABS/ASC with no ill effect other than losing ABS and Traction Control... should I just remove the wheel speed sensor connectors for this weekend until I have time to sort out a fix for the ABS?

[yeaseth]

I've had issues with the solenoids on my e30 ABS unit. I run an ABS delete kit on my E36 for track/autocross use.


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[MemphisRob]

I've had issues with the solenoids on my e30 ABS unit. I run an ABS delete kit on my E36 for track/autocross use.


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I've looked at the ABS delete kits. How different are they vs. just defeating the ABS "electronically"?

I know it would be lighter..I had to take out the ABS pump assembly when replacing the brake booster/MC and that thing had to weigh 10lbs.

[yeaseth]

https://youtu.be/brFQklBp-b8

You can pm me if you are interested


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[XnWarden]

Brake pedal going soft is almost always air in the system. Have you inspected for leaks near the calipers and master cylinder?

[MemphisRob]

Brake pedal going soft is almost always air in the system. Have you inspected for leaks near the calipers and master cylinder?

I have bled the system at the calipers pretty well. To be fair, I don't believe I have any leaks but I haven't really gone over it meticulously searching.

The part that that makes me doubt the leak possibility is when the ABS was "defeated" the soft pedal went away entirely.

I dont know why the ABS/ASC faulted but it could be a dirty/defective wheel speed sensor. I replaced the rear already last year, but I do get some very heavy brake dust from track pads.

[mslevin]

Air in the ABS system maybe? When you bled the brakes, did the reservoir run dry at any point?

[MemphisRob]

Air in the ABS system maybe? When you bled the brakes, did the reservoir run dry at any point?

Not likely but possible.

How would I get the air out of the ABS module?

[mslevin]

Not likely but possible.

How would I get the air out of the ABS module?

Haven't tried it myself but... http://www.bimmerboard.com/forums/posts/1218017

[marvinstockman]

Try pulling the ABS fuse, or just pull the connector to a wheel sensor, which in either case will kill the ABS.

[yeaseth]

Try pulling the ABS fuse, or just pull the connector to a wheel sensor, which in either case will kill the ABS.

Killing the ABS unit electronically will only keep the ABS from activating. Fluid will still be running through it regardless. There could be air in the ABS unit. If the problem goes away you know it has to do with that system, but if the problem stays you can't rule out the ABS unit from being the culprit.


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[MemphisRob]

Killing the ABS unit electronically will only keep the ABS from activating. Fluid will still be running through it regardless. There could be air in the ABS unit. If the problem goes away you know it has to do with that system, but if the problem stays you can't rule out the ABS unit from being the culprit.


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so.. would this advice be good? http://www.m3forum.net/m3forum/showp...5&postcount=13

[yeaseth]

Yes that's perfect, I couldn't find that write up before


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[MemphisRob]

Yes that's perfect, I couldn't find that write up before


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Pic of ABS IMG_8783.jpgIMG_8783.jpg