ABS intermittent

[aeronaut]

I have one i have rewired. Would be willing to send to you to try out if you have the same 3 channel 95 m3 abs pump. It is sitting spare in my garage, and if it works for you would just ask you to send me back your old one in case i need one (can rewire it if i ever need it).

Wow, that's very gracious and helpful, as I'm instructing next weekend and pretty busy. YES! Sending PM.

[aeronaut]

Ok, 'new' used ABS pump/valve installed. THANKS OLEMISS!!! Track day tomorrow (although it's the track that didn't reveal any problems last time). We shall see.

[olemiss540]

Ok, 'new' used ABS pump/valve installed. THANKS OLEMISS!!! Track day tomorrow (although it's the track that didn't reveal any problems last time). We shall see.

Any error codes on startup? ABS light currently off? Good luck and let us know how she BRAKES! A video wouldnt hurt :-)

[aeronaut]

No error codes (from OBDI stomp test, or from BWM scan of ABS computer). When ABS light comes on, it stays on until power cycle. Then off until next hard braking into ABS (only on track).

So, today, all good!! However, this was on Summit Point Shenandoah, and I"ve been fooled there before (that all was fixed). The real test will be in 2 weeks on Summit Main. But by the end of the day today, I was braking heavy and hard, and Shenadoah isn't a smooth track, with bumps in the braking zones.

Fingers crossed!!!!!

Video or 2 coming.

[olemiss540]

No error codes (from OBDI stomp test, or from BWM scan of ABS computer). When ABS light comes on, it stays on until power cycle. Then off until next hard braking into ABS (only on track).

So, today, all good!! However, this was on Summit Point Shenandoah, and I"ve been fooled there before (that all was fixed). The real test will be in 2 weeks on Summit Main. But by the end of the day today, I was braking heavy and hard, and Shenadoah isn't a smooth track, with bumps in the braking zones.

Fingers crossed!!!!!

Video or 2 coming.

Awesome news!

[aeronaut]

I'd call it, excellent not bad news. I'm certainly very hopeful, but I'm reserving a reaction of utter happeness until I'm on Summit Main.

[aeronaut]

After a track day on Summit Main with no ABS issues, I'm calling my ABS problem officially fixed!!
For those who find this thread later, and don't want to read the full thread:
- ABS intermittent (shuts off) under a very specific set of track conditions. Problem could not reproduce on the road.
- Turn car off/on, ABS resets and is fine until next track session.
- Things tried that didn't help: Sensors replaced, ABS 'codes' read by BMW dealer (no errors found), ABS computer replaced, brake pedal travel sensor replaced.
- Replacing ABS pump (with a used unit) finally fixed the problem.

[Greg S]

Likely a torn solenoid ribbon wire inside the ABS pump, re-wire it. But of course, do you homework and check the easy/obvious things first.

After a track day on Summit Main with no ABS issues, I'm calling my ABS problem officially fixed!!
For those who find this thread later, and don't want to read the full thread:
- ABS intermittent (shuts off) under a very specific set of track conditions. Problem could not reproduce on the road.
- Turn car off/on, ABS resets and is fine until next track session.
- Things tried that didn't help: Sensors replaced, ABS 'codes' read by BMW dealer (no errors found), ABS computer replaced, brake pedal travel sensor replaced.
- Replacing ABS pump (with a used unit) finally fixed the problem.

Who would've guessed

[aeronaut]

I know, right!

[aeronaut]

Ok, I wanted to update this thread for the record. After additional ABS failures since above. I (hope) I've FINALLY figured out the problem. This was painful. After much debug, testing, and random parts replacement (brake booster replaced, all abs sensors replaced, pedal travel sensor replaced, ABS computer replaced, 2 ABS pumps re-wired and replaced, ground wires checked, wiring checked, install of proportioning valve, etc), I had to step back and think. Then it hit me, after looking at my records, this all started when I replaced the brake booster (replaced due to booster failure, not due to ABS issues).

So how could that be making the ABS system give warning, and almost always only when on track? Then, it hit me. What's the difference between on-track bracking and street. The brakes are hotter, more efficient. Meaning, less pedal travel for equivalent braking (I haven't run street pads for several years, I just leave my PFC08s on). I realized on-track, once brakes were hot, there were cases where I could get into ABS on a wheel with minor pedal travel (eg trail braking deep into a turn).

So what's the common theme here? Brake booster, travel pedal sensor, and ABS engagement with light pedal pressure. Oh but I changed the pedal travel sensor!? And, it tests 100% accurate.

OH WAIT, those little plastic nipple things that come in the bag with the pedal travel sensor. I used the same color as original, blue, when I replaced the brake booster, and then when I installed the new pedal travel sensor.

Let's try the white longer one, so that the computer will actually see pedal travel when my ABS is kicking in. White nipple installed.

ABS problems fixed.

An f'ing 1c piece of plastic.

This blue nipple, now replaced with the longer white one.

I hope this fix 'sticks'. 4 full track days without ABS issues.

BPTSnipple.jpg

[ThreeD]

Good job man. Sounds like you got it!

Sent from my Pixel XL using Tapatalk

[TXBDan]

Interesting. Funny i was just reading about that. Apparently the official procedure when installing a new travel sensor is to log it with the BMW computer and adjust it via those tips until the signal is with in a proper range.

Stupid travel sensors. The folks without them are lucky!

[aeronaut]

Interesting. Funny i was just reading about that. Apparently the official procedure when installing a new travel sensor is to log it with the BMW computer and adjust it via those tips until the signal is with in a proper range.

Stupid travel sensors. The folks without them are lucky!

After all my troubles, that makes perfect sense. Somehow, computer uses rate of change, or direction of change, or such, to decide if/when to actuate ABS.
And, 100% agree...STUPID TRAVEL SENSORS!! lol

I have been tempted to wire in a variable resistor in its place, set it to different values between 500 and 1200 (or whatever the range is) and see what happens. Easy enough to do.

[TXBDan]

That's an interesting idea. Yeh, if the computer acted only on its value and not something more advanced, that pot could act as a "ABS Threshold" adjustment.

[aeronaut]

Wouldn't that be cool! Would love to have an 'almost off' setting. lol

[JBasham]

Thanks again for the information you keep updating the thread. I'm starting ABS light diagnosis myself this week. Had a couple days of madness on Summit Main. Including a 700-degree spin at the exit of Turn 3, without ever leaving the pavement. The flagging crew gave me much well-deserved grief.

[aeronaut]

Thanks again for the information you keep updating the thread. I'm starting ABS light diagnosis myself this week. Had a couple days of madness on Summit Main. Including a 700-degree spin at the exit of Turn 3, without ever leaving the pavement. The flagging crew gave me much well-deserved grief.

Was your mega-spin on Sat? I was instructing on Jefferson, I think I heard it. LOL
Let me know if I can help in any way.
What year is your E36? M?

FYI, even if my ABS issue is finally fixed, I'm really glad I installed a proportioning valve to move the bias where I want. Even with ABS working this last weekend, I tweaked the bias a bit. And, I want to run a test where I run a session with ABS and without, same day same track. I *feel* faster with ABS, but data shows I might be quicker without. But no way I could run quicker with ABS off without a proportioning valve.

[bzm3ltw]

I'm replacing the vacuum booster in my 98 M3 sedan track car and have been following this and related threads. I found this on the eeuroparts website for

BMW Brake Booster Vacuum Sensor - Genuine BMW 34331182594 Brake pedal travel sensor.

The label in the picture states:

ACHTUNG! Die Farbe der Distanzkappe muss den Farbpunk am Bremskraftverst. entsprechen
(Roughly: WARNING! The color of the tip cap must match the color of the dot on the vacuum booster.)

[aeronaut]

Good find, and very interesting....I just checked the Bentley manual and I didn't see any mention of that. I'm pretty sure my booster is lightly coated in rust and doubt I'll see any paint dots on it, but I'll check.

[m3bs]

Shouldn't you be able to match the color of the tip on the old sensor?

[aeronaut]

Yes. Of course. But my current belief is manufacturing tolerances in the BOOSTER can require different length tips.

[JBasham]

Was your mega-spin on Sat? I was instructing on Jefferson, I think I heard it. LOL
Let me know if I can help in any way.
What year is your E36? M?

FYI, even if my ABS issue is finally fixed, I'm really glad I installed a proportioning valve to move the bias where I want. Even with ABS working this last weekend, I tweaked the bias a bit. And, I want to run a test where I run a session with ABS and without, same day same track. I *feel* faster with ABS, but data shows I might be quicker without. But no way I could run quicker with ABS off without a proportioning valve.

Ha, thanks, you probably could've SEEN it from the Jefferson too. It was on Tuesday, though. I diagnosed the problem last night. First thing I did was look up the pinout in the Electrical Troubleshooting Manual for my particular model, which was really helpful.

I'm such a McFly. I had cut both the signal wires to the rear sensors. I have been scraping out the sound deadening and tying down the wiring. The previous owner had a bunch of random security system wires running around. The ABS sensor wires coming in from the trunk weren't in a harness bundle, weren't tied down, and looked unlike any BMW wires I've ever seen.

I may be getting back to you about the proportioning valve. I did the 330i/325i E46 caliper swap over the winter and I'm still not sure whether I will have too much rear bias. I'll find out when I get back to Main next month, with functioning rear ABS. With ABS in the front only, it was waaaayyyyyy too much rear bias . . . .

The car is a 1994 325is chassis. The drivetrain is a Ford V8.

[fbirch]

Ok, I wanted to update this thread for the record. After additional ABS failures since above. I (hope) I've FINALLY figured out the problem. This was painful. After much debug, testing, and random parts replacement (brake booster replaced, all abs sensors replaced, pedal travel sensor replaced, ABS computer replaced, 2 ABS pumps re-wired and replaced, ground wires checked, wiring checked, install of proportioning valve, etc), I had to step back and think. Then it hit me, after looking at my records, this all started when I replaced the brake booster (replaced due to booster failure, not due to ABS issues).

So how could that be making the ABS system give warning, and almost always only when on track? Then, it hit me. What's the difference between on-track bracking and street. The brakes are hotter, more efficient. Meaning, less pedal travel for equivalent braking (I haven't run street pads for several years, I just leave my PFC08s on). I realized on-track, once brakes were hot, there were cases where I could get into ABS on a wheel with minor pedal travel (eg trail braking deep into a turn).

So what's the common theme here? Brake booster, travel pedal sensor, and ABS engagement with light pedal pressure. Oh but I changed the pedal travel sensor!? And, it tests 100% accurate.

OH WAIT, those little plastic nipple things that come in the bag with the pedal travel sensor. I used the same color as original, blue, when I replaced the brake booster, and then when I installed the new pedal travel sensor.

Let's try the white longer one, so that the computer will actually see pedal travel when my ABS is kicking in. White nipple installed.

ABS problems fixed.

An f'ing 1c piece of plastic.

This blue nipple, now replaced with the longer white one.

I hope this fix 'sticks'. 4 full track days without ABS issues.

BPTSnipple.jpg

Very interesting outcome. Thanks for taking the time to post your follow up info.

My E36 race car exhibited the same symptoms – ABS would never fail on the street, only on track and only after enough laps to put significant heat into the system. Like you, I surmised the problem was heat related. I surmised it was related to the heat caused by ABS activation cycles, since it would only lock up after several hard laps during the first session of the day, and then 1-2 laps in subsequent sessions.

The solenoids in the ABS actuator draw a huge amount of current and they will likely get hot after banging on them for multiple laps. In my case it was always the same wheel that locked up (right front), so I surmised that one of the two solenoids that control that wheel was overheating or seizing up after enough activation cycles. So I replaced the ABS pump/actuator and did two 20-min sessions during which I abused the brakes as much as possible. No wheel lockups, where I would most definitely have gotten them before the change. I disassembled the original pump/actuator and inspected closely for wire problems (none found) and did some repeated activation cycles of the solenoids with a power supply, expecting to hear one of them seize up (inconclusive results).

After reading your follow up post, it’s possible that in swapping the old ABS pump I may have changed something (e.g., a tiny bit of air in the lines) such that I now have a tiny bit of additional pedal travel (not perceptible), thus “fixing” the problem in a way that’s different from what I thought. If my problem reappears, I’ll try your approach of using a longer shim on the pedal travel sensor.

Do you know of a way to buy a set of tips without buying a whole new pedal travel sensor?

Based on your theory, it seems you'd want to use the longest tip in the set that still produces 250 Ohms with no pedal pressure. You could do this by starting with the longest tip in the set and putting an Ohmmeter directly onto the sensor terminals. Keep reducing the tip length until you see 250 Ohms with no pedal pressure.

FYI, I have StopTech BBK calipers and floating rotors on the front end. When hot, these brakes produce a rock solid pedal with very little travel. What brakes do you have on your car?

[aeronaut]

My history with my ABS problem is complicated enough and long enough, that it wouldn't surprise me if I had 2 issues over the course of the problems. Likely a bad ABS pump AND the wrong sensor tip. I'll never know for sure.

I don't know of a source for tips other than a new travel pedal sensor. If I needed a length I didn't have, I'd fab up something.

I have Porsche Boxer S calipers on front, and OEM on rear. (95 M3)

On track, these cars see a huge number of ABS cycles compared to the life of a normal car. We tax these systems pretty hard.

I will also add, driving w/o ABS and with a balanced system front/rear (proportioning valve) VS with ABS, is like 2 different cars. I really enjoy driving the car w/o ABS. I have a track day tomorrow. I may try back to back session with and without ABS, and see time differential. That data analysis might be iteresting. My guess is ... w/o ABS, I'll apply brakes sooner with a longer ramp to max brake, but the max might be a little higher.

[JBasham]

They just reopened Seat Time registration for Monday, so if you can push to that day, you'll pick up two more sessions over FATT on Friday.