brake warning at 3000 rpm

[Glen]

I am sorry if this is a common issue that has been dealt with before, but with so many members, and so many threads, I frankly got tired of searching. :)

I have a 1985 635csi which runs and drives great, however, as I row through the gears everything seems normal, until I hit 3000 RPM in 5th gear, then my ABS warning light, and the brake light both come on.
my brakes work perfectly, but the lights will stay on until I shut the car off.
If I drive around town, the lights never come on...only in 5th gear, and only at 3000 RPM.

do any of you have a clue as to why this is happening, and what I can do about it?

Thank you, each and all, in advance for any light you may shed upon this subject.

[86_6series]

High speed alert caused by confusion to sensor usually from rusted impulse on the hubs.
Slow speed alert would be defective impulse sensor.

You could try cleaning and removing as must rust as possible.
Or of course replacing with new hubs.

Front #1 hub

https://www.realoem.com/bmw/enUS/showpa ... Id=31_0175

https://www.google.com/search?q=3121113 ... 1IppLGbgtM:

Rear #5 hub

https://www.realoem.com/bmw/enUS/showpa ... Id=33_0173

https://www.google.com/search?q=3341112 ... 7PwSqGDZsM:

Front pulse generator #2

https://www.realoem.com/bmw/enUS/showpa ... Id=31_0379

If you replace this use one listed for an E32, longer than needed but not as short as 5 series. No 6

series listed.

Rear pulse generator #17

https://www.realoem.com/bmw/enUS/showpa ... Id=33_0202

[Brucey]

if the ABS light comes on at about 75-80mph then it normally indicates that one of the rear sensors is failed or at least the rear sensors are not sending 'clean' signals (eg because the toothy rings are not perfect, or there is too much rust on the sensor, which is magnetic).

I suspect that at lower speeds, it being a rear wheel drive car, some discrepancy between the front and rear sensor signals (and/or side to side at the rear) is tolerated, because at those speeds you might have some wheel slip or even outright wheelspin. However at higher speeds such discrepancies are less likely to be tolerated, because wheelspin is less likely to occur.

cheers

[86_6series]

Brucey,
Years ago I had the high speed problem and replacing the hubs solved the problem, they were just too rusty.
Then a few years ago when I got to about 15 mph, no wheel spin just normal take off the light went on.
Wound up being the front right sensor. Bought the one listed for an E32 a little longer in length but
worked out solving the problem.

Bob V

[Brucey]

Brucey,
Years ago I had the high speed problem and replacing the hubs solved the problem, they were just too rusty.
Then a few years ago when I got to about 15 mph, no wheel spin just normal take off the light went on.
Wound up being the front right sensor.

yes, it makes sense and is also what I've found to be the case. I didn't mention it previously but if there is any difference between the front wheel signals which is not explicable by footling differences in wheel diameter or turning a corner, it means that one of the front wheels is skidding and can't provide enough traction for useful braking, or there is a failed/bad sensor signal. Control of the front brakes is usually vastly more important than control of the rear brakes too, if you want to slow down.

So the ABS system is more sensitive to front wheel sensor faults; if there is a fault it tends to manifest itself at ~15mph. Below this speed the ABS system is effectively 'off'; the wheel sensors probably don't generate a strong enough signal to be measured accurately anyway.

If the rear sensors used the same protocol as the fronts, you would quite likely trigger the ABS every time you get the slightest wheelspin, which would be very tiresome.

So the bottom line (for this and many other rear wheel drive cars which use Bosch ABS) is that

- if the light comes one when the car is stationary, it usually means the ABS pump isn't running properly or the system isn't developing enough pressure.
- if the ABS light comes on at ~15mph it is probably a bad sensor/signal from a front wheel
- if the ABS light comes on at about 75mph then it is probably a bad sensor/signal from a rear wheel.

A front wheel drive car would use a different protocol.

FWIW I recently 'repaired' an ABS system (on a Jag, also rear wheel drive and also using a similar ABS system) which manifested the ~15mph fault; in this case there were just a few fragments of rust on the end of one (front, obviously) wheel sensor, and this was (to my surprise) enough to mess the signal up. I must have looked like a miracle worker; I looked at the front wheels sensors first (which I knew to do by when the light came on) and guessed which one would be more likely to be rusty; I guessed correctly, so was able to fix the car in a few minutes, having only removed one wheel out of four.

cheers

[clipper47]

Bruce, Thanks for this information. The ABS light on my 635CSi comes on occasionally at about 15mph but not always. Sometimes when I shut the car off and restart it the light goes out and stays out for days. I thought perhaps this was a relay problem but I guess not now that I have read this posting. The front sensors on my car have less than 10k miles on them so I am hoping that these are not the problem. Last year I had the same problem and once the wheel sensors were cleaned up the problem disappeared but it came back this fall. This car is stored for about 5-6 months every winter in cold but dry storage.

[Glen]

Thank you all very much...you are awesome!

I have a deep love for almost all things automotive, but have far too little experience with BMW to just tinker around and guess.
The people in here have been a great source of information, and highly supportive. :)

[Brucey]

…. The ABS light on my 635CSi comes on occasionally at about 15mph but not always. Sometimes when I shut the car off and restart it the light goes out and stays out for days. ....

The Jag had been doing exactly the same thing for a long time. Interestingly the jag's toothy wheels were entirely corrosion-free, so the fragments of rust that had managed to stick onto the end of the sensors must have come from somewhere else.

On the BMWs I have worked on, the ABS sensors are usually corroded into the upright and I only disturb them if they are electrically faulty (eg they have gone open circuit). You can get access well enough to clean them by other means, of course.

cheers

[clipper47]

…. The ABS light on my 635CSi comes on occasionally at about 15mph but not always. Sometimes when I shut the car off and restart it the light goes out and stays out for days. ....

The Jag had been doing exactly the same thing for a long time. Interestingly the jag's toothy wheels were entirely corrosion-free, so the fragments of rust that had managed to stick onto the end of the sensors must have come from somewhere else.

On the BMWs I have worked on, the ABS sensors are usually corroded into the upright and I only disturb them if they are electrically faulty (eg they have gone open circuit). You can get access well enough to clean them by other means, of course.

cheers

This has been a problem with my 635CSi for about 3 years. I thought perhaps it might be a sticky relay as I can't quite understand why it only happens occasionally and will quite often be resolved by turning the ignition off and on again. I cleaned all of the sensors last year but was careful to not twist them in the housing. That was a big mistake that I made years ago which resulted in me buying two new front wheel sensors. I guess I will have to try to clean the magnets again but thanks to your advice it seems as though only the fronts need this treatment. Thanks again.