ABS cutting in too early

JonF

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I have a 2002 1150GSA with the simple non-servo ABS. Most of the time the brakes are fine, but now and again the front wheel's ABS cuts in, releasing the brake, which is allowing the bike to roll maybe another metre before the brakes cut back in. It's only ever done it at low speed, and it's never anywhere even close to the threshold for losing front wheel grip. Bike has a full service history, it's never been crashed. Battery has recently been replaced which hasn't changed things. Anybody out there got any ideas? As it's only ever done it on the front, I wondered whether the front sensor could be faulty.
 
I have a 2002 1150GSA with the simple non-servo ABS. Most of the time the brakes are fine, but now and again the front wheel's ABS cuts in, releasing the brake, which is allowing the bike to roll maybe another metre before the brakes cut back in. It's only ever done it at low speed, and it's never anywhere even close to the threshold for losing front wheel grip. Bike has a full service history, it's never been crashed. Battery has recently been replaced which hasn't changed things. Anybody out there got any ideas? As it's only ever done it on the front, I wondered whether the front sensor could be faulty.
Frightening when that happens, isn't it?

My bike did that after I fitted TKC80 tyres. I put it down to the big gap between the blocks on the front tyre centre line causing the front wheel to momentarily lock up. Was quite happy to remove the ABS after it did it a couple of times. Gently braking to stop behind a car and the brakes switch off for the next metre. Not fun!

I reckon that this is a design fault with the first generation ABS.
 
I reckon that this is a design fault with the first generation ABS.

Well my bikes abs works as it should with TKC's fitted and i've never heard of anyone else having this ABS problem with TKC's.
And i know just as many riders who've run with TKC's as standard tread tyres.
 
I would just do as Steptoe suggested you know it makes sense
 
Check all the teeth are ok on the abs sensor ring

Had a look when I got in from riding home this evening (it did it twice on the way home, and it's not down to diesel or anything else on the road). Teeth all look OK, although a little dirty. Will give it a clean up with some brake cleaner later, see if that makes any difference.
 
In my part of the world the roads are really slimy at the moment which might be the cause of your problem. I've had a few slips and slides over the last couple of weeks even when being very careful and the roads look to be spillage free. I barely touch my brakes at the moment and I have the odd ABS cut in.

Wait for the roads to dry out, or get rained on for a good 12 hours, and see if you get the same issue.

Regards

RobC
 
I've been getting this issue for a while and it is not down to anything on the road. The ABS is cutting in early at such low speeds and with such gentle braking that it's not down to loss of traction. I've had the bike a good while and know how it responds, and I've done pretty much the same commute for the best part of twenty years, mostly on GS's. The way the bike has responded to the front brake has definitely changed. Something is causing the ABS to cut in when the road conditions don't merit it.:nenau
 
I would book it into BMW and let them test it properly
I couldn't ride round thinking I had a brake fault
 
Those old ABS systems have always been a bit crude and at over 20 years old it may well be time for a new sensor. Check the clearances before you do anything else, especially if the wheel has been out recently.
 
Those old ABS systems have always been a bit crude and at over 20 years old it may well be time for a new sensor. Check the clearances before you do anything else, especially if the wheel has been out recently.

Wheel hasn't been out for a few months, since the last front was put on. However, that was also my thinking. The bike's not quite that old - it's a mere 14 - but it's been used quite hard since I bought it four years ago. Will give it a thorough check over and clean tomorrow, and if that doesn't cure it I'll put a new sensor on.
 
I've never had this issue with a bike, only on a car (well I have, TBH, but that was with a demo Yam GTS with HCS years ago, which I handed back to the dealer at the end of the ride). My car was afflicted with just the meerest ABS intervention, when right down to almost walking speed, sometimes. Really annoying, rather than dangerous in my case, but it would be a bit more worrying with only 2 wheels I guess.

We tried cleaning the reluctor ring windows, checked it was secure & running true & found plenty of debris from the sintered brake pad material around the face of the ABS sensor. We checked the sensor gap, the wheel bearings for wear/play, the wiring right back to the ECU, but just couldn't get the fault to clear. The messages looked OK when we scoped the sensor, but it is difficult to replicate real life road conditions without access to specialised gear. Anyway, the problem was only cleared by replacing the ABS sensor & wiring - the sensor must have been corrupted in some way, presumably by water or road/pad debris. Not the most scientific approach I know. In the OPs case though, working through the same process may help.

The only other generalised thoughts I had was with the relatively recent tyre change. Was the ABS sensor removed first & protected away from damage & only replaced once the whole wheel change was complete. Could the sensor wires have been pinched/trapped during the process. Were the wheel bearings checked for wear & the axle torqed up correctly, with any spacers in their correct places.

Good luck sorting this ....................... KEN
 
I've never had this issue with a bike, only on a car (well I have, TBH, but that was with a demo Yam GTS with HCS years ago, which I handed back to the dealer at the end of the ride). My car was afflicted with just the meerest ABS intervention, when right down to almost walking speed, sometimes. Really annoying, rather than dangerous in my case, but it would be a bit more worrying with only 2 wheels I guess.

We tried cleaning the reluctor ring windows, checked it was secure & running true & found plenty of debris from the sintered brake pad material around the face of the ABS sensor. We checked the sensor gap, the wheel bearings for wear/play, the wiring right back to the ECU, but just couldn't get the fault to clear. The messages looked OK when we scoped the sensor, but it is difficult to replicate real life road conditions without access to specialised gear. Anyway, the problem was only cleared by replacing the ABS sensor & wiring - the sensor must have been corrupted in some way, presumably by water or road/pad debris. Not the most scientific approach I know. In the OPs case though, working through the same process may help.

The only other generalised thoughts I had was with the relatively recent tyre change. Was the ABS sensor removed first & protected away from damage & only replaced once the whole wheel change was complete. Could the sensor wires have been pinched/trapped during the process. Were the wheel bearings checked for wear & the axle torqed up correctly, with any spacers in their correct places.

Good luck sorting this ....................... KEN

Thanks for your comments Ken

I do loads of miles, as the bike's a year round commuter, so it goes through a lot of tyres. I always get them fitted by a very good BMW independent, and I very much doubt he'd have snagged the sensor wires. Will have a good look at the weekend in proper daylight. I'll take the sensor out and check its facing for signs of wear. As the bike gets ridden on a 70 mile round trip right into central London, with all the muck and clattering about that entils, I could well imagine the sensor had got damaged in some way.
 
Ken's story rings a bell. I have Nissan Navara that would have it's ABS kick in a around 3mph. The brake pedal would vibrate a lot and the brake force would disappear for a second or so. I could never make it happen on demand and it hasn't done it for a while. The only thing I changes was a front wheel bearing and rear prop-shaft bearings back in the summer.

By the way, my GS and I used to do a commute into Central London from Dorset three times a week. "Muck and clattering about" sounds about par for the course. Take is easy and I hope the new sensor fixes the issue.

Regards

RobC
 
Something else just popped into mind. I used to have a ZZR1400 which had EBC brake discs. They had vertical slots and at low speeds I could feel the leading edges of the brake pads dip into them which caused a nasty judder. Most noticeable at less then 10mph where the front wheel would get to the point of locking. Have you changed discs and/or pads recently?

Regards

RobC
 
Hi Rob, no, haven't changed disks and they're still (nearly had it) original BMW ones.

However, been out and about on the bike today, lots of short low speed runs. No problems today. Maybe the quick clean I did on Tuesday has helped. Will give it a proper clean at the weekend.
 
Hi Jon. Did the clean sort it? I had this happen last night exactly the way you describe. My bike is filthy from commuting through the grime of the last few weeks so maybe that's the place for me to start if it worked for you. Cheers.
 
Hi Jamie, it certainly seems to have helped. Since I gave it the quick clean, I've only had the ABS cut in once, and that was on a loose bit of road. I've got a couple of weeks off over Christmas, and I'll give it a careful, proper clean. If the problem comes back in the New Year, I'll try a new sensor.
 
Hi, just been reading about a lads front wheel bearings starting to fail, first thing he noticed was the ABS acting strange. May be worth double checking your bearings. Good luck.
 


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