Brakes applying themselves

[fatbaldbob]

04 1150GSA Twin spark Servo ABS 52000 miles.

Had a few scary moments recently with the bike and it happened again on the way home from work today. Riding along as normal and bike felt like it was losing power, opened throttle nothing happened, bike starts to slow rapidly, pulled in clutch fearing a lock up and bike comes to an abrupt halt and without me even touching the brakes. Check bike and find front brake is on and the bike wont move, turn off ignition reset system and brakes come off This has now happened four times at varying speeds, no pattern to it but usually after the brakes have not been used for some time (whilst riding), the front just mysteriously applys itself. No the hand guard is not fouling the lever, and the whole brake circuit ABS and Servo had a fluid change 3000 miles ago. Anyone experienced this or any Idea whats going on.

 

[Fanum]

No idea but looking at it logically , as the brakes 'reset' after turning off and on, it must be an electronic problem rather than a physical one (like warped discs heating the fluid for example)

Steptoe will probably give a more definite answer, but just as a guess, I'd say it's the ABS control unit wiring or something along those lines

 

[fatbaldbob]

I see your point, however just to confuse matters, as the brakes are linked shouldn't the back brake have applied it's self too?

 

[roddy]

is the linked part of servo's not a common misconception ? I was lead to believe the front/rear brake circuits where actuated seperately or have I got it wrong

I just popped out to garage to check this linked bit, and funnily enough when you apply the front the rear activates as well and when you apply the rear it's only the rear that seems to activate, you learn something everyday.

sorry for the off topic bit

 

[hank]

A friends workmate had a nasty spill when the brakes on his R1150R came on by themselves, which is one of the reasons I am seriously thinking about junking the sevos etc.

A short can cause the brakes to activate with no rider input . Check and redo the cable ties around the head stock and handle bars, most of them were overtightened by untrained gorrilas in the factory and can lead to broken wires and short circuits.

Hank.

 

[RW1102]

Hi there, check the rear pads for wear, if the rear pads are worn down the mechnism can over compensate and apply excess force onto the front brake

 

[fatbaldbob]

Thanks for that Hank obviously not a one off problem then, I have already removed the cable ties years ago.

 

[fatbaldbob]

Rear pads are fine Rob, I can see your point under normal circumsatnces but the brakes are applying themselves

 

[Fanum]

Hi there, check the rear pads for wear, if the rear pads are worn down the mechnism can over compensate and apply excess force onto the front brake

Wossthatallabouthen?

As for the linky bit.........there were a couple of different versions.......
Mine are the Evo linked ones (IIRC that's what they called them) that the front lever applies both front and rear, but the rear pedal only applies the back......

Depending on what sort of version you have (and Neil will be the one to know) that'll indicate where the problem is most likely to be I guess....But the fact that its only applying the front would indicate (to me just having an uneducated guess anyway) that it'll be a fault within the ABS servo circuit that controls the front system......Hopefully it won't be TBH 'cos you'll hthen be looking at a new unit at around a grand, or a recon/second hand unit, or removing the abs unit altogether which will be far cheaper and some would say the better option....there's a good thread on doing it yerself here somewhere

As above, I'm only guessing on this one.....you do need to find someone who knows what they're talking about

 

[Steptoe]

years ago before servo brakes i had a couple K series bikes with ABS that locked the brakes on ( according to BMW it couldn't happen .

Both were ex police bikes with the ABS ECU positioned upright behind the battery. Both the ABS ECU's had filled with water.

Sorry, it's not much help with your current servo problem though.

 

[MikeP]

Is there anything that might be causing electrical interference?

 

[fatbaldbob]

Rang my local BMW dealer and spoke to their bike mechanic today, surprise surprise they have never heard of such a problem on a GS, however it is a known problem on the K series, his diagnosis is a faulty valve in the servo, the soultion replace the lot for about £1000 no thanks. Just to add to my misery for some unexplicable reason the battery was totally flat this morning and I had to get a jump start. Flat batteries normally stop the servo operating below 11 volts so BMW informed me, which compounds the matter even more as if I've got battery problems I should be losing braking power, never mind it applying the brakes by it's self.

 

[judys boy]

Dont mean to offend but I'm glad that I got one of those 1200's that always give trouble and not one of the reliable 1150's

 

[Fanum]

Rang my local BMW dealer and spoke to their bike mechanic today, surprise surprise they have never heard of such a problem on a GS, however it is a known problem on the K series, his diagnosis is a faulty valve in the servo, the soultion replace the lot for about £1000 no thanks. Just to add to my misery for some unexplicable reason the battery was totally flat this morning and I had to get a jump start. Flat batteries normally stop the servo operating below 11 volts so BMW informed me, which compounds the matter even more as if I've got battery problems I should be losing braking power, never mind it applying the brakes by it's self.

Ah!!!!!

Electrickery works in funny ways, especially with GS abs systems......I wouldn't be surprised that if you changed your battery, you lose the servo problem

Gotta be better than a grand for a new servo

Gel batteries have a very good shelf life too, so you wouldn't lose out by having a spare.

I think that's what I'd try first

 

[fatbaldbob]

Changing the battery is plan one (it's still on the original after 52000 miles), followed by removing the whole servo / abs system if it still gives grief, followed by a change of bike as plan 3.

 

[Den]

Its good to see that your brakes are paying attention and working diligently.

 

[fatbaldbob]

Possible theory on the problem

Checked battery with multimeter this morning 12.3v, 14v engine running so there dosen't appear to be a problem. Then went for a run to look at potential new bikes, next time I turned bike of, it wouldn't start battery appeared flat again? Based on battery check earlier I thought no way should it be flat, so I checked connections and wiggled wires and low and behold it started.

Based on this I have a potential theory for the brake problem which perhaps some of the more learned members could confirm or deny as a possibility

If I had a bad connection to the battery and whilst riding the battery disconnected for a split second, would this fool the abs system into thinking the ignition had been turned off then on again, causing it to go through its self check and therefore applying the brakes? If so it should be an easy fix once I sort the wiring fault.

I did look at new bikes and fancied a new F800GS but BMW didn't want mine in part ex as the mileage is too high to resale as an approved used bike, I now know they won't take a bike in with more than 21000 miles, apparently we are not supposed to put more than 3000 miles a year on them.

 

[Fanum]

Based on this I have a potential theory for the brake problem which perhaps some of the more learned members could confirm or deny as a possibility

If I had a bad connection to the battery and whilst riding the battery disconnected for a split second, would this fool the abs system into thinking the ignition had been turned off then on again, causing it to go through its self check and therefore applying the brakes? If so it should be an easy fix once I sort the wiring fault.

No, in theory.

If the abs fails, it's supposed to fail 'safe', which in BMW's mind means turning off the servos and letting the rider come to a safe stop using only 'residual braking', which you'll find much discussion about, here.

PS check the battery with the bike OFF and a load applied.....you may well find that the voltage drops off suddenly if a cell is knackered.....it's still a prime suspect in my mind, but perhaps that's just wishful thinking on your behalf that the ABS unit isn't ferrked. (and I don't believe in coincidences like that either )

Test the battery with a load on it

 

[fatbaldbob]

Checked wiring to battery and main earth cable had worn through the sheath and started cutting its way into the tank. Sorted that and retested battery again as described in the previous post and the lowest it dropped was to 11.77 volts, so i'm guessing the battery is fine.

That said my commute home yesterday was 120 miles and the fault never appeared again however I did have an abs warning light which reset no problem. Appart from the battery problem as described earlier, I rode 50 miles this morning again with no problems.

Maybe if I ignor it it will go away by it's self

 

[Fanum]

Wouldn't surprise me in the slightest if fixing the shorting battery lead will have cured it tbh.....just ride carefully