Tobers gets brake failure

[Tobers]

Set off from home today. Did all my usual morning checks & all OK including the brakes. Got to the end of my road and "eeeeek" no brakes. Or more accurately, there was residual braking which got me slowed down after an f-heavy pull of the lever.

Looking down, the brake failure light was flashing. I switched the bike off, did all the checks on handguards fouling the lever (nope) rear brake pedal badly adjusted (nope) front ABS cable correctly routed (yes) etc.

Started up again - still no servo activity, brake failure light still flashing. I repeated switching off & on several times, and also disengaged ABS, but still no change.

As Vines is only a couple of miles away, I carefully rode over there. Halfway there, the brake failure light went out and the servo worked again. I switched off and on again, and the servo didn't work and the light was flashing again.

Got to Vines, left the bike running with the light flashing and Darren checked the bike out, did the same checks as he (handguards etc etc), confirmed it was ferked, and then immediately took it in for a tech to check.

They replaced the front brake light switch in the right grip which was faulty, and replaced the rear light cluster which was corroded. They dismantled a new 1200 to scavenge the parts.

Excellent service by Vines, but they shouldn't have had to do anything in the first place.

Also, Darren (Vines service dude) said that when riding the bike round to the workshop the servo cut in whilst he was braking & turning into the workshop. The additional braking force stopped the bike suddenly and nearly had him off.

So, all rather unpleasant. I can confirm that this isn't a "possible" or "imagined" fault, but an actual fault. I've read all the threads on this issue and know what's what.

Seems to me that there are too many single points of failure for this servo braking systems e.g. front brake switch, rear brake switch, ABS cable, servo itself, rear light cluster, handguard interference with front brake lever. A problem in any of these causes total servo failure which isn't fault-tolerant enough.

I'll be writing to BMW...

Whilst waiting for the f'ing thing to be fixed, Darren leant me an HP2. Fun bike - vibrates like a 12" dildo (apparently) as no balancer shaft, light & quick, "interesting" suspension with loads of dive on braking which was quite cool (at least the brakes worked!). Nice stripped down simple bike - a bit of a hoot but a bit focused to use on my daily commute.

 

[Pukmeister]

Glad things didn't turn nasty mate. Keep us posted with the response from BWM.

 

[Tricky]

Sorry to hear about your ABS/servo problems Tobers.

As yours is an early (04) bike could some of the problems (inc gearbox etc) that you have experienced, be just that? or does the issue with the ABS/servo bikes betray a deeper more fundamental problem with this set up?

Mine is a non-ABS bike but without wanting to re-open the well documented debate for and against ABS/servo's - it is something that I have been thinking about for a while. My intention being to replace mine after 4 or 5 years and have ABS on the new bike.

Maybe the system will be better/more refined/less problematic by then...

 

[Engineer]

BMW must have got the message by now that this system is just not reliable enough - I bet they are frantically redesigning it as we speak. You can also bet that BMW won't be giving free upgrades as the current system meets all legal requirements.

 

[Arthurwg]

Your lucky! Just think what might have happened if you had been traveling at 85mph on the M6. When this first happened to me they said it was a loose connection at the battery. The second time they replaced the entire wiring harness.

 

[marcparnes]

Seems to me that there are too many single points of failure for this servo braking systems e.g. front brake switch, rear brake switch, ABS cable, servo itself, rear light cluster, handguard interference with front brake lever.

Just curious as to what effect the tailight cluster has on the braking system failing. I hadn't heard of that one before.

A couple of weeks ago I was railing along chasing a friend through some twisties when I hit a horrendous pothole. The bike bottomed with a *bang* but I continued the chase. It was a big enough hole that I was sure the cast rims were going to be pretzels which they weren't The brakes worked find but when I restarted after waiting for the rest of of our crew the brakes would not reset as evidenced by the flashing ABS light and wooden brakes. It turns out that when I bottomed it hit the bottom of the foot brake lever so hard that it bent the lever and the tang where it attaches to the frame misaligning the brake switch and snapping the little pushrod that goes between the pedal and the master cylinder. I was able to short the switch out so I would have brakes for the ride home. On the way I decided to stop at the dealer to buy a new pushrod. Of course the little pushrod only comes as an assembly with the $110 master cyllinder. Forget them, I made my own

Having had a couple of these bikes with the servo system I've learned that switch failures and the like will not normally become evident until you restart. In other words, if the switch faults the brakes aren't going to fail until they try to reset. That makes it doubly important to ensure the light goes out when you start off. Of course if the servo itself fails all bets are off and you better have the grip of Hercules and the balls of an Orangutan

 

[FIN_GSer]

Well, I had the same failure.
There is a way to get brakes working even with failed switches.

First some explanation....
When power is switched on the computer makes self check. One check point is: "Are brake levers free", if not -> servo will not start. (Bike assumes, driver is pulling breke lever and thus can not do proper self test.)
When brake levers are free, the switches are "on". When braking, switches are "off". When the switch is "off" (eg. braking), brake light will be on and servo pump gets started.

Typical failure mode of micro switch is: No contact = "off". (the other oner is short cicruit)
When bike is started and switch is failed the servo assumes: brake lever is pulled, do not start. -> Total Servo/ABS failure.

The trick:
Pull brake lever detector switch cable from the switch and short circuit the cable. Switch bike power of and back on.-> Tada! Brakes boot OK, no warning lights.
Brakes even work quite OK. There must be some internal brake pressure detection to put servo pump on even without lever switch.
BUT there is some drawbacks:
1. There is no brake lights.
2. if you take short circuiting wire off, the servo will run forever (or untill you put wire back or switch bike off)

Be sure to keep piece of wire or at least some paper clips with you when you go a bit further from BMW service..

FIN_GSer

 

[Activmoto]

Tobers,
Interesting to read your experience, I see you rear light cluster may have contributed to the ABS failing. The corrosion in the cluster may have been contributed to by the fact the lens has no seal and just parking in the rain means water can enter.
BMW have done a lot of work in so called cost engineering i.e. making things cheaper but I think this is one example were they have not thought about the possible consequences, or maybe they did.

 

[Mouse]

Couple of comments about this ...

Firstly, the rear light cluster. It's very exposed to the elements, I've had mine off once to clean and grease the contacts, which were starting to corrode. Annoyingly, to get the thing off, you have to remove most of the plastic under seat cover - or at least so it seemed to me,

Secondly...

snapping the little pushrod that goes between the pedal and the master cylinder. I was able to short the switch out so I would have brakes for the ride home. On the way I decided to stop at the dealer to buy a new pushrod. Of course the little pushrod only comes as an assembly with the $110 master cyllinder. Forget them, I made my own

Funnily enough, I recently snapped that little pushrod myself. However the local dealer sold me a new one for about £15. Not cheap for a little rod, but cheaper than a master cylinder!

 

[Activmoto]

Firstly, the rear light cluster. It's very exposed to the elements

Mouse,
How did you get water in your rear light

 

[DodgyGeeSer]

Another brake-failure here..
On my way to work on the motorway, tried to slow down, and realised that I only had residual braking. Took it handy, and the residual braking was enough to get me to work.. Planning on doing a bit of diagnosis before I call my dealer/BMW. Anyone have a checklist? From Tobers post, I guess it would be:

1. handguards fouling the lever
2. rear brake pedal badly adjusted
3. front ABS cable correctly routed
4. Check self-installed Autocom unit, for connections which may have come loose
5. Check rear light cluster for corrosion/moisture

Anything else?

 

[Mouse]

I'm not sure anyone has actually confirmed that corrosion in the brake light can actually cause a servo problem - after all what is the difference between a connection corroding through and the bulb blowing? Certainly worth checking though.

Obviously you need to check the front ABS sensor cable is routed correctly, but more importantly you need to make sure it's not been damaged.

Also check the brake pedal switch has not been fouled by a foreign body - I've had mine knobbled by things like twigs, mud, small animals (only joking) when green laning. Not likely to be a problem on your daily commute though

 

[Tobers]

Note that Vines detected a fault in the brake light switch on the handlebar lever and replaced that, so there's another thing to check somehow. I guess the switch was in the "on" position - same as if the handguard is on the lever.

The simplest thing to check would be if the brake light is on with no levers pressed or pulled. If so, then you're boogered.

 

[DodgyGeeSer]

After a quick informed inspection (thanks for the informative post Tobers), the problem is #1: Handguard fouling lever... Brake-lights on with no levers pressed or pulled (or so I thought!).

Must have hit a few potholes on the way home last night, which must have caused the handguard to move inwards, preventing the brake lever from disengaging fully. Is the handguard an adjustable item? Must try and locate some torx heads.

*Edit*: The handguard had rotated, reducing the brake lever's free play. Sorted. Until the next time!

Thanks for the helpful replies fellas!

 

[TheJoker]

Tobers, first of all; glad you're OK! Failing brakes are no fun thing!

I've had my tail light unit changed under warranty due to corrosion too. Went last winter...
Since my ABS cable issue I've also had one brake failure - garage didn't find anything in the onboard computer. After a restart it hasn't surfaced again.

If you figure out an address to BMW to write to, can you please PM me or post it here so I can get my thumb out and write to them regarding my ABS failure.

I completely agree - the BMW ABS/Servo system is too complicated and prone to errors for active riding, well, all riding really.

 

[motozen]

Riding with residual braking only is something you can get used to.. it's not as horrible as you might think at first. I rode 2700 km on residual braking only and on one occasion I had to make a "panic" stop. No high drama, just a very strong pull on the brake lever and I came to a quick stop.

I had the same situation as Tobers.. first fault was caused by a shorted stop lamp bulb, second fault was caused by a bad front wheel ABS sensor.. third fault, I traded the bike in for one without servo/ABS.. I'm so glad I did.

As pointed out, there are too many variables that cause the servo to shut down. In the case of a bad ABS wheel sensor, why not just shut down the ABS since it can be manually disabled, why shut down the whole system..

Anyway... just wanted to tell you that riding with residual braking only is something you get used to very quickly.