GS1200 (servo version) - rear brake problem

[MRA]

Dear all motorraders,To those who are familiar with problem I'm currently facing, your opinions, guesses, advices are greatly appreciated.My 2005 GS1200 (with servo) recently developed this problem with the rear brake. Upon starting the engine, everything appears to be normal, no faults or errors indicated. But when the rear brake pedal is pressed, there's no braking on the rear wheel....after pressing the brake pedal a few times, the ABS warning light will start blinking. The opinion from an independent workshop is that the ABS pump could be faulty (could be due to the broken diaphragm). Diagnostic computer check shows no fault as well. The bike is hardly used and has 25K km on the clock.Taking the bike to Glenmarie workshop in a couple of days for a check, but at the same time making a research of what could be the problem.

 

[t2ribena]

there were some issue with the early integral brake system where some bikes losses the brakes due to the ABS pump...as the rear brake line system is pressurized at all time, your issue could be the pump as when the hydraulic line pressure is low, the rear brakes would not work...it could also be a leak somewhere...if I am not mistaken, there is a backup system that support the normal operation using the legacy hydraulic brake system...

best have it check at reputable workshop...

 

[MRA]

there were some issue with the early integral brake system where some bikes losses the brakes due to the ABS pump...as the rear brake line system is pressurized at all time, your issue could be the pump as when the hydraulic line pressure is low, the rear brakes would not work...it could also be a leak somewhere...if I am not mistaken, there is a backup system that support the normal operation using the legacy hydraulic brake system...

best have it check at reputable workshop...

t2ribena,

Thanks for your response, and I think your opinion is most likely correct. My research on the internet also points to the same direction...the ABS pump.

Can you elaborate on the back system and how to activate it? Does it come on automatically when the ABS pump is down? There is no braking at all on the rear wheel. BTW, the bike is at the Glenmarie workshop now for diagnosis and troubleshooting. Initial feedback is that the pressure at the ABS pump is low for the rear brake.

 

[t2ribena]

the rear brake backup circuit is a separate hydraulic line that is operated from the foot brake and it is not part (independant) of the integral brake circuit...this is on the newer Integral ABS II system...

for the servo assisted system then it could be different as sufficient pressure is required before the servo system can function and the rear brake circuit being dependent on the primary integral circuit in this case it still points back to the pump/ servo system if it malfunction...this is one of the reason BMW redesign the integral system which is now on the newer bikes which has a backup system in case the integral function failed...

the following is the schematic for the previous version (servo)...notice that the brake caliper circuit passes through the ABS pump/servo and this decoupling of the lever to caliper means that the system is fully dependent on the servo/ pump for its function unless there is a bypass system in the unit itself...

below is the schematic of the newer system...notice that the foot brake circuit is connected directly to the rear caliper via a 2 to 1 brake line/valve (the other one is from the integral circuit), so in this system when you depress the foot brake, the fluid displacement directly activates the rear caliper. So when the integral brake fails, the rear brake is still functioning...unlike the earlier version...

t2ribena,

Thanks for your response, and I think your opinion is most likely correct. My research on the internet also points to the same direction...the ABS pump.

Can you elaborate on the back system and how to activate it? Does it come on automatically when the ABS pump is down? There is no braking at all on the rear wheel. BTW, the bike is at the Glenmarie workshop now for diagnosis and troubleshooting. Initial feedback is that the pressure at the ABS pump is low for the rear brake.

 

[Jacko]

Could be Abs pump problem. Change the pump and everything back to normal. Be prepared of the ABS pump pricing that sell in Malaysia around Rm 13,000 (+/-)
Get it from Singapore, is cheaper RM 10,000 (=/-).

 

[MRA]

Could be Abs pump problem. Change the pump and everything back to normal. Be prepared of the ABS pump pricing that sell in Malaysia around Rm 13,000 (+/-)
Get it from Singapore, is cheaper RM 10,000 (=/-).

Thanks Jacko,

Yes, you are right, it's the ABS pump. The price quoted by the BMW workshop in Glenmarie is unbelievable! (pls don't blame the tax for this)...This is another area where Auto Bavaria Malaysia needs to improve on, besides the service quality debated in another thread by the forummers. I'm now in Italy, and the price of the same ABS pump here is only Euro975! (which is equivalent to RM4K based on today's exchange rate)....hah...may be this is the last BMW for me. I had a Honda ST11 before for 9 years with ABS and traction control system which worked brilliantly and trouble free for the entire period of ownership.