Another R1150 GS ABS Thread

[PatrickMullen]

I've spent weeks reading posts and testing the unit, but I want to be sure before I pull the ABS off the bike completely.

Bike in question is a 2003 R1150 GS Adventure

The problem

1. Rear brake is in residual braking mode: no sound from the servo when the rear brake pedal is pressed. Stopping power is the same with engine on as it is with engine off in the rear brake.
2. I get the following lights on the dash: Gen ON, ABS flashes at 4Hz =At least one brake circuit in residual braking function mode.

Other context

• Front brake works fine. The servo whines as normal and I get far more power when the bike is on vs off
• Issue arose as I pulled the front brake to come to a stop at a set of lights. Loud squealing sound, followed by a harder grab of the front discs than normal.
• Went away after a day, bike was fine for a few days, now it's gone completely in the rear.

What I've checked

1. Battery voltage is OK, on start-up and up and while running
2. ABS sensor gap measure ok both front and back
3. Tail light works perfectly—both parts of the bulb are illuminating when either brake is applied
4. Hand protector is clear of the lever for front brake
5. Triple checked the brake switch and cleaned contacts, made sure the pedal is closing the switch fully, it is
6. Micro switches both working. I've tested them at the ABS unit, and I can hear them when the lever is pulled a small amount (light "pop" at the unit)
7. Brake pads are new
8. Fluid has been flushed—incl. brakes, module and reservoir under the tank. Done in correct order, twice.
9. Made sure the "big plug" is connected right at the top of the module. Cleaned contacts.

Is there anything else I'm missing here that could cause the rear brake to die? Thanks in advance to anyone who dares venture into yet another iABS II thread

 

[theoneandonly]

i'll do you a favour ......come and drop it off, and i'll swap you for my rt.

 

[Ian J Hartley]

You haven’t excluded the rear ABS sensor. Which is the only external component that might be having an effect as it’s a closed loop system.

The Servo unit has Two electrical motors which each drives its own pump. One for the front brake and the other for the rear brakes.

The bike has a linked braking system from the front brake lever only which is why you had the hard stop from the front when the rear circuit wasn’t working. Normally the front and rear brakes are both applied proportionally.

Having dismantled one these, the motors are not well protected. They aren’t sealed so water can ingress, and the internals get full of carbon dust, and rusty.

When you bled the braking system, you would have heard the front brake power circuit (motor pump) operating from the front lever. Likewise when you operated the rear brake pedal you should have heard the rear motor pump operating. If both systems are working during bleeding, when the bike is static. Then maybe it could be the rear ABS sensor.

If it’s not the ABS sensor, then you are probably looking at a servo pump unit removal.

Good luck.
Ian

 

[PatrickMullen]

Thanks Ian. The servo wasn’t running during the rear brake bleed, which made the task far harder I might ad.

More than anything I want conviction that removal is the right next step, so this is really helpful—thank you.

 

[Ian J Hartley]

So if the servo motor pump wasn’t running for the rear brake bleed, then it looks like the motor is stuck or failed.

It works sort of like this. As you press the brake lever, the fluid from the control circuit operates a pressure transducer. This triggers the pump motor to run which pumps high pressure fluid from the servo reservoir to the brake callipers. The high pressure fluid from the pump has its own pressure transducer to monitor the high pressure.

If you remove the electronic control unit from the servo unit it is possible to measure the resistance across the motor windings which should be low ohms. Or you could put a fused 12v supply to the motor to see if it runs. At this stage, you have nothing to loose. If the motor doesn’t turn with direct voltage, then you are looking at servo removal. Let me know how you get on.

I do have some used spares (cleaned and serviced motor pump units), but they do require stripping the servo unit down to replace. Not a difficult task, but only for some one with technical skills.

Ian

 

[PatrickMullen]

That’s so helpful, thanks Ian.
I think I’ll remove the whole unit for now, and start fiddling with it off the bike, now knowing I can test it removed.

Having now experienced the failure, my confidence in the servo unit is very low so I’d rather it’s gone now. I was lucky it went at low speed.

Thanks again