ABS won't reset

[wouteRT]

Today i've had an strange ABS fault. Under freezing, but dry, conditions i've started my 1100RT and it picked up quit easily.While engaging the clutch I heard a different sound than usual. Instead of Tjietjie there was a tsjie-klang. Immediately the ABS lights came on alt-flashing. Even after 80 Km's riding and switching Engine off/on it still persists. To make the problem complete and ad a new code to the IBMWR oilhead maintenance manual page 72 here's the rest. Oke it's now the 3d time this happened. 1e time was last year end of Februar on a freezing and foggy morning. The same thing as written above happened. The dealer spend a whole day trying to find a reason other then the faultcode given by the diagnostic tester. This was a errorcode 13. Plungertest fault, defective ABS2-Hydraulic system. Please replace..........Yeah sure......About 1400 Euro (1500 $) ....May be caused by bad battery......Was brand new. To be sure a new battery was placed, with no results. Now they had two different diagnostic testers, where the newest couldn't reset the system, but when they did the reset on the older version....Tataa...Every thing worked as usual.

The bike just had the annual maintenance so brake fluid was oke. Test it they said. After a whole year driving 11000Km in all weather conditions, without a single ABS problem, last week the same weatherconditions as last year and again klang Later that day to the dealer and they gave a reset after seeing the same code 13. The whole week no problem, until today. Again Friggin'freezing cold (but this time dry)...klang....I've tried the resetmethod as desribed in the manual page 72 and even an other one not described in the manual, to no result.

Does anyone have a clue?? Could there be moisture in the hydraulic system? Is it accesible for repairs or is it a closed system? The battery is always on tricklecharge.

Thanks for any ideas tips etc..

Wouter Stam

The netherlands

[bmwmick]

Wouter,

Have you tried getting the fault code by attaching an LED to the diagnostic connector? http://www.largiader.com/abs/absfault.html or the page 72 instructions from the Oilheads document?

 

I have disassembled two ABS-II units that had "piston faults" and in both cases it was a mechanical problem with the electro-clutch mechanism.

 

There is a main shaft that is driven by the electric motor. When the ABS is initialized, the ABS control unit (mounted on the side of the Hydro Pump assembly) energized one or both of the clutches. With the electric motor spinning the main shaft, the clutch assembly tries to spin with the shaft rotation. This rotation causes a chain to wrap around the clutch and pulls down on one or both pistons. (these pistons are small diameter (1/2" or so) and they maintain the pressure in the brake circuits by means of 4 heavy springs) when the pistons are moved down, the capacity of the brake circuits gets slightly larger so the pressure drops.

The control unit also monitors these pistons by watching for a signal from two coils. The pistons each have a metal rod attached and these rods are moved down through the coils. The induced voltage in these coils is monitored by the control unit. If the voltage is too low or the movement is too slow, a "piston fault" is indicated.

 

When I first started hearing about the piston faults, I (like many dealers) felt it was a result of not flushing the fluid annually. This is not the case. There is only about two tablespoons of brake fluid in these piston chambers and I have never seen any corrosion in there.

 

I would suggest you replace the Hydro pump. Either new or used with low mileage from a salvage company. We have one in the USA, http://beemerboneyard.com/abshycoun.html $395

 

It would be interesting to remove the bottom cover from your unit to see the condition of the chains and rollers. Both of the one I disassembled had problems in that area. The bottom cover is crimped at the edges and sealed with clear silicone RTV.

 

DO NOT remove the top of the unit unless you take some precautions for the heavy springs. I disassembled mine in a large vise to relieve the pressure of these aprings. The top cover will spring up with explosive power about 8" when the bolts are removed.

 

Good luck!

 

Mick

Tucson

[Ken H.]

As Mick is alluding to, it is not impossible (especially given a persistent code 13) that the ABS unit is indeed the culprit. An expensive thought to be face with for sure, but maybe real.