[CharlieVT]

A kind gent on this board, kinch, sent me a "dead" ABS unit. There was no information regarding what kind of failure occurred.
I am curious what different fault reports might be reported by the MoDiTec computer when an ABS unit is bad. Does it just report "bad ABS" or is there more info than that?

Pics attached of the unit I have disassembled.
I suspect that this unit may have had a failure of the electronic box because I couldn't find anything wrong in the mechanical/hydraulic section.

There is a lot of pent up spring compression and disassembly is a bit of a puzzle until the sequence is figured out and the needed tools fabricated. I had to modify some fasteners to remove them and had to fabricate a couple special tools to get the unit disassembled but I believe that these units could be rebuilt. I did not find any sealed ports making passages inaccessible. I kind of doubt it would be worth the effort however. If someone were to have a collection of bad units that they could pull parts from and a way to bench test the units it might then make sense. Swapping out a bad circuit board for a good one would be an easy fix if there is a way to tell if it is the circuit board and not the mechanical unit that is the problem.

I have a pretty good understanding of how the unit works, having studied it while taking it apart. I bench tested the main motor and main motor relay, both okay. I have no way to test the circuit board other than to reassemble the unit and install it on my bike and see what happens, I'm not willing to do that. There are a couple of electrically activated clutches that are controlled by the ABS circuitry that I didn't test. I could apply a variable voltage source and increase up to 12v just to check them but at this time I don't see the point. I'm not planning on trying to put this unit back into service at this time. There are also two field effect sensors that tell the ABS circuitry what the status of the pistons is, that would be a pretty easy check for someone with a working knowledge of electronics.

I do think that it makes sense to activate the ABS unit on your bike periodically by locking up the brakes and making the ABS unit function. I believe that this will move fluid through the unit in a way that does not normally occur. Doing this ensures that fresh fluid from brake fluid changes travels through parts of the ABS unit that it would not otherwise. I can see how the pistons could become gummed up and not function properly.

This is posted for general information and was done for my own entertainment. The practical solution for someone with a bad ABS unit is probably to source a known good one from a recycler or bite the bullet and get one from BMW.

 

[seahabit]

Go get em' Charlie. I, among others will be locked in on this thread. Thanks for tackling it.

 

[rhawk]

I agree with CVT about "exercising" the ABS unit periodically to keep the fluid stirred up.
When I had an ABS fault, I was able to clear it myself using the info in the thread titled
"It works!!! - ABS 2 fault reset" by BDC. However the fault returned on my next ride.
I cleared the fault again ... then really hammered the brakes (front then rear) on a downhill slope several times to activate the ABS. It's been a thousand miles + now and no fault yet !

 

[Voyager]

A kind gent on this board, kinch, sent me a "dead" ABS unit. There was no information regarding what kind of failure occurred.
I am curious what different fault reports might be reported by the MoDiTec computer when an ABS unit is bad. Does it just report "bad ABS" or is there more info than that?

Pics attached of the unit I have disassembled.
I suspect that this unit may have had a failure of the electronic box because I couldn't find anything wrong in the mechanical/hydraulic section.

There is a lot of pent up spring compression and disassembly is a bit of a puzzle until the sequence is figured out and the needed tools fabricated. I had to modify some fasteners to remove them and had to fabricate a couple special tools to get the unit disassembled but I believe that these units could be rebuilt. I did not find any sealed ports making passages inaccessible. I kind of doubt it would be worth the effort however. If someone were to have a collection of bad units that they could pull parts from and a way to bench test the units it might then make sense. Swapping out a bad circuit board for a good one would be an easy fix if there is a way to tell if it is the circuit board and not the mechanical unit that is the problem.

I have a pretty good understanding of how the unit works, having studied it while taking it apart. I bench tested the main motor and main motor relay, both okay. I have no way to test the circuit board other than to reassemble the unit and install it on my bike and see what happens, I'm not willing to do that. There are a couple of electrically activated clutches that are controlled by the ABS circuitry that I didn't test. I could apply a variable voltage source and increase up to 12v just to check them but at this time I don't see the point. I'm not planning on trying to put this unit back into service at this time. There are also two field effect sensors that tell the ABS circuitry what the status of the pistons is, that would be a pretty easy check for someone with a working knowledge of electronics.

I do think that it makes sense to activate the ABS unit on your bike periodically by locking up the brakes and making the ABS unit function. I believe that this will move fluid through the unit in a way that does not normally occur. Doing this ensures that fresh fluid from brake fluid changes travels through parts of the ABS unit that it would not otherwise. I can see how the pistons could become gummed up and not function properly.

This is posted for general information and was done for my own entertainment. The practical solution for someone with a bad ABS unit is probably to source a known good one from a recycler or bite the bullet and get one from BMW.

Is that top roll pin rusty? It looks so in the picture, but if it is inside the o-ring seal I wonder how it got rusty? Might water have gotten into this unit?

 

[gunny]

Charlie:

Thanks for sharing.

I sometimes grab a lot of brakes as I roll into the car port at a slow speed. Leaves a skid mark on the concrete and lets me know that ABS is working.
Have only had top grab a lot of brakes once, felt like the hand of God grabbed me and brought me to a very fast stop.

Now if I can find the time to see why the ABS lights come on in the wife's Tahoe.

 

[CharlieVT]

Is that top roll pin rusty? It looks so in the picture, but if it is inside the o-ring seal I wonder how it got rusty? Might water have gotten into this unit?

The cover that goes on that section of the unit is just crimped on with a bead of sealer. I suppose a little moisture could have gotten in there and caused the corrosion on that pin.
I don't believe that water got inside this unit.

Nothing else inside the unit suggest water got in there, and it would be hard to imagine how water might get in given where the unit is located on the motorcycle. Water/moisture in the brake fluid however was a definite possiblity and that was something I was looking for. I've rebuild brake calipers of bikes that were parked in the rain for years that we seized; I know what that looks like.

It was next to impossible to check movement of the pistons in the ABS unit before disassembly and decompressing the springs. There is a hugh amount of pent up spring compression when the unit is assembled. These springs are working against the hydraulic pressure of the brake system when brakes are applied.

Once I had decompressed the springs, the pistons moved freely (i.e. they weren't seized), and the was no evidence of deposits, foreign material, or other junk in any of the passages. It was all nice and clean and new looking. This is why I don't think there was water damage and I don't think the problem was related to the mechanical components of the ABS unit.

The ABS unit functions by first activating the motor which causes the "crankshaft" to turn. (You'll note that the assembly does look a little like a crankshaft or camshaft with bearing journals holding the shaft in place.) There are two clutches on the shaft, one for each brake (note that this unit is off a 2000 which does not have the linked brakes so the front and rear brakes are separate systems.) When the ABS is activated for either brake, the respective clutch is activated which then causes a cam on the shaft to rotate which then pulls a chain which lifts a piston. The lifting of the piston is opposed by the springs. Hydraulic pressure in the system and the pulling of the chain oppose the spring pressure resulting the movement of the piston. When the piston moves, hydraulic pressure in the system decreases. The the more the piston moves, the more pressure drop in the system. Obviously, the piston movement is pulsed, being controlled by electrical pulses to the clutches. I don't know if the duration or intensity (or both) of the electrical pulses is varied by the ABS circuitry, but those pulses are modulated by input from the wheel sensors.

Pic before shaft journals were removed:

After journals were removed:

Piston components:

 

[Boatzo]

Good show Curtis, Glad I don't have one of those (I think)

 

[gunny]

I understand the principle of how ABS works.


Appears that this device has some sophisticated electronics. Did BMW make it or was it made for BMW? The ABS for HD is made by Nissan. Possible that the maker would share a schematic and logic for the older units? Would think that the pre-linked ones to be ancient technology. With a schematic and logic, know of a couple of folks who would relish digging into the electronics of a failed unit just for the challenge.


Dealer capabilities seem to be limited to resetting faults and testing for operation, no means to analyze which electronic component has faulted and no means to repair any of the components involved.

 

[CharlieVT]

I understand the principle of how ABS works.


Appears that this device has some sophisticated electronics. Did BMW make it or was it made for BMW? The ABS for HD is made by Nissan. Possible that the maker would share a schematic and logic for the older units? Would think that the pre-linked ones to be ancient technology. With a schematic and logic, know of a couple of folks who would relish digging into the electronics of a failed unit just for the challenge.


Dealer capabilities seem to be limited to resetting faults and testing for operation, no means to analyze which electronic component has faulted and no means to repair any of the components involved.

There is a lot going on in that control unit. My guess would be that BMW either bought it "off the shelf" from a manufacturer, meaning that the unit is used in other applications and could be sourced elsewhere, or BMW contracted its fabrication to their specs meaning they are only available from BMW and only as part of a complete ABS unit.

I'm sure a good electronics tech could sort the thing out, but knowing what the electronics are supposed to do would probably take a hugh amount of familiarization time. I used to dabble in electronics years ago when integrated circuits were starting to replace individual transistors in most consumer electronics; things were a lot easier to fix back then. In my experience, the modern stuff is hard to fix reliably; even after repair failure is likely to happen again.

I'd like to be able to tell if an ABS circuit board is bad or not, but I'd replace, not attempt repair of a bad one.

There is a lot going on in here:

The housing has the letters FTE cast into it. Maybe someone knows the company?

Printed on the housing are the numbers 602 and 30/99 (part # and date of manufacture?):

 

[gunny]

Agree, electronics have gotten a whole lot smaller and more sophisticated. When it was just transistors, diodes, resistors and capacitors, I'd dive right in. This stuff is sort of small and my eyesight isn't what it was 40 years ago.

Seeing as you mentioned it, take a look here. I plan to go over there and see if theres anything there of use.

http://www.fte.de/Company_en.FTE

Looks like a big company. Be sweet if they offered a rebuild/repair service or even parts.

 

[gunny]

Curtis:

I think the 602 and the 30/99 to production numbers.

Here a link to some of their cross reference charts.

http://www.fte.de/handel_new_parts_en.FTE?ActiveID=1308

Might find something of use there.

Is there a part number on the circuitry? That might end up being a dead end, may need LT specific software loaded.

Going for a ride, will get back to using Google when I get back to see what I can find.

 

[HarryM]

Regarding water in this unit, that white stuff on the gearwheel looks very much like emulsified oil.

 

[Mugszy]

Regarding water in this unit, that white stuff on the gearwheel looks very much like emulsified oil.

Thought it was white grease for the gears... I imagine that would be the only way to lube these parts and keep them running free.

 

[CharlieVT]

Thought it was white grease for the gears... I imagine that would be the only way to lube these parts and keep them running free.

Yes, white grease. Looks normal to me.