"brake failure" warning after full bleed.

I finally got a "scrap" unit last week. I have rebuilt my unit with one motor and pump from the scrap one. I finished off bleeding it yesterday (took ages) and it seems to be working as intended. Servo assistance and ABS all seems to work, and no fault codes.

I don't know how long it will last but being completely clean, it should have a good chance of lasting a few years. I suspect the underlying issue is that there are so many places where moist fluid can stagnate that even regular bleeding is not flushing out all the old fluid. In my case, it hadn't had the fluid changed by me or the previous owner, so probably over ten years!

Smiffy

Good result then….

It’s always good to hear that parts can be repaired, when the norm is usually replace with new, or a work around to live without it.

You have now become the resident expert on servicing and repairing Servo ABS brake pump units.

Fortunately my problem was clearly visible once the pump was apart.

Things have moved on. A few weeks ago I pushed the bike off the centre stand, and grabbed the front brake to stop the bike rolling forwards, it did nothing. Both brakes work fine when the ignition is on, but with it off, residual braking on the front is next to nothing. I have had the top cover off the ABS/servo so that the output pistons can be seen to move. It seems like the fluid must be getting pushed backwards through the pump, or escaping past the seal on the outside of the secondary piston, or past the "check ball". The casing around the secondary piston looks to be crimped in so probably won't come apart easily.

DevonAl has kindly donated his unit which he has bypassed. I've stripped that down today. With fluid in the wheel circuit, I get resistance when I push the secondary piston in, so it hasn't got "my problem", so I have cleaned everything and re-assembled.
The insides were pretty clean, Al did say it had been regularly and properly flushed, but he said he had experienced intermittent issues. What I did find was a butter like deposit in a couple of places in both the front brake circuits. Next is to try it on the bike.

So I put this on the bike (Al's unit, cleaned, with my electronics). Everything worked, but intermittently. Rear pump would sometimes not run, sometimes stay running, faults all over the place, all suggested to me that the pressure sensors were unreliable.
Swapped the pressure sensors for mine (as I had no reason to suspect they weren't working), all back together then nothing would work, fault reader couldn't connect to the ABS. I found that out one of the pins under the connector had bent over flat. I wouldn't have though it was possible to miss align the plug, but there you go. Straightened the pin and everything works, no fault codes. I still need to give it a proper road test, and strip my unit down to work out what caused the lack of residual braking on the front wheel. but that can wait for another day.

A note for anyone else trying to get these things working, when the fault code reader is "connected" to the ABS, the brake failure warning is on steady (not flashing) and the servo doesn't work normally. You need to come out of the ABS menu on the fault reader, switch the ignition off and on before the servo returns to normal working.