I've been busy with 'honey-do' things and trying to source good quality parts for my upcoming brake, convenience module, window motor, and driver's side door lock issues.
Finally think I've ordered most of the required parts & they're starting to arrive. It's amazing how quick some deliveries happen after placing an order.
I've been thinking about how to clean the hydraulic portion of the ABS unit that contains the solenoid valves and pump with it still installed on the car. Only plan I have come up with is to:
1. use the normal pressure flush to all the calipers until good clean fluid comes out of each of them.
2. reverse pressure flush from each caliper. Brake fluid will have to be suctioned from master cylinder to keep it from overflowing during flushing. (What I plan to do myself is to disconnect the two hard brake lines that feed the ABS unit from the master cylinder & connect two drain lines to catch containers. This would help prevent flushing crud up into the master cylinder.)
The reverse flush is intended to try to clean the tiny internal filters ( one for each solenoid valve ) and flush the particles out of the ABS.
3. Finish with another pressure flush from the master cylinder to each of the calipers.
This would hopefully clear particles that might be restricting the fluid flow inside the ABS hydraulic module. This is not nearly as good as removing the ABS unit and doing a thorough cleaning of it's innards, but would be much better than simply trusting that your ABS will function properly as it is.
I've been researching possible solvents to use that won't damage the internal seals, solenoid coils, or wiring. Most solvents would harm rubber, plastics, coil wire coatings, and wire insulation. I haven't found any that are really trustworthy. If there was a good solvent it could be pumped through to help clean the ABS internals.
From my searching and reading internet available info, the ABS unit gets contaminated and also experiences corrosion due to the brake fluid not being changed often enough.
Particles build up inside the unit and that can partially or completely block the brake fluid flow to one or more calipers. Sometimes the brakes will pull to the left or right and sometimes a wheel or wheels will experience lockup or have no braking action at all. This failure can occur without the ABS unit kicking in due to slippery conditions. All brake fluid flows through the ABS unit and the paths must be clean and clear of obstruction to have proper pressure at the calipers. The Porsche and BMW racing enthusiasts seem to have discovered the problem due to their brakes failing on dry surfaces. If they have the problem of ABS flow failure then it seems logical to expect that non-racing enthusiasts that have neglected their brake maintenance would have equal if not more contamination and corrosion hidden within their brake system.
There has been very minimal testing of ABS systems on vehicles. This is primarily due to the complexity of the test station and measuring equipment. I found one study that test the ABS function on over 200 vehicles. The document shows an ever increasing failure rate due to the age of the vehicle ( up to ten years as tested ) and the number of kilometers the vehicle had been driven since new.
The older the car and the more kilometers driven significantly increased the failure rate.
The testing study:
https://ec.europa.eu/transport/road_safety/sites/roadsafety/files/pdf/projects_sources/cita_study_3.pdf
Page 38 starts the failure rate by age. Page 52 gives a summary. The failure rate of older cars shows a decline due to the fewer older vehicles tested ( not because they got better with age ).
This shows that there is an increasing trend for ABS equipped vehicles to have significant failure as they get older and are driven for more distance ( km or miles ).