Spent a little more time today searching for ABS & related topics that might pertain to my car.

I found another link today that discusses ABS fluid chambers and solenoids failing due to old brake fluid. ( lots of information on this site - mostly good )

Troubleshooting ABS Modulator Mechanical Problems

Same site brake pad topic:

New Study On Brake Pad Failure Modes And Corrosion Find Some Vehicles Pose A Significant Safety Risk

Same site, pressure transfer from driver to calipers

How Do Fluid And Friction Change Brake Pedal Feel?

I've finished with most of my searching.

I know there will probably be other opinions, but this is what I believe:

1. My car is 23 years old, I doubt if the ABS has ever been activated. It might even have some of the original factory brake fluid inside the ABS. The previous owner kept it in her garage, drove it once a week, never in bad weather. No reason for the ABS to activate. During my ownership I don't ever recall driving in slippery conditions.

2. I suspect the Mercedes method of using a pressured container is not to flush the ABS but is a reliable way for 'one' mechanic to replace most of the old brake fluid with new fluid. That mechanic does not have to keep checking the master cylinder for sufficient fluid. I do not believe the 30 lbs of pressure will cause any of the ABS solenoid valves to open. This pressure is far less than the pressure created by the master cylinder during braking. During normal braking the ABS solenoids are only activated if the ABS controller detects what it thinks is a slipping wheel.

3. Old brake fluid is most likely the number one cause of brake failure. It 'sucks' in moisture that causes corrosion and also electrolytic corrosion of the dis-similar metal parts. Also the brake fluid seems to have additives to reduce corrosion. With age these additives no longer protect the brake system. Corrosion results.

4. If the brake fluid is not changed before it absorbs too much water or the additives are lost, corrosion particles can partially or totally plug the tiny passageways inside the ABS hydraulic modulator. Besides the passageways there are filters inside the ABS that can become plugged and restrict fluid flow. This can restrict brake fluid pressure and also cause a solenoid to not move freely & possibly not move at all. The movement of the pistons of the pump portion of the ABS can become slowed and even stopped due to corrosion. This probably leads to damage to the brushes of that motor due to excessive current loading.

5. Pressure testing the brake fluid pressure at the calipers would probably indicate if there is severe flow restriction.

6. If I ever drive & experience slippery conditions I do not believe I can rely on the ABS working properly due to it's age and probable corrosion and particles blocking the action of the ABS pump, solenoids, and proper fluid flow.

7. I've found one company that is large enough and has multiple world wide locations that can probably be trusted to check and hopefully clean and repair my ABS hydraulic and the electric portion of the modules solenoid control. It is: Home (GB) | BBA Reman they have a site in the US, Canada, England (hdqtrs), France, Germany, Netherlands, Spain, India, Poland, and Mexico.

They quoted a charge of $750 and less than a week turnaround. There is a much lesser charge if it is not repairable.

8. To me the best way to have confidence the ABS will work as intended is to remove it, the master cylinder, and the calipers and clean and repair/replace if it appears they have problems. It seems there are caliper kits available, I haven't found one for the master cylinder, but there are new good brand ones available. If the ABS looks like it needs new parts hopefully they can be found in workable condition from another ABS unit. If not, then hopefully bba-reman.com can repair it. Also new rubber brake lines should be installed to replace the ones that are 23 years old.

9. I think two days time would be sufficient if I have kits and a few used ABS units. Til then I'll try to not drive in conditions that might need the ABS to work.

Nice obsession.

This. ^^^ Just test your car. You'll know if the system is working. If it does work, there is no way you can definitively ensure it will always work in the future, no matter what parts you proactively replace / rebuild. Replacing an ABS unit that is working normally would be a significant waste of money, but it is your money, not ours. If the system is not working, it's more likely to be a speed sensor or other electrical fault, not the ABS unit itself.

I do hope that after all this effort and expense, you also have the best of the best tires mounted, as those will make far more difference (IMO) in real-world stopping distances.

Side note... yes you can use less than 29psi pressure to bleed ABS (not ASR!) systems, all you need is enough pressure to get flow from all 4 caliper bleed screws. Or as mentioned previously, you can still use the pump-the-pedal method if you don't mind risking MC damage. Gas models with ASR require pressure bleeding and generally need the 2-bar (29 psi) pressure specified in the FSM, job 42-0010.

__________________
Dave
Boise, ID
Check out my website photos, documents, and movies!

I now regret that I didn't reliably change the brake fluid every two years on my vehicles. That would have been the best way to be confident that there was minimal corrosion that could cause brake failure. But it seems that the fluid in the ABS might not have been completely changed even then.

How can the ABS reliably be tested? Did all wheels slip and get proper control timing and pressure when they slipped? It can't really be trusted, it's 23 years old and reliable sources say it can have hidden blockage and component failure. I'm mostly teasing, but it wouldn't surprise me if the government said ' all cars older than 20 years must be removed from service because they can't be trusted to be reliable and present a serious safety hazard'. As far as brakes go, I believe they would be spot on. Doubtful if most older cars have properly serviced brakes.

The only way most of us would know is when we needed the ABS most, hopefully we live through it. There is no way in the current maintenance procedures to have any confidence that the ABS is prepared to work properly. Very few of the Bosch test units were sold & those are rare to find. All I can think of, is to do what some of the BMW and Porsche racers have done. Take it apart and inspect it, clean it, and replace any parts that show corrosion or are not working, that's the only way I can think of having any confidence that the ABS is prepared to work when needed.

Since the ABS hydraulic portion can cause brake failure when making normal stops ( without the ABS activating ) is reason enough to check the innards of the ABS on older cars.

Not much time and really not that much money. Caliper kits, new master cylinder ( can't find a kit for my 95 ), brake fluid, a couple of salvage ABS units, should be able to be obtained for about $400. Doubtful if I would need to send the unit to be cleaned and repaired. But if I did have to send it in, I'd feel lucky that I found the unit was defective.

The most I would spend is probably less than a new set of Michelins cost and about two days of my time. And as an old joke goes " what's time to a hog? " I've spent far more than that on other problems that are not life threatening. Most of us probably know how important good tires are. Good reliable brakes are equally as important. I learned a safety lesson in the mid 60's when my new car blew the 3rd Firestone tire in less than 15,000 miles. Luckily Michelin radials were available and have continuously proven to be a trustworthy tire. In that car I also experienced my first brake failure from fluid vaporizing, I came within a fraction of a second and probably an inch of rear ending a Volkswagen that had stopped in the left hand lane of the I-5 freeway to make an illegal u-turn. Last I saw of that car was out my left window when I slipped sideways past it. I still cringe when I think about it.

I don't want my car to be a ' fair weather ' and ' low speed ' only car. I want to trust it at high speed and in bad weather conditions.

It is ' better ' as far as the quietness and comfort than my wife's new Prius. We recently had the heat reducing window film installed just for the long trips we plan to make. The film works really well, much more comfortable to both of us. Plus sunglasses are not required unless driving into the sun.

I have always used the pedal to flush brake fluid and it never had any problems. The ABS worked like designed and Im sure that the ABS valves are pass through and only work when requested.

I have also flushed BMW X drive brakes like this and they have zero issues - In those cars the ABS is what makes the diffs work like lockers. (constantly working)

__________________
2012 BMW X5 (Beef + Granite suspension model)

1995 E300D - The original humming machine (consumed by Flood 2017)
2000 E320 - The evolution (consumed by flood 2017)

It’s been suggested a few times already - find an empty gravel road or empty wet parking lot and test the ABS! Try it going straight, try it turning.

Sixto
98 E320s sedan and wagon
02 C320 wagon

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 ).

Aye yaye yaye. This has definitely been raised to obsession level, as others have noted. You are really going way overboard. I have had a Motive Power pressure bleeder for many years. I had a 1995 E300 which I sold at 467,000 miles. During my 10 years plus of ownership, I flushed my brakes, I think, 3 times, possibly 4. This is 3 or 4 times more than most cars get their brakes flushed in their entire lives. Hook up the Motive Power unit to the MC. Fill it with fresh brake fluid. Pump it up to 30 psi, give or take. Open the farthest bleeder with a plastic hose on the nipple and let it flow into a container. Let a good flow go through. If your brakes have not been flushed, it should be easy to see when the new fluid reaches the caliper. Keep checking the pressure bleeder reservoir so as not to run dry, and pump it back up.

Lather, rinse, repeat on the other three calipers. Now stop obsessing and get on with your life. You have just finished a job which most will never do, and it is easy and does not take very long.

Rgds,
Chris W.
ex 88 300E
ex 95 E300D

__________________
Objects in closer are mirror than they appear.

I have the motive brand bleeder. Just bleeded my wifes GL350 for the third time in 5 years, super easy. Connect cap to master cylinder, fill bleeder with 2 liters of ATE Gold, pump up to 28 psi and start bleeding. Does a great job.

I used to use the ATE Super blue every other bleed, easy to see when it was bled out but the US government decided they cannot sell blue brake fluid here.

Little scary pumping reservoir up that much but no issues. I have bled my w124, Sprinters, ML, GL with great results.

__________________
1995 E300 (W124)
1999 ML430 (w163)
2011 GL350 (x164)
2016 Sprinter 144" 4X4 lowtop (906)
2004 E500 (W211) 4matic Wagon (Gold)
2004 E500 (W211) 4matic Wagon Avantgarde (silver)

I know how to pressure bleed, reverse bleed, gravity bleed, etc...

My objective was to obtain ' proof ' that pressure bleeding would flush the ABS unit of all old fluid. I could not find any website that confirmed that pressure bleeding would do that for my car's type ABS unit. I doubt if it does that because there are tiny screen filters that can trap particles that interfere with fluid flow.

It seems virtually all the responses think I'm a little ( or a lot ) whacko. That's ok, at least I've provided information with pictures that shows both age and mileage will cause the ABS unit to fail. It's up to y'all to determine what to do with that info.

I'm not going to be the one that drives a car that has a very high possibility of having a brake failure. Luckily I've found a brand new shrink wrapped Bosch ABS unit that fits my car. I still intend to take my old ABS apart to check it's condition and see if it is feasible to clean it.

If the brake fluid has been changed every couple of years since new, then there is a greater chance the ABS will function as intended. If the brake fluid hasn't been changed regularly ( and probably if the car is just old or has high mileage ), THE BRAKES MAY NOT HAVE PROPER STOPPING ABILITY EVEN WITH NORMAL BRAKING. This failure can occur even on dry non-slippery surfaces.

I think panicking and replacing the ABS unit out of fear is way over the top. If the ABS unit fails, you just have standard brakes. The stopping power of the car is not affected, depending on the surface, your control ability may be compromised if you're not a skilled driver. Take the car out, get up to 30mph or so and slam HARD on the brakes, enough to lock them up. If the brake pedal pulsates, the ABS is fine. There's no way to flush the ABS pump without cycling it. If the brake fluid is maintained as it should be, there's no reason to ever flush the ABS pump.

__________________
Current stable:
1995 E320 149K (Nancy)
1983 500SL 120K (SLoL)

Black Sheep:
1985 524TD 167K (TotalDumpster™)

Gone but not forgotten:
1986 300SDL (RIP)
1991 350SD
1991 560SEL
1990 560SEL
1986 500SEL Euro (Rusted to nothing at 47K!)

I have power flushed all my MBs with the Motive unit and it works great. Well except the 2014, they did it as part of the servicing for the CPO, so it will be due this coming spring.

You can engage ABS just going down your street (assuming you don’t live on a busy street). Get up to about 25 and stomp on it and hold it in (pretend a kid or dog just ran out in front of you). Just be sure no one is behind you. This will engage the BAS (first introduced on the W210) as well as ABS. You will feel the pulsing in the pedal and the car will come to a controlled stop with no squeals and most importantly no pull to one side or the other.

__________________
The OM 642/722.9 powered family
Still going strong
2014 ML350 Bluetec (wife's DD)
2013 E350 Bluetec (my DD)

both my kids cars went to junkyard in 2023
2008 ML320 CDI (Older son’s DD) fatal transmission failure, water soaked/fried rear SAM, numerous other issues, just too far gone to save (165k miles)
2008 E320 Bluetec (Younger son's DD) injector failed open and diluted oil with diesel, spun main bearings (240k miles)

1998 E300DT sold to TimFreeh
1987 300TD sold to vstech