DIY: Brake fluid flush

1MOREMOD wrote

Never heard of trying to force air thru the system. That's the opposite of what you want.

Duckengine wrote

No, not trying to force air through system. Brake booster Reservoir is full before pressurizing pressure bleeder and refilled before it reaches the min line.

Duckengine wrote

No, not trying to force air through system. Brake booster Reservoir is full before pressurizing pressure bleeder and refilled before it reaches the min line.

Duckengine wrote

Hello all. Time to flush the Brake system and put in some new fluid. Driver rear bleed screw frozen and then broke. Tried to get it out on the bench to no avail and so bought a new caliper. Put it all back together and then using a pressure bleeder, bled all four calipers with 500 ml of new fluid. First go with pressure bleeder was air pressure only (no fluid) at about 12 psig. Took the car out for a spin and virtually no pressure but I could pump it and build pressure enough to lock up the brakes. Try bleeding again with same method as previous and a slight improvement but not much. Tried again a third time with traditional pump brake process. No improvement. Tried again with the pressure bleeder but used fluid in the pressure bleeder instead of just air as done the two previous attempts. Flushed almost an entire liter through the calipers but still have little pressure on the pedal and need to pump it to get pressure which is firm and can lock up (activate ABS) the brakes. I'm about to give up and take it in but thought I would reach out to see if there are any obvious steps or considerations I am missing. I have read this entire post and others and I'm convinced I am not doing it wrong but I do think I am missing a step not specifically described as it relates to my e92 M3. TIA to all those that reply.

BzsBimmer wrote

I think somehow you got air in the system. You have DCT so no clutch to bleed or worry about. You may need to run through INPA or take it to an indy to pulse the ABS system.

Typically I find, right after a brake flush, you need to start the car and press on the brakes and top off fluid prior, during, and after.

Assuming you went furthest from master cylinder to front, everything you did sounds correct however, the output of your effort points to air in the system.

Since the air/gas is MORE compressible than the fluid, it would make sense that you can eventually build up pressure.

There COULD be some other issue causing your symptom like a leaking master cylinder. The caliper you replaced could also still have air in it since it was new.

admranger wrote

Slight correction...

Also, OP, you can manually activate the ABS to try to pump some of the air out and then re-bleed. Just find an empty parking lot, accelerate, jam on the brakes like you're Mr. Brembo and viola', ABS activation. For even easier activation, do this while turning.

1MOREMOD wrote

Possibly tap the new caliper with rubber mallet as bleeding. Did this during st40 install.

BzsBimmer wrote

I think somehow you got air in the system. You have DCT so no clutch to bleed or worry about. You may need to run through INPA or take it to an indy to pulse the ABS system.

Typically I find, right after a brake flush, you need to start the car and press on the brakes and top off fluid prior, during, and after.

Assuming you went furthest from master cylinder to front, everything you did sounds correct however, the output of your effort points to air in the system.

Since the air/gas is MORE (thanks admranger!) compressible than the fluid, it would make sense that you can eventually build up pressure.

There COULD be some other issue causing your symptom like a leaking master cylinder. The caliper you replaced could also still have air in it since it was new.

elp_jc wrote

Pleasant clutch bleeding surprise folks. After half an hour of turning the bleeding valve a full turn with my vacuum machine attached to it (no freaking s p a c e -why the hell the system censors that word????) and no fluid, I knew I was dealing with a check valve. Got out from under the car, opened door, push clutch pedal with hand and it went in like butter. Did that 10 times more and I was done. Clutch worked perfectly after closing it. Next time it's going to take me 2 minutes after removing shield.

Here's the drill:
- Remove belly pan (3 screws in front, 2 in back, and 2 on each side).
- Remove cap from valve and loosen it one full turn with a 1/4" ratchet and 11mm standard socket.
- Valve will just spew fluid when you push the clutch pedal, so use any method you want to catch it that won't splash. This is a one-person job folks .
- Push clutch pedal slowly (and return slowly as well) about 10 times, and you're done.
- Screw valve clockwise with ratchet until you feel a 'click' and it stops turning. DO NOT apply too much force since it's PLASTIC.
- Reinstall belly pan and you're done. This is the easiest clutch I've ever bled, and the most effective way is by pushing the pedal, but I never do it that way since helper can screw up. No chance for that here; great feature .

By the way, rear brakes require a 9mm closed wrench and front 11mm, and are regular valves (the way I like them on the brakes). Job done in about an hour with a vacuum bleeder (the best way IMO). Fluid was clean (no debris inside the reservoir, like most of my new cars), which was good news, so no need to destroy the filter to clean the reservoir. Just amber in color. From now on will do it yearly, like all my other vehicles. Just $10 and an hour of my time. Well, probably 2 hours since I like to clean the undercarriage . Hope this helps folks.