[terrywang]

Moved car to make space for a garage door repair job, found liquid on floor, felt something bad happened, checked, it was brake fluid, found rear left caliper leaking into inside of wheel and ground.

History

- Did a brake fluid change on 20 Jan, didn't notice any leak when taking it out for a drive on weekends

- Installed M Performance style brake pad cover, used some force to push the rubber into place, car was not started so the pedal barely went down

Would this damage the brake system? - some research indicated may be use to some extend, but wouldn't cause any immediate damage. Question: would this increase the pressure (like pumping)?

- a friend came over, helped to take the wheel off using professional tools (my impact wrench didn't work, no breaker bar) used brake cleaner to clean up things, removed the dust cap to observe and diagnose easier, applied brake multiple times to see if it leaks from the bleeder screw, no leaks found...

- 99% sure bleeder screw was the only point of leak, no other point of leak (part #10 in the diagram)




- opened reservoir cap to check fluid level, still in between min and max (did this release some pressure?

- took it out for 15 mins drive and check again, no obvious leak, weird

My friend recommended keep watching / observing for a few days.

After some research, the bleeder screw can be stripped or damaged. I reckon the simplest potential one-shot solution is to replace the bleeder valve (may be stripped or damaged somehow - based on the paint chip-offs on the caliper - some rude brake fluid job done by some before...) with a genuine BMW one?



https://www.fcpeuro.com/products/bmw...ew-34116780509

Is it a DIY job or better to get it done at a workshop?

TIA, any advice is appreciated.

[terrywang]

Initial discovery, even some sign of leak on the top of the caliper, once cleaned up with wheel off using break cleaner, haven't seen this again.


So far bleeder screw is the single source of leak identified...

[ggggbmw]

I strongly suspect that you didn't quite tighten the bleeder enough when you did the fluid flush. Then, pressing hard on the brake pedal while installing the covers was likely enough to push fluid past the not-tight-enough bleeder screw.

If it doesn't leak anymore after re-tightening the bleeder, you should be fine.

By 'tight', I don't mean crank down as hard as you can. I typically tighten to just snug, then give it maybe a 1/16 turn of an additional tightening.

Would be nice if there was a torque setting for those screws, but I've never seen one. If anyone has one, please enlighten me.

If you torque it down too much you risk deforming the seat in the caliper, or stripping the caliper screw threads. At that point you are looking at replacing the caliper.

[terrywang]

@ggggbmw you may well be right!

After tightening it a little bit with the wheel off, it seems to have stopped leaking...

I found the torque spec for the ventilation valve (bleeder screw), it should be 10Nm.

The guy who did the brake fluid replacement job for me said he had never torqued BMW bleeder screws using torque wrench (hardly ever saw any leaks, now he has...).

34 00 Brake test and brake bleeding
Tightening Torques
Type Thread Tightening specifications Torque
1AZ Vent valve
F80 / F82 / F83 / F87 WAF 11 10 Nm

And more specific ones (for Brembo made ones - I believe OG F87 fixed caliper + front 4 pistons / rear 2 pistons M Performance brake was made by Brembo) there is even more specific ones:
front 18Nm
rear 10Nm

[ggggbmw]

terrywang Thanks for posting that TIS torque info. I'll have to try it the next time I bleed brakes. (Soon. It's almost track season and time to put the SRF in.)

I'm curious where you got the link and info. newtis.info has been shut down for a couple years now.

[terrywang]

UPDATE: I have bought a 5-25Nm 1/4" drive torque wrench and re-torqued the bleeder screw, took it out for a spin (15mins), checked, clean no leak but I'll keep an eye on it in the next 48 hours to see.

If it continues to leak, I'll replace the bleeder screw. Hopefully, the caliper thread is not damaged (screw is aluminium? I reckon the caliper is steel harder, screw will be the first to strip?).

I used a crawler to keep an offline version of the newTIS for OG F87 (my build only unfortunately) before it was shutdown. I thought I was accessing the online version...

[terrywang]

Purchased bleeder screws (a pair), replace the existing one with a new one, it performs even worse than the original one(thought to be stripped).



I inspected the original one, it definitely has had better days (I can see marks of abuse by mechanics worked on it) but the treads are good. I used brake cleaner to give it a good clean and wipe, put it back in and hand tight, then torqued it to 10Nm, stepped on brake pedal immediately after several times, no sign of leak around the screw neck.

One thing I noticed: there was blue threadlocker like stuff at that the original bleeder valve screw's neck (right below the hex that goes into the caliper threads).

Does anyone know if blue threadlocker is used on bleeder valve screws? cc F87source

Thanks in advance.

[F87source]

Originally Posted by terrywang

Purchased bleeder screws (a pair), replace the existing one with a new one, it performs even worse than the original one(thought to be stripped).



I inspected the original one, it definitely has had better days (I can see marks of abuse by mechanics worked on it) but the treads are good. I used brake cleaner to give it a good clean and wipe, put it back in and hand tight, then torqued it to 10Nm, stepped on brake pedal immediately after several times, no sign of leak around the screw neck.

One thing I noticed: there was blue threadlocker like stuff at that the original bleeder valve screw's neck (right below the hex that goes into the caliper threads).

Does anyone know if blue threadlocker is used on bleeder valve screws? cc F87source

Thanks in advance.

There shouldn't be any thread locker on these bleed valves, since it wouldn't survive the harsh chemicals and the very high temps the calipers get to.


I suspect the threads are likely damaged. My advice is try to tighten the valve by hand a bit more and see if the leak stops. If it doesn't then it's likely the caliper threads are unfortunately damaged. This means you'll need to either rethread it with a larger thread or helicoil or timesert it.


The blue color you're seeing could be paint from the caliper body.