I just installed the r53 calipers,rotor and stainless brake lines on my r53 and thought rather than waiting for my wife to get home I’d use my Motive Power bleeder. Pumped it up to 15 psi and came back to the right rear and could see fluid pouring out from the left wheel area. Turned out it was spraying from the master cylinder but can’t tell where since brake fluid is everywhere. I hope I didn’t blow out a seal or something never had trouble with it before. So are we not suppose to use those on these cars? I have a hell of a mess!

 

It should be fine at 15 psi. Did you check the seal to the reservoir before you put fluid in the bleeder?

 

yes it looked fine and there was no fluid on top it’s coming from the back when I put pressure on it. I heard a slight hiss and thought it was coming from the two Hesse where they connected

 

It looks like it’s coming from behind the master cylinder where it bolts to the booster. I have bled the brakes and are firm. I cleaned up all the brake fluid took it for a drive and sure enough there’s a leak. Is there a seal at the back of the master cylinder that I blew out when pumping up to 15psi?

 

There is an o-ring/seal that goes between the master cylinder and the brake booster, It's possible that it went bad. 15psi should be ok, but with a 20 year old seal, it might have been too much. The good news is the master cylinder isn't too expensive, and it's a fairly straight forward job. https://www.realoem.com/bmw/enUS/sho...diagId=34_1219



The bummer is you'll have to bleed the brakes again... Usually I don't put brake fluid in my power bleeder. I just fill up the reservoir, and use the bleeder to pressurize the system. I don't think it would have saved you this time, but it reduces the places brake fluid can leak out and get on things in the engine bay.

 

I took a mirror and the leak is coming from the back seal that the reservoir sits on and looks like those can be replaced for $6 a piece.

 

Something similar happened to me when I used my pressure bleeder to flush my brake lines. I had a massive leak from the master cylinder area but mine turned out to be a cracked brake fluid reservoir. I had never seen that before and I fix cars for a living!

 

what I still don’t I understand is that my brakes feel perfect but is still slightly leaking from the black seal from the reservoir.

 

I think you’re on to something, I went back to check and wiped throughly and with a mirror I can see the top edge crease start to get wet. The reservoir looks to be a two piece and at fist thought it was coming from between the two. But it’s not. I can’t see no crack but like I say the ledge of the top half starts to get wet so I’m betting it’s that. Thank you for posting cause I wouldn’t have checked that. Now hopefully I can order just the reservoir.

 

Update I found the crack in the reservoir, right after the “ MIN” fill line the crack starts at the top and runs down and stops at the bottom of the letters making think it read “MINI” but the last “I” is the crack so that there me off.

 

I’ve heard of people cracking the reservoir at like 30 psi, but I’ve never seen it. I guess the plastic starts to fatigue after nearly 20 years.

 

I only had 15 psi and heard a pop

 

I was able to get just the brake fluid reservoir. I think I got it from my local dealer.


I had an unfortunate incident with my pressure bleeder (Mityvac) a few years ago that taught me to keep the maximum pressure to about 15 psi, so that's the pressure mine was at when I discovered my leak. I'm pretty sure the reservoir was cracked prior to my attaching the pressure bleeder. My R53 has spent all but 3 of its 18 years in the desert heat of Arizona, so I have am not surprised that plastic part failed.

 

found a cracked reservoir on one of my cars when I pressure bled it

 

Now will I have to bleed the complete brake system when I replace the reservoir?

 

If your brakes are working now, you might get away without bleeding. In theory, you ought to be able to replace the reservoir without introducing air into the system. If it were me, I’d probably swap it and take it for a spin and see how the pedal feels. If the pedal feels good then I’d leave it alone, if it’s spongy, I’d bleed them.