Brake fluid loss - questions

[Adnan]

Hi,

A couple of weeks ago I received a low fluid warning so I topped it up and all was well. Today, the same warning popped up and upon inspecting the brake reservoir area, I can see that fluid has leaked down from the master cylinder area (did a number on the paint on the frame, of course).

A couple of questions - topping off is not unexpected as brake pads wear so I didn't look for leaks the first time but can a change from Castrol LMA to Valvoline synthetic (DOT 3 and 4 compatible, non-silicone) cause cylinder failure? I have always used LMA but this time, I couldn't find it at my local store.

Secondly, since it's so hard to tell under there, can a reservoir leak? Since there are two plugs and a side outlet for the clutch, is this a possibility or should I just assume the master is finished?

Thanks for your suggestions,
Adnan
'91 535

[Jr ///M5]

There are two rubber grommets between the master cylinder and the reservoir. Depending on which master cylinder you have, here are the part numbers.

ATE- 34311160133
Lucas Girling-34311163464

Look around the master cylinder area for the labeling that identifies your master cylinder. The rubber grommets are about $3 each at the dealer.
All you need to do is remove the remaining fluid in the reservoir and pull it straight up, remove the old grommets, clean the area of debris and pop in the new ones and install the reservoir, fill with clean brake fluid and you're done.

It's a typical problem on older E34's. Just don't touch the brake pedal when the reservoir is off.

[Adnan]

use dot 4 when you refill, a top off with dot 3 is usually what kills the old grommets, fortunately the rest of the system doesn't mind the dot 3 so a flush is not required

Hi Winfred,

Thanks for the caution on DOT 3. The top-off was with the new stuff, which is DOT 4. I don't recall if LMA is 3 or 4. The good thing is that you both think that the grommets are the likely suspects, a relatively easy task.

I'll pick them up tomorrow, assuming the dealer has them and give it a quick try.

Regards,
Adnan

[Torque]

use dot 4 when you refill, a top off with dot 3 is usually what kills the old grommets, fortunately the rest of the system doesn't mind the dot 3 so a flush is not required

lol I've read this a lot, but since I topped off with DOT3, all my seepage around the grommets has stopped. Coincidence? Who knows.

[winfred]

use dot 4 when you refill, a top off with dot 3 is usually what kills the old grommets, fortunately the rest of the system doesn't mind the dot 3 so a flush is not required

[Jehu]

Hi Winfred,

Thanks for the caution on DOT 3. The top-off was with the new stuff, which is DOT 4. I don't recall if LMA is 3 or 4. The good thing is that you both think that the grommets are the likely suspects, a relatively easy task.

I'll pick them up tomorrow, assuming the dealer has them and give it a quick try.

Regards,
Adnan

I replaced these recently. You are well advised to extract or otherwise remove the existing Brake Fluid before pulling those two lines out. I pulled them without first doing that and Brake Fluid of course spewed before i was able to get a rag over the end and raise it above the level of the reservoir . So far everything is still intact and i don't think any fluid got anywhere other than the inside of the body panels and such which i sprayed with Brake Cleaner. Be careful not to break those tubes .The Dealer told me will only sell them with the new master cylinder. Though i imagine they could be found elsewhere you'd still be without brakes. I used slip joint pliers.Grabbed the hard platic plug squeezing hard and pulled straight up with even ,steady force careful not to rip too fast lest i break those tubes or my radiator vent pipe which is the same plastic .