scottalexander

I've been watching a number of e60 brake pad changes.

When the DIY'ers compress the piston back into the caliper on all 4 wheels, they never check the brake master cylinder fluid level.

Why don't they check to see if the brake fluid is overflowing and it needs to be siphoned out?

Isn't that a critical step?

lcc014

I did check, but I did not see fluid level going up too much to the point of overflow out of reservoir.

NoQuarter

I do.... But you shouldn't have to.

When the pads are new and the fluid level is correct, there is no reason someone should add fluid to the reservoir as the pads wear down. The fluid level is OK at the minimum thickness of the pads. I do not add fluid to my own cars.

However, if I buy a used car, best not to assume anything and I keep a close eye on it.

ripley

Some people recommend loosening the bleed nipple on the caliper and let the old fluid in the caliper out at that point and then to up the reservoir if needed.

rice_rocket88

As stated above.. if it was proper level when there was new pads, it should not overflow, there's not that much fluid that goes up when you compress the pads... if not it was someone that always topped it to the max all the time, even then it shouldn't overflow but you could always take a peek when you're walking over to the next set of brakes. Literally just finished doing my cousins minivan this weekend and he asked the same question, I told him to go look and he said it didn't move high enough for him to see. When we were done I told him to check it again and he said it was the same level. Of course his pads were probably still 30-40% life left, he was asking if he should leave the pads. My answer is... we had it all taken apart, and for the $30/$40 worth of pads, might as well all use new hardware than to bother putting new pads in before/after/during winter

Allen

while it's not a "critical" step...you should most definitely keep an eye on the fluid level. BTW...maybe a dumb question, but does removing the reservoir cap make it easier to compress the caliper piston?

rice_rocket88

hella yes it makes a difference compressing the caliper.. The reservoir is pretty sealed so that air doesn't go in to contaminate the fluid.. so if you compress the piston, the fluid has to go somewhere!

If the brakes aren't super worn down, your brake fluid will not overflow, but this weekend I did a job on a volvo suv that literally hit the metal of the pads. Upon compressing it, the reservoir pretty much overflowed.

NoQuarter

This is not because the pads were worn down. This is because someone felt compelled to add more fluid after the pads were worn - that is not necessary but one needs to assume people do this and check the level anyway.

edit: to add that I don't think these are as sealed as you think. As the fluid level decreases, a vacuum would form. However, opening the cap is certainly easier than pushing the air back out through a small opening.

rice_rocket88

Oh for sure.. I think every time that car was in for other maintenance it was topped up.

banglenot

I usually do this, since the fluid in the caliper is usually the most hydroscopic and dirty, and hell, why not avoid forcing it up into the brake lines?

Then when I'm bleeding the brakes the volume in the caliper is small and what's left in there is easier to force out with new fluid.

Sure, detail oriented, but it gets the old fluid directly to where it belongs: in the waste can.