Brake fluid leak while changing pads
 

Just a quick question -

I was replacing the front rotors and pads on my 1989 300E and as I was compressing the caliper piston, a small bit of fluid leaked out at the very end, from around the piston. I used a C-clamp and the old pad face against the piston to compress it. I've done quite a few brake jobs and I was careful about compressing the piston. I had left the brake fluid reservoir top slightly open to allow for the fluid to rise.

I had to compress the piston fully to make room for the new pads. At the very end of the compression - with the piston almost fully in - that's when a bit of fluid leaked out. The fluid leaked out from the outside perimeter of the piston (between the piston and caliper).

I wiped the fluid off and it didn't leak anymore. I installed the brakes and test drove the car. Brakes are firm and solid - everything feels fine.

I haven't noticed any leaking fluid under the car or on the driveway.

Is this something I should be concerned about or was it just a bit of fluid getting forced past the piston seal when I compressed it?

TIA!

The momentary leak suggests the caliper bore is less than perfect. The fact that presently the caliper has no leaks suggests the seal is riding on a good surface. How many miles/years are on the caliper?

Or, maybe the piston was momentarily overextended, allowing for fluid to escape, suggesting a non-problem.

Try "standing" on the brakes while the car is stopped to check if the pedal creeps to the floor and to check for leakage at the calipers. Does the car pull to one side during firm stops (hands off the wheel)?

I guess the sure thing to do is to disassemble the calipers and examine the piston/bore for any corrosion, pitting, or other defects.

Thanks for the reply Kestas.

AFAIK, the caliper is original - so 320,000 Kms. It has served me well. ;)

Braking seems firm and normal - no real pulling to either side. Actually, it did seem to pull to the left during firm stops but I later found out that this was due to my tires being pointed slightly left at the time of braking due to the road slant (is it just me or are new roads getting more and more pitched?). I just installed new tires and they track like mad.

The caliper that leaked is on the right (passenger) side.

Most two-lane roads are crowned (high in the middle, between the two lanes). Many other roads are also crowned. This would cause the car to veer to the right.

Other roads are banked, such as certain freeways. The slant can go either way, depending on the curve direction.

All this is done so the roads can shed water in a rain.

If your car is pulling to the left, this goes against the crown direction and suggests the right caliper isn't grabbing as much as the left.

Given the age of the calipers, it may be time to overhaul or replace them. Nowadays, a completely rebuilt caliper doesn't cost much more than a rebuild kit, hence people rarely rebuild calipers anymore. Calipers are generally replaced in pairs when replacement is due to age.

i bet there was a little liquid that had seeped into the boot and when you pushed it back it squirted out.

are you sure it wasnt water?

i would just keep an eye on it.

tom w

Situation fixed!
 

Ended up taking the car to my tech. Checked the brakes. Turns out the brakes are fine - dry as a bone and everything operating as it should. I'm guessing that perhaps a little bit of fluid was forced out when I compressed the caliper fully - or maybe it was even water, as suggested, since we had some heavy rain prior to my doing the brakes.

The pulling ended up being caused by a bad ball joint. Replaced that and my car is riding like new and braking smoothly.

Thanks again for the input.

You probably had worn the pads to the limit. I have seen this loss of brake fluid many times when pushing a piston back from its limit. On a client's car I replace the caliper from the liability stand point. Most of the world lawyer population is here in California. On my own car I do what you did and just keep an eye on it. It usually heals itself.