What could be the source of a slow brake fluid leak?

[jt15833]

Over the last 2 months my car has taken about 2-3 weeks of regular driving to go from MAX to near MIN. It's a 95' and I've got 300zx calipers / SS lines up front. That install was done years ago and the braking system was good up until 2 months ago. I have done 2 HPDE events recently which probably really stressed the braking system, so I'm thinking maybe a hard line connection somewhere is funky.

*I've checked under the brake master cylinder and under the pedal inside the car, both are dry, although the paint is gone from the brake booster under the master cylinder.

The leak seems pretty slow, and related to how hard I've been braking, so I don't think a caliper seal could do this but I'm not expert. I had one idea of spray painting connections/inside of calipers (tape the seals up) white, so the brake fluid would remove it and help me find it. MAybe could work?

Any tips/insight appreciated! Thanks in advance.

[OutToWinPAHC]

a bad bleeder or the master seeing it has signs of a leak

[IanS]

I would look at a bad caliper connection or a caliper piston seal.

That is some pretty fast fluid leakage, I would pull your wheels off and just check over the braking system. That kind of leak will show up as wetness. Brake fluid doesn't really dry, so you should be able to see where its leaking relatively easily. Just scan all the hardlines with a flashlight, and check for fluid, or dirt buildup on a single caliper. If it has been going on for a while, dirt will have started to cling to the perpetually wet brake fluid.

[JDM240SXcoupe]

I had a problem like that. It was the caliper piston seal. How I notice, my rim was full of fluid n dirty while other rims where semi clean. Fix, replaced it.

[Jfornachon]

You mentioned that the booster pain was gne at the master. Did you remove thw master? I bet you the master is leaking. The back of the master is not under any pressure but it can leak quickly out the back.

Have a great day,
Jared

[jt15833]

I'll take a look at the wheels, and the master looks like the culprit but its not wet =/

thanks for the advice, i'll report back after i get a good lookover

[Jfornachon]

I'll take a look at the wheels, and the master looks like the culprit but its not wet =/

thanks for the advice, i'll report back after i get a good lookover

I can be leaking into your booster and you will never see it till its filled completely. Then you will have to get a new booster.

Have a great day,
Jared

[AZ89two4Tsx]

Check the hose on your slave cylinder.

[jt15833]

which slave?damn if i check every one of these suggestions its got to be there. she won't get some attention for a whole week but ill rpeort my findings

[AZ89two4Tsx]

Edited for retarded-ness.

[float_6969]

He's talking about brakes, why would he check the clutch?

Anyway, it's probably at the master, and you need to check the booster. Sometimes when the master leaks, the fluid goes into the booster and you won't see the leak until the booster fills up. If this happens, you'll need a new booster too, and those are EXPENSIVE (unless you can find a used one)

[alms24sebring]

The first thing is to check for wetness. Brake fluid doesnt just wash away and dry up. It is also very possible that the rear seal on the brake master cyl is bad and is leaking in your brake booster. Just take off the 2 nuts off and look inside or on the back of the resevior. The lines will move with it so dont worry about them bending.

[Jfornachon]

Did you find the leak?

Have a
great day,
Jared

[jt15833]

Haven't found it yet, there was a period of 2 weeks or so where the level in the master cyl. didn't drop at all, which would making finding this leak all the harder. Checked this morning and I was about 1cm below MAX (not to say it did this overnight, I checked maybe 1 wk ago).

I will inspect inside the booster and pull all wheels and look today. It's probably best to pull that calipers to check, if I don't see anything off the bat, right? I think those seals will best be seen when its at least unbolted from the car.

[night_krawlers]

correct, sometimes it slowly leaks between the booster and master

[jt15833]

Well pulling the master cylinder didn't reveal any clues, neither did looking at the inside of the rims which has a pretty uniform and solid coating of dust on them, which I'd expect to show dripping brake fluid at speed well.

I'm going to pull each wheel and caliper tomorrow and inspect, and getting pretty nervous about having a ghost issue especially with such an important system. Any tips/help appreciated, here's a pic of the pulled master cylinder

[ricebike]

please update when u find the leak

i'm going to tackle a similar problem with a friend's vehicle this weekend (not a nissan)

but these guys pretty much cover the bases of tracing your whole hydraulic system (don't forget to check the hoses as well as the hardlines that were mentioned earlier)

[93240guy]

I had a problem like that. It was the caliper piston seal. How I notice, my rim was full of fluid n dirty while other rims where semi clean. Fix, replaced it.

^^ ditto. Had my front end jack up for two days.( don't know if it matters ) But came back and found a nice puddle of fluid on the ground and on the rim. Never noticed when the car was sitting flat tho.

[float_6969]

Are you running stock rubber lines, or SS lines? If it's a rubber line, it could also be leaking through the rubber.

[jt15833]

thanks for the reply float - SS up front and stock 95'ers in the back.

I actually found the leak, the bottom of the driver side rear caliper was wet, upon removal the seal between the piston and caliper body was damp with brake fluid. I got two new duralast calipers from Autozone and put em on.

Thing now is - I bled them upon fresh install til what I thought was good, but when I drive it, I don't get any action to the very bottom of the pedal travel. BArely any brake engagement in top 60% of brake pedal travel. I'll try to bleed again per procedure, but what about bleeding the master cyl, from it's bleeder? When in the 4 wheel stage can I do that? MAybe the fluid got too low during initial bleeding =/

Thanks for all the help guys, we nailed it.