I went to the track last weekend, a nice little 2.25 mile circuit with one 110 mph straightaway (w/out pulley). In the afternoon I started popping my hood after each session, and I noticed that the brake reservoir looked like it was sweating. Sure enough, a swipe with a paper towel revealed blue brake fluid. It came back after every session, and I could even see a little bit pooling under the master cylinder. I replaced the master a few weeks ago after the pedal wouldn't stay up, and that problem's been fixed, so I doubt the master's leaking. Plus it's all over the reservoir, which sits higher than the master. Any ideas? Is this "sweating" something that normally happens to you guys on the track, or should I replace the cap and/or reservoir? (sorry, no pics)
Is the fluid level above the max marks on the side of the reservoir? Is the flexible seal under the cap in good shape? There shouldn't be fluid escaping from the reservoir even under high G turns. Hose off any fluid that gets on your paint.
I'd give Todd at TCE or or the TSW guys a buzz--I've never heard/seen that; brake fluid should never escape the resevoir like that. Did you bleed them yet? I wonder if the fluid boiled if it would be enough to force fluid back out the resevoir.
@cct1: Yeah, I bled the brakes Sunday night after the second day, no air. Kind of surprising since I've been boiling brake fluid for as long as I can remember. Over the course of the last 18 months I upgraded lines (Grassroots Garage SS) and fluid (Super Blue), then track pads (CT XP10/8), then calipers and rotors (TSW MDM), then ducts (Sneed's), then higher temp track pads (CT XP12F), then replaced the master cylinder, and finally this weekend they didn't boil. The rubber inside the cap didn't look torn, but maybe I just need to replace it anyways. I can't think of anything else to upgrade/replace. =/
Do you use a pressure bleeder? If it holds pressure then replace the cap. If it doesn't, look for a crack. http://www.motoringalliance.com/forums/attachments/brakes-wheels-tires/438d1273797422-r56-brake-bleeding-dscn1721.jpg
This isn't a real fix but!!!!, I've seen more then one MINI with a wrist-sweat band around the cap to absorb any sweating..
@k-huevo: Pressure bleeder holds pressure, but it falls very slowly, like 1 psi per 5 minutes. It does the same thing on my BMW, though, so I didn't think it was a problem. That's a good way to check for a crack, though. @cct1: Just OEM. The local parts guy gave me a small discount, but it still took a week to ship. The brake bias is built into the master cylinder, no reason to change it. @N2MINI: Yeah, that's actually what Dan recommended. So you've seen other cars with this issue?
Chris- bluesmini (I think) Is an instructor and I saw it on his car as well.. He was instructing at the first Phil Wicks at VIR 1-1/2 years ago or so, and he comes to the BMW Center usually.. I got to ride a session with him at VIR.. His car is well "sorted" and quick..
Just an update: overfill was definitely the cause of the sweaty brakes. Fill to the MIN level for track work.