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Brake fluid enigma....

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I have a problem with brake fluid oozing out from underneath the cap on my master cylinder reservoir. The car can either be used or sit tucked away in it's room idle for weeks and it still happens...brake fluid somehow leaches out from beneath the cap and eventually puddles around the perimeter of the reservoir, waiting to build up and drip down onto my precious paint. Since I am using Castrol GT/LMA, this is bad. I have tried everything, from complete new reservoir, new cap, new cap gasket, new brake fluid. It still happens and I am at wit's end. What would cause this to happen. Is it a brake fluid condensate evaporating up and out? Is someone sneaking into my garage at night with an eye dropper full of this evil bile waiting to wreak havoc with my paint? I am not going over to the other side and using synthetic. Everything in my system is new, literally. Is the cap too tight? too loose? Or is it supposed to be that way? I have taken to draping a towel beneath the reservoir lest I forget to check the darn leak for a few days. There are no cracks nor holes in my reservoir. My car is down for a few weeks till I can do a major tuneup. What gives?

Bill
 
Mine does exactly the same thing
It's obviously a Triumph/Girling conspiracy. /ubbthreads/images/graemlins/eek.gif
 
It's a Lockheed/Girling thing... even when you run DOT-5 like I am. Both my Triumph and my Mini do this. If you find an answer and way to prevent it let us know!
 
I see that same thing on mine, but not to the point where it actually drips. It seems a bit wet around the perimeter but never builds up to the point of dripping. I thought I read somewhere once that if the cap is overly tight this can happen, but what gets me is that in order for the fluid to leak from around the cap you'd think the car would have to be in motion and the fluid sloshing around in there. I see this happen, as you do, when the car just sits idle. Fortunately, my engine bay paint is shot, so if it did drip I wouldn't really be concerned. But if I had nice paint in there like you, I'd be annoyed.
 
I remember reading somewhere that the cure to this problem was to loosen the cap.

Seriously.


The reservoir is plastic and it's apparently posible to overtighten it so that it deforms and fluid gets past the gasket in the lid. You need it snug, but no tighter. Post back if this works, mine is still off the car. Seems to work on my father's 69 though.

edit: Whoops, didn't see that dotanukie said the same thing.
 
I'll add my $0.02, my car had some blistered paint under the master cylinder when I got it, and the fluid still finds its way out somehow despite having a new master cylinder. One of the reasons I switched to silicone when I overhauled the brake hydraulics.
-Dave
 
I agree with Dave. Dot 5 is the way to go if you want to preserve the paint. I just got through converting mine over... it's a pain the butt to purge and replace the fluid though.
 
I had a similar problem before I rebuilt my car and the cure was a new cap with seal and to just snug it up, no overtightening. You might check the rubber seal in the cap, mine was deformed from the PO cranking down on the reservoir cap. I had a heck of a time getting it loose!!! Anyways, that was the cure for the dreaded seeping in my case.

Mark
1970 TR-6
 
Tight cap, deformation, bad seal, yeah OK, I can buy that.
But TR6BILL has a point, these things seem to almost sweat fluid out the top of the plastic reservoir!
How else does it get out of there when you haven't driven it in a week.
Is there some kind of vent hole where it gets loose from? /ubbthreads/images/graemlins/eek.gif
 
It does not have to be plastic reservoir for this. My TR3 with a metal reservoir will do same thing. But only when the cap is not tight.
 
All brake and clutch caps should have a vent hole as AltaKnight was asking about. Sometimes they aren't easily noticed, but the cap has to be there or the fluid level couldn't/wouldn't go down when you press the pedals. I've never thought the fluid was coming out of the vent hole... but perhaps it is. Maybe the solution is to NOT fill the reservoir so full and to properly tighten the cap.
 
A lotta guys in the air cooled VW clubs go with silcone for the same reason. My TR3 and Bug both seep fluid. Now have silicone in my bug, my TR3 seepage seems to be diminished, at least, with a new seal.
 
Unfortunately I didn't like the silicone fluid at all. I ran that in my car for over a year and hated it every time I stepped on the pedal. I have a basically new brake system, front to rear including new hard lines and everything, and I bled the system at least a half dozen times, including bench bleeding the master cylinder a few times. I could never get it to where the pedal didn't feel spongy, so I finally went back to the Castol GT-LMA and now have a nice rock hard pedal. If I have to be a little more careful with the fluid so be it.
 
What I didn't see mentioned was a gasket leak between the master cyl and resevoir. A slightly oversized o-ring (in thickness) will solve that. In the 15 years I've had the car fluid has never leaked out the top of the resevoir.
 
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