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TR6 TR6 Puddle of Brake Fluid on the floor

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DaveGT6

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I went to the garage this evening to work on the fuel sender & evap system of the TR6. As I was trying to find the canister end of the vapor line thats supposed to go from the tank to the canister in the engine bay I noticed a puddle under the drivers side just behind & inside of the front tire. Long, depressing story shortened; the master cyl evacuated about half of its contents sometime in the past 24 hrs. I raised the car & had to stop working so couldn't really investigate but I'm not real sure what to look for other than loose fittings or a hole in the cylinder casting. Can anyone offer some clues as to where to start? I knew it would need a rebuild this winter since the pedal would sometimes slowly go to the floor after stopping & holding a foot on the brake, but I really didn't anticipate this. I'm just glad the brakes didn't fail on our sunset drive yesterday. Also,this is the 1st LBC I've had with a booster on the brake system... if it matters.
Any & all suggestions & guidance appreciated.
Dave
 
Well, first, how do you know it is the MC that is bad? A leaking caliper, hose or hard line can drain the reservoir as well. And when the MC leaks, it usually leaks into the booster.

I would start by doing some more investigation as to what route the fluid took to the ground. Another possibility is a blown seal in the PDWA and fluid leaking out through the switch. (Not the switch's fault, the cavity under it is supposed to be dry.)
 
If you haven't ready make sure to get the fluid off the paint on the floor or touch it up, as that is where the rot starts....
 
DaveGT6 said:
I noticed a puddle under the drivers side just behind & inside of the front tire.
Click to expand...
There's a brass junction block in that area (brake line from the master - then two lines - one to each front caliper).
 
Sorry, didn't mention that the bottom of the booster drum was wet & so was the sheet metal below that the whole way down to the frame.
Later this afternoon I'll have time to work on it & hopefully figure out what happened.
 
Dave - What usually happens is that a corrosion pit develops at the base of the rear seal in the MC and when it extends beyond the seal the fluid leaks out. You may find fluid inside the driver side footwell, too. If you inspect the MC and find this is the only pit it can be repaired with metal filled epoxy and honed flush. This is a "safe" repair, btw.
 
You were right on the mark Brent. I pulled the MC, disassembled, and cleaned it. The chamber nearest the open end has a corroded/pitted area about where the seal rests covering the bottom half of the cylinder. At the blind end of the chamber where the other seal rests there is a similar but narrower mark almost the whole way around. I'm surprised the brakes worked at all! The MC on the GT6 only had a few small corroded pockets when looking into the cylinder and it would hardly work (has a new MC now). Corrosion & pits must be like real estate; location, location, location.
A new MC for the TR6 will be ordered. I'm not taking a chance on the brakes! This'll also give me time to clean up that area of the engine bay and paint it (there was no paint there for the brake fluid to remove so even a rattle-can paint job will be an improvement.) And time to check out the rest of the system.
Oh - the one bit of good luck, The brake fluid didn't get into the footwell of the car.
 
Don't forget to check inside the booster.
 
when you install the new Master cylinder, hopefully you wont have to adjust the little ball screw on the booster. I purchased a new brake booster and they had no directions telling you to adjust that little ball screw out and I think the clearance was like .010" I just adjusted it out, drove around the block, adjusted and drove, at one point I got it too far out and the plunger inside the MC wouldnt come back far enough and relieve the pressure on the brakes and I drove a block with the brake like ON and they got hot. but with some adjusting I got the breaks to work with a nice peddle.

Hondo
 
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