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Triumph TR6 - Brake Problem

After going back to the car after a longish run yesterday I found a small puddle of brake fluid under it. On investigation this had been expelled from the small breather hole on top of the reservoir cap. Anyone any suggestions as to whether this is a problem with the servo or the master cylinder. I did very occasionally find the brake pedal went further down than normal but other than that the brakes seem to be working OK. I haven't topped up the reservoir recently so it's not overfilled.
R. Algie

Never experienced this myself Ron, but it maybe a "series of unfortunate events!"

How long has it been since a fluid change?

If a caliper piston has seized, there maybe enough contact to generate a lot of heat and boil the brake fluid. Together with a little air in the system, the expansion of the air could force some fluid back past the m/cyl seals, IF they were a bit dodgy.

As you can't get any more fluid into the system than you have put in, air (or maybe water) is probably the culprit.

Roger H

I think you should do some serious investigating before you take another longish run. As you know, there is no such thing as overfilling the brake MC. You must have some sort of back pressure in your system. Try disconnecting the hose for the brake boost. Is your brake servo unit full of brake fluid? It should not be. With the bonnet up, engine running, and the MC screw lid off, apply the brakes and see if you see the level rise significantly. Maybe your tipping valve is in need of repair and is allowing brake fluid to go back into the reservoir. You must be getting a LOT of fluid back into the reservoir in order to fill it up to the point that it comes out the vent hole The only place I would think that you could "store" that amount of fluid would be in the servo unit. It can not be comming back up the brake lines. Like I said, try the brakes with and without the boost hose attached. Also have a close look for brake fluid down in the foot pedal area.
Ron, it sounds like you are in need of a MC repair kit.
An intersting one this is. It will be interesting to hear what you discover. Was this your first drive of the season?
Good luck
Rick C
Rick Crawford

Ron wrote: On investigation this had been expelled from the small breather hole on top of the reservoir cap.

That's a new one on me - are you positive about that? That would almost certainly be from an overheating caliper as Roger suggests, and I would have thought the brakes would have gotten spongy, too. Next time you take a drive stop at some point and touch the rotors. If one is really hot you'll have found the culprit. The thing to do then is overhaul the calipers.

Brent B

Thanks for your suggestions.
Further info, the brake system was completely rebuilt when I restored the car about 3 years ago, new caliper seals and pistons, new rear cylinders, new pipes & flexibles, master cylinder rebuilt with new seals, the servo wasn't touched apart from cleaning the air filter. I've never hade to top it up since, so it can't have filled the servo. Other than the couple of times the pedal travel increased the brakes feel and work as per normal.
Rick, I tried your suggestions, the vac pipe to the servo looks clean and dry inside, with the engine running and the cap off I stood heavily on the brake pedal several times for up to about half a minute and there was no change in fluid level, there is no fluid in the footwell area. The level of the brake fluid at present is approx the bottom of the hole the cap fits on so I haven't actually lost a lot of fluid.
I'm glad I used silicone fluid or I would have had an inner wing to respray as well!!
R. Algie

Hey Ron,
Try and get those brakes fixed before I come over for a holiday in July....I don't want to go for a ride in dodgy brakes !! hahaha
Charlie B.

"The level of the brake fluid at present is approx the bottom of the hole the cap fits on so I haven't actually lost a lot of fluid."
Could you explain what you are saying here please.

Maybe your situation then is as Brent and Roger say. Afterall... "I've never hade to top it up since, so it can't have filled the servo".

With no increase in fluid level in the reservoir or no fluid in the foot pedal area then maybe a caliper. You would think though that you would have a major pull to one side as you apply the brakes at speed if seized caliper..
I am having difficulty imagining that/how you would get that much fluid back up into the reservoir that would be sufficient a quantity to start to come out the top (tiny hole) of the reservoir cap. Did you do the test with brake boost assist hose on AND off?

Also you mention you are DOT5. Have you bled the entire brake system after a period of time from when you first installed and bled? Also, silicone brake fluid is non-hydroscopic. So if there is any air or water in the brake lines well it will still be there. Thinking about this and Brent and Rogers comments, I can imagine that if you have air or water in the lines then hot calipers well the fluid could get pushed back up the line to the reservoir.
Be carefull on your test drive. Agreed on the DOT 5:)
This is deffinitely a new topic/situation to this BBS.
Rick C
Rick Crawford

I think I'll try a run and check the temperature of the discs [rotors] although I would be surprised as they had new pistons and seals fitted and the bores were clean and corrosion free. I don't think a lot of fluid has been expelled, but I think a small amount of silicon on the ground will spread out and look worse than it is.
If I can't find an obvious solution over the next few days I'll probably renew the master cylinder for peace of mind.
R. Algie

Just another thought - was the handbrake fully released on the long drive?

If all is back to normal now, it may have been the case although I wouldn't have thought the volume of fluid affected by the rear wheel cyls heating up was enough to do as you say. Even so, any movement of fluid back past the m/cyl seals indicates they should be checked.

Did you go up or down any unusually steep hills or driveways?!!

Roger H

Charlie, have you forgotten July's the monsoon season in Scotland, at least with global warming the rain's getting warmer!!!

Took the car for a 10 mile run today without using the brakes and the front discs and rear drums were cool, did another 5 miles with normal braking and the discs were evenly warm, then tried some heavy braking but was unable to repeat the fault.
I've had a good look at the sectional diagram of the master cylinder and I'm beginning to wonder if it is an intermittant internal fault caused by a faulty seal allowing the front brake plunger to flood the rear brake plunger which is fed from the smaller front section of the reservoir.
I can't really see how a faulty servo could cause this problem so I've ordered a new master cylinder, I'll post any results here for future reference.
Any further thoughts or suggestions welcome.
R. Algie

Master cylinder has been renewed and I've now done about 500 miles without the problem re-occurring, so hopefully the MC was the problem.
R. Algie

This thread was discussed between 30/03/2005 and 08/05/2005

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