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Triumph TR6 - Brake Master Cylinder

Heads up on a potential m/c issue.

I installed a new oem brake master cylinder, filled, flushed, bled and op checked the system; all OK. Then overnight, most of the fluid for the front circuit leaked from the reservior to cylinder body joint. It appears that the o-ring under the reservoir that sits in a recess in the cylinder body isn't being sufficiently compressed as it is either too shallow and/or the mating face on the molded reservior is slightly concave. The seal for the rear circuit is OK.

I haven't taken my old one apart yet to compare it as I spent too much time cleaning brake fluid from the inner fender(!!).

Anyone ever experience anything like this?

1974 Magenta
Wayne

Wayne- Shouldn't that be "Was Magenta"?
DON KELLY

I had a similar problem with my '73 way back in '75. If I remember right, it started leaking and tightening the mounting screws didn't stop the leak. I took it to an import shop, and they simply put two o-rings (one on top of the other), and put the resevoir back on. Never had another leak. (ok - the car burned in '77, but the fire started on the other side of the car.) Perhaps you can find an o-ring with a thicker ring, but same overall diameter.
Bob Blair

I did exactly what Bob described - took the gasket to a hardware store and bought a thicker o-ring.
Brent B

Wayne I have heard of original brake cylinders developing that same problem over time. I think mine did late last fall just as it was heading off to storage. I'm glad that I run DOT5 fluid so I don't have to worry about paint being removed. At the sametime, I am concerned that when I do decide to repaint, getting that silicone off the paint is going to be a pain.
SID
Sid Turner

Thanks all. I overhauled the whole brake system incl. PDWA & cylinders and after much thought decided to stick w/ DOT 3/4, needless to say I am having some second thoughts.

Rgds, W

1974 Magenta (w/ bare metal spot on inner fender)
Wayne

I seem to be experiencing a similar problem with a new master cylinder mounted...look like a gravity leak of brake fluid where resevoir meets MC. What size o rings do i need to get to halt this ... 2 of one size or one larger ring?

oh yes..dot 4 so guess I get to repaint some of the engine bay now!


thanks

bob
Bob Craske

Bob - I don't know what size o-ring; just take the old one down to the HW store and match the diameter with one thicker than the original. Use 1 o-ring, not 2.

BB
Brent B

Brent

I believe I will need neoprene o-ring or is there another material that will stand up to dot 4?

thanks

bob
Bob Craske

Hi Guys:

Same problem I think. Went down to visit the 6 at Easter & found after starting that I had no brake pedal. Checked the master cyl & almost empty. Topped it up and still no pressure. Bled right front & rear & still not a good pedal so I have a leak I cannot locate yet. No fluid on the floor under the car or in the brake drums; the wheel cylinders are not leaking. Ran out of time & patience as only +2Deg C in garage last weekend. Checking this weekend & will advise findings.

Bob
Bob Evans

Bob C. - neoprene should be ok there. It's natural rubber in dot 3 that's a problem.

Bob E. - Uh-oh. Sounds like the dreaded "leak at the MC rear seal into the booster" problem. The next thing you'll probably find is fluid in the footwell when it starts leaking from the booster.

BB
Brent B

During my restore with literally all new brake and clutch components DOT5 was the logical choice. Also all rubber components where given a rub down with rubber grease.

Wayne..."(w/ bare metal spot on inner fender)" THAT should have convinced you to go DOT5.

It should be kept in mind that the only way to switch from 3 or 4 to DOT5 is as you did Wayne a COMPLETE overhaul of either hydraulic system.
Wayne, I suggest CASTROL LMA as your DOT4 with a bi-annual flush.
Bob E..." No fluid on the floor under the car or in the brake drums" yup..hopefull new carpets are not in order.
Rick C
Rick Crawford

I tried a 15/16x1/8 O ring and it stopped the leak, however it is not that much bigger than the opriginal so I'd also consider a 15/16x3/16 but that size isn't an off the shelf item around here.

The best seal material for brake fluid is EPDM or EPR, at least according to what I found on the web. I believe silicone, teflon and neoprene are also OK. Nitrile, polyurethane and I believe Butyl are not compatible.

I only use LMA in this car.

off topic: Of course, the day after my m/c incident, I was taxiing a small airplane and one of the toe brakes went to the floor, I think I'm under an o ring curse.
Wayne

Brent/Rick:

Bet you're right and it's leaking into the booster. No carpets on order - they're new! Just my luck but it appears I'm not alone on this one. Going down to visit her tomorrow. Will update.

Bob E
76-6
Bob Evans

FYI

If you replaced your master cyclinder in the last year, there was a bad batch produced that may have had overmilled seats for the o-ring that sits between the resevoir and the MC. Supposidly hundreds were returned and replaced only to exhibit the same problem. It was recommended to replace the o ring with a square profile ring of similar size to solve the problem..

bob
Bob Craske

I installed a new master cylander last winter. Worked good all year but now one resovoir is empty and a big puddle under the car. It is a MC leak, not lines or wheel cylanders. Must be a bad batch and I will check the O ring. Thanks for the info.

dave
David B

Bob C:

Do you or anybody else tuned in know where the bad batch of MC's came from? I'm going to buy a new MC rather than a repair kit and I'm dealing with a Moss distributor and getting a discount. TRF also carries the MC. If the Moss batch is defective it would be nice to know. Or, is this problem now corrected?

Thanks,
Bob E
76-6
Bob Evans

Bob

From what i was told, the bad ones are now out of circulation so any new ones purchased recently should be ok.

bob
Bob Craske

This thread was discussed between 28/03/2005 and 10/04/2005

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