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Delayed brake release

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Tgt6 Avatar
Tgt6 Joao Simoes
Ann Arbor, MI, USA   USA
1973 Triumph GT6 MkIII "GT6 Cabriolet"
1973 Triumph GT6+ (MkII)
Greetings folks.
My 56 Xk140 DHC has the standard brake drums and a vacuum booster.
Aside from a somewhat abrupt action when it first engages, no doubt due to them being 4 wheel drums, they have always worked well.
It has been sitting for a few months and this Christmas break I took it out and the brakes now seem to be 'sticking'.
I will apply them and they feel even more abrupt than before and once I release the pedal, they remain applied for a second or so, then they fully release.
Thoughts?

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mk21965 Avatar
mk21965 Stuart Brainerd
Stony Creek, CT, USA   USA
Sounds like hoses are closed down

astralcc Barry Hartman
Helston, Cornwall, UK   GBR
This can also be caused by a sticking servo. If you have an original type with a piston and leather seal instead of a replacement modern diaphragm type they can stick in the bore causing sudden application of the brakes and delayed release. I had the same problem on an Austin Healey 3000 and eventually the piston held the brakes on permanently.

The cure was to strip the servo and hone the cylinder bore. It then worked OK.

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PeterT Peter T
Oxford, Oxford, UK   GBR
I had this problem with my Mk2. The cause was as described by Barry. I took the vacuum booster to pieces and re-installed it about three times before I properly understood the problem. In the repair manuals, they warn you to be careful when you take the top off the vacuum cylinder of the servo as the spring that pushes the piston back will cause the piston to fly out. Well mine wasn't flying out; the piston was sticking. Put a little brake fuid on rubber (or leather) seal and it will be fine until the next time the seal drys out. Why does it dry out? That's probably because there's a leak allowing a constant flow of air through the booster. The first place to look is the check valve between the inlet manifold and the vacuum chamber it should close once the pressure in the vacuum chamber is reduced. If it doesn't, there's a constant flow of air that drys out the vacuum/air piston.

To test for this, you don't need to take the servo apart.There's a pipe to the brake booster to atmosphere - it may have a small wire wool air filter on the end of it. Pour a little brake fluid down that pipe and pour some into the small air filter as well. If a dry seal is the problem, this should resolve it. Actually, for a Mk2, putting some brake fuid in the filter is a standard service action. However, you should still do some checks for leaks into the vacuum side of the system, especially the check valve.

And, of course, it could as Stuart said, be a collapsed tube. Personally, I's do the test above first, because it's very easy.

Tgt6 Avatar
Tgt6 Joao Simoes
Ann Arbor, MI, USA   USA
1973 Triumph GT6 MkIII "GT6 Cabriolet"
1973 Triumph GT6+ (MkII)
Thanks. I appreciate the reply.

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