[Healeys] BJ8 Brakes not releasing

[Bob Spidell]

Sure sounds like the servo. There's a rocker-type valve that gates either
vacuum or atmospheric air to the upper half of the large servo (gas) piston.
Unbraked, there is engine vacuum on both sides of the piston; when you apply
brakes atmospheric air is allowed into the top area of the piston, which
applies the pressure differential to assist manual braking. The rocker valve
is actuated by a small slave piston driven by the system M/C. The large gas
piston in turn applies pressure to a 'secondary' M/C which drives the brakes.
Sounds like the rocker isn't releasing and allowing vacuum back into the gas
piston, which should retract the secondary M/C in the booster and release
pressure. There could be something wrong with the rocker valve, but I doubt it
because it's butt simple and I think it would be more likely to leak than
stick. More likely, something is not allowing the servo's slave cylinder to
release. There is a large rubber seal on the gas piston and if it's sticking
that could be the problem.

You have three choices:

1) send the servo off to be rebuilt
2) buy a replacement servo; it'll be different than the Girling and comes with
brackets to fit it up
3) rebuild the servo yourself

I rebuilt mine with success many years ago. Others report less 'luck.' Study
the shop manual to understand how the servo works--they're quite clever. The
cylinders can be sleeved if necessary, just like any other brake cylinder. DO
NOT allow the shop to media blast; esp. the area around the rocker valve. This
is a machined surface and has to be smooth and unmolested to seal properly.
Rebuild kits are available from the 'usual suspects,' and I have a source in
GB. It's possible based on mileage that the large gas cylinder internal wall
will need to be re-coated with a dry lubricant. This is available but not
cheap. The large rubber seal around the gas piston gives some people problems,
but all-in-all it's an interesting project and if you fail you can then go
ahead and fit a replacement or have yours professionally rebuilt (no guarantee
here, either). The rebuild kits run around $100 and sleeving, etc. would of
course be extra.

Guess you can tell what I recommend.

Bob




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Bob Spidell - San Jose, CA

----- Original Message -----


Our BJ8's (Phase II) brakes are not releasing properly.

...

Geoff and Carol
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