Subject: [Healeys] BJ8 Brakes not releasing

From: <[email-masked]>
Date: Mon, 29 Apr 2013 14:35:48 +0000 FILETIME=[D7517610:01CE44E6]

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

We acquired the car last summer and the brake issue developed over about a 6
week period. It got so severe we had to take the car off the road. The rear
wheels (drums) remained cool but the front wheels (discs) got too hot to touch
after just a short city drive.

Since then I have...

- Replaced the brake fluid (by bleeding the brakes until the fluid "ran
clean")..
- Replaced the rubber bits in the calipers..
- Replaced the pistons in the left side caliper assemblies.. (the right side
pistons seemed to be fine)..
- Replaced the flexible hoses to the front brakes..

Although the car had been very well looked after by the previous owner, my
understanding is it had not been driven very much at all over the last 5 years
or so.

The interesting thing is that with the engine not running, the brakes release
properly. With the engine not running and the car on a slight slope,
regardless of how hard I apply the brakes, it will start to roll as soon as I
take my foot off the pedal. With the engine running however, after I apply the
brakes and remove my foot from the pedal, the car will not move. If I let sit,
after 3 or 4 minutes the brakes will release and the car will start to roll. I
observed the same behaviour late last summer once, although I only had to wait
about 30 seconds.

Other symptoms are..

- Thebrake lights go out when I take my foot off the brake as one would
expect, even when the brakes have not released.
- I had replaced the brake fluid before I replaced the rubber bits in the
calipers, but I still found a lot of "junk" in the fluid in the calipers.
- We do not appear to be losing brake fluid.

My "prime suspect" at this point is the vacuum booster itself. To be more
specific, I suspect there may be dirt or other contaminants  in the fluid in
the booster, or possibly lack of lubrication somewhere.

Before I go any further, any thoughts/comments/suggestions on further tests or
flushing the fluid without disassembly or other possible causes would be
appreciated.

Geoff and Carol
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From: Bob Spidell <[email-masked]>
Date: Mon, 29 Apr 2013 15:17:17 +0000 (UTC)

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

--------------------------------
Bob Spidell - San Jose, CA

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

...

Geoff and Carol

[email-masked]

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From: Bob Spidell <[email-masked]>
Date: Mon, 29 Apr 2013 15:41:33 +0000 (UTC)

Having thought about it a bit more, I'd wager a C-note--Canadian or American dollars, whichever is worth more today--that the problem is with the seal on the inner wall of the large vacuum/gas cylinder. I suspect the dry lubricant has been worn down--or the rubber seal has become brittle or sticky--and this causes the gas piston to not be able to retract after braking (it does have a large spring under it). Since your symptoms seemed to have come on gradually this is logical. Actually, the seal is formed by a leather seal, and the rubber ring is there to keep pressure on the leather seal. 

Usually, the servos fail when the seal on the gas piston shaft--known as a 'gland seal'--becomes brittle and/or breaks causing the servo to suck brake fluid into the vacuum cylinder (if you're losing brake fluid mysteriously you may find it in the gas cylinder). For this reason--and general principles--if you choose to rebuild yourself you should do a full rebuild with a kit (even though, theoretically, you may be able to get by with just re-coating the inside of the gas cylinder with a dry lubricant). 

I used an older version of this product, and it has worked well for many years: 

http://www.associatedindustriesinc.com/store/solid-and-dry-film-lubricants/sandstrom-28a-solid-film-lubricant/ 

Bob 

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

Geoff and Carol 

[email-masked]