Bonaldi Brake Booster

[Biba <biba@domain.elided>]

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Tom writes:
Has anyone figured out these old style Bonaldi Brake boosters.  The
 one on my 67 GT Veloce will not release.  I have to disconnect the
  vacumn hose from the engine to stop it from actuating even with no
  force on the brake pedal. I haven't found a manual that covers the
  booster.

  Tom Guadagni
   Dublin   67 GTV
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Tom, I'd suggest bringing it by, but that could present some problems.
Having gone through the same while restoring a '69 Duetto BUT with 2
Bonaldi Boosters, I know what you're going through. A source that helped

was a friend let me photocopy the brake booster portion of his Honda
N600 Sedan shop manual. They're not identical, but are similar in
principal. It was amazingly detailed with cutaway drawings indicating
how it works throughout the cycle.

If you're somewhat brave, they can be rebuilt. If not, try to find a new

one. 2 years ago they could be found (with some digging) in the States.
If you choose to rebuild, you'll probably need both kits - Major kit, 7"

diaphragm & Pentagonal air valve kit. They can be purchased here at IAP
and possibly other places.

Totally dismantle it, being careful to keep everything in order. Also,
there is a part called the plunger valve, located beneath the smaller
diaphragm which must be removed. You might have to blow it out by air
pressure. It has a small seal on it and should be replaced (it will be
in the air valve kit). Clean all with rubbing alcohol.

Check out the various bores. Since it's body is aluminum, don't be
surprised if the the bores need some cleaning up. Even if not, seals
seat much better if bores are roughed up slightly. I purchased 3
different sized steel rods for each of the bores. I then wrapped 400
grit wet/dry sandpaper around each, lubricated with brake fluid and
rotated in a combination circular and up and down motion.

The main bore is stepped, so you'll need a rod for each size. Then you
need a small one to hone the bore for the plunger valve. I strongly
suspect it is the part which will not allow the brakes to release. But
do everything while you have it disassembled. Clean again and
reassemble. I use ATE brake assembly paste.

Did this solve all the problems on the Duetto? Not exactly. It turned
out the bores in the calipers were sticking, so I rebuilt all of them.

Did that solve it? Not exactly. The only thing left was the brake bias
union. The one they always tell you not to touch. Since this car had sat

for 9 years, it too had vast amounts of yuck in it. Unfortunately I
couldn't find replacement seals, so I cleaned, honed, reassembled,
crossed my fingers and VOILE' it worked.

No more locking up. Was that the problem in the first place? No. I'm
sure it needed to be gone through thoroughly.

A footnote: Flashback. The car is now restored (I think), I've cleaned
the boosters (but not replaced diaphragms, renewed the seals, etc.) I go

to a CarNight (a little local social affair) and tell my story to Allan
Ward. He laughs and laughs. Then tells me he raced (or was supposed to)
a brand new '69 Duetto at Willow Springs, but couldn't because the
brakes locked up in the hot pits.

I was convinced I'd never get it. What were the odds with a 27 or so
year old example?

Footnote II: I have a good core I could rebuild for you, but it would be

very expensive since I foolishly paid $90 for it and it would need both
kits which are slightly over $100 (for the 2), etc. I believe Dunlop
also made the booster and know that Benditialia and Lockheed did also so

it must have been used on a variety of cars.

Good luck!

Biba
Irwindale CA
AlfaCyberSite http://home.earthlink.net/~Biba/

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