Bonaldi / Bendix Booster Rebuild - Page 8 - Alfa Romeo Bulletin Board & Forums
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post #106 of 109 (permalink) Old 08-07-2018, 03:12 AM
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Your solution may unfortunately be a temporary one I fear. The bore into which that bullet is sliding in has begun to deteriorate due to either corrosion of the Aluminum ...or due to breaking down of the rubber of the little piston seal causing rubber to be deposited on the walls of the bore. Either one will reduce the clearances between the piston and the bore...hence the sticking. The heavier spring allows the piston counter this increased friction but eventually this too will not be sufficient. If it were me...I would remove the unit and clean out the bore that the valve resides in immediately before it's too late. I have taken apart a few of these units already and on some...I could not remove the bullet valve no matter what I did. If the bullet still would be the time to do this...M2CW.

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1969 1750 GTV 105.5 , 1972 Montreal
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post #107 of 109 (permalink) Old 08-07-2018, 03:46 AM
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Thanks 1750GT, but I hope not....
In the booster rebuild I described, the rebuilder said he had to resleeve "everything".
I did also describe removing and lubricating the bullet. In doing so, I checked and cleaned the bore.
Anyhow...fingers crossed.
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post #108 of 109 (permalink) Old 08-07-2018, 11:21 AM
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Out of curiosity, just what is the market for these? I've got a couple of used ones from the very old days of the mid 60's GTVs and the Austin Cooper S Minis in my spares storage. I do have a rebuild kit for one, but it is likely a tired kit by now.



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1991 164S, stock
1994 164LS (~Q)
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previously owned since 1964:

62 Morris MiniMinor 850, 67 Austin 1275 Cooper S (Downton 3/4 race), 64 Giulia Sprint GT (1st red one made), 72 Fiat 128 Sedan, 75 Alfetta Sedan, 78 Alfetta Sedan, 78 GTV, 81 GTV6, 86 GTV6
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post #109 of 109 (permalink) Old 04-30-2019, 12:15 AM
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Sticky Bonaldi booster solved

Ok, so the air valve still isn't doing what it should do....What to do?
Thought #1: Bypass booster (just remove and block off vacuum hose for now), order and install a 20mm M/cyl. Old M/cyl leaking anyway. Tick. Done. Brakes not as good as before, but NO STICKING.
Thought #2: How about a left-field fix for the booster of replacing the air valve with an auxiliary, electrically-powered valve to let the fresh air in, to keep the booster working. It could be run off the brake light switch. Nope - if I disconnect the existing line from the air valve to the booster, I can't restore vacuum to the rear half to create pressure equilibrium when I am not braking.
Thought #3: How about creating a secondary air inlet to the rear of the booster? Nope, that would still leave the pesky air valve in play...and it's not working properly now to restore said vacuum.
Thought #4: How about reversing things and putting the electric valve in-line with the vacuum supply line? That is, turning the vacuum on-and-off, not the fresh air. Why not give it a try. Not sure if the air valve wouldn't still find a way to interfere, but...
Bought one, bodged up a test loop of pipes, and...
- Stronger brakes thanks to the 20mm M/cyl, with minimum increase in pedal travel,
- still have boost,
- no apparent side effects from switching vacuum on and off instead, including brake modulation.
Here is a pic of the unit and as installed. I needed to buy 10mm barbs to suit the vacuum hose, plus a piggy-back spade connector to go onto the brake pressure switch.
Not textbook, but I am stoked.
Valve cost $17, with postage. Barb's $5.
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Last edited by Ranz; 04-30-2019 at 12:24 AM.
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