Bonaldi / Bendix Booster Rebuild - Alfa Romeo Bulletin Board & Forums
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post #1 of 109 (permalink) Old 11-21-2006, 05:28 AM Thread Starter
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Bonaldi / Bendix Booster Rebuild

Has anyone rebuilt a Bonaldi / Benditalia / Bendix brake booster (they are the same I believe). I know the simple solution is to buy a reconditioned unit, but I am in fact only cleaning the booster as it has been on the shelf for a good while without covers on the vacuum and hydraulic ports.
The vacuum chamber / air valve sections are no problem, it is the hydraulic cylinder I am wondering about, I see with a rebuild kit there are various seals and a circlip that you get, but on this cylinder there is no circlip to remove to gain access...any ideas?

Not knowing what the seal system looks like inside the cylinder, I am reluctant to try to rinse of flush out any dirt that may be in there.

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post #2 of 109 (permalink) Old 11-24-2006, 12:39 AM
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Hi, there is nothing too much to worry about inside the booster. The bronze bush you show in the photo should be a very light press fit (assembled by hand and retained by the diaphram assembly) so they come out with little effort. Try holding a suitably soft block of wood on the ali face and giving it a good knock down onto a solid surface. Behind the bush is a wire clip retaining the rest of the assembly. It is lightly spring loaded so ease it out and be careful and do it somewhere clean. Easy as you go and take photos as it comes apart and you will be fine. Good luck
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post #3 of 109 (permalink) Old 11-25-2006, 02:11 PM Thread Starter
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Thanks very much, you were spot on! The bushing took a little bit of coaxing but did come out relatively easily. Glad I did so, because with the amount of gunk and corrosion I found inside the cylinder, the booster surely would not have worked properly once installed.

So I think I understand how this thing actually works now, someone please correct me if I am wrong.

Under normal operation (no braking), the vacuum is applied to the front side of the booster "can" via the banjo fitting/air passage, and also to the back side of the can via the air valve (pentagon attached to the hydraulic cylinder) . With both sides of the can at equal vacuum, there is no assist to the brake. Once the brake pedal is pressed, the hydraulic pressure increases, and moves a small piston that actuates the air valve . This new position of the air valve no longer allows vacuum to pass from the banjo fitting to the back side of the can, and simultaneously allows ambient air pressure to the back side of the can (via the small "filter" on the air valve). Under this condition, the two sides of the big can are no longer at equal vacuum, causing the diaphragm to move inward and push a small rod/piston into the hydraulic cylinder, causing more hydraulic pressure, and effectively giving assist to the braking.

The arrow in the attached picture points to (as I've assumed) the small piston that actuates the air valve. Is there any way to clean/service this part? On the brake booster currently in my gtv, I am pretty sure that this is the part that is sticking (in the "up" position) resulting in vacuum assist sometimes even when the brake pedal is not pressed. Since the inside of this hydraulic cylinder was quite dirty, I want to ensure the same thing doesn't occur.

andrew

ps it looks like there is still a check valve in the cylinder, does this come out somehow also?
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post #4 of 109 (permalink) Old 11-28-2006, 12:17 AM
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Just a thought

I have read somewhere else on the BB about a possible cause of the sticky booster. The external vacuum pipe that goes from the pentagonal valve to the diaphram housing has a little rubber bend as it goes around the corner. This can collapse with age and I think cause sticking brakes.

Otherwise the little piston you show just needs to be clean and make sure the ali housing bore is nice and clean with no corrosion.
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post #5 of 109 (permalink) Old 11-28-2006, 12:35 AM Thread Starter
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thanks

Thanks, I think that I will reassemble it now, and give it a go on the car. Very good point about the hose, because if that leaks, then the booster is giving assist (even if you don't want it...). I have headers on my car, and given the proximity of this hose to the hotter than stock exhaust (meant literally in this case!), I am sure the hose is not in great shape after 37 years of service (on the car now is a Lockheed booster still with original crimping, no V-band or other evidence of a rebuild).
thanks for your help.

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post #6 of 109 (permalink) Old 11-28-2006, 12:36 AM
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be very careful when you clean that bore. Being that the housing is aluminum, if you over hone it or polish it to much, you can over bore it and then it won't seal.

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post #7 of 109 (permalink) Old 11-28-2006, 04:36 AM Thread Starter
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The bore was in pretty good shape, so I only used a paper towel to clean it out.

I guess the only hesitation that I still have is not knowing if that little piston that actuates the air valve is siezed or not. It looks like I would have to used pressure (hydraulic or air) to get it out, since there is nothing to grip on to to pull it out (or even budge it for that matter). Shall see on the car if I have power assist or not...

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post #8 of 109 (permalink) Old 05-27-2007, 07:55 AM
I know this is kind of an old thread but I thought I would post what I learned this weekend. I have been rebuilding the boosters on my '69 Spider and didn't see any way to remove the air valve piston. While fooling around I found that if you run the booster plunger back and forth in the right sequence the air valve piston will pop out. It's easier to describe with pictures:

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How the heck do you get this out? And what the heck does it look like?

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So I inserted the booster plunger and ran it up and down to see that the spring was working and see which port was drawing air.

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With the piston in the fully compressed position I covered the side port with my thumb and drew the plunger back and...

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Out popped the piston! Actually this is re-inactment of the actual event. In truth, It shot out about 3 feet - I was lucky it didn't go down the floor drain...

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ANd this is what it looks like. It has a small rubber seal on the end.

That's it. Hope this helps someone...

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Last edited by gprocket; 05-27-2007 at 04:23 PM.
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post #9 of 109 (permalink) Old 05-27-2007, 10:45 AM
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I tried rebuilding mine, but they both leaked like crazy. It was the biggest waste of $200 I have ever seen. Its one of the reasons I went to the single circuit system.

Will

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post #10 of 109 (permalink) Old 05-27-2007, 04:35 PM
Will:

What rebuild kit did you use and where did it leak? I actually have two sets (4 total) of these boosters - two that came off my recently working spider and two from an unknown parts car. I disassembled all of them and spider units mostly just to paint the bodies and replate the booster housings. Otherwise the spider units were in good working order. I soon found that the spares were anything but - the plungers are seezed and I can't get the bronze bushing out of the nose. There was lots of hydraulic oil and rust in the booster housings and sludge everywhere. I thought it might worthwhile to rebuild them but by the time you get done buying kits for the body and the air valve you may as well just by a new assembly.

Interestingly, I imagine that the bulk of the cost of the rebuild kits is for the rubber vacuum diaphrams. In my case, all the diaphrams look brand new - no wear or distortion whatever. If I could just find that filter element in the air valve, a couple of cup seals and a couple springs I would be in business for a few bucks max. Alais, no luck so far...

Last edited by gprocket; 05-27-2007 at 04:39 PM.
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post #11 of 109 (permalink) Old 05-27-2007, 06:15 PM
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Both of mine leaked from the large diaphram to begin with. Then they leaked from the small one. After that they leaked from elsewhere. I pulled them completly apart replaced all the gaaskets and seals, and they still leaked. I guess sitting for 30 years finished them off. At first it was only the rear one that leaked, I thought I fixed it, then the front one leaked, thought I got that one dialed in only to have the rear start leaking from another place. I was stuck between a rock and a hard place and chose to ditch the second one all togther. I have to say the car stops just fine.

Will

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post #12 of 109 (permalink) Old 05-28-2007, 12:35 AM
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Filter Alternative

I made my filter elements by pulling a standard industrial pneumatic silencer to bits to get the silencer element out which is essentially a filter (a Festo unit worth about $8). Then I machined the outside diameter to fit which took a couple of minutes on the lathe. I had a new nose seal made by Sealjet here in NZ. Nearly six months down the track, although not many miles have gone by the boosters seem to be working a treat.
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post #13 of 109 (permalink) Old 05-28-2007, 06:54 AM Thread Starter
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I actually purchased a filter kit from a Mini shop (I noticed that the servo on my Mini was very similiar) and in fact it works just fine on a Lockheed booster. The filter assy for the Bendix looks identical also (but I have not verified this).
Here is the link
http://www.minispares.com/Product.aspx?pid=36143
I replaced the whole filter assy (including the new plastic cover), but I don't see any reason why you couldn't reuse the original metal cover, which looks better on an Alfa.....
At the end of the day, the filter assy was not my problem, so I didn't really solve anything, but nevertheless, at least there seems to be a source for these parts.
The comment about it being cheaper and less hassle to just replace the whole booster is probably quite true, given that the complete boosters are readily available. But if you are sure that you filter assy is the culprit, then replacing the filter assy is certainly much less expensive that the entire booster.

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post #14 of 109 (permalink) Old 05-28-2007, 08:07 AM Thread Starter
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By the way gprocket, thanks for the hint (photos and all) on how to continue with the disassembly!!

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post #15 of 109 (permalink) Old 05-28-2007, 09:55 AM
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I just took out both boosters from my '69 spider and came across this post so I thought I'd get the collective wisdom of the forum on my situation.
The symptom was that I was losing brake fluid and getting white smoke out the tailpipe.
When I disassembled the boosters, both had lots of fluid in the the chambers. The diaphragms look fine and the small air valve diaphrams look ok too. The rubber seals in the cylinders don't look too bad either. Still pliable.
What would be the failing part causing fluid to enter the chambers? The cylinder walls and the larger rubber seal? Is that it?
The power assist seemed to be working ok before the incident with the white smoke. Should I just rebuild the cylinder and expect that it will be fixed? I see that IAP has a rebuild kit for $88. Is there a better source? Who sells complete boosters?

Colin,
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