Booster binding front brakes - 1971 GTJ - Alfa Romeo Bulletin Board & Forums

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post #1 of 16 (permalink) Old 01-10-2017, 11:10 PM Thread Starter
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Booster binding front brakes - 1971 GTJ

I have recently completed the restoration of my 71 GTJ. I'm very happy with my work but I have a problem with the brakes - they are binding and on disconnecting the boosters, the problem goes away. During the restoration, I took the boosters apart and gave then a thorough clean. I didn't use any new parts in the reassembly as all looked ok and the brakes had been working perfectly before the restoration. The front brakes bind a little when I brake to slow down rather than braking to a hard stop. If I brake softly to a stop, the brakes bind. If I then depress the pedal firmly, they release. I assume there is a return valve in the booster that is not working unless the brakes are used firmly? Can anyone identify what I need to do to rectify the non releasing of the brakes - I assume due to the booster still applying pressure to the calipers? Thanks.
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post #2 of 16 (permalink) Old 01-12-2017, 12:07 AM
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Why only front brakes? If it was the booster it should bind front and rear brakes, or no?
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post #3 of 16 (permalink) Old 01-12-2017, 10:07 AM Thread Starter
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Has separate boosters for front and rear.

BTW - booster brand is Bonaldi - hoping someone can identify what my problem is. Thanks.
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post #4 of 16 (permalink) Old 01-12-2017, 02:03 PM
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Watching with interest since I have what may be a similar problem. My '76 Spider has a single booster, and the brakes stay slightly dragging after driving. I have added a thin shim between the master cylinder and booster, and this solves the problem, but I'm trying to understand the root cause (nothing is adjustable).

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Has separate boosters for front and rear.

BTW - booster brand is Bonaldi - hoping someone can identify what my problem is. Thanks.


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George Schweikle

1976 Spider (Dedicated Autocrosser, "SPICA, No Carbs")
1991 Spider Veloce (Retirement cruiser)
Scuderia Non Originale
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post #5 of 16 (permalink) Old 01-12-2017, 03:31 PM
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Conedriver -
Zero (or too little) clearance between the pushrod and the master cylinder piston can do this. As things heat up in the engine bay during a drive, the expansion of the components is just enough to keep a tiny amount of pressure applied....enough to make the brakes drag. The problem disappears when things cool down, so it is hard to diagnose. Your solution of shimming the master cylinder away from the booster restores the necessary clearance. It only takes things to be a few thou out for there to be a problem. Or it could be as simple as the repro parts suppliers are skimping on the thickness of the gasket they supply. You should be able to detect minute movement in the pedal before the pushrod contacts the cylinder piston.


Wilsonjsw-
Being RHD, none of that should apply to us with standing pedals. Unfortunately, I have no experience with boosters alone causing this, but recall some discussion here on the board...tried a search?
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post #6 of 16 (permalink) Old 01-13-2017, 01:18 PM Thread Starter
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Yes I've searched extensively but haven't found anything - unless my search ability could be better?
Interesting that no one has come up with a solution though? There must be a return valve that's not working fully?
Maybe I just have to buy a new booster - I see that Alfaholics have new Bendix boosters for GBP205 and the Bendix looks the same as a Bonaldi.
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post #7 of 16 (permalink) Old 01-14-2017, 06:37 PM
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You don't say what brand and grade brake fluid you use.

Probably not your problem but this can and does happen sometimes with the 164, and the problem seems to be brake fluid boiling because the tightly packed 164 engine compartment is hotter than other Alfas. After a couple of times of this happening and then changing master cylinders with little effect, changing to ATE Blu (now 200), a higher temperature fluid from the standard called for, eliminated the problem and hasn't returned since.

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89 Milano (wife's daily driver since 1989, Shankle Sport)
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94 164LS (~Q) (trip Alfa since 2000)
72 Morgan 27 (water time since 1976)

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 #8 of 16 (permalink) Old 01-16-2017, 01:37 PM
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I have a theory the binding isn't related to the booster at all.. Could it be the brake pistons are sticking and not releasing? I have had some issues with that when the car sits a long time. Could it not be a free movement of the caliper pistons? As for the recent restoration, well sometimes brakes are done too early in the process and sit for months and years before they are used. Just throwing in my 2 cents.

I just don't think the booster has anything to do with what I am reading and it might be the easy one to accuse.
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post #9 of 16 (permalink) Old 01-17-2017, 04:51 AM
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Ranz,

My opinion, too. However, it seems a little strange that this situation would appear after many, many years of replacing "plug and play" brake components. Maybe the law of averages just caught up with me since someone on the forum mentioned they had heard of this condition on an Alfetta. BTW, I'm using a .025 in. shim to achieve the necessary free play.

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Conedriver -
Zero (or too little) clearance between the pushrod and the master cylinder piston can do this. As things heat up in the engine bay during a drive, the expansion of the components is just enough to keep a tiny amount of pressure applied....enough to make the brakes drag. The problem disappears when things cool down, so it is hard to diagnose. Your solution of shimming the master cylinder away from the booster restores the necessary clearance. It only takes things to be a few thou out for there to be a problem. Or it could be as simple as the repro parts suppliers are skimping on the thickness of the gasket they supply. You should be able to detect minute movement in the pedal before the pushrod contacts the cylinder piston.


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George Schweikle

1976 Spider (Dedicated Autocrosser, "SPICA, No Carbs")
1991 Spider Veloce (Retirement cruiser)
Scuderia Non Originale
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post #10 of 16 (permalink) Old 01-24-2017, 11:47 AM
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I've had boosters stick, the separate inline type like you have, not the integrated one like on hanging pedal cars. On my last dual-circuit Duetto, one circuit was binding. Removed the vacuum hose, plugged it, voila, no more binding. Drove home, rebuilt booster, all good. Never so much as touched the MC.

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post #11 of 16 (permalink) Old 01-26-2017, 12:00 AM
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Quote:
Originally Posted by gdimassa View Post
Here you can find an explanation how the booster works:

http://www.agcoauto.com/content/news/p2_articleid/129

Maybe in your, some dirt or some rust lock it.
You can try to open it an clean. At the moment I have still never find a guide how to open ATE booster even if I think it is possible, as soon as I will have time I will open mine.
Finally, I decided to open my Benditalia booster...
To open it is not so difficult
-) with a screwdriver unlock the case, there are two lock points​


-) with an hammer and a punch rotate the case few degrees an it will open



-) In my booster there is a some brakes fluid, some years ago there was a master cylinder leak, and the diafram is broke


Now I am cleaning everything, and I am in contact with a shop that sells brake booster parts, the worst is their catalogue doesn't take into account the vehicle, but only the parts measures. I will let you know...

Last edited by gdimassa; 01-26-2017 at 07:53 AM.
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post #12 of 16 (permalink) Old 02-03-2017, 12:06 AM
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Found all the replacement, now I have to reassemble it, any advice to close it?
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post #13 of 16 (permalink) Old 02-03-2017, 11:00 PM
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Here are the replacement parts:



In the next days I will work on the reassembly...
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post #14 of 16 (permalink) Old 02-10-2017, 04:47 PM
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a bit late on this, but I had a similar problem with a booster not releasing, traced it to the vacuum line being kinked. I had used a pieces of straight tubing, but needed a 90 degree bend. once I got the correct hose from CL, the problem went away.

Stan Swanson, Eerie Erie, Colorado, '67 GTV (daily driver), '71 GTV (Kyle's), '91 164 (snow car), '56 Lotus 11(gone to Oz), '59 Cadillac M+M Hearse, '74 MGB
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post #15 of 16 (permalink) Old 02-11-2017, 06:30 AM
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Sounds like the non-return valve in the servo isn't releasing the vacuum after you've lifted off the brake pedal. The other thing that can happen is the rubber elbow on the underside of the servo goes soft (being above the exhaust manifold) and collapses - it allows a vacuum to be pulled but then holds it. Easy to check that one by removing the rubber elbow when the brakes are locked on & seeing if the brakes then free themselves. Most likely the NR valve though. And yes, Bonaldi/ Benditalia/ Bendix are interchangeable.

Ian

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