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post #1 of (permalink) Old 11-13-2002, 09:43 PM Thread Starter
 
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Gm Dual Diaphram Brake booster ID?

I have been scrapping here lately for the GM dual diaphram brake booster but have questions on IDing one. I have seen two types of these boosters. The one on a '88 Caddy DeVille (like the article shows) was larger diameter and not so thick. The one on an '85 S10 Blazer was smaller in diameter but much thicker. Can anybody help with which one I need to do the conversion? It will be going in with an AMC 304 so clearance may be an issue on the larger diameter booster. Also, would taking the Master Cylinder be of any value. They want $25 more for the Master Cylinder. Just wondering if the conversion would be easier with the MC that is bolted onto the GM booster. I am considering four wheel discs so my stock CJ one will not work for that change I know, but what if I stay front discs, rear drum. Thanks.
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post #2 of (permalink) Old 11-14-2002, 09:47 AM
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Re: Gm Dual Diaphram Brake booster ID?

can't answer your question about the booster because I got one from a 85 suburbon. I kept the chevy master cylinder also. Seems to be just fine.
post #3 of (permalink) Old 11-14-2002, 10:45 AM
 
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Re: Gm Dual Diaphram Brake booster ID?

I used the 84 CJ7 m/c and it fit perfectly. The rod between it and the booster needed lengthening slightly. You can either cut a short piece of correct diameter rod and grind it down to length, or weld up a small amount on the end of the existing rod.

My dd booster came from a brake shop, so I don't know the exact origin, but was told that it came off an S10. It is much longer than stock (ie thicker). Definately no larger in diameter. Its close enought to things as it is with the motorcraft carb.

I'd be tempted to use the chevy master cylinder if you are having to replace it. That way the rod should be correct length.

Tim
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post #4 of (permalink) Old 11-14-2002, 01:11 PM
 
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Re: Gm Dual Diaphram Brake booster ID?

the booster and MC i got came from an Astro van. it was fairly easy to remove, but did not have the correct rod on it. i took it to a rebuilder who put the correct rod in it and rebuilt it. after the rebuild, they said they could have put a rod in that had a threaded end so it could be adjusted...i wish i knew that before.

i haven't finished the project, but my brakes never felt right. the pedal is very difficult to get started, but once it starts moving, the brakes work easily. i always thought it was a booster problem...until yesterday when i saw a big puddle of brake fluid under one of my rear tires. i'm hoping what i thought was a booster problem is really a wheel cylinder problem.

matt

oh, the cj lines went right into the astro MC without any adapters.

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post #5 of (permalink) Old 11-14-2002, 05:24 PM
 
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Re: Gm Dual Diaphram Brake booster ID?

Matt,

Couple of questions:

1) What year Astro-van, do you know?

2) What kind of rebuilder did this for you? If I was looking for one locally, what would I look for?

TIA
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post #6 of (permalink) Old 11-14-2002, 05:35 PM Thread Starter
 
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Re: Gm Dual Diaphram Brake booster ID?

I am really wondering if the Suburban one is the one smaller in diameter but fatter or the bigger diameter thinner. There are plenty of cars/trucks to pick from in the yards, just for the $40 and an hour of work, wanna be sure it is a dual diaphram. Thanks,
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post #7 of (permalink) Old 11-14-2002, 09:18 PM Thread Starter
 
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Re: Gm Dual Diaphram Brake booster ID?

Does yours look like this?
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File Type: jpg 945109-GM Booster.jpg (32.0 KB, 54 views)
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post #8 of (permalink) Old 11-15-2002, 09:53 AM
 
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Re: Gm Dual Diaphram Brake booster ID?

Yeah, mine looks like that. Kinda like a volleyball that was flattened on one end. That should be a dual diaphram booster. Made a huge difference for me. No problem apply sufficient pressure to lock em up anymore. Before the booster swap, it took a whole leg press to make em just start to squeal on concrete. Now it's foot only.
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post #9 of (permalink) Old 11-15-2002, 12:22 PM
 
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Re: Gm Dual Diaphram Brake booster ID?

blues:

1) not sure, but my dad's 86 astro booster and MC was identical

2)they were a booster rebuilder, i found them by calling around and looking in the yellow pages.



my booster is similar to the one in the pic, but my MC had ports on the other side just like the CJ's.

FYI, my grill support rod hits the side of the MC reservoir now, it needs bent a little.

matt
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post #10 of (permalink) Old 11-16-2002, 10:38 AM
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Re: Gm Dual Diaphram Brake booster ID?

I took my booster and master cylinder from an 86 Trans Am. It is the dual diaphragm booster just like the one in your pic. On my CJ I had to change the holes into slots in order to fit the booster bolt pattern but other than that it went right together. The T/A had 4 wheel discs, and I have the proportioning valve for that set up on the shelf.

I was running 4 wheel drums on my CJ, with no proportioning valve. With the booster hooked up the brakes would lock up with very little pedal travel and no effort. That set up required a VERY light foot on the brakes, I do not recommend it. I ended up disconnecting the booster vacuum. I am in the process of swapping in a 44 front with discs, and with that set up I will be running an adjustable proportioning valve. When I finish my 60 for the rear it will have discs and I will use the 4 wheel disc valve.
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