Moparts Tech Archive

Brake System

A body small brakes

drum from a 73 A body and be able to use it that way? Also, I assume I can still use my factory backing plates if I don't go to big brakes, but am not sure. Glad you guys around here have knowledge.
Moser told me most people go with b body brakes because of lack of drums available, but that can't be the case, there are too many big bolt pattern A bodies still around. It must be just for more braking power, but my 340 Demon has great braking, and I would rather not upgrade to big brakes UNLESS it will save a lot of money in the long run.
I am just assuming that the drums will work from the big bolt A body such as the 73 Dart, etc. Sorry for all the questions, Sometimes ladies over analyze this stuff trying to understand it. Basically, if I can use my brakes and backing plates with the new big bolt axles and just buy new drums I would rather do it that way. Thanks for all the help, I just want to make sure I order the right axles and everything works right.

Thanks for the reply, I will try to clarify. The car is a 72 Demon 340 with factory 10 inch brakes and 8 3/4. It is factory small bolt pattern, but I am ordering the large bolt axles from Moser. They told me it was better to change the brakes to B Body *backing plates and drums* but if I don't have to, I really don't want to. They made it sound like I would have a hard time finding a drum to fit if I didnt go to the B Body brakes, and I just thought that a drum from a large bolt pattern A body should fit. I wasnt sure though, thus the post. Also, i wanted to make sure I could use my existing backing plates with the new axles. Hope this clarifies things

Does the rear end have to be 8 3/4 on the donor car?
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Schultz
New Member
Posts: 99
From: mounds view,mn
Registered: Oct 2001
posted 07-14-2002 01:06 AM

Do you have factory 9in or 10in drum brakes? I don't really follow the question as it's posed. I have a 67 dart. It originally had 5x4in bolt pattern 7 1/4 rear with 9in drums.(which I blew up)
The replacement rearend is a 8 3/4 rear out of a B-body and it has 10x2 1/2in drums. I had the housing narrowed and then called Moser, gave them the dimensions, and told them I wanted the 5x4 1/2 (bigger)bolt pattern. I also upgraded from 7/16? to 1/2 in wheel studs. When I bought drums(from Checker Auto)I just said I wanted 10x2 1/2 units. I then got a blank stare, so I had to make up a 68-72 B-body that could have possibly have had an 8 3/4 rear with 10x2 1/2 brakes. I believe the drums cost me $30.00 apiece. I do not beleive that the drums are make specific. I believe a 10x 2 1/2 (for 1/2 in studs)drum is the same for all.(check to make sure they look the same as I had two different drums that had identical part numbers. They had slightly different design, both would work,but I wanted a matched set)
I hope this helps? There was also 11x2 1/2 brakes that I beleive were offered on B-bodies.
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DoctorDiff
Moparts Member
Posts: 380
From: Polson, MT
Registered: Jan 2002
posted 07-14-2002 12:54 PM

Any standard 4.5" bolt circle drum and backing plate will work. This includes A body, B body, C body, E body, F body, Van, and D l00 pickup.

No, any modern Mopar rearend with a 4.5" bolt circle will have good donar brakes.
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GregZ
Moparts Member
Posts: 3747
From: Southold,NY
Registered: Nov 1999
posted 07-14-2002 04:35 PM

I may have missed it, but i did not see anyone explain why you cannot use the 4.5" A body DRUM ONLY on the conversion axles . If you tell Moser you are using the small bolt brakes, you will get axles with a SMALL register for the drum. This is what centers the drum. The big bolt pattern drums have a large register. They can make whatever you want, but you need to tell them exactly what parts you are using. The larger brakes also make the rear end width slightly wider.

If you use small bolt pattern brake hardware, you need to use the small bolt pattern drums . I re-drilled the factory small bolt pattern drums when i switched to Moser axles. You can send your drums to them, and have them drill them. It's not too expensive.
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DoctorDiff
Moparts Member
Posts: 380
From: Polson, MT
Registered: Jan 2002
posted 07-14-2002 08:47 PM

The reasons for changing to the 4.5" bolt circle are usually:
1. To run commonly available wheels.
2. To run commonly available brake components.
3. To obtain the correct lug stud, and register size for the 4.5" bolt circle wheels.
Due to the oddball brake offset of the early A-body axles, there are no 4.5" bolt circle drums that will mate properly with the afforementioned early backing plates.

If you are trying to save money on the bolt pattern conversion, and you want to retain your old brake hardware, you could have your original axle flanges plug welded and the bolt pattern changed. I've done this several times for customer's cars. If you use 1/2" Ford studs, with a small knurl, there is ample material in the stock axle flange for the bolt pattern conversion
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Duster Don
New Member
Posts: 3
From: New Philadelphia Ohio USA
Registered: Jun 2002
posted 07-15-2002 08:24 AM

I did this very thing on my Duster. i bought new drums at Auto Zone for $35.00 ea. The back of the drums are notched for the backing plate. My brakes were 10x2 the drums were for 10x2.5 I took the drums to a machine shop and had them cut the brake shoe surface down 3/8 inch then I had to grind the edge of the backing plate down so the drum did not drag on the backing plate about 1/8 inch all the way around. It works great. The machine shop charged me $20.00 each to cut the drums down. I hope I made this clear for you. If you have any questions email me and I will try to explain it better.
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valiant dave
New Member
Posts: 49
From:
Registered: Mar 2002
posted 07-15-2002 10:21 AM

I went the cheapy route first and had my axles and drums redrilled problems I seen are
the flang is to small and the center register
is to small also puts all the stress an the wheel studs and the studs are pretty close to the edge of the flange I got to feel it was just to dangerous to chance my life or the cars life if one failed so I put b-body brakes on and ordered the Moser 4.5 axles
axles were 299.95 shipped to my door and the brake parts came from a junkyard for 50 bucks
and new shoes and all the hardware was another 30 bucks
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rhinodart
Moparts Member
Posts: 138
From: Round Lake Beach, IL 60073
Registered: Nov 1999
posted 07-15-2002 12:13 PM

I alway use the 11" brakes. I figured that more surface area the better stopping power, although they do weigh quite a bit.
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Mark Nixon
Moparts Member
Posts: 4305
From: Just this side of reality, South 340 miles....In NEBRASKA!!
Registered: Jul 2000
posted 07-15-2002 02:43 PM

One basic difference that seems to be overlooked here:
The A body 8 3/4 SMALL BOLT axles are @ 3/8" shorter from the BEARING out as compared to the LARGE BOLT conversion axles.
This affects not only the width of the brake, but where the brake shoes track on the drums.
This means that there is NO large bolt drum that will work on the narrow 10" A body backing plates with the big bolt axles!!

Your simplest solution is to use ANY large bolt pattern backing plates AND drums, be they 11" or 10", 8 1/4, 9 1/4 or 8 3/4 non-A body.
Your stock E-brake cables will work with whatever backing plate/drum combo you choose.

EDIT!!
After reading your ORIGINAL question over more carefully, there IS an alternative for drums IF you have the axles MADE for the original A body backing plates.
That ONE alternative is to use a '66-'70 B body drum from a Slant 6 Car with a 7 1/4 rear end.
This is the ONLY 10" drum with a 4 1/2" bolt circle and the narrow (1 1/2") shoe width!!
END

Mark.
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