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Is There A Way to Tell What Brakes A Car Came With

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Scrappy View Drop Down
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    Posted: Jun/21/2021 at 4:25pm
Y'all,

Apologies for the lack of  "?" in the title -- I hit the character limit. Tongue

So, I am back to square one on finding a new hub for my '79 Spirit that came with a 304, 4-speed, and AMC 20 rear end.  The reason I am asking in this subforum instead of the Transmission & Drivetrain subforum is that according to one supplier, the original brakes are supposedly the key to getting the right hub.  The car has a disc conversion, the original brakes are nowhere to be found in the remaining parts stash/pile, and the person who did the conversion is deceased (and thus I cannot ask him).  So, is there a definitive way to decode what rear brakes this car had originally, so I can determine what hubs it's supposed to have?

The aforementioned supplier says "you probably do not have the 2-1/2 brakes," so the 10"x2-1/2" assembly probably won't work, they don't have any 10"x1-3/4" assemblies, and I haven't heard back on whether the 9"x2" assemblies will work. 

In case it isn't clear, I don't directly care what the brake size was -- I am in search of that info so that I can find the proper hub.

Thanks,
Shawn

EDIT TO CLARIFY:  I am not asking whether this car originally had drums or discs -- I know it had drums and that no AMCs came with rear discs from the factory.  The point of this discussion is to determine which drums it came with.


Edited by Scrappy - Jun/22/2021 at 11:02am
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Post Options Post Options   Thanks (0) Thanks(0)   Quote billd Quote  Post ReplyReply Direct Link To This Post Posted: Jun/21/2021 at 4:37pm
You actually found someone with NEW hubs???????
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Scrappy Quote  Post ReplyReply Direct Link To This Post Posted: Jun/21/2021 at 4:47pm
Originally posted by billd billd wrote:

You actually found someone with NEW hubs???????

I wanted to ensure there was no question as to what I would be getting when I ordered the drum/hub assemblies, so I asked this:

"Are these NOS or new parts, or are they used?"

The answer was:

"These would be NOS parts. Only AMC supplied hub and drum assemblies."




Edited by Scrappy - Jun/21/2021 at 4:49pm
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Post Options Post Options   Thanks (0) Thanks(0)   Quote tomj Quote  Post ReplyReply Direct Link To This Post Posted: Jun/22/2021 at 12:20am
Wow.

Well it will be easy to tell -- new hubs will be smooth inside. OR SO I HEAR -- not having ever seen a new hub, but that's what the TSM says -- first installation cuts the splines in the hub, the axle being harder than the hub.

Brakes vs hub: I am skeptical. No AMC came with rear disc brakes, they were all drum brakes in the rear. There were a couple different size rear brakes, 9" or 10". As far as I know the hubs are the same. The hub depends on the axle and the axle depends on big (AMC20) or small (AMC15) axle assembly.

I wouldn't be surprised if there are different AMC *part numbers* for a hub with the two 1/4-20-tapped holes for the drum retainer, or without, or other we-care-a-lot-less-about-such-trivia-in-2021 details.

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Post Options Post Options   Thanks (0) Thanks(0)   Quote 1948kaiser Quote  Post ReplyReply Direct Link To This Post Posted: Jun/22/2021 at 6:13am
the new hubs are smooth inside as i put a set on the gremlin. had to use a breaker bar and pipe to get them on and cut. the v8 and 6 cyc brakes are installed different on the rears. how i know is did the right side and turned to the page for 6cyc and after installiing found i had the wrong page in the tsm so had to take it apart and redo it as the v8.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Buzzman72 Quote  Post ReplyReply Direct Link To This Post Posted: Jun/22/2021 at 8:00am
I don't know what brakes were on the '79 304 Spirit.

My '77 304 Hornet AMX had the 10" x 2-1/2" rear drum brakes. [Oddly enough, more square inches of brake for the lowest HP 304 AMC ever built.]
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Post Options Post Options   Thanks (0) Thanks(0)   Quote billd Quote  Post ReplyReply Direct Link To This Post Posted: Jun/22/2021 at 9:02am
Originally posted by tomj tomj wrote:

Wow.

Well it will be easy to tell -- new hubs will be smooth inside. OR SO I HEAR -- not having ever seen a new hub, but that's what the TSM says -- first installation cuts the splines in the hub, the axle being harder than the hub.

Brakes vs hub: I am skeptical. No AMC came with rear disc brakes, they were all drum brakes in the rear. There were a couple different size rear brakes, 9" or 10". As far as I know the hubs are the same. The hub depends on the axle and the axle depends on big (AMC20) or small (AMC15) axle assembly.

I wouldn't be surprised if there are different AMC *part numbers* for a hub with the two 1/4-20-tapped holes for the drum retainer, or without, or other we-care-a-lot-less-about-such-trivia-in-2021 details.


No, check the later parts books - hubs are indeed different. The hub part number is based on the brake size right in the AMC parts books.
Nothing to do with the retainer bolts. It's hub offset based on brake size. 
Found that out when looking for Eagle rear axle parts years ago. Since the larger brakes require a larger and even deeper drum, they changed the hub to move the drum farther away from the backing plate. It's the only way to get wider drums on for larger brakes since the axles themselves are the same length and the axle tube and backing plates are the same - you must move the drum out for larger brakes - you do that with a different hub. 
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Post Options Post Options   Thanks (0) Thanks(0)   Quote billd Quote  Post ReplyReply Direct Link To This Post Posted: Jun/22/2021 at 9:09am
Originally posted by 1948kaiser 1948kaiser wrote:

the new hubs are smooth inside as i put a set on the gremlin. had to use a breaker bar and pipe to get them on and cut. the v8 and 6 cyc brakes are installed different on the rears. how i know is did the right side and turned to the page for 6cyc and after installiing found i had the wrong page in the tsm so had to take it apart and redo it as the v8.


There are specs for axle depth in the hub. You use whatever force is needed to force the hub onto the axle until you reach the depth spec. using a greased washer and the axle nut. Then you remove the nut and lubricated washer, wipe away the grease, and reinstall the correct washer and nut using the proper torque. It takes a lot more torque to set a new hub onto the axle the correct depth than the final spec. 

I always use the same procedure for putting used hubs back on as I've found otherwise that 250 pound/feet of torque may not set it back to the depth spec. If it's supposed to be on the axle to a depth of xxx I put it back on to that depth. And in 45 years of doing dozens of AMC axles, I've never lost one. 

I know that procedure is for new hubs on axles - but what if you put the hub back on and it's not on as deep as it was originally? The splines are not as engaged as they once were, the same tension isn't there. That torque spec is to hold, not to push it on to the correct depth, it's to hold it there. 
In the 70s we used to do a whole lot of axle seal and bearing work and routine maintenance on cars with high mileage, etc. every month it seemed we had a Rambler of some sort come in for axle service (former Rambler dealership so most of our customers had AMCs)
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Mopar_guy Quote  Post ReplyReply Direct Link To This Post Posted: Jun/22/2021 at 10:14am
Originally posted by billd billd wrote:

No, check the later parts books - hubs are indeed different. The hub part number is based on the brake size right in the AMC parts books.
Nothing to do with the retainer bolts. It's hub offset based on brake size. 
Found that out when looking for Eagle rear axle parts years ago. Since the larger brakes require a larger and even deeper drum, they changed the hub to move the drum farther away from the backing plate. It's the only way to get wider drums on for larger brakes since the axles themselves are the same length and the axle tube and backing plates are the same - you must move the drum out for larger brakes - you do that with a different hub. 
That's interesting. I wouldn't of thought they would do that.

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Post Options Post Options   Thanks (0) Thanks(0)   Quote billd Quote  Post ReplyReply Direct Link To This Post Posted: Jun/22/2021 at 10:24am
Originally posted by Mopar_guy Mopar_guy wrote:

Originally posted by billd billd wrote:

No, check the later parts books - hubs are indeed different. The hub part number is based on the brake size right in the AMC parts books.
Nothing to do with the retainer bolts. It's hub offset based on brake size. 
Found that out when looking for Eagle rear axle parts years ago. Since the larger brakes require a larger and even deeper drum, they changed the hub to move the drum farther away from the backing plate. It's the only way to get wider drums on for larger brakes since the axles themselves are the same length and the axle tube and backing plates are the same - you must move the drum out for larger brakes - you do that with a different hub. 
That's interesting. I wouldn't of thought they would do that.


Imagine a brake drum that has to be 1/2" wider for car A than car B due to the larger brakes.
They use the same axle, the same axle tube, they have two choices - offset of the backing plate or offset the hub for the different brakes. 

I was looking for different parts for my SX4 and thought oh, this will be simple, it's the 15 and there's a hub for sale on eBay that's for a 15, I'll check the part number - then I looked in the parts book and crap, the hub for sale on eBay is for the smaller brakes, won't work. 
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