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AMC 20 axle replacement - length

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Post Options Post Options   Thanks (1) Thanks(1)   Quote Trader Quote  Post ReplyReply Direct Link To This Post Posted: Mar/14/2019 at 3:58pm
Seems like an ongoing issue.
Has anyone tried taking the hub to a machine shop and have them bore out the taper, press in a new piece of similar cast and machine a new taper and key way?
A good press fit of 0.002" to 0.004" (guess) should never let go. Can look that up (or calculate) in the Machinery's Handbook for the press fit depending on bore, material and torque.
Although solid axles may be cheaper!
   
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Post Options Post Options   Thanks (0) Thanks(0)   Quote SentencedToBurn Quote  Post ReplyReply Direct Link To This Post Posted: Mar/19/2019 at 1:43pm
Originally posted by farna farna wrote:

Well, it doesn't work well to put a used hub on a different axle. The hubs are made of a bit softer material than the hardened axle. The fine splines in the axles embed into the hub as the axle nut it torqued, mating that axle to that hub. All the keyway does is line the two up so if you take the hub off to service the seal or bearing you put it back on exactly as it came off (prior to 1957 AMC/Nash told you to mark the unkeyed hub and axle before removing). A used hub will have splines from the previous axle that may not line up well with the new. The new splines cut into the hub over the old, and that usually weakens the hub material, making it easier to spin a hub even when properly torqued. It may cause the hub to slide a bit further back on the axle, which causes interference between the brake drum and backing plate/shoes. So you can't clean up the inside of an old hub and use on a different axle either.

For a stock care mildly driven (just a cruiser) you might get by with it though. Some have, most don't have so much luck, but then most I've heard of that try and fail are horsing around with their cars a bit, that's how they spun a hub in the first place! AMC didn't specify a re-torque interval for the axle nuts because the cars weren't intended to last much more than 10 years/100K miles. 40 years later it's probably a good idea to re-torque the axles every 10-20 years, regardless of mileage.

Hey sorry for late reply mate, we had a bit of stuff going on here.
I didn't realise that about the hubs, will keep that in mind.

Will get the old hub first, and will see if the splines match i.e. the number etc and the condition of them. And if any doubt I'm thinking of just replacing both with solid axles and if the bolt pattern doesnt match then I'll just chuck different wheels on the back and be done with it. Except then I gotta sort the brakes too, so will see if this old hub will be ok for now.


Edited by SentencedToBurn - Mar/19/2019 at 1:52pm
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Post Options Post Options   Thanks (0) Thanks(0)   Quote SentencedToBurn Quote  Post ReplyReply Direct Link To This Post Posted: Mar/19/2019 at 1:54pm
Originally posted by Trader Trader wrote:

Seems like an ongoing issue.
Has anyone tried taking the hub to a machine shop and have them bore out the taper, press in a new piece of similar cast and machine a new taper and key way?
A good press fit of 0.002" to 0.004" (guess) should never let go. Can look that up (or calculate) in the Machinery's Handbook for the press fit depending on bore, material and torque.
Although solid axles may be cheaper!
   

That would be a great option but as you say sounds like it's a bit of work, solid axles might end up being cheaper. Except in my case where then I'd need to change the brakes too since i'm running 5x4.5 bolt pattern and all replacements seem to be either 5x5 or 5x5.5 which means i'd need to change brakes too. 
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Post Options Post Options   Thanks (1) Thanks(1)   Quote farna Quote  Post ReplyReply Direct Link To This Post Posted: Mar/20/2019 at 5:52am
When you put the used hub on torque it to 250 foot lbs then measure the axle stick-out from the outer edge of the hub. Should be 1.30" on the AMC 20 (1.17" on AMC 15). This is from the 74 TSM.A slight bit more should work, you will have to check for brake shoe and drum/backing plate interference. There could be hub/seal interference, but I do know several people have re-used spun hubs over the years, so I don't think that is an issue.

There are ways around the issues. I know one guy who cut the backing plate and made it a little deeper. A good bit of tricky welding (has to be even all the way around), but he was a good welder and it worked. IIRC he said it had to be around 1/8" deeper to work with the spun hub.  He reused the spun hub after cleaning the axle splines, not a different hub. Don't recall if someone split a second backing plate and mounted it behind the axle flange or that was just discussed (you'd need to cut the center out of one backing plate to hold the axle and seal).

All that is transparent once installed, and cheap if you can do it. It also works fine as long as the hub is torqued properly. The end of the axle sticks out that much further, and it could interfere with a hubcap, but I don't think it would. I recall someone talking about grinding the edge of the drum or backing plate. Grinding the drum could cause balance issues, and the brake shoes may contact the inside of the drum doing either of those. Might be plenty room inside for another 1/8" or so back though...


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Post Options Post Options   Thanks (0) Thanks(0)   Quote Steve_P Quote  Post ReplyReply Direct Link To This Post Posted: Mar/20/2019 at 3:28pm
The factory had a shim for this; it went on the hub and spaced the drum out.  It is similar to the 65-70 front disc Magnum wheel shim but IIRC its thinner, maybe .06 thk for the rear.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote farna Quote  Post ReplyReply Direct Link To This Post Posted: Mar/21/2019 at 5:09am
Didn't know that!! Why I didn't think of just shimming the drum I have no idea... sometimes the simple and obvious eludes people... it HAS to be more complicated than that, doesn't it? I've never even heard of anyone using a (pretty obvious, really!) shim, just the more dramatic solutions mentioned. 0.06" would be about right -- about 1/8"...
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