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AMC 20 axle replacement - length

Printed From: TheAMCForum.com
Category: The Garage
Forum Name: Transmission & Drivetrain
Forum Description: If it's between the engine and wheels, it goes here
URL: https://theamcforum.com/forum/forum_posts.asp?TID=98920
Printed Date: Mar/29/2024 at 4:13am
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Topic: AMC 20 axle replacement - length
Posted By: SentencedToBurn
Subject: AMC 20 axle replacement - length
Date Posted: Mar/10/2019 at 11:23pm
Hi everyone

I was about to order a replacement RH axle for my 66 classic, and realised that the length of mine is different to what is listed as standard:

https://www.morris4x4center.com/axle-shaft-kit-rear-amc-20-2-piece-29-25-passenger-side-8127071k.html

This axle is 29.25" and when I measure the axle I removed it comes to 31.14". I'm measuring end to end i.e. the overall length of the axle.

The number of splines is correct, it's at 29, however I'm not sure whats up with the length difference.

The other weird thing that may be related to this is that the outer oil seal (the 5 bolt hole one) doesnt actually fit mine. My outer oil seal is a 4 bolt hole. Pic: https://postimg.cc/ZW0DwfXR

However I'm pretty sure its an AMC20 diff since the diff housing has a 12 bolt cover. Not sure if its some kind of a weird variant of one of these diffs?

If anyone has come across this and knows maybe of a different type of axle that will fit me, or maybe I'm measuring it wrong - please let me know.



Replies:
Posted By: SentencedToBurn
Date Posted: Mar/11/2019 at 8:49pm
So I ended up finding an axle which is very close in length to mine at 31.5" instead of mine which is 31.14":
https://www.summitracing.com/int/parts/omx-1653030

Now the problem seems is that my bolt pattern is 5x4.5 and all the hubs that are sold with it are 5x5.5 e.g. there is a 31.5" axle with a hub but it's only a 5x5.5
https://www.summitracing.com/int/parts/omx-1653032




Posted By: tufcj
Date Posted: Mar/11/2019 at 8:55pm
There were many axle lengths used, depending on year and model.  The axle you're looking at is for a Jeep.  The 5x4.5" hubs are very difficult to find these days.

Your best bet may be cut to length one piece axles from DoctorDiff.

https://www.doctordiff.com/amc-1-piece-passenger-car-axle-pkg.html" rel="nofollow - https://www.doctordiff.com/amc-1-piece-passenger-car-axle-pkg.html

Bob
tufcj


-------------
69 AMX
74 Javelin AMX
67 Rogue

If you need a tool and don't buy it...
you'll eventually pay for it...
and not have it.
Henry Ford


Posted By: tomj
Date Posted: Mar/11/2019 at 10:53pm
can't hubs be re-drilled for the new pattern? would of course require good precision. pop out the 5.5 space lugs, drill between the open spaces.



-------------
1960 Rambler Super two-door wagon, OHV auto
1961 Roadster American, 195.6 OHV, T5
http://www.ramblerLore.com



Posted By: tufcj
Date Posted: Mar/12/2019 at 8:15am
Originally posted by tomj tomj wrote:

can't hubs be re-drilled for the new pattern? would of course require good precision. pop out the 5.5 space lugs, drill between the open spaces.

The flange that centers the brake drum is also larger.  You'd have to machine that off as I don't think it's large enough to just machine down.  I don't think you could machine the center hole in the drum large enough.  

Bob
tufcj


-------------
69 AMX
74 Javelin AMX
67 Rogue

If you need a tool and don't buy it...
you'll eventually pay for it...
and not have it.
Henry Ford


Posted By: SentencedToBurn
Date Posted: Mar/12/2019 at 1:28pm
Originally posted by tufcj tufcj wrote:

There were many axle lengths used, depending on year and model.  The axle you're looking at is for a Jeep.  The 5x4.5" hubs are very difficult to find these days.

Your best bet may be cut to length one piece axles from DoctorDiff.

https://www.doctordiff.com/amc-1-piece-passenger-car-axle-pkg. - https://www.doctordiff.com/amc-1-piece-passenger-car-axle-pkg.html

Bob
tufcj

Hey thanks for your reply, sounds like the "cut your axle to length" is probably the best option so far!

I have one guy here in NZ that has an old axle and hub, just waiting fo the measurements, with any luck I might be able to use that, otherwise that one piece sounds like a good option.

Reading through the instructions for the 1-piece axles, sounds like those parts are all that's needed, might be a good option, defintely sounds like the most reliable one.

Thanks Bob!


Posted By: SentencedToBurn
Date Posted: Mar/12/2019 at 1:31pm
Originally posted by tomj tomj wrote:

can't hubs be re-drilled for the new pattern? would of course require good precision. pop out the 5.5 space lugs, drill between the open spaces.


Hey yeah I had a thought about that initially but I have attempted that years ago with a different make and the centre hole for the drum didnt fit (back then I never measured it and found that out once all work was already done) so this was my concern. Sounds like Bob confirmed this is the case here too.

I'm thinking if the axle that I'm waiting to be measured isn't what I need then I'll probably go with the single piece conversion kit.


Posted By: farna
Date Posted: Mar/13/2019 at 6:14am
The AMC 20 doesn't have a fill plug in the rear cover, the plug is up in front near the pinion shaft. If you have a plug in the rear cover it's an AMC 15. The 66 Classic should have an AMC 20 though, as it would have come with a 232 six or a V08. Only cars with the 199 had the AMC 15, and I'm not positive the 66 big cars with 199 (only a few fleet models that I know of) would have had the 15, as no others would have used it. Seems like a waste of resources to make an AMC 15 just for a couple hundred cars (axle shafts and TT would be different, not much cost in changing axle tube lengths), and we know how AMC was with wasting resources!


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Frank Swygert


Posted By: SentencedToBurn
Date Posted: Mar/13/2019 at 6:20pm
Originally posted by farna farna wrote:

The AMC 20 doesn't have a fill plug in the rear cover, the plug is up in front near the pinion shaft. If you have a plug in the rear cover it's an AMC 15. The 66 Classic should have an AMC 20 though, as it would have come with a 232 six or a V08. Only cars with the 199 had the AMC 15, and I'm not positive the 66 big cars with 199 (only a few fleet models that I know of) would have had the 15, as no others would have used it. Seems like a waste of resources to make an AMC 15 just for a couple hundred cars (axle shafts and TT would be different, not much cost in changing axle tube lengths), and we know how AMC was with wasting resources!

Hey yup you're exactly right, its a 232 and it doesnt have a plug there. Just the few parts that I got before for AMC20 didnt fit so reason for my confusion.

It looks like I sorted a hub with my bolt pattern locally, the dude is shipping it up soon - its rusy as but i hope it'll clean up ok, and then I'll get one of the axles new. If that doesnt fit, then I'll follow the advise above and go with the cut-off single piece axles.


Posted By: farna
Date Posted: Mar/14/2019 at 4:53am
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.


-------------
Frank Swygert


Posted By: Trader
Date 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!
   


Posted By: SentencedToBurn
Date 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.


Posted By: SentencedToBurn
Date 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. 


Posted By: farna
Date 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...




-------------
Frank Swygert


Posted By: Steve_P
Date 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.


Posted By: farna
Date 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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Frank Swygert



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