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AMC 20 axle replacement - length

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    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.


Edited by SentencedToBurn - Mar/10/2019 at 11:26pm
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Post Options Post Options   Thanks (0) Thanks(0)   Quote SentencedToBurn Quote  Post ReplyReply Direct Link To This Post 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


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Post Options Post Options   Thanks (1) Thanks(1)   Quote tufcj Quote  Post ReplyReply Direct Link To This Post 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.


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Post Options Post Options   Thanks (1) Thanks(1)   Quote tomj Quote  Post ReplyReply Direct Link To This Post 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.

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Post Options Post Options   Thanks (0) Thanks(0)   Quote tufcj Quote  Post ReplyReply Direct Link To This Post 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.  

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Post Options Post Options   Thanks (0) Thanks(0)   Quote SentencedToBurn Quote  Post ReplyReply Direct Link To This Post 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
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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!
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Post Options Post Options   Thanks (0) Thanks(0)   Quote SentencedToBurn Quote  Post ReplyReply Direct Link To This Post 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.
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Post Options Post Options   Thanks (1) Thanks(1)   Quote farna Quote  Post ReplyReply Direct Link To This Post 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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Post Options Post Options   Thanks (0) Thanks(0)   Quote SentencedToBurn Quote  Post ReplyReply Direct Link To This Post 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.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote farna Quote  Post ReplyReply Direct Link To This Post 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.
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