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model 20 answers |
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1970390amx
AMC Addicted Joined: Jul/11/2008 Location: colorado Status: Offline Points: 3314 |
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1970 390 4speed Bittersweet shadow mask AMX
1970 Amx missing most everything, or in a box |
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WARBED
Supporter of TheAMCForum Joined: Feb/12/2011 Location: Edinburg TX Status: Offline Points: 1688 |
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hey. Glad I found this post. I've a done many a AMC 20 in cars and Jeeps and am about to do one in a Gremlin with 401. So I though since its been about 5 years since i did a 69 AMX diff I thought it would be a good idea to refresh my memory so like most I reached out to You Tube, And a fright I got. There was just one guy (AMC 20 Tear Down & Rebuild | Drum Brake How To | Jeep CJ5 Project, Pt9) That really sortof new what he was doing and the only one that didn't put the axle bearings and race in backwards. Yes I watched 5 guys do it wrong and installed the outer race first then the bearing. Tried to explain to them that the AMC 20 is a semi floating design but it fell on deaf ears. Just bought a 70 AMX that I will also be going through soon.
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59 American 2dr S/W. 70 390 AMX. 70 232 javelin. Kelvinator fridge ice cold beer storage.
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WARBED
Supporter of TheAMCForum Joined: Feb/12/2011 Location: Edinburg TX Status: Offline Points: 1688 |
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My thrust block was a bit different. just 2 halves but no center pin. mine came out once with an axle but a long piece of 1/2 pvc pipe and grease just slid it back in since we were just replacing axle seals and didn't want o disassemble diff.
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59 American 2dr S/W. 70 390 AMX. 70 232 javelin. Kelvinator fridge ice cold beer storage.
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PHAT69AMX
AMC Addicted Joined: Jul/07/2007 Location: West Virginia Status: Offline Points: 5926 |
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I think it would be really helpful to know, and feel it has never been clearly figured out, explained, & documented, just WHY the 1970 ONLY Passenger Side AXLE is SHORTER than 1968 & 1969 !
There is some still even yet clearly figured out REASON WHY 1-Piece Axle companies WANT THE EXISTING STOCK AXLES SENT TO THEM in order to make & sell you new 1-piece axles... I would really like to know SPECIFICALLY why ONLY the passenger side Axle is different for 1970 ONLY. AND why many say the 1970 Housing is narrower... when the SAE Papers show SAME REAR TRACK WIDTH of 57.00" for all 3 years of AMX, 1968, 1969, & 1970 ! AND the Parts Book shows A DIFFERENT HOUSING PART # for 1970 only ! ???? BUT the same 2-Piece WLD Twin-Grip "Posi" Case / Carrier for ALL 3 YEARS ! Recent Parts Book "digging" appears to suggest, MAYBE... There was a SIDE GEAR CHANGE, SIDE GEAR "RING" CHANGE, CLUTCH PACK CHANGE... 1968-69, "this" Side Gear. this "Side Gear Ring", these Clutches of this thickness, these axles. 1970, "this" Side Gear. -NO- "Side Gear Ring", these Clutches of this thickness, these Axles...
Man it's a bummer not to have a parts stash anymore of known vintage to do accurate "discovery" on. |
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davec1957
AMC Nut Joined: Jul/09/2010 Location: Massachusetts Status: Offline Points: 385 |
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My '70 AMX has a stock 3.54 twin-grip rear differential. In my old age, I'd really like to drive the AMX at highway speeds at fewer than 3200 RPM, so I bought a used AMC model 20 3.15 ring and pinion set, with the intention of replacing the 3.54 gears with the 3.15 gears (the 3.15 seems like a reasonable compromise between off-the-line performance and highway cruising). Two questions: 1) Is this a reasonable thing to consider having done, or is there a better way of achieving the desired result? My guess is I should have bought an entire model 20 axle assembly with a 3.15 diff instead of incorrectly thinking the ring and pinion gears could "easily" be swapped out. 2) Can such a swap be performed on my existing 3.54 axle without losing the twin-grip capability?
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1970 AMX Bayshore Blue 390 4-spd GoPac
1970 AMX Commodore Blue 390 4-spd GoPac |
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mbwicz
Supporter of TheAMCForum Joined: Feb/20/2019 Location: Buffalo, NY Status: Offline Points: 2001 |
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Dave, the gears can be swapped from your axle while maintaining the twin grip.
The other reasonable option for lowering the cruise RPM would be to swap to an overdrive transmission. |
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1970 AMX, one step forward, one step back. Both steps cost time and money.
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SC397
AMC Addicted Joined: Apr/30/2009 Location: Michigan Status: Offline Points: 5480 |
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My 1970 AMX is original and has the same width axle as my 1968/1969 AMX's. I just went through and measured 7 rear ends that I have and the only difference in all of these is the passenger side axle tube. Some are at 18" inside axle flange to center housing and some are at 18 1/2"All of the axle tubes on the driver's side measure at 17 5/8" - So all the axles on the driver's side are the same. The spring perch cc are all the same at 43 3/8"-43 1/2" All of these rear ends have the 18" tube on the passenger side 68 AMX - Original from my car. 69 AMX - Original from a scrapped AMX 70 AMX - I measured the one in my AMX that is original 71 Hornet - original in my car. All of these rear ends have the 18 1/2" tube on the passenger side 4.10 gear unit out of a Gremlin but unknown if original. It does have a later casting number on the center section 3212478 vs 3186891 on all of the rest. 3.54 gear unit out of I don't know what. 4.56 gear unit out of I don't know what.
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WARBED
Supporter of TheAMCForum Joined: Feb/12/2011 Location: Edinburg TX Status: Offline Points: 1688 |
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Moser and the rest want the original axles because AMC 20 is a semi floating design. it uses a thrust block in the carrier that the axle butts up against and shims to determine end play, so the axles have to be the exact length. Many install the axle bearing backwards defeating the thrust block's purpose. but they still use the tapered roller bearing design. You can't use a tapered bearing independently has to be used with another tapered roller bearing, hence the thrust block.
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59 American 2dr S/W. 70 390 AMX. 70 232 javelin. Kelvinator fridge ice cold beer storage.
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SC397
AMC Addicted Joined: Apr/30/2009 Location: Michigan Status: Offline Points: 5480 |
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I am going to put a copy of this here so that I can find it again. It shows what the 1966 Tweener AMC20 ring and pinon looks like compared to the later more common one.
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Buzzman72
AMC Addicted Joined: Sep/15/2009 Location: Southern IN Status: Online Points: 2726 |
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Rick, did anyone ever determine if this change would work for the torque-tube AMC 20s?
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Buzzman72...void where prohibited, your mileage may vary, objects in mirror may be closer than they appear, and alcohol may intensify any side effects.
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