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Another AMC 20 Question |
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fmahannah 
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Joined: Nov/20/2010 Location: Dahlonega, GA Status: Offline Points: 520 |
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 Topic: Another AMC 20 QuestionPosted: May/19/2018 at 11:46am |
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I finally have the rear out of my 74 Javelin and getting ready to convert to a factory twin grip and 3:54 gears. It is currently 3:15's and open diff. Please excuse my ignorance but this is my first attempt at rebuilding a rear end Once I cleaned the crud off of everything I can see some things that make me a little nervous. For one thing one of the welds that secure the axle tube seems to have been redone pretty recently with some weld spatter and even a piece of wire still attached. The other side looks old, rusty, and factory. Which makes me think they might have spun a tube but not sure how they did that with a 304 and 3:15 open diff? The second thing that bothers me is that when I spin either axle hub and watch the space between the hub and bearing retainer plate I can see the spacing change as if the axle or hub is bent. It is like this on both sides so I am wondering if at some point somebody separated the two piece axles and then put them back together but did not line up the pressed fit splines the way they were originally? And last but not least .... I know that if you spin one wheel and the other wheels spins opposite it is an open diff. But if I can also do the following and I am not sure if they would be considered normal? I was driving this car before I took it apart so I am hoping these things are OK? 1. Spin one hub or the other by hand, yoke where driveshaft attaches does not spin 2. Grab yoke and spin it and hub spins as expected 3. Hold either axle hub tight and can spin the other one with no resistance and the yoke does not spin 4. Hold the yoke tight and can spin either hub easily Any advice appreciated before I sink a ton of money into this drivetrain. Thanks!
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74 Javelin AKA Ghost
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304-dude
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Joined: Sep/29/2008 Location: Central Illinoi Status: Offline Points: 9082 |
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Posted: May/19/2018 at 12:43pm |
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A bit confused by what you expect on your rear end with a limited slip.
If your talking about open diff... any number of things can be done while turning one hub. A limited slip is easy. With the car blocked, and parking brake released jack one rear side up with the tranny out of gear or in neutral. Try to turn the wheel. Should be impossible. Over 200ft-lbs to turn a pré 72 rear. About 150ft-lbs for 72 on up rears. Edited by 304-dude - May/19/2018 at 12:46pm |
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71 Javelin SST body
390 69 crank, 70 block & heads NASCAR SB2 rods & pistons 78 Jeep TH400 w/ 2.76 Low 50/50 Ford-AMC Suspension 79 F150 rear & 8.8 axles Ford Racing 3.25 gears & 9" /w Detroit locker |
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jpnjim
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Joined: Nov/25/2007 Location: New England Status: Offline Points: 2752 |
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Posted: May/19/2018 at 1:19pm |
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There are pages you can google that will help you see if your housing is straight or bent.
A bent housing can be straightened, an otherwise straight housing could have been bent if the tube was welded to the housing improperly. As far as the axle ahafts spinning, or not spinning, the open diff and spider gears will all be replaced when you do the swap so what it's doing now shouldn't be the end of the world. But in a normal working open diff (or a worn out LSD): Holding the pinion while one shaft spins makes the other shaft spin in the opposite direction. Holding one shaft while spining the yoke makes the other axle shaft spin Holding one shaft while sponning the other shaft makes the yoke spin. at least 1 of the other 2 should rotate when a shaft or the yoke is spun by hand. Off topic, How are the 3.15's you removed? The 3.15's in my Javelin are questionable so I wouldn't mind a spare set if you were going to sell them. Thanks
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71 P-code 4spd Javelin/AMX
some Jeeps and some Fords |
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fmahannah
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Joined: Nov/20/2010 Location: Dahlonega, GA Status: Offline Points: 520 |
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Posted: May/19/2018 at 1:38pm |
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I have not pulled the guts out yet. Waiting to make sure the unit is worth it before I order the parts as they are $$$. Getting the twin grip from American Parts Depot and just that is $450. If the gears come out and look OK I would part with them
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74 Javelin AKA Ghost
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fmahannah
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Joined: Nov/20/2010 Location: Dahlonega, GA Status: Offline Points: 520 |
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Posted: May/19/2018 at 2:02pm |
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OK I just did the tests you listed below and it is working the way you said it should. Thanks! "Holding the pinion while one shaft spins makes the other shaft spin in the opposite direction. Holding one shaft while spinning the yoke makes the other axle shaft spin Holding one shaft while spinning the other shaft makes the yoke spin. at least 1 of the other 2 should rotate when a shaft or the yoke is spun by hand." Now I have to order a lot of parts LOL. Does anyone recommend a ring and pinion set from someone other than the Yukon Gear YG M20-354 that I am looking at?
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74 Javelin AKA Ghost
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fmahannah
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Joined: Nov/20/2010 Location: Dahlonega, GA Status: Offline Points: 520 |
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Posted: May/19/2018 at 2:06pm |
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Also replacing my rear leaf springs which are 5 leaf. Eaton's are really pricey ($500+) so I am looking at a set from McVeigh's Truck Springs or Stengal Bros. Am I risking bad steel by going with cheaper springs or has anyone bought from them and had issues? Thanks again ...
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74 Javelin AKA Ghost
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PHAT69AMX
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Joined: Jul/07/2007 Location: West Virginia Status: Offline Points: 5926 |
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Posted: May/19/2018 at 2:27pm |
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iirc a "stock" '74 Twin Grip is a "Cone" type Posi, which work but are not really "serviceable"...
Earlier Twin Grip Posi carriers were Clutch Type and serviceable... And the "most serious" Twin Grip Posi carrier is the Detroit Locker style. Mainly wanted to point out just for info, later Twin Grip carriers were "Cone Type" I think...
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fmahannah
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Joined: Nov/20/2010 Location: Dahlonega, GA Status: Offline Points: 520 |
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Posted: May/19/2018 at 2:30pm |
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74 Javelin AKA Ghost
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PHAT69AMX
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Posted: May/19/2018 at 2:49pm |
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Ok, no intention to say what should or should not be done, just info for an informed decision.
I've not dealt with them, but National DriveTrain shows quite a bit available for AMC 20. They show $160 for 3.54 Gear Set and $111 for a Master Rebuilt Kit with Timken Bearings. A saving grace for AMC Model 20 diffs is the Jeep market. |
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ADAM12MATADOR
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Joined: Dec/03/2011 Location: New City, N.Y. Status: Offline Points: 518 |
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Posted: May/19/2018 at 2:53pm |
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I happen to have a new pair of Eaton rear springs the i got for my 73 Gremmy. Went with a 4 link so i wont b using them. Let me know if your interested.
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