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Model 20 Strength |
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jpnjim
AMC Addicted Joined: Nov/25/2007 Location: New England Status: Offline Points: 2752 |
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Hummers run Model 20's with 2.73's and 37's
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71 P-code 4spd Javelin/AMX
some Jeeps and some Fords |
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tufcj
Supporter of TheAMCForum Supporter of TheAMCForum Joined: Jul/10/2007 Location: Watkins, CO Status: Offline Points: 4097 |
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BUT.... a Hummer has a portal axle that gears down at the hub. It has a final drive somewhere somewhere around 4:1. Bob tufcj |
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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 |
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jpnjim
AMC Addicted Joined: Nov/25/2007 Location: New England Status: Offline Points: 2752 |
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That's what all the winkie faces were for Back to your original post, I'm surprised you went through all the driveshaft U-joints In Cherokees and Comanches the little 1310 would survive no matter how stupid I got. Eventually I went 1410 when the 5:1 T-case went in, but I wonder if the greater joint angle in a CJ was what was killing your stock joints.
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71 P-code 4spd Javelin/AMX
some Jeeps and some Fords |
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one bad rambler
AMC Addicted Joined: Jan/09/2008 Location: On The Island Status: Offline Points: 2007 |
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This is almost like the 998 trans vas 727 question....if you take away all the weaknesses like you did you will be just fine..Gary with the 68 American wagon ran a model 20 for years with out an issue until he switched to a different type of slick and got violent tire shake causing damage to the ring and pinion...
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68 AMX 390 4 Speed,68 American,64 American 2 Door Wagon Altered Wheelbase,78 Concord Build 360,727,8.8
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79redspiritgt
AMC Apprentice Joined: Mar/12/2015 Location: dayton texas Status: Offline Points: 49 |
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are you spraying that 550hp?
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PROSTOCKTOM
Supporter of TheAMCForum Joined: Jun/20/2010 Location: Indiana Status: Offline Points: 2458 |
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Comparing a Model 20 to a 9" Ford and saying, The Model 20 has a 8-7/8" ring gear compared to the 9", so it will be plenty strong is a bad comparison of overall strength. You only have to look at the physical thickness of the ring gear and of the pinion diameter to see which one is superior. Then look at the pinion bearings. The 9" has 3 bearings instead of 2 on the Model 20. Now the concerning part I read from the original posters thread is the use of a Detroit Locker with 550 HP on a dragstrip. A Detroit Locker is not a full spool and it will at times not distribute power equally to both tires. I have a friend that took out a Christmas tree at the starting line running a Detroit Locker and ended up parked in the side of the car in the other lane. If you really care about your car put a spool in it and leave the Detroit Locker for the rock crawling guys. The dragstrip is not the place to find out what unequal power to the tires is all about.
Tom
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jpnjim
AMC Addicted Joined: Nov/25/2007 Location: New England Status: Offline Points: 2752 |
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I agree about the strength of a 9" vs our 8.875" axles, there's no comparison, the 9" starts out stronger, and there's a much (much) higher ceiling when you figure in all the aftermarket support. My only disagreement would be the 9" uses a smaller 1.313" pinion shaft than the M20 (^the gear head of a 9 is MUCH bigger tho and probably what you were referring to), either way, the 9's 3rd "pocket" bearing makes all the difference in the world, and adds a ton of strength and support (when you have a factory "N" case, or better anyway). Another of the 9"s strengths is even the weaker style factory sheetmetal housings can be easily reinfoced, big bearing 9" truck housings are pretty strong right off the bat, and aftermarket plate housings can be found everywhere. By comparison M20 tubes and center sections are pretty weak, and more difficult to reinforce. Jeep Truck housings are supposed to be stronger to start with, but I've never gotten into one of them to know that for sure. Even if the truck housings are thicker castings than the passenger car & CJ versions (not sure about that) and if the axle tubes are beefier (pretty sure this is true), you still have the same 8 bolt ring gear where everything else in this strength range has 10 or 12 bolts holding the gear. The 2.25" pinion offset of the 9" also makes it stronger by design. I don't know where the crossover point is for dropping an M20 for a 9" (or better), depends on so many things like weight, traction, transmission, traction, driving style, but people will know when they've reached the point of more money not fixing the M20. Good point on the Detroit Locker going peg-leg on you at the track That would be bad. I daily drove a Jeep MJ with a spool for a year or two, it's not as bad as it sounds, but in a Hot Rod I bet I would have gotten a few "Harsh Noise" tickets for squealing tires around some corners no mater how slow I went (concrete road surfaces were the worst )
Edited by jpnjim - Nov/04/2018 at 10:21am |
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71 P-code 4spd Javelin/AMX
some Jeeps and some Fords |
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