I've given up on the idea of an axle swap for my j10, and am sticking with the stock model 20, although it has the one piece axles and nodular pumkin, throwin' a Detroit and 4.88s in. Any opinions on strength?? The second is, the Dtroit says up to 4.56s, but the 4.88s are so new, it'll still work, right??:confused:

I personally hate model 20's. There weak and ive seen them break moser shafts with jeeps running 35" BFG's on a not so hard obstical. Plus if you painted one tan and stuck a nipple on the diff cover, the pumpkin would look like a tit :D Ok that has nothing to do with I know but the above info does... just my opinion though. :smokin:

I have not heard anything good about the 4.88 gears. something about a bad tooth design for the amc20. (This coming from a reputable R&P seller)

I would stick to the 4.56. While you have it apart, have the housing trussed.

The AMC20 is what I would call a misunderstood axle. That I am slowly watching popularity of it come back. at least the FSJ version of it. R&P is stronger than a D44, the axle shafts themselves are nearly as strong. the weakest point is the housing, which is easily fixable. Now I wouldn't run 44's on it, 38's would probably be pushing it.

When it comes down to it though, it's all in how you drive that decides how long your axle will survive. I have seen guys with the same size tires take the same line. the D60 snaps, the toy axle with birfs survives. it's all in the driver. :)

any other people hear about the 4.88s for amc20s??? I havent picked up the gears yet, so its not too late, but I am gonna start with a 35 and prob end up with at least a 36 maybe even a 38 when these 35s I have wear out, and Im gonna move them with a 258/t176 combo, need gears!!! I'm worried 4.56s wont be enough!!! Engine swap is out of the question, maybe a4.0 or mopar mpfi kit, but Im keepin the six!

I have a 91 4.0HO,T-18, and 4.56's in my CJ7 and I run 35" tires. The only time I feel that isn't slow enough is on the harder obstacles. Most of the trail is second or third gear. On the freeway the gears are too tall. I can only do about 60 to 65 mph. When I had the t-5 in it still freeways were not a problem. I am running a CJ 20 right now that I have trussed and I haven't had a single problem with it, other than the pinion nut loosening up. Locktite!! I am going to switch everything over to the waggy 20 that I have. As far as the motor, go 4.0. That's all I've got to say about that. :D

4.56 to 4.88..... I don't think there is so much of a different there that you would ever notice. IMHO

I would presonally stick to the 4.56, besides your D44 pinion is already gonna be small with 4.56. it's just gonna get smaller with 4.88. :) (though I haven't actually heard of anyone breaking even a 5.38 pinion on a D44)

yeah, I know I'm gonna be kinda high in the RPM range, I,ve just learned from experience that you overgear, so when the urge hits, (and mind you it hits often!), I can move to a taller tire, like a 36x12.50 swamper, even a 38, I just think the 38s would toast the Model 20, no matter how built, it would prob be time for a 60! I looked on teh charts and at 65 they say I would be at just under 3100 RPM at 65 with my t176(no OD sucks). I just want to make sure the 4.88s will hold up(not worried about the front, itll hold up) The brand is Yukon, and I called to see what brand they are re-boxxing for my gears, and they are US gear and Ohio gear respectively.

BIG J!! Here comes my .02 which is a lot of what yer already reading...

4:56s and not the 4:88s ... I have heard the same about the teeth issue. Either way I don't think the 4:88s are compatible with the 4:56version Detroit. I maybe wrong though!

twaldher is right awn!! The FSJ version of the AMC20 is much better than the CJ20 by far. A lot of people have passed over the FSJ version because they didn't know they were better than the CJ, and more importantly why. Too much mythology coming from a lot of heresay and limited # of individuals who more than likely had a bad experience, most likely related to their skills, or lack thereof. People like talk a lot of BS to save face! To them I give a hearty GET FAWKED!!:flipoff2:

Trussing your AMC would be a good way to get some added beef, just stay aware of your ground clearance. And remember your truss isn't Superman's Cape! :D

I have been running 36" tires on my Wide Tracks and haven't had one problem yet! But it was said before about it being about the driver's habits. Mario Andretti I am not, and not a Zues of the Sluice yet, but good enuff I guess.

Keeping your 6 is a personal choice. If you do upgrade to the 4.0/4.2 do some good research. Unfortunately I don't remember all of the techno chatter about which is better but I DO remember that one of them is prone to head issues. I also heard a lot about EFI issues but remember hearing a lot of good stuff about the Howell set-up. It may not be the best, but it was definitely better than the others so many were :mad3: about!

I am in no way qualified to say anything about the tranny you have or what would swap in. But I am sure there has to be something you can use to give you some better options and driveability. It might be auto or stick. So you may have an option if you are lucky. I bought an NV4500 out of a rollover cuz I thought, just not well enuff, that it would work really well with the super low first gear and a 27% 5th gear overdrive. It is an awesome tranny but I decided to go with a TH400/450 instead. Now I have an NV for a doorstop!:emb3:

You have a lot of different things you can do. It is just a matter of researching and then deciding which avenue you wanna take. Just take your time so you don't end up with a similar doorstop!:eek:

Best of luck with your Jeep. This is THE forum to go to for whatever you may need!!

Tigger4x :jeep:




Hey Osama! If you don't like the horns, Don't wave the BIG RED flag at the bull!! :nuke: :nuke: & kisses :barf: ... :usa:

Originally posted by tigger4x


twaldher is right awn!! The FSJ version of the AMC20 is much better than the CJ20 by far. A lot of people have passed over the FSJ version because they didn't know they were better than the CJ, and more importantly why. Too much mythology coming from a lot of heresay and limited # of individuals who more than likely had a bad experience, most likely related to their skills, or lack thereof. People like talk a lot of BS to save face! To them I give a hearty GET FAWKED!!:flipoff2:


careful, dont' talk up the waggie 20 too much... I still want to be able to pic up the entire axle drum to drum for $50 when it comes to getting spare axle shafts. :flipoff2:

:rolleyes:Ooops! Oh yeah, the 20, itsa piece a crap... yeah yeah, that's it... sure yeah! ;)

BTW, you gotta 60 layin' around:question: Trade ya my 20 + $50 and some :beer:S ?!? :laughing: :laughing:

Never mind... psychic Cleo just called ... she sed to expect a BIG 'OL :flipoff2: ... :laughing:


Tigger4X :jeep:

Just a quick question for all you FSJ AMC20 guys. And yes I did the search with no luck. What is the width of a 84 J-10 HD20, WMS to WMS? And can the axel flange lug holes be filled and redrilled for 5 on 5.5 safely?

If I remember right the FSJ AMC20 is 63"... for the J10 I dunno.
As far as the fillin' and redrillin'... a reputable shop would know the metalurgy(sp?)...
and if it would be okay to do it without losing strength.

By the same token, I would check with a few shops to make sure you don't get fed
some load of BS just to get yer $$$!

Personally, Im with Rockbuggy on this one, I wouldnt want a model 20 anything under my rig, heck, I hate the 30/35 combo I have now.. Its all good.. I picked up a D44 front today that I need to start working on :)
Scott :grinpimp:<><

speakin of waggies i know a gentleman by the name of scott probert who runs 38" hawgs on his AMC20 with 3.31 gears. he also lincoln locked the carrier.

he runs it on the street and on the trail (mostly trail) and has had it for at least a year now with no problems at all.

the reason AMC20s can't go lower than 4.88 (and also why 4.88 isn't cool IMO) is cuz the pinion is 1.62" in diameter (same as a 60). 8.875" (ring gear diameter) divided by 4.88 (ratio)=1.81" which is just .1" larger than the pinion on each radius.

personally, i'll stick with 4.10s cuz i have an auto and will run 35s mostly. with stick you might go up to 4.56 and be just fine, if a little bit slow on the highway :)

can someone show me housing flex pics? it always looked pretty solid to me. that doesn't mean i'm not gonna truss it for good luck ;)

:confused:What does it take to stop the misinformation and let the rumors subside?!?

The FSJ AMC20 is different from the CJ version!! The FSJ is STRONGER!

So many people have run the CJ AMC20 and had bad experiences... I don't doubt that one bit! Some of it is due to it just being weak and some of it due to people doing stuff to it and NOT knowing what they were doing(completely). Who knows... BUT there are so many running the FSJ AMC20 that don't have problems!! IMHO, The FSJ version has gotten a bad rap because of its little brother.

Anywho, thats my .02!

Tigger4X :jeep:

Ok I'll throw my .02 in the ring.

1) The FSJ housing uses thicker tubes. Sure you can truss it but it's not as weak as a CJ housing. My friend Jeff bends the crap out of trussed Waggy 44's in the race Jeep too. Not much of a difference I can see between a FSJ 20 and a 44.

2) the 5 on 51/2 pattern can be drilled. (done it) At the same time you can use a waggy FRONT 44 and keep the 6 lug. Or you can use the waggy/Chevy knuckles on out for high steer and keep the 6 lug. or you can just use the waggy outers etc.

3) The width on a Waggy rear 20 is 58.5" and wider on a J10.

4) If you are considering an upgrade to a 30 spline 60 which can be bought in CA for cheap from a pick n'pull, Then go ahead and debate. If you are going to debate spending money to "upgrade" to a 44 from a FSJ 20 you are wasting bandwidth and $$$$

Jus' bit the bullet and plunked down 380$ for a 4.56ed Detroited 14 bolt, gonna get rid of those monster brakes and the full floater stuff for some moser axles and 1/2 ton brakes, bu thanx anyways guys, after all is said and done I am only gonna spend about 200$ more this way, and have some piece of mind, now just gotta shave as much as possible off the bottom of this monster!

Measured the J-10 AMC20, WMS to WMS is 62". For the guy who redrilled his axels for 5 on 5.5. Did you have to plug any of the original holes or was there enough meat left on the flange without filling?

SS406CJ ... Anytime you redrill like that, IMHO you should refill the old holes.
BUT, why redrill your 5 lug:confused: I beleive that means you would be using the CJ version of the AMC20 which is inherrently weaker then the FSJ version(previuosly explained in this thread a couple times). The FSJ AMC20 is STRONGER and is ALREADY a 6 lug!
Maybe I am not hearing it correctly. ... :question:


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