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  • Model 20 rear question

    I apologize for the length of this post; don't know a quicker way to explain my situation.

    I've done many things over the years on the various Jeeps I've owned, but one thing I've never messed with is a differential/axle, other than to replace stripped 2-piece axles, brakes, etc., so I'm approaching this situation with a lot of ignorance.

    I recently have been the recipient of what I think is a fairly nice AMC 20 wide track rear, with welded tubes, 1-piece axles, 3.31 gears (so-so, I know), all new brake hardware, and a currently not installed bolt-on truss-looks like the one that 4WDH sells.

    But in looking at this thing I realized that it seems the spider gears have been welded or otherwise locked up to make a spool. The axels are locked firmly together, without question. But other than the fact that they don't move at all, the spider gears look normal, as well as the carrier; I can see no evidence of welding. Would the carried have been removed to do the welding in such a way that it's not visible simply by removing the cover? Could something else have been done? Also, I don't want a spool. This Jeep sees more highway driving than off-road, even though it's not a DD. I have 2 other model 20's, a quite rusty wide track, 3.54 ratio with trac-lock (I know trac-lock isn't much better than an open diff, I'm not concerned about that right now), and a narrow track (currently being driven) with 3.73 gears and open diff.

    Can the carrier/spider gears be swaped from axle to axle? I assume that since we're dealing with 3 different ratios the ring gear would have to stay-removed from the current carrier and installed on the replacement carrier? Would that require a complete fresh setting-up, like a new R&P (something I have NO experience with)? I do plan on installing a locker sometime in the future, as well as 4.10 gears, but the budget just won't allow that anytime soon. I'm trying to determine if it's practical to try and get this axle road-worthy. I don't mind doing as much work as necessary, within my capability, and I can spend a little to get it done, but the money is tight right now to do much more.

  • #2
    Hey jeepstir, don't fel bad, I'm fairly ignorant with diffs to. My worst though is performance mods on the engine. I can rebuild em stock, but know little about "stroked, blueprinted etc." Anyway, back the Q's. Have you rolled the ring gear around while the cover was off? I've seen some "lincoln lockers" where they only welded one side. I'd look close at where the spiders meet each other, and where they meet the carrier. If they welded to the carrier, and only ran one bead, it can be hard to see. Especially since the weld doesn't rust or oxidize, becuase of the lube. I'm fairly sure your open carrier will fit, as long as you swap the pinion also. It's not to hard if you've turned some wrenches. I'm sure someone knows a link for setting the backlash. And most autoparts stores have a tool loan or rent program. As far as the swapping a trac-loc to non trac-loc, I'm not sure. I'll let someone else handle that one. (and corect me if I'm wrong on anything above) Hope all this rambling helped you some.


    • #3
      as far as I know all the carriers for the 20 are the same the only thing that changed was the width or the rear and that has only to do with the axel length

      when replacing the carrier the gear lash shoud be rechecked


      • #4
        whatever you end up doing you have to make sure you match the front gears with the rear ... or the first time you put it in 4wd ... you can kiss a U-joint goodbye! I have swapped out ring and pinion setups from axel to axel with no problems ... but I am not saying this is the "right" way to do it.

        If you want to swap them out, and you have the others setups, I would just pull the entire carrier ... make sure you keep track of the shims .... and pull the pinion gear out and slap it into the WT set up ... it should fit with no problems ... If you want to do it right ... you will need to get a new crush sleeve to set the bearing preload on the pinion and a dial indicator to make sure the backlash is set right on the carrier ... or you could just put it all in, tighen down good and run it till something gives up .... the worst that will happen is you burn up a bearing ....

        if you are going to swap it out later anyway ... that will just set your timetable! Good Luck ~
        Last edited by Bret; 09-11-2006, 09:59 AM.


        • #5
          Thanks for the advice guys.

          Bill, yes, we spun the diff many time closely examining both sides, and just can't find any evidence of a weld of any kind, which is why I'm so puzzled by this.

          And Bret, I definitely understand about matching ratios front & back! Thanks for the reminder though, never hurts. That's why I want to keep the 3.31 for now-I have the matching 3.31 front axle, which appears to be stock. So the pinion will not be touched for now.

          Gear lash, bearing preload, crush sleeve, shims.... that's the stuff I don't understand! Maybe it's time to do some research. Maybe it's time to learn. And maybe learning on old stock gears is the way to go. If I screw up I haven't wasted a few hundred $$$ nice new R&P. Just for starters, if I pop the axles out and pull the carrier, just to look more closely at it, then put it back, is there anything that can get out of whack? Where are the shims mentioned?


          • #6
            no, you should be cool ... when you pull the main caps off that hold the carrier bearings into the case ... the shims will be on the outside of the bearings ... near the tubes ... sometimes you really have to pry on the carrier to get it out ... and when it comes, the shims go flying ... so just try to watch it as close as possible ....
            Last edited by Bret; 09-11-2006, 10:56 AM.


            • #7
              Thanks Bret. Maybe I'll get the guts to tackle this soon!


              • #8
                it might just be that they just rebuild the carrier and it may have a limited slip that was shimmed very very tight. we used to do this all the time when i was heavy into muscle car build ups and such. we would shim them so tight that a mallet and a drift were sometimes needed to cox the spiders back into place. it allows some slip...say when you are turning shap into a parking space, but rest of the time it would be almost impossible to turn one wheel or the other


                • #9
                  Not to rain on the parade here, but if you plan on installing a locker in the future anyway, why bother swapping the carrier now? What is the worst that could happen, you break a spider gear and have to swap the carrier anyway. On the plus side you get to learn what a locked rear end feels like.

                  P.S. The open carriers should swap just fine, the only change I know of was the 2:56 gearset that jeep used, it was special. I don't kow about the track-lock. I seem to remember seeing a footnote for a set of 1pc axles that said not to use them with the track-lock. I just don't remember where.


                  • #10
                    I seem to remember seeing a footnote for a set of 1pc axles that said not to use them with the track-lock. I just don't remember where.
                    Thats for the PowerTrax limited slip, part#202920, if you install that locker, you cant use 1 piece axles. (Using a trac-loc carrier) Part #202900 is for an open carrier (mod 20) and does not have that footnote.