Can I do a gear change on my CJ?

[jpcoutts]

I bought a non-op CJ5 a while back and got it running in no time. That's the good news, the bad news is the PO swapped the rear axle and the gearing in the front and rear axles don't match. I've been looking for an axle with the correct gear or a set with matching gears without luck. I am tempted to do an R & P swap myself but I've never done it before. Is that something anybody here has ever tried?

[tgreese]

Never set up an axle myself, but I do know the years and ratios and what will work in place of the front or rear you have now.

Details please. What year CJ? Which gears?

Would try to do the gears myself, though I understand the procedure is complicated, and there is a lot of trial and error involved. You might read the TSM and look at what's involved. It will include a step-by-step and describe the tools you'd need.

[SJTD]

It takes some tools to do it properly. Obviously you need a press. And a case spreader though a lot of guys don't use it. Then you need a jig to initially set the pinion depth and a dial gauge to set the backlash. I suppose you could do it all trial and error checking the contact pattern with bluing then resetting the pinion depth based on that but it would be a tedious process.

I suppose, that assuming the existing gears are set up properly one could use the numbers on the existing pinion and the new one with some math to compute the shims for the new one.

The procedure is in the factory service manual. It's the same for all Dana axles so look at that then some youtube vids.

I haven't checked but the tools are prolly available on Amazon nowadays for not too much.

[Yeller]

It’s not terrible but really need a press and set up bearings for the carrier. A case spreader is helpful but not required, I know a lot of shops that have been doing them for decades without one. You will need a bearing splitter and a dial indicator with mag base as well. It is a tedious process but doable. Are you gearing the front or the rear? I ask because the set up on the front is critical but not as critical as the rear. There a 50/50 chance it’s all perfect just installing the new gear with the existing shims but there’s always the one that’s a bugger and takes assembling and disassembling 10 times to get it right.

[jpcoutts]

It's a '79 CJ5 258 with T18/model 20 t-case and an AMC model 20 rear axle. It's really tempting to give it a try. I suppose the worst that can happen is I ruin some gears if I don't get it right. Whoops, I had the t-case misidentified.

[Yeller]

I’ve always had good luck putting gears in a M20, set up was always easy, I’m sure it will make me a liar though LOL. There’s a ton of YouTube stuff out there to help keep you pointed the right way.

[devildog80]

Before you start, what are the individual gear ratios of the front and rear axles?
Find that out, then decide which ratio you want for your use of the rig, and that will tell you which axle you need to change gearing to match the other.

[tgreese]

What ratios? The 3.07 or 3.54 M20 is a low-value axle, unless it has been beefed up with aftermarket shafts and the tubes trussed/welded. Unless the front is an odd ratio (4.10s, 4.54s, such), I'd look for another axle. Easy and affordable.

[jpcoutts]

There’s a ton of YouTube stuff out there to help keep you pointed the right way.

Thanks. Good suggestion, I hadn't thought to look and see what's out there.

[Srdayflyer]

its doable, i did my first swap years ago the time i spent doing that job wasnt worth mytime the 2nd go, found a local shop that does nothing but axles, i bought the gear sets and let them source the other stuff, besides they had all the shims,seals and bearings on hand, and drove away 2 days later light 750.00 bucks and warrantied but not the weeks i spent before . some times stepping over a dollar to pick up a penny isnt worth it, but hey everyone loves their project levels,

[Srdayflyer]

that was for both axles,

[SJTD]

Not everything on youtube is reliable info which is why I recommend looking at the Book first to understand what's involved.

[Yeller]

Here’s a decent article ti get you started
https://www.motortrend.com/how-to/how-t ... c-20-axle/

[jpcoutts]

Thanks Yeller. I'll check that out in detail.

[seventynine]

I didn’t see which axle you want to change the gears in?

What ratios do you have between the front and rear? I have done a bunch R&P swaps in less than ideal “shop environments” with a Harbour Freight 12 ton press, a bearing separator, and a dial indicator with a magnetic base.

One nice thing about the model 20 rear is that the carrier shims are on the outside of the bearings so you don’t have to press off the bearings to adjust the shims for the backlash.

The CJ AMC 20 has some weaknesses … mostly the two piece axle design though one piece aftermarket kits are available. The tubes are weak and can also spin in the housing. Some minor welding would help that part easily. It depends on how you want to use the Jeep and how hard you want to beat on it.