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Your Jeep - Tech Questions

Jeep Cherokee Rear Three Quarter
Verne Simons
| Senior Editor, Jp
Posted April 1, 2013

Jeep Tech Questions Answered!

Dodge Dana 44 Swap?
I’ve been reading your magazine for a long time now and a lot of the articles have got me thinking about how to make my ’01 TJ just a bit better off-road. I’m currently running a stock open Dana 30 in the front and a Dana-turdyfive with a Truetrac in the back. For years it has served me well, but I am concerned about going to 33-inch tires. I have a chance to get a set of Dana 44s from a Dodge pickup and am wondering if this is a good choice or not. Yeah, I know, they would need to be shortened and have all new mounting tabs welded on. Are there other problems that I might run into? Any help would be appreciated. Do you make garage calls?
Jim Smith
Newark, DE

We can tell that you read Jp, and we think you are right that running 33-inch tires on a Dana 35 is a liability for you and your Jeep on any off-road trail. An upgrade is a great idea, but unfortunately it’s never quite as easy as swapping in those spare axles you or your pal may have laying around. The axles you have access to may be decent candidates for a swap, but I am not sure because you didn’t tell us what year and model Dodge truck the axles came out of.

For starters, Dodge pickups didn’t use Dana 44s front and rear. Most 1⁄2-ton pickups from the ’70s-’00s will have a Dana 44 front and Chrysler 91⁄4 rear. The Chrysler 91⁄4 is a good, durable axle with 31-spline, 1.30-inch axleshafts and a ring gear that’s arguably stronger than a Dana 44. Some older Dodge 1⁄2-ton trucks from the ’70s could be equipped with a Chrysler 83⁄4 rear axle with a drop-out centersection much like a Ford 9-inch. The ’73-’79 Dodge Dana 44s will have a less-than-desirable semi-floating Unitbearing design, 5-on-41⁄2 bolt pattern, and a passenger-side-drop diff. The ’80-’84 units are the best, with locking hubs, 5-on-51⁄2 bolt pattern, passenger-side-drop diff, and a solid driver-side axleshaft. The ’85-’93 axles are the same as the ’80-’84 versions, but with a two-piece CAD (central axle disconnect) shaft in the long-side tube. Finally, the ’94-’01 Ram trucks have a semi-floating Unitbearing design that’s better than the ’70s models, 5-on-51⁄2 pattern, and a driver-side-drop diff that matches the T-case output on your TJ. The late-model axles are a CAD design as well, but it’s not that bad.

When contemplating swapping a front axle you have to think about what side of the vehicle the differential is on. Your TJ requires you to run a driver-side-drop axle. If your donors are the pre ’94 versions, you’ll have to re-tube the axle centersection to get a driver-drop differential. Alternatively, you could get a different passenger-drop T-case and re-route your exhaust. Those are both expensive possibilities that we would not recommend unless this kind of fabrication is old hat to you.

In any case, any axle (other than a Dana 44 from another TJ) is gonna require all kinds of cutting, fabbing, and welding of new brackets. Also, narrowing a rear axle requires special jigs and tools and that means a custom axle shop is going be necessary if you want to narrow your replacement rear axle. If you really want to build junkyard Dana 44s for your TJ, check out our story “Used Dana 44 Axles for Jeeps - Junkyard Built, Part 1 and Part 2,” (May and June, ’07). The axles we used did not require any shortening, but that’s not to say it was a direct swap. There was quite a bit of fab involved.

AMC 20 Haters
I have an ’85 CJ-7 into which I have swapped a 4.3L Chevy Vortec V-6 and a TH700R4 transmission. I currently have an AMC Model 20 with Moser one-piece axles and 4 inches of lift. I plan to add lockers but after reading y’all’s opinion of the Model 20 in the Sept. ’12 issue I was considering swapping in a Ford 9-inch. Which leads me to my question, will the low-pinion Ford change my driveshaft angle much? I currently have a 25-inch Tom Woods CV driveshaft. I have had no problems to date with vibration. I have access to a big-bearing 9-inch out of a ’65 pickup, but sometimes a free part is not necessarily the best solution, but if the drive shaft angle won’t be an issue I think I could build a stout rearend based on this unit. What do you think? Any other ideas?
Monti Vandiver
Muleshoe, Texas

Well, one thing for sure is that a Ford 9-inch is infinitely upgradable and has a huge aftermarket backing. It’s also a relatively lightweight axle, but all 9-inches are not built the same. Make sure yours is worth using before spending much time or money on it. Most 2WD pickups are 28-spline unless they’re camper specials. The 4x4s and some Broncos got 31-spline shafts. Vans could be either, but most are 28-spline and the vans are about 3 inches wider, so make sure your “free axle” doesn’t have one of these issues. Also, the 9-inch you have at your hands may be quite a bit wider than the Model 20, check the wheel mounting surface width first. A wide rear axle looks odd and can make tight turns off-road a little more difficult. You also didn’t tell us what tires you are or will be running. Tire size makes a difference. A Model 20 might be okay with 33s and a locker. A Ford 9-inch, properly upgraded, can live with 40-inch tires and a locker.

Now, back to your driveshaft, because your shaft is 25 inches long and you are already running a double-cardan shaft, I think you will be okay as long as you don’t up the lift amount much. You may need to have the driveshaft shortened, but then again a Model 20 pinion is pretty long and as we know the Ford 9-inch pinion will be at least a little lower than the AMC. If necessary, I am sure Tom Wood’s Custom Drive Shafts will be happy to shorten the shaft for a fee. If you have an issue with maxing out the double-cardan joint, it will be at full droop. If this happens you can rig up one center limiting strap to keep the joint from binding. As for other options, if you only plan on running 33s or 35s you might be able to get away with using a Dana 44 rear axle. If you want tires bigger than that or if you have a really heavy right foot, then you should probably look into a Dana 60 or a built-and-narrowed Ford 9-inch.

Automatically Different
I have a ’90 YJ with a 2.5L and an AX5 transmission. I am currently trying to convert it with a direct bolt-on, non-electronically controlled transmission. I’m not sure which tranny to use. Is it the TF999, the TF904, or the AW4 or none of these? I am currently doing a spring-over and figured why not tackle a transmission swap too! Any advice? I’m baffled.
Matthew Duffy
Arizona City, Arizona

We’ll generalize a bit here and kinda lump ’em together for the sake of brevity, but the TF904 is a three-speed auto with a non-lockup converter. The TF909 is essentially a TF904 with lockup converter and the 30RH is an electronically controlled TF909. These are light duty and were mostly used behind four-bangers. The TF999 may or may not have a lockup converter and were mostly used behind six-cylinders and some V-8s. The 32RH is a TF999 with lockup converter and is electronically controlled via the ECM (kinda like the difference between a TH700R4 and 4L60E). Which to use? We’d go with the TF999 with or without a lockup converter.

Pow, Excuse Me!
I have a ’78 CJ-7 with an AMC 360ci, factory TH400 auto, and Edelbrock 600 cfm carburetor and intake. It has headers and dual exhaust with Cherry Bomb mufflers. The passenger-side exhaust will backfire when going down hills. I really replaced everything, wires, plugs, ignition box, even the whole distributor. I’ve checked the timing and for vacuum leaks, but nothing seems wrong. I’ve seen someone else with this same problem. What gives?
Via email

So the Jeep backfires going downhill? Cool! Probably what happens is the engine runs rich for a second or two after you pull your foot off the throttle. This causes fuel to exit the engine into the hot exhaust and pow. Not sure you can do anything to prevent it. I’d enjoy it. I guess you could put some quieter mufflers on it. Then even if there is a backfire it won’t be so loud.

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