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May 2013 Your Jeep - Tech Questions

Posted in How To on May 1, 2013
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Photographers: Jp Archives

Idle Issue
Your article about changing the 2.5L throttle body to a 4.0L (“Dethrottled,” Jan.’13) has me asking a few questions. I have a throttle body from a ’91 4.0L Cherokee with automatic transmission that is in good shape. First of all, will it work on a ’95 2.5L Wrangler with manual transmission? And second, is there a way to change the idle after swapping out the 2.5L IAC and TPS to the 4.0L body? My engine in stock form idles at approximately 800 rpm but when I put the larger throttle body on it the idle jumps to approx 1,100 rpm and does not settle down any lower. I’ve driven the Jeep for several minutes to get the engine completely warmed up, but that doesn’t help lower the idle. I like the additional power it seems to have at the lower end. Drivability would be great if the engine would go back to a normal idle. Any suggestions you might have would be greatly appreciated.
Jim Poindexter
Via email

First off, we advised Jim to make sure that he had swapped not only the idle air control (IAC) motor but also the IAC housing from his 2.5L throttle body to the 4.0L throttle body. As stated in the original article, the 2.5L IAC is specific to the 2.5L IAC housing. We also told Jim to check for vacuum leaks which can cause an elevated idle. This could be from a bad gasket or an open port. Unfortunately for the simple solutions gods, neither of these things was causing the problem. Jim got back to us and confirmed that he had swapped both parts of the IAC and that there were no vacuum leaks on the Jeep. Honestly, at this point we were a bit stumped, but Jim kept at it and finally found that a grub screw under the throttle lever (pictured) was screwed in a little too far, and that was causing the elevated idle. Thanks, Jim, for helping us help you and solving your own problem. Here’s to hoping this helps someone else out there in Jp reader land.

Fordjeep or Jeephord?
I was thinking of putting a 4.0L Jeep engine in my Ford pickup. My Ford has a 300ci I-6 now. The Ford is an ’81 model, and the addition of horsepower and torque would be greatly enjoyed. Will the Jeep engine marry to the Ford C4 tranny. Or should I use a Jeep auto transmission.
David Boedeker
Summerville, SC

Believe it or not, I once had visions of building an old ’60s Mustang with a Jeep 4.0L in place of the old Ford 200 I-6. At the time it seemed like a great way to get a more modern engine in an older car, and it would look like (to the untrained eye) someone had modernized the Pony’s old-school engine. Plus, the 4.0L would make more power and torque than the smaller V-8s that these cars came with from the factory. Looking back, I am not sure it would be worth doing this swap in a Mustang when you could get an H.O. 5.0L V-8 pretty cheaply that would easily make more than enough power. Having said that, I guess it could be a good option for you depending, on what you want from your truck. I don’t think there is an adapter for mating a 4.0L to a C4; I could not find one. You could probably have a custom one made, but I doubt it’s worth the cash. Now if you were to do this, I’d use an AW4 transmission from a Cherokee. It has a lower First gear than your C4 and it has an overdrive. I would also look for an H.O. 4.0L from a ’91 or newer Cherokee. You’ll also want the computer and you’ll have to get the engine wiring harness and have it modified to run outside the XJ. You could send the XJ harness to Hotwire Auto ( to be pared down if you’re not comfortable doing it yourself.

Now back to if you should do this swap. If your truck is a 2WD work truck or parts runner and you want to keep your it running down the road for a long time and wouldn’t mind a little more horsepower you could swap in a Jeep 4.0L. If your Ford is a 4x4 and you want to modify it for wheeling I’d stick to a V-8 swap and there the path of least resistance is gonna be adding a 302ci or 351ci Windsor engine. In this case, the 4.0L ain’t gonna have enough grunt to move all that truck around off-road especially when you start adding bigger tires and heavyduty parts. Your time and energy would be better spent on a V-8 swap.

I have a ’93 Dodge Club Cab 4x4 and was wondering if I could put a four-door Jeep body on it—any info would help. Keep up the great work and I love your magazine!
William Roberson
Cleveland, TN

So depending on how good you are at fabrication, this is probably doable, but it ain’t gonna be easy or cheap. You are gonna need to locate a JK body or a custom built YJ or CJ four-door Jeep body like the aluminum tubs offered by Aqualu ( Or, try getting in touch with a Jeep specialty junkyard like Collins Brothers ( or Davey’s Jeeps ( for a pair of clean, usable tubs or parts of tubs you can merge together. Either way is costly, though.

Then you can start pulling the Dodge body and carefully removing all the wiring and other components that you’ll want to re-use. You might be able to re-use things like the steering column, the brake system, the parking brake system, the pedals, and so on from the Dodge. You will probably also want a factory service manual for the Dodge so you can figure out the wiring. Once you get the Jeep body in hand, you can start adjusting the Dodge’s wheelbase to fit the wheelbase of the Jeep body. The easiest way to do this is to move the rear axle and all its hangers and mounts. You’ll also have to remove all the Dodge body mounts and build or modify stock Jeep body mounts to make the new body fit on the Dodge frame. You’ll almost certainly need a new radiator that will fit behind the Jeep grille and still keep the Dodge engine cool. I am sure I have missed some details of what you’ll need to do. It’s gonna be hard and will take a while, so be ready to devote lots of time and a good chunk of change to this project if you have to do it. If you still want to do this swap, we’d also recommend looking at the ’07 Ultimate Adventure Jeep that 4-Wheel & Off-Road magazine built a few years back. They combined a JK body and a 1-ton Dodge diesel chassis. They modified the frame to fit the wheelbase by shortening it in the center and lopping off the extra frame front and rear. I think that’s his easiest route other than trying to move the suspension mounts/axles around on the Dodge frame. It’s not exactly the same as what you want to do, but it’s gonna give you an idea of just how much fabrication is going to be necessary. Good luck! If I were you, I’d sell or part out the Dodge and save my lunch money for an ’07 JK.

J-Truck Parts Depot
I am in need of a good parts connection, I have a ’72 J4800 and she needs a few odds and ends, like a headlight-ring for a razor grille and miscellaneous other parts. Could you please let me know where I can find parts for this truck?
Lakewood, CA

(Editor Hazel replies) You can check the for sale forums of sites like since these things pop up there from time to time. Or, we’ve also dealt with the Willys/Full-size Jeep junkyard, Montana Overland (montanaoverland. com), from time-to-time for parts like this. The prices aren’t rock-bottom, but they don’t gouge you either.

For other new replacement parts you can try places like BJ’s Off Road (, Team Grand Wagoneer (, and others you can find with a quick Google search. Crown Automotive ( also has a lot of parts for these vehicles, but they don’t sell direct to the public, so you’ll have to go through one of the company’s distributors which you can find on its website.

Flat Towing?
Okay, so far I’ve read I can flat tow my ’69 Jeep with a T-14 tranny in gear and the T-18 T-case in Neutral for long distances. Has anyone towed like this? Also, no one has said anything about locking hubs on the rear axle. I’ve seen locking hubs on the rear ends, but, I heard it makes the axle weak.

Yes you can flat-tow your Jeep with the transmission in First gear and the Spicer 18 in Neutral (a T-18 is a Borg Warner transmission). I do this with my ’49 CJ-3A all the time. Just make sure the T-case is actually in Neutral or you will be dragging tires or spinning the engine over. You also can flat tow if you pull the rear driveshaft and unlock the front selectable hubs. This way the front hubs will turn, and the rear axle will turn, but that’s it. I’ve done this on long tows like from Ohio to Arizona.

You can convert some rear axles to be full-floating and run rear locking hubs. Then when you flat tow, all you have to do is unlock all four selectable hubs.

Now, will rear locking hubs weaken your rear axle? Not really, but sort of. Once this conversion is completed, the locking hubs may become the weak link in the rear axle and you could break a locking hub (like you could break a front locking hub), especially if you are running lockers. The answer is to carry a spare hub or a solid drive flange to replace the hub if one breaks. Full-float kits are not available for every axle, but I suspect that you are running an offset Dana 44 with your Spicer 18 T-case. You can convert later 19- and 30-spline offset Dana 44s to full-float with locking hubs using a kit from ATV Manufacturing ( We detailed the installation of ATV’s rear full-floater conversion in the story “Early Axle Upgrades,” (Oct. ’09).

Uphulstrey…or Is It upholstery?
I’m looking at stretching a CJ-2A to a TJ frame length. I remember seeing an article about a custom top a few years ago where this was done. The body would be approximately 10 inches longer in the area behind the doors. Who could build custom doors and a top for a CJ-2A? Thanks for a great magazine.
Via email

Brad, I don’t remember what article you are talking about, nor do I know of a place that regularly modifies Jeep tops, but I do have a few ideas. First you could try contacting Beachwood Canvas Works ( They might be able to help you. Otherwise I would look locally for a boat upholstery shop. A good buddy of ours has had Jeep soft top parts modified at a boat shop near us. They usually will have experience custom making or modifying tops for boats, and honestly, a Jeep top ain’t that far off from their bread and butter.

The Shafts on a TJ Go round and round…
I’m pretty new to Jeeps—I’ve loved them since I was little riding in my dad’s ’84 CJ-7. So I decided to get myself a ’99 Wrangler Sahara about 3 months ago. It’s been my favorite vehicle I’ve ever owned, and it’s also my first 4x4. I was changing my front brakes and noticed that my front driveshaft was spinning when I turned the wheel and I was wondering if that was normal. I would think it would get disengaged to keep from wearing the front differential, but I really don’t know. Any help would be greatly appreciated.
Name withheld
Via email

Yep, that’s totally normal. Unlike your Dad’s old ’84 CJ, your TJ does not have any locking hubs so the wheels and tires turn the front driveshaft all the time. That’s fine as long as the T-case is in 2WD while on-road (Running 4WD on dry paved roads is bad!). You can add locking hubs with a custom kit from Rugged Ridge, but they are not cheap, and while they will reduce wear and maybe increase gas mileage a little tiny bit, the price is hard to justify. The kit allows you to retain your 5-on-41⁄2- inch bolt pattern. It comes with little bitty locking hubs that will probably become the weak link on your drivetrain if you have 33-inch tires or lockers or both.

Honestly, wear on the front differential with the stock setup is not that big of a deal because there is very little load on the ring and pinion.

NP435 rebuild
I have been told that a decent shade tree mechanic should be able to do a rebuild on the NP435. That being the case, what books should I look for?

We too have heard that rebuilding the NP435 is fairly simple, but honestly we have not done it…yet. We can, however, direct you and like minded Jeepers towards a few resources that will be helpful. First, you could look into finding an original factory service manual from for a Chevy, Ford, or Dodge that originally came with an NP435. (Editor Hazel had an ’85 Dodge Ramcharger with an NP435 if you need a place to start looking for a manual and you have a Dodge NP435.) Novak Conversions is a great place to get information, too. In fact, Novak’s website even talks about how easy it is to rebuild an NP435 and it sells a master rebuild kit that comes with thorough instructions for the rebuild of various types of NP435s. Novak also can get replacement parts if something you need is not included in the rebuild kit. Novak’s site also tells us that you are gonna need some good snap-ring pliers, a small press, and some bearing pullers. Check it out at

Vibration or a Clunk?
I’ve got a ’90 Wrangler with about a 3-inch Rough Country lift. At take-off there is a vibration and the transfer case shifter shakes back and forth. I’ve already replaced the two rear driveshaft U-joints. Because of the lift, is the geometry off between the transfer case and the rear end? Whatever it is, how would you suggest I correct it?

OK, so is it a vibration or a couple of clunks? Why do I ask? Well, it could be a couple of things. First, if it’s a vibration, that only occurs during hard acceleration it’s probably your pinion angle. What’s happening is that when you accelerate from a stop the rear axle wraps up a little bit and this puts the U-joints in your rear driveshaft out of phase. For more info on how your rear pinion angle should be set, check out “Driveshaftology: The Ins and Outs of Driveshafts and U-Joints,” (June ’12). You should be able to adjust your YJ’s pinion angle with leaf spring shims or by cutting off and welding on new leaf spring perches. Look for steel shims if you go that route, and you probably should replace the U-bolts and leaf spring pins at the same time.

We also have experienced a series of clunks at start off in our ’97 TJ when transmission/transfer case mount was totally worn out and about to fall apart and the driver-side motor mount was basically torn in half. During acceleration the T-case and transmission would jump around a little and cause theclunking. We drive ’em hard here at Jp!

The Direction of Goodyear
I’m reading “Red’s Rubicon Return,” (Jan.’13). In the article you said that the tire shop mounted two of your MT/Rs backwards.

How do you know? I’ve been to a couple of Jeep shops and several tire shops around Toronto. I’ve spoken to several club members that have MT/Rs. Nobody knows if they need to be mounted a certain way. I have the Kevlar ones—there’s no label on the tire indicating left or right. Goodyear doesn’t list a left or right when ordering.

Clearly the tread runs in one direction, but I can’t find anybody (including a Goodyear rep) who knows if they perform better one way or the other.
Steven Caplan
Via email

(Associate Editor Trasborg responds:) The new Goodyear MT/Rs with Kevlar aren’t directional like the Goodyear MT of the ’90s, so it is a common mistake to make. In much of Goodyear’s information, the company speaks of the unique asymmetrical tread design. But wait, doesn’t asymmetrical mean directional? Well, as it turns out, no, not necessarily. When we went to the unveiling of these tires a few years back, this was one of our big questions and concerns. With the old MTs we hated that our spare was only going to be oriented correctly for one half of the vehicle and it messed with tire rotation as well. We were provided Jeeps with the new MT/Rs already mounted, but had an opportunity to mount tires on our own Jeeps as well. On one Grand Cherokee, we purposely mounted them backwards from the intended orientation. Both off-road and on- the Grand Cherokee with them

"backwards” seemed to do just as well as the other Jeeps that had them on the “correct” way. Over the miles, however, the “backwards” tires wore worse and developed some weird wear patterns as compared to the ones mounted correctly. So today we always mount the tires as the Goodyear engineers intended.

We’ve mounted an additional four sets of MT/R with Kevlar tires since then, and on every set there is a “This side inboard” or “This side outboard” near the bead. It is part of the mold, and when the tire is poured, it becomes a permanent part of the tire. It is in every set of MT/R with Kevlar we’ve seen, and we’ve mounted and run everything from a 31x10.50R15 to the 315/75R16s shown here.

If, perchance, Goodyear has changed the mold, or you have a tire of another size than the ones we’ve run, see the attached picture of the tread. Basically, the tightly packed section of tread needs to be inboard as the tire sits on the Jeep.

Now, why isn’t this directional? Yeah, we had problems with that too. Basically, it isn’t directional because the tire was designed to work just as well going forward as going in reverse. Also, it doesn’t mess with the tire rotation pattern because wherever the tire ends up on the Jeep, the tightly packed pattern ends up on the inboard portion of the wheel. Not like you are going to put a wheel on the Jeep backwards.

Then the other question is if the tires on the passenger side are effectively rotating the opposite of the tires on the driver’s side, then why did that Grand Cherokee wear worse and start developing a weird wear pattern over time? As to that, sadly, we don’t have an answer. We originally wrote it up to something wrong with the Jeep. But since then, that Jeep has run other tires and not exhibited any strange wear patterns.

Write us!
Got a tech question you’re just itching to get answered? Send it on in to:
Jp magazine, Your Jeep
831 S. Douglas
St., El Segundo, CA 90245
or e-mail it to

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