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March 2010 Your Jeep

Posted in How To on March 1, 2010
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Cliff Notes
The Project: I have a '83 CJ-7 and a '00 Explorer 5.0L V-8 that want to be together. I found a very pretty NP435 Ford four-speed on Ebay for $50. I believe I can overcome the technical obstacles to the swap, but I'm having second thoughts about the transmission. I know people love the old granny tranny off-road, but I'm hearing it shifts like a dump truck on the street with long, heavy throws. First gear is useful only for pulling stumps, the ratios are too wide, not to mention the Rat-Fink shifter.

What It's For: My Jeep lives in the middle of the Mid-lantic Megalopolis. The black helicopters have taken over Paragon, so the closest dirt road is now way up at Rausch Creek. The CJ goes everywhere (unless it's raining, 'cause there might be nothing left but a rust stain). Stirring the pot in traffic gets old, even with a civilized stick, so I'm thinking an automatic might be better for the Jeep after all. The 4R70W auto that was attached to the Exploder engine got away, but I could probably scrounge another one up.

Questions: Is the big computer-driven slushbox going to leave room for my Dana 300 and a working rear driveshaft? I'd like to have a highway gear, so a smaller three-speed auto like a C4 or C6 is less than ideal. Is the NP435 really that bad on the road? Are there ways to teach the old four-speed better manners? I've seen a shift lever kit for a T176 that looks identical to the pieces on the NP435. Can I use that to tighten up the action? The lever I have could be used for pulling very large wine corks.

Speaking of driveshafts, what are the chances that the NP435 with a 6.5-inch bellhousing and a 4.25-inch adapter will bolt to the Dana 300 where it sits? It looks pretty close.

Tech Notes: It's an '83 CJ-7 with a 258 six, TF999 automatic, Dana 300, Dana 30 front axle, AMC 20 rear axle, 3.55:1 gears. (I know, but some P.O. swapped in a set of narrow axles out of a '77. Cute, huh?) Has 31-inch tires, will probably not go bigger than 33-inch, about 2 inches of lift from shackles and what looks like some kind of replacement leaves.

I have all the Explorer harnesses right back to the taillights, the computer (the '00 V8 Explorers all had automatics), the relay box, and the OEM starter. For the NP435, I have a Ford F-series bellhousing with hydraulic clutch linkage and an AA adapter; still need a truck flywheel, clutch, and starter. I plan to use FRPP shorty headers that fit the Explorer GT40P heads, but I don't know if I will need a mini starter to clear the headers.

The Jeep only has to pass '83 emission standards (the 258 needs a pity pass to get through DMV here), so I don't much care about codes or check-engine lights.
Jay McMillan, Wilmington, DE

I'm a huge fan of the NP435. In fact it's my all-time favorite four-speed. My '85 Dodge Ramcharger had one (same 6.68:1 First and other gear ratios as Ford, but different bellhousing/t-case bolt patterns). I bought it with 73K on the odometer and then put an additional 200K on the truck with zero tranny problems. The last 100K were with 37-inch and larger tires and monster off-roading. I think I only changed the oil in it once. Yeah, it shifts like a bread truck, but you get used to it. I got to the point where I could actually power shift that sucker at LACR drag strip. Bulletproof, durable, and just an all around good unit in my opinion.

As for the Explorer tranny, guys swap them out for TH700R4s, so that should tell you something. I'm sure they're fine in an Explorer, but most Ford autos don't like to run at angles. Regardless, I think you'll be able to make a rear driveshaft work in that as long as you keep the lift somewhat small. You can also take the engine swap install as an opportunity to move the engine forward to make more rear driveshaft room.

The NP435 is pretty good on the road. That is, it's not really noisy. The split between 3rd and 4th isn't that tight, so downshifting can't really be done at freeway speeds. With 3.55s you'll have a top speed of probably 50mph in Third gear. There really aren't any performance shifters for that tranny. It sort of is what it is. Check the early Bronco guys like Jeff's Bronco Graveyard, Wild Horses, or James Duff for the flywheel or any replacement components for that tranny you may need.

Regarding the driveshafts, I just don't know. I bet you'll need to move something because nothing is ever that easy, but there's a decent chance your existing driveshafts will have enough travel left in the splines to work with the new tranny. Since you've got the components right there, I'd say you've got a better idea than I do.

Liberty Or Bust?
My son is currently serving in the military down in Georgia after being overseas. I would like to take his '94 YJ to him that we brought back to life after rescuing it from the salvage yard. It is pretty much stock except for a hard top, 32-inch tires, and a body lift. Oh, and the CJ front end. My question is, do you think it would be okay to tow it 1,100 miles with my Jeep Liberty CRD with a 5,000 lb tow capacity? I am concerned about the transmission. I heard that it is a weak link. Any guidance you can give me would be greatly appreciated.
Bob Cilino, Bath, New York

PS. The white Jeep on the left is the one that I will be towing.

I'd plumb an aftermarket transmission cooler into the tranny return line and keep the tranny in the tow/haul mode the entire time you're towing. That'll help keep the tranny temps down and will go a long way towards ensuring longevity.

As for the weight, if your tow rating is 5,000lbs you'll be pretty much at the vehicle's limit. I'd estimate your YJ weighs about 3,500 lbs and the average twin-axle car hauler weighs about 1,200 lbs. Make sure you run a trailer brake controller so that the trailer can aid in stopping. With hauling that much weight with that vehicle, braking will actually be your biggest concern.

Stability is going to be your second biggest concern. Watch your trailer tongue weight. You'll want enough to keep trailer sway at bay. It'll be better to squat the rear of the Liberty a little more than normal if it aids in stability. You'll probably reposition the YJ on the trailer a few times in the first couple dozen miles until you find the sweet spot.

Power-wise, that CRD diesel has plenty. Hope some of this helps. Good luck delivering the Jeep to your son. Give him a big thanks from all of us at Jp for his service.

Haulin', Not Crawlin'
I'm doing a quick rebuild of a '80 CJ-5 with a '79 258, T-18 tranny, and a Dana 20 T-case. All the drivetrain components are rebuilt. I'll be looking at running 31- or 32-inch tires. The CJ-5 is still running the original 2.73:1 gear ratio in the axles. This vehicle will be used mostly for road-running, with maybe some easy off-road work in the snowbelt of the Midwest. What I'm looking for would be the best overall ring and pinion ratio.
Leo Riley, Via E-mail

I'd think 3.73s would be a good ratio considering your focus on street use and the lack of an Overdrive gear in the tranny. That'll give you an engine speed of about 2,950rpm at 70mph with the 31s, which should be okay for the 258. The 32s would drop the rpms by about 100rpm.

The 1-Millionth Gearing Question Ever
I have a question about gearing my '95 2.5L Wrangler with the stock 4.10s. I am running 33x12.50 tires right now. I do have some engine mods which help to push the tires a wee bit, but I still can't use Fifth gear. I have been contemplating regearing, but I don't know much about it. I like to trail through the woods and play in the mud and am not so much a rock crawler. It's also my grocery getter and I run the highway on occasion. What would be a good gear to run? My friends have recommended 3.73s, but your article "Gearing for Power" seems to say otherwise. I would like to gain Fifth gear back.
Mike Cooper, Carlisle, Pennsylvania

Honestly, 33s and a 2.5L suck. Your friends are dead-wrong. With the stock axles, 4.88s are the lowest you can go. If you're keeping the stock axles, put in 4.88s. If you're swapping axles and they'll take it, go to 5.13s or 5.38s if you want to keep the 33s and still use Fifth gear.

I've got an '89 Wrangler with the 2.5L. I used to run the stock 4.10 gears with 29- and 30-inch tires without too much trouble. I then went to 31x11.50-15 Swamper LTBs and it got pretty gutless. I'm now running 4.88s in the stock axles and, although I still downshift on big hills from Fifth to Fourth, I'm pretty happy with the performance from the stock engine.

As for 3.73s, you'll lose a lot of off-the-line acceleration and ability to maintain speed. Gearing is mechanical advantage. A 2.5L isn't a very strong engine and doesn't make a lot of torque. To use a bicycle as an analogy, if you've ever peddled a mountain bike or 10-speed up a big hill, you'll know. Go on the small gear on the rear sprocket (like the 3.73) and you're spinning fewer revolutions, but it takes more force from your legs to push the pedals down. Go to the large gear on the rear sprocket (like the 4.88s or 5.13s) and you're spinning more revolutions, but it takes less leg force to get up the hill. The 2.5L just doesn't have the oomph to pull the 3.73 gear. While you may find yourself shifting from Fifth to Fourth frequently with the 4.10s, I think you'll find yourself shifting from Fourth to Third with the 3.73s. With that tire size, the 3.73s are better-suited to a 4.0L six or a small V-8.

Fact-Finder Let me start by telling you that I think a lot of the info in your magazine is over my head. I am a Jeep guy from way back, but there is a lot I don't know about the world of custom suspensions, axles, and gears. I currently drive a '99 TJ Sahara. I have added a 4-inch Skyjacker lift and 33x12.50R15 BFG ATs. I have had the Jeep for ten years, but only started tinkering with it in the past year. I know it is a 4.0L six, and an AX-15 transmission. I do not know the particulars on the T-case, axles, or the gears. Justin Nelms, Moultrie, Georgia

Your T-case is a New Venture Gear (NVG) 231J, commonly known as a NVG231. Behind the 4.0L engine it's got a 23-spline input gear. The 2.5L four-cylinder models got a smaller 21-spline input gear. The low-range ratio is 2.72:1 which is provided by a three-pinion planetary gearset, and it runs a 1-inch wide chain inside. There are components available to upgrade it with a 32-spline slip-yoke eliminator, a stronger six-pinion planetary gearset, and wider 11/4-inch chain and front output shaft.

Your front axle is a low-pinion Dana 30 with 27-spline shafts and Dana 44-sized Spicer 297/760-series U-joints. The rear axle on most TJs is usually a Dana 35 with 27-spline C-clip axles, however it's not unusual to find the much better Dana 44 axle with non-C-clip, 30-spline shafts in Sahara models of this era. This link should help you identify your rear axle based on the diff cover shape:

With the exception of the Rubicon models, TJs with the 4.0L engine were commonly offered with 3.07, 3.55, or 3.73 axle gears. I'd wager you have 3.55s. Look for a stamped sheetmetal tag on either the front or rear axles held on by one of the diff cover bolts. This tag should have the gear ratio stamped on it. The front differential will be open. The rear differential could be a Trac-Lok limited-slip or an open diff.

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

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