Pete Trasborg
Brand Manager, Jp
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Jp Archives
Many people think the editors can get anything they want thanks to simply working for the magazine. The fact of the matter is that we have a ton of projects going and many of them you don't even read about in these pages. We are out there swapping parts, scrounging junkyards, combing online ads, and bribing friends just like you guys are. Heck, we are even on our backs in our driveways to do most of our swaps like you guys are. The difference for us is we've been doing this for a combined total of more than 50 years, and we've built and beat more Jeeps than many people have ever owned.
The point is, by being paid in peanuts for so long with so many projects we've gotten rather adept at saving money when swapping parts into our Jeeps. In this article we are going to look at swaps into Jeeps with Jeep engines. If you've swapped in another engine, the pros and cons of each component are still applicable. So, without further ado, here are our 11 favorite junkyard transmission and transfer case swaps to make your Jeep perform better, last longer, and still get you home from the trails.
Transmissions
Aisin AX-15
Donor Vehicle(s): Behind the six-cylinder in '89-'99 XJ, MJ, YJ, TJ and the '93 ZJSwap into: Any pre-'89 ('86 and earlier CJs will need an adapter or T-case swap) Jeep with the inline-six, but especially the '87-'89 YJ, XJ and MJ with the BA10/5 Peugeot transmission (might need to change the T-case input gear to 23-spline). It is also a good swap into '87-'03 four-cylinder Wranglers using Advance Adapters kit (PN 712563 (external hydraulic) or PN 712564 (internal hydraulic).
Identify: 16 1/2-inch-long case, 23-spline output, five forward gears, thick aluminum mid-plate which the front and rear halves of the case bolt through
Gears: 3.83, 2.33, 1.44, 1.00, 0.79 (First through Fifth); 4.22:1 Reverse
Pros: Good all around Overdrive transmission that shifts nicely, quiet, and is relatively lightweight.
Cons: Not a very low First gear and the unit has only marginal strength for V-8 swaps.
Comments: This is the Rodney Dangerfield of Jeep transmissions in that it gets no respect. With a mediocre First gear, the rock crawlers aren't tripping over themselves for it, and with enough strength for a six-cylinder, but likely not enough for a healthy V-8 the mud guys don't want it either. That said, it is likely the most common manual transmission in Jeeps still on the road. The '93 and earlier units got a goofy hydraulic throwout bearing which can prove problematic. The '94 and later units got an external slave setup. The later parts can be swapped to the early transmissions by using the bellhousing, input bearing retainer, clutch fork, throwout bearing and slave cylinder from the '94 and up unit.
New Venture NVG3550
Donor Vehicle(s): six-cylinder '00-'04 Jeep Wranglers and '00-'01 Jeep Cherokees
Swap Into: Any Jeep with up to 300hp, again with the 23-spline stipulation for the Peugeot-shod Jeeps, and the possibility of a transfer case adapter or swap for the '86 and earlier CJ's
Identify: Five-speed Overdrive transmission with composite shift tower, 16 3/4 -inch long case, and a 23-spline output.
Gears: 4.01, 2.33, 1.39, 1.00, 0.78 (First through Fifth); 3.57:1 Reverse
Pros: The most heavy-duty of the aluminum-case manual transmissions ever put in a Jeep; this transmission is also coveted for its lower First gear, and praised for its strength as evidenced by its OE installation behind small-block V-8s.
Cons: In a daily driver, especially one with the carpet-delete option, it is noticeably noisy at idle and lower road speeds. Also, it doesn't take normal gear oil, but special Syncromax oil which is more expensive and can be harder to find (read: you need to take more fluids with you on trail runs).
Comments: For its size and design it is one of the most heavy-duty transmissions you can score. For swapping into '93 and earlier Jeeps, be sure to grab the bellhousing and all associated clutch parts.
BorgWarner T-18
Donor Vehicles: Various Ford trucks, Jeeps, and International Trucks from '66-'90 with the 70's and early '80s seeing the bulk of the production.
Swap Into: Anything that needs a bulletproof four-speed transmission
Identify: This is the tough part. Jeep alone used 18 variants of this transmission. The Ford T-18s are the more standardized ones. Not all T-18s had the desirable 6.32:1 First gear. Turn the input and count output revolutions. If less than 6:1 it's not the T-18 everyone wants. Case length is 11 7/8 inches with a height of 17 1/2 inches and features both a cast-iron case and cast-iron top cover.
Gears: The ratios vary, but the most desirable unit has: 6.32, 3.09, 1.69, 1.0 (First through Fourth); 7.44:1 Reverse
Pros: Very heavy-duty transmission, the best of all OE Jeep manual transmissions in terms of sheer strength and abuse it can take.
Cons: No Overdrive, long-throw shifts, and finding the right one can be tough.
Comments: If you ever stumble across a Jeep with a T-18 you owe it to yourself to at least check the First gear ratio. If the transmission doesn't have the low First gear, grab the 1-inch spacer/adapter between the transmission and bellhousing and the bellhousing itself. These parts are often not included with second-hand T-18s. Check out novak-adapt.com for more info.
GM Muncie SM420
Donor Vehicles: Chevy Trucks from '48-'67, busses, and various military applications behind diesel engines.
Swap Into: Any Jeep that needs the lowest low gear in a manual transmission, or has rear driveshaft length issues.
Identify: It has a cast-iron case, cast-iron top cover retained by eight bolts, the case is 10 3/4 inches long, a power take-off port only on the driver's side of the case, and a bulge near the front on the passenger side are dead giveaways.
Gears: 7.05, 3.58, 1.71, 1.00 (First through Fourth); 7.05:1 Reverse
Pros: More heavy-duty than any aluminum Jeep transmission, its ultra-short length makes it a great swap for shorter Jeeps, and a very low First gear means greater control for the rocks.
Cons: The bulge in the passenger side of the case can mean driveshaft clearance issues in passenger-drop front axle Jeeps, the low First gear is useless on the street, and the newest SM420 you are likely to find is at least 40 years old. To bolt it to a Jeep engine will require some kind of adapter, incurring more cost.
Comments: While they are rare to find in junkyards anymore, they can still be had for dirt cheap from the guys who are now hot-rodding the trucks these originally came in. The long throw of the shifter can get tiresome living with day to day, but if you can get past that, and only essentially having a three-speed Jeep on the street, then this is a good little transmission. Certainly it is the best manual transmission to swap into a flatfender due to its small size and legendary durability
GM Muncie SM465
Donor Vehicles: GM trucks, Blazers, and Suburbans from '69-'01
Swap Into: Any Jeep that needs brute strength. Can live behind high-horsepower engines with ease
Identify: At 12 inches long, and 18 inches tall with a cast-iron case and top cover it isn't all that hard to pick this transmission out of the Chevy/GM lineup. The clinchers are the two PTO ports (passenger and driver's side), the large ribs of the case, and the 6.55:1 First gear.
Gears: 6.55, 3.58, 1.57, 1.0 (First through Fourth); 6.55:1 Reverse
Pros: Most heavy-duty four-speed light truck transmission and likely the most reliable to boot. It is still easy to find in junkyards, and easy to get parts for with tons of aftermarket support.
Cons: At 18 inches tall, it will hang down lower than your transfer case and could take some planning to make work. Also, like the SM420 it replaced, the low-low First gear is almost unusable on the street rendering your Jeep essentially a three-speed for most uses. It won't just "bolt-in" to many Jeeps, requiring adapters, machine work, or fabrication to install.
Comments: Big and beefy, put any engine you want in front of it and you won't have to worry about it. Like the other truck-style transmissions, the throw is pretty long, especially that Reverse gear. Some stick massaging might be required to keep the stick out of the passenger in Reverse or out of the dash in First.
New Process NP435
Donor Vehicles: Ford trucks from '66-'92 and Dodge trucks from '64-'93
Swap into: Any Jeep that needs a bulletproof transmission with a low First gear
Identify: It is 107/8 inches long with a cast-iron case and an aluminum top cover. There are three different First gear ratios available: 6.68, 4.90, and 4.56:1. Spin the input in low to count output revolutions.
Gears: 6.68, 3.34, 1.74, 1.00 (First through Fourth); 8.26:1 Reverse
Pros: Similar weight and length as the SM420, but much more readily available in junkyards, and it is 60lbs lighter than the SM465.
Cons: Aluminum top cover stick shift retainer pins can strip out, or wallow out holes over time, multiple First gear ratios and output/input configurations can make finding the right one difficult.
Comments: This is basically Ford and Dodge's answer to the SM465. With its low First gear, ultra low Reverse gear and strength make it a good candidate for any Jeep, but especially one with a Ford or Dodge engine.
New Venture NV4500
Donor Vehicles: '93 and up Chevy truck, '95-'04 Dodge truck
Swap into: A Jeep with enough wheelbase to handle it that needs a heavy-duty five-speed Overdrive transmission.
Identify: It has a cast-iron case, an aluminum top cover, an aluminum tailhousing, PTO ports on both sides, its 18.9 inches long, has either 6.34 or 5.62:1 First gear, and weighs about 200 pounds.
Gears: 6.34, 3.44, 1.71, 1.0, 0.73 (First through Fifth); 6.34:1 Reverse
Pros: Big, beefy truck-style transmission like those listed above, but with the addition of an Overdrive for better street manners.
Cons: Big, heavy, and somewhat balky shifter movements make for fitment issues and more effort to drive every day. More transmission than 80-percent of the Jeeps out there need, nonetheless popularity drives up the price. One of these could easily run you double what its four-speed counterparts would cost.
Comments: It's got beef, that's for sure, but some units develop Fourth and Fifth gear issues with age, so beware of the screaming deals. For the amount these things demand make sure that it is ready to go as-is because opening it up and rebuilding it isn't that cheap either. And, finally, make good and sure you really need something this big. Most Jeeps don't.
Aisin-Warner AW-4
Donor Vehicles: '87-'01 XJ/MJ, '93 to '94 1/2 ZJ with the six-cylinder engine
Swap into: Any '87 and up Jeep that came with an automatic transmission and a 4.0L engine.
Identify: Look under a Cherokee with an I-6 and an auto, and there you go. It is 25 3/8 inches long, has a removable bellhousing, has the standard 6-bolt flange on the tailhousing, and a 1/4 pie-shaped neutral safety switch on the passenger side near the bellhousing.
Gears: 2.80, 1.53, 1.00, 0.75; 2.80:1 Reverse
Pros: Well respected Overdrive automatic transmission with a stand-alone controller that is a bolt-in to most six-cylinder Jeeps with Jeep parts that can be found in the junkyard.
Cons: Not a good swap into a Jeep with a V-8 or stroker, it can run hot when wheeling: a larger cooler is a necessity if a lot of time is spent rockcrawling or towing, and its longish length can lead to a really short driveshaft with goofy angles in lifted Jeeps with stock wheelbases.
Comments: With an Overdrive, this transmission is a more livable automatic than any YJ or early TJ slushbox, and it wheels better than the four-speed in the later TJs. However, if you swap this transmission into an automatic-equipped TJ, you will end up with a check engine light because it won't talk to the TJ computer and you'll need to swap your stock ECM out for a computer out of a manual transmission TJ. When you pull the AW-4 from the donor, make sure to get the TCM (transmission control module) as well. The TCM is often found behind the glove box or behind the dash near where the driver's knee would be.
Transfer Cases
Dana 300
Donor Vehicles: '80-'86 Jeep CJs
Swap into: Any universal series Jeep that is getting a passenger drop front axle, any '79 and earlier Jeep that is getting a different transmission, or any lightweight full-size or full-size with an anemic power plant.
Identify: A cast-iron case with an aluminum rear output housing, aluminum shift rail/shifter mount casting, common round 6-bolt mounting arrangement, a centered rear output, and an inspection cover on the bottom.
Gears: 1:1, 2.62:1
Pros: A lower low range than its predecessors, while still having a cast-iron case and direct gear-driven architecture, it also has the more modern 23-spline/6-bolt round attachment and input which facilitates installation with many modern transmissions. Many consider this the pinnacle of Jeep transfer cases.
Cons: Leaks from the shift rails are not uncommon, stock clocking is almost 25-degrees down from flat, and the stock single stick shifter can become stuck and balky with remarkable ease.
Comments: A swap to a twin stick setup can solve the balkiness issue, and a clocking/adapter ring from either Advance Adapters or Novak Conversions can allow you to clock the case flat or bolt it to an AX-15 or other YJ/TJ transmission, while a flip-kit or Stak 4x4's complete aluminum replacement case can allow it to run with a driver's side drop front axle. There is no shortage of aftermarket support including heavy duty outputs, 4:1 gear kits, twin-stick shifters and even complete aftermarket rebuilt units.
New Process NP231
Donor Vehicles: '88-'06 Wrangler '88-'01 XJ/MJ, some ZJs with the inline-six, and '88-'96 Dodge Dakotas and Rams
Swap into: Any '87 XJ/MJ or YJ to replace the NP207, Grand Cherokees with a full-time 4WD case, or any Jeep that came with an NP242
Identify: The easiest way is by looking at the aluminum and red tag next to the rear output above the fill plug.
New Venture Gear NVG241OR
Donor Vehicles: '03-'06 Wrangler Rubicon
Swap into: Any Jeep equipped with a driver's side drop front axle and a transmission with a common round 6-bolt pattern and 23-spline output.
Identify: Like the NP231, look for the tag near the rear output above the fill plug. The case itself looks a lot like an NP231, but it has a balancer on the output requiring a flanged driveshaft, more bolts holding the case halves together and a larger nose area where the input is (which houses the planetary low range).
Gears: 1:1, 4.0:1
Pros: With a bigger chain, more bolts holding it together, and a larger planetary set, this is a much beefier T-case than the NP231.
Cons: Its size can be a detriment to clocking it flat, and not everyone needs the 4:1 gears.
Comments: Only available in the Rubicon Jeeps to date, the JK NP241 won't easily swap into the earlier TJ/YJ/XJ/MJ/ZJ Jeeps. The TJ cases though will bolt up in most applications with minimal fuss. The stock shifter linkage will likely have enough adjustment to work too. The front driveshaft should be able to be kept, but the rear will need modifications. There is no mechanical speedometer output so earlier Jeeps will need another solution for speed pickup.
