Aisin Jeep AX15 Transmission: Complete Guide & Review

Vehicle Transmission

Jeeps, Toyota turbos, and Dakota trucks all have one thing in common – transmission. At one point, these vehicles had an AX15 transmission, which worked beautifully in handling power and torque from these machines. As many consider it one of the finest manual transmissions ever made, it would be fascinating to know how compatible it is with current 4×4 vehicles.

The AX15 transmission is recognized by many as the best manual transmission ever installed in a Jeep. It comes in internal and external release bearing designs and can be mated to GM, Chevy, Dakota, and even Toyota engines. This gearbox continues to impress off-roaders and seasoned mechanics.

Tough construction, strong transmission, and flexibility all form part of the AX15 appeal with both the off-roading community and Jeep’s avid following. Learn more about these highlights, as this article helps you discover whether the AX15 is the gearbox of choice for your next build project.

Aisin AX15 Transmission

The Aisin-Warner AX15 is a split-case five-speed transmission built by Aisin and used in vehicles with AMC and Mopar 4.0/4.2-L I6 engines. Vehicles included:

The AX15 is also known as the AN5/AR5/MA5 in GM and Isuzu applications, and the R series in Toyota Celica and Supra Turbo hot-rods. The AX15 transmission came after the Peugeot BA10/5 and was installed in Jeeps from 1988 to 1999.

Jeep AX15 Transmission

Located in the assembly’s rear quarter, the AX15 transmission shifter mated to the NP231 and NP207 transfer cases and had a 23-spline output shaft and brass synchronizer rings. The Jeep AX15 transmission between mid-1988 and 1993 featured an internal slave cylinder, later restyled to an external release bearing design for easier upkeep. These AX15s had a different input bearing retainer, input shaft, and pilot bushing to accommodate the external throwout bearing.

All versions have an AX15 fluid capacity of approximately 3.3 quarts (75W-90 GL-3 AX15 transmission fluid required). However, this gear oil is now obsolete, so vehicle owners use GL-4/GL-5 or 50W fluids as an alternative (check for compatibility). Some Jeep owners use Redline MT90 manual transmission lubricant, Mobil1 10w30 full synthetic, Pennzoil synchromesh, or Royal Purple synchromax and have tested their compatibility with the AX15. Additionally, all its gears are helically cut and fully synchronized. Gear ratios are as follows:

Gear Ratios
1st3.83:1
2nd2.33:1
3rd1.44:1
4th1.00:1
5th0.79:1
Reverse4.22:1

The AX15 transmission is very popular with the off-roading crowd and with rock-crawlers. It also has huge aftermarket support – from adaptors, bolt one up, pilot bearings, clutch discs, to input gears.

Bellhousing Interchangeability

In addition to AMC I6/Mopar Jeep engines, the AX15 transmission makes a very clean adaptation to most GM engines and their hood housing. Due to its better transmission, it is also well-fitted to Chevy and Gen. III V6 and V8 engines and the Windsor Ford V8/I6, cover housings featuring the butterfly transmission bolt pattern.

How to Identify an AX15 Transmission

The AX15 transmission can be deceivingly similar to its siblings and occasionally mixed up with the AX5. But in reality, it has several differences from case material to pilot tip to OE application. For instance, the 4WD version of the AX15 featured a ribbed die-cast aluminum case and mid-plate. It likewise had a slightly shorter length of 16.5 inches compared to its 2WD length of 16.75 inches and used dowel pins for cover housing alignment.

You can find AX15 identification code numbers on the transmission gear case’s bottom surface, which indicates the month and year of manufacture and serial number. I have also gone ahead and consolidated information that will show you the differences among the Peugeot BA10/5, AX5, and AX15 for easier distinction from other seemingly similar transmissions:

AX15Peugeot BA10/5AX4/AX5
OE Applications
’88-’99 YJ/TJ/XJ/MJ,’93 ZJ, Dakota/Durango
78-’89 XY, YJ94-present XJ,
’87-’98 YJ/TJ
Gear Ratios (:1)
3.80, 2.33, 1.44, 1.00, 0.79
3.39, 2.33, 1.44, 1.00, 0.793.93, 2.33, 1.44, 1.00, 0.83 w/AX5
Length (in)
16.75
16.7510.25
Weight (lbs)
94
9479/94
Input Splines
10
Stickout length is 7.5 in
1014
Output Splines
23
(with 0.5-inch protrusion)
2121
Notes
Strong enough for a V8, quieter than a NV3500
Light duty, not worth rebuildingOE with AMC 4-cylinder

Aisin Jeep AX15 Transmission Specs

The AX15 shift mechanism is integral and mounted in the shift tower portion of the adapter housing, which is used to attach the transmission to the transfer case on 4WD models. 2WD models use standard extension housing. First to fourth gear ranges are in line for smooth shifting. Fifth and reverse gear ranges are separate but also in line. Due to its reverse lockout mechanism, the shift lever must be moved through neutral first before shifting to reverse.

Gearbox Garage shares valuable information about the differences between the AX15 and AX5/Peugeot shifters. It is a tad long but includes repairing, cleaning, reassembling, and breaking down each component.

You can improve transmission shifting, vehicle performance, and driving pleasure by getting a B&M Precision Sport Shifter (view on Amazon). It features a 303 stainless steel stick, CNC-machined aluminum base, and nylon pivot ball.

For lubrication, the recommended fluid is Mopar 75W-90, API Grade GL-3 gear lubricant, or equivalent. AX15 fluid capacity is 3.10 liters/3.27quarts in 4WD models and 3.15 liters/3.32 quarts in 2WD models. The correct top-off level is to the bottom edge of the fill plug hole. Inspecting the gear case’s mating surfaces, intermediate plate, adapter or extension housing, and front/rear bearing retainer seals for wear or damage can prevent leaks from occurring.

AX15 Transmission

Retrofitting the Peugeot and AX5

Installing the AX15 transmission in place of the Peugeot BA10/5 or AX5 will give you gains on drivetrain strength and is a perfect retrofit for Jeeps equipped with larger tires and lower gears in the axle & transfer case. This transmission is also ideal when upgrading to a larger V6 or V8 engine. However, be warned that the spline count and bellhousing patterns between an AX15 and AX5/Peugeot are different despite looking similarly close. As such, you may need to do a transfer case linkage modification and may require an AX15 transmission rebuild kit. The kit includes a new bellhousing (view on Amazon), transfer case shifter linkage, a cross-member adapter mount (for the stock Peugeot rubber mount), a slave cylinder kit, and a transfer case input gear.

AX15 Transmission Rebuild & Tips

Here are some rebuild tips for performing a Peugeot-AX15 swap:

Peugeot BA10/5 to Aisin AX15 Conversion

  • Since the Peugeot BA10/5 is quite an old transmission, moving to an AX15 requires either a correct-diameter pilot bushing to be sourced from different Jeep applications or an OE one to be machined. The output shaft, in particular, is the same length between the AX15 and the BA10/5, but the former has a stronger 23-spline diameter compared to the latter’s 21-spline.
  • When switching from Peugeot to AX15 transmission, use an ’89-’94 OE AX15 bellhousing. It shares the same internal slave cylinder with BA10/5, and it is also the most economical and most straightforward option. You may also follow other people’s lead by adapting Jeep Iron Duke four-banger or ’75 Land Cruiser external slave cylinders to the AX15 bellhousings if you happen to be working with a ’95-and-up assembly. As for the rubber bellhousing grommet that stabilizes hydraulic lines, you must source this from a dealer or Jeep replacement parts supplier to reduce the occurrence of hydraulic problems.
  • Jeep owners can typically retain the factory clutch and release bearing when retrofitting a BA10/5 since the AX15’s input shaft is of the same diameter. But there are instances that replacement clutch kits would sometimes include a new release bearing, which provides better clamping force than a stock system. It also makes for accommodating larger tires without overwhelming the hydraulic lines. Otherwise, replace the clutch assembly and release bearing in concurrence with the transmission swap, and resurface/replace the flywheel as needed.
  • A short shifter is recommended to avoid thrust clearance issues. To achieve this, you can go the route of getting short-stick applications for the AX15 from Jeep parts dealers. Another option is to find a short tower from an AX15-equipped Jeep XJ or heat and bend a stock AX stick.
  • If you are working with an NP231 transfer case, you can build it with six-pinion planetary gear sets, a heavier sprocket, and a wider chain to mitigate stress from larger tires and lifts higher than 3 inches. You may also opt for a stronger slip-yoke eliminator, or SYE, that helps eliminate oil leaks and cures lifted-Jeep driveline vibration by allowing more driveshaft length.
  • To offset the difference between an AX15 and Peugeot mounting pattern, many experienced mechanics and Jeep owners construct their own plate to pair the existing mounts to the AX15 transmission. Others modify an Advance Adapters plate designed for an NV3550 conversion. Doing this will raise the tranny about 3/4 inch and increases the driveshaft angle.
  • Never grease the clutch/tranny input-shaft splines or a sealed-brass replacement. However, you may do so lightly on a new bearing type pilot.

You need to look into other things that include the condition of input bearings, synchronizers, shift fork, and gears – especially if you are working with a rebuilt AX15 or one that is sourced from another vehicle. These components are bound to wear out for wheelers with high mileage. Watch this video for a demonstration on how to check on these parts and get them up to snuff:

Cost of an AX15 Transmission

Allstate Gears offers rebuilt AX15 transmissions that cost around $799 with a refundable core deposit of $250. New units, which are quite challenging to come by, are priced at $1,730. When outfitting your Jeep with an AX15, make sure you know the front pilot shaft tip’s diameter to purchase the correct rebuilt type. A rebuilt Jeep AX15-R1 works with a pilot shaft tip of 0.59 inches and an AX15-R2 for pilot shaft tips measuring 0.75 inches in diameter.

Novak likewise sells new AX15 units for less at $1,625. These units have the 1994-1999 configuration and come with all available upgrades and enhancements. They include new shifter components, an anodized aluminum shifter knob (available in black or clear), and a stronger gear alloy that would fit the external slave cylinder clutch system and ~3/4″ pilot shaft tip. They can also adapt to the following transfer cases:

  • Dana 18 (’41-’71, longer CJ6/CJ7/CJ8 Jeeps)
  • Dana 20 (’62-’79, longer CJ6/CJ7/CJ8 Jeeps)
  • Dana 300 (’80-’86)
  • New Process Jeep 208, 219 & 229
  • New Process 207, 231, 241OR, 241, 242 & 249

Cover housing and transfer case adapters are not included in Novak’s selling price but can be easily added to your purchased transmission package.

Advance Adapters also offers new units at $1,632.12 and is a top preference for many Jeep owners. The new units they offer specifically feature a 13° tailhousing rotation and are exact replacements for ’97-’00 Jeep TJ Wranglers. They will not work directly with a Jeep Cherokee, which has a 23° tailhousing rotation and will require transfer case linkage (view on Amazon) modifications and a new input gear (sold separately). Quadratec resells Advance Adapters 26-AX15 units with lower shift tower assembly and reverse switch included for $1,749.99.

Disassembled Vehicle Transmission

Frequently Asked Questions

  • How much does an AX15 transmission weigh? The standalone weight of the AX15 transmission is 110 lbs.
  • Is the AX15 a good transmission? The Aisin Jeep AX15 transmission is regarded as one of the better transmissions installed in Jeeps due to its ability to support the horsepower and torque output of V8 engines. Many Jeep owners praise its quick-shifting ability and smooth, positive gear changes. They consider it an ideal choice if you want an indestructible piece. Some outfitters even offer a kit that can put the AX15 behind a Corvette LS1 with 400 lb-ft torque.
  • Who makes the AX15 transmission? Aisin-Warner is the maker of the AX15 transmission. Aisin is a Japanese Fortune-500 company that develops and produces automotive components and systems for major OEMs, including engine, drivetrain, body and chassis, and aftermarket. It is half-owned by the Toyota Group of companies. The parent company is Aisin Seiki Co., Ltd., founded in 1949.
  • How strong is the AX15 transmission? Although the AX15 is a solid medium-duty transmission, it is by no means meant for hard driving. However, it is deemed indestructible by a lot of Jeep owners. Naturally, failures will occur due to worn-out components, drivers who do not know how to shift, or high mileage. Besides these, the AX15 is a very reliable and stout transmission. Be sure not to overestimate your AX15, though, as it won’t pair that well with a 5.7-liter Camaro/Trans-Am engine either.
  • How much torque can an AX15 handle? The amount of torque it can handle depends on the engine that it is mated with. For a 4.2-liter straight 6 engine (’87-’91 Jeep Wrangler models), it can handle 210 lb-ft. For a 4.0-liter straight 6 (’91-’99 Jeep Wrangler models), it can handle 220 lb-ft – only 45 lb-ft shy from the capacity of a 3.6-liter Pentastar V-6 (from ’11 onwards) engine. Others rumor that it can handle up to 300 lb-ft, similar to an NV3550.
  • Are all AX15 transmissions the same? Aisin Jeep AX15 transmissions have variances depending on the manufacture year. For instance,’ 89-’91 AX15 input shafts have a smaller 15-mm pilot tip than those produced from ’92-’99, which had (~19/32″) pilot tip. Release bearing systems changed – ’93 and older models used an internal slave cylinder while’ 94-’99 used an external one. The shift lever and turret for YJs, TJs, and Dakotas were taller due to the higher seating position relative to the transmission, whereas XJs, MJs, and ZJs have a short one. The bellhousing also varies depending on what engine the transmission came behind – choices are 2.5-liter Jeep (found in Dakota’ 96+ and AMC/Jeep), 3.9-liter Dodge V6, and 4.2-liter/4.0-liter Jeeps.

Conclusion – Aisin Jeep AX15 Transmission

The Aisin Jeep AX15 transmission is one of the most successful manual transmissions fitted to Jeep vehicles – so successful that when it changed to the NV3550 after 1999, many Jeep owners got disappointed with the results. In mint condition, it resells well and can extend your Jeep’s off-roading life for another decade or so. Used for the right application and with the correct configuration, it is a beast that can superbly harness the power. So, if you’re looking for a transmission assembly that is as robust as your 4×4, then the AX15 is perfect!

Kris Peter

Adventure seeker and off-road enthusiast. I love the thrill of going off-road and taking on the elements.

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