The Aisin-Warner AX15 Transmission was a standard shift 5 speed transmission used in Jeeps between 1988 and 1999. It is a medium-duty transmission that is found behind the AMC 4.2L I6 and AMC 4.0L I6 engines. It is well known that this transmission can handle even more power than the stock 4.0L, with many running the AX15 behind LS swaps and stroker inline-6’s.
There were two main types of AX15s – those between 1988-1993 and those manufactured after 1994. Before 1994, the slave cylinder was internal which required the opening-up of the transmission to repair the slave cylinder and any leaks it may have. In 1994, AX15s were upgraded and fitted with an external slave cylinder that can be replaced within a matter of minutes with the transmission still in the vehicle. If you are in the market for an AX15, I would search for one made in 1994 or later.
Need help changing the fluid or performing other repairs? Jump to the write-ups section below.
The AX15 transmission is sensitive to GL lube that contains sulfur. Sulfur reacts with the brass parts in the transmission leading to premature failure. Mopar recommends 75W-90 API Grade GL-3 gear lubricant. GL-3 lubricant is discontinued, and can very rarely be found for purchase. Fortunately, these transmissions have been approved to run on Synthetic 10W-30 Motor Oil. Others recommend Redline MT90 as another safe option.
The correct level can be set by simply filling to the bottom edge of the fill plug hole.
More information about the AX15 can be found here.
Gear Ratios
| Reverse | 4.22 |
| 1st Gear | 3.83 |
| 2nd Gear | 2.33 |
| 3rd Gear | 1.44 |
| 4th Gear | 1.00 |
| 5th Gear | 0.79 |
Fluid Type and Capacity
| Lubricant | 75W-90 GL-3 or GL-4 |
| Capacity (2WD) | 3.32 qts (3.15L) |
| Capacity (4WD) | 3.27 qts (3.10L) |
Other Specifications
| Weight | 94lbs |
| Length (2WD) | 16.75″ |
| Length (4WD) | 16.5″ |
| Input Splines | 10 |
| Output Splines | 23 |
| Pilot Tip Diameter | 1989-91: 19/32″ 1992-99: 3/4″ |
Transfer Case Compatibility
The AX15 was attached to the New Process Model 231 transfer case.
You can adapt the Jeep Dana 30 transfer case using a kit by Novak found here.
It is also possible to adapt the New Process Model 207 transfer case to this transmission, but you will need to shorten the input shaft of the transfer case to 2.1″ of stick-out length to prevent bottoming out.
Engine/Bellhousing Compatibility
As is, the AX15 is compatible with the AMC 4.2L I6 and AMC 4.0L I6. It may be adapted to Ford, GM, and other AMC engines with adapters.
Write-ups and Tutorials
AX15 Full Rebuild
The Jeep Repair currently doesn’t have their own write-up on rebuilding an AX15, but will soon! In the meantime, YouTuber “UCanDoIt2” does a video series on rebuilding his AX15. Find the first video here
