This is NOT my post. I am copying it from another forum as I feel it is a great resource for TJ owners.
I'm swapping over an AX15 into one of my '04 Rubicons to replace the NV 3550. Despite only having 52K on it, the 3550 had water in it when I bought it a few months ago and shifting it feels like stirring a broomstick in a bucket of gravel in the 1-2 range, especially in the 2 to 1 downshift. I have 3 rebuilt AX 15s laying about and figured I'd give it a shot. For the YJ readers, some of the measurements and photos may be useful even though the NV3550 was used in the TJ, not the YJ, from 2000-2004.
I read what I could find on this forum and others about this, but found the information disappointing at best--the threads deteriorated rapidly into the merits of one transmission over the other with unsubstantiated claims and innuendo, a raft of trolls submitting useless drivel, and none of these well-intentioned but poorly informed threads ever came to a conclusion or were ever closed out. So, figured I'd do my own writeup on this, and I am not going to entertain discussions of which is better and why, why I chose to do this or which can handle more torque or other scatological diatribe.
I am going to show measurements of both of these, how they mate to the NP 241J that is in this Rubicon, etc and enough photos and details to bog down the server. Here we go.
AX 15 on the left, with bellhousing, and NV 3550 on the right.
Side-by-side, NV top, AX bottom. Notable differences--there is no intermediate plate in the NV, and the front case half is shorter in the NV than the AX, while the rear case is way longer. Larger, square shift tower opening in the NV than in the AX.
Overall length of the 3550
Length of the AX 15. They are the same length.
Bellhousings. NV 3550 on right, AX 15 on left.
Length of 3550 bellhousing.
Length of AX 15 bell--they are the same.
Length of the NV 3550 gear case.
Length of the AX 15 gear case. They are same-same.
Location and fit of the CPS between both of these bellhousings are the same, the AX bellhousing will bolt to the NV 3550 without any need for clearancing, and the NV3550 will also bolt to the AX 15 bellhousing with the same 9 bolts--size, thread pitch and length. The clutch forks are the same and interchangeable, as is the throwout bearing fit. The starter bolts up to either of these bellhousings, and properly engages the flywheel without need for adjustments. Clutch spline count, input shaft length and pilot snout (0.750") are also the same. The 1991 and older AX 15 featured a 0.590" pilot snout, and the AX 15s 1993 and older came with a flat-faced input bearing retainer which was used with the Internal Clutch slave cylinder (AKA "concentric bearing") used in these editions.
Since TJ Wranglers used the external clutch slave version AX 15 up to 1999, and the same 4.0 engine was used in the TJ up to the end of the series in 2004, while the NV 3550 replaced the AX in the 2000 to 2004 model Wranglers, it is not surprising that there are these interchangeabilities. Until I checked it out for myself though, it was all innuendo because I could not find a thread legitimately documenting this information.
I'm swapping over an AX15 into one of my '04 Rubicons to replace the NV 3550. Despite only having 52K on it, the 3550 had water in it when I bought it a few months ago and shifting it feels like stirring a broomstick in a bucket of gravel in the 1-2 range, especially in the 2 to 1 downshift. I have 3 rebuilt AX 15s laying about and figured I'd give it a shot. For the YJ readers, some of the measurements and photos may be useful even though the NV3550 was used in the TJ, not the YJ, from 2000-2004.
I read what I could find on this forum and others about this, but found the information disappointing at best--the threads deteriorated rapidly into the merits of one transmission over the other with unsubstantiated claims and innuendo, a raft of trolls submitting useless drivel, and none of these well-intentioned but poorly informed threads ever came to a conclusion or were ever closed out. So, figured I'd do my own writeup on this, and I am not going to entertain discussions of which is better and why, why I chose to do this or which can handle more torque or other scatological diatribe.
I am going to show measurements of both of these, how they mate to the NP 241J that is in this Rubicon, etc and enough photos and details to bog down the server. Here we go.
AX 15 on the left, with bellhousing, and NV 3550 on the right.
Side-by-side, NV top, AX bottom. Notable differences--there is no intermediate plate in the NV, and the front case half is shorter in the NV than the AX, while the rear case is way longer. Larger, square shift tower opening in the NV than in the AX.
Overall length of the 3550
Length of the AX 15. They are the same length.
Bellhousings. NV 3550 on right, AX 15 on left.
Length of 3550 bellhousing.
Length of AX 15 bell--they are the same.
Length of the NV 3550 gear case.
Length of the AX 15 gear case. They are same-same.
Location and fit of the CPS between both of these bellhousings are the same, the AX bellhousing will bolt to the NV 3550 without any need for clearancing, and the NV3550 will also bolt to the AX 15 bellhousing with the same 9 bolts--size, thread pitch and length. The clutch forks are the same and interchangeable, as is the throwout bearing fit. The starter bolts up to either of these bellhousings, and properly engages the flywheel without need for adjustments. Clutch spline count, input shaft length and pilot snout (0.750") are also the same. The 1991 and older AX 15 featured a 0.590" pilot snout, and the AX 15s 1993 and older came with a flat-faced input bearing retainer which was used with the Internal Clutch slave cylinder (AKA "concentric bearing") used in these editions.
Since TJ Wranglers used the external clutch slave version AX 15 up to 1999, and the same 4.0 engine was used in the TJ up to the end of the series in 2004, while the NV 3550 replaced the AX in the 2000 to 2004 model Wranglers, it is not surprising that there are these interchangeabilities. Until I checked it out for myself though, it was all innuendo because I could not find a thread legitimately documenting this information.
