lgrant

I’ve got a 99 XJ and I’m looking to do a transmission hack to achieve:

1. Lock into 4th gear (overdrive) along with torque converter lockup for highway cruise. A healthy 4.0L, with something close to stock wheels/tires, will pull a majority of hills when traveling at highway cruise – no need to downshift and lose lockup. Staying in 4th gear and staying in lockup is a much more pleasurable driving experience. Please do not confuse TC lockup with the 4th gear, which is overdrive of the 3rd gear.
2. Be able to select 2nd gear when the gear shift selector is in 1-2 position. I could be wrong but it seems like 2nd gear is not available (at low RPMs) for helping control descent on steep grades. When in 4WD Low, at times 1st gear becomes too slow while at the same time 3rd gear is way too fast.

Please have a look at the below schematic – much of it comes from others that have come before me and info they have posted. Also I understand that there have been commercial applications available for purchase in the past that are no longer available. Those applications would probably make for a smoother, easier to use application but if no longer available, then maybe this post has some value? Further, let me say early on that I am not an EE major or an electrician. Accordingly, the schematic could, no doubt be drawn more professionally. I just drew it up in something I could understand.

Comments on schematic:
1. S1, S2 and S3-TC are the solenoids we find in the AW4.
2. Resistors – apparently needed to keep the TCM from throwing a code and triggering the CEL. I’ve seen 1,000 ohm, 1 watt specified on other schematics. No guarantees on those values being ideal.

How it would work:
1. To achieve lock into 4th gear and TC lockup, one would move the DPDT switches #1 and #3 from the regular TCM operation to the other position. Presuming a vertical throw of the switch, let’s say you go from the bottom position (TCM normal) to the top. Switch 1 would lock S1 and S2 into the off position which would give a lock into 4th gear. Also switch 2 would lock S3-TC into the on position which would give TC lockup as long as the switch is in this position. The switches would be thrown as the vehicle accelerated through 40 mph and then reversed to the TCM normal position as the vehicle decelerated through 40 mph.
2. To get a lock into 2nd gear, the shift lever would be in the 1-2 position, switch 2 would be in the lower throw position (normal TCM operation - no TC lockup) and switches 1, 3 and 4 would be in the up position. That forces S1 and S2 into the on position, which gets one 2nd gear.

Switches 2 and 3 may be superfluous – almost certainly #3 and maybe #2. And if #2 was not needed, then that would be a great advantage in that one would not need to remember to move switches 1 and 2 to TCM normal when slowing down below ~40 mph. The brake light switch and/or the TPS would kick it out the TC out of lockup. The unknown if whether the TCM, trying (but unable) to manipulate S1 and S2, would kick the TC out of lockup?

Let’s get some comments from the electrician and electronics folks.