When my friend Jennifer started having trouble with the transmission in her Jeep Cherokee, I was really surprised. The AW4 in the Cherokee is a very reliable transmission. However, hers was becoming very sluggish to engage either drive or reverse when cold. It would work fine once warm but was taking longer and longer to warm up each morning.
Another friend of ours had a transmission available as he was parting out his old off road Jeep. I made the trip to Kentucky to help him swap parts and picked up the left overs. Loading it on the trailer was fun since it had no brakes after the axle swap. But it did prove the transmission worked fine.
The swap began with removing the transmission and transfer case from the donor Jeep. Since both Jeeps had the 231 transfer case I decided to simply swap the transmission and transfer case as a unit.
I began by disconnecting the transmission control and sensor wires at the firewall. There are three connectors. Also the transmission kick down cable needs to be disconnected from the throttle linkage. The battery cable needs to be disconnected at this time as well.
With the Jeep on the lift, I removed the two drive shafts. Then the starter and the inspection plate from the front of the transmission. Next, I unplugged the wires to the oxygen sensor and removed the bolts holding the exhaust to the manifold. I also unbolted the transmission filler tube from the backing plate.
I fabricated a mount for my hydraulic lift table to hold the transmission and transfer case so I could lower it down once it was loose. I cut the exhaust between the muffler and tail pipe to make it easier to handle.
With the transmission supported by my table, I removed he cross member. This is when I discovered that the transmission mount was broken and had been for some time. The transfer case shift linkage was slightly damaged due to the movement, so I left it in place and simply disconnected it from the transfer case. The exhaust came down with the cross member as well.
Next I removed the cooling lines from the side of the transmission. It took quite a while to clear the dirt and mud out of the quick connects to get them to release. I used a dental pick to scrape between the tube and the connector.
Next I removed the four bolts that secure the torque converter to the flex plate. I was surprised at how easy the engine turned over indicating that it was low on compression, although it ran well.
Then I lowered the transmission slightly to get better access to the upper bolts. Then I removed the crank shaft position sensor.
Next I removed the two large bolts on either side of the transmission that secure it to the block. Then using the proper socket and about three feet of extensions, I removed the two inverse torx bolts from the top of the transmission.
With the transmission loose I began to drop it down. That is when I noticed I had missed one of the bolts that secures the cover plate to the transmission. With that last bolt out, the transmission slid out easily.
The only glitch was that I made my holder too tall and it would not roll out form under the Jeep. I had to use my engine hoist to lift the axle enough to clear the bell housing. I then used the hoist to lower the transmission transfer case unit to the floor.
Then I towed the donor Jeep back out into the yard.
Next I put Jenny’s Jeep in the shop and began disconnecting the stuff under the hood. When I disconnected the transmission control wires I noticed one of the plugs was different and filed that away in my mental notes for later.
The exhaust was broken between the tail pipe and the muffler so I did not have to cut hers to drop it. Otherwise, I used the same procedure to drop her transmission and transfer case as a unit as I did the donor Jeep.
I had a really hard time with the transmission lines on her Jeep however. The plastic quick connect pretty much crumbled away instead of releasing. On one I had to unscrew the coupling from the transmission to get it off the line. The connection to the radiator was easy on hers however because a previous owner had cut off the quick connect and just clamped the hose to the metal line.
While working with the lines however, I think I found the cause of the transmissions early demise. Right at the oil pan both lines were crushed. On line was nearly pinched off. Looks like sometime in its history this Jeep suffered a track bar failure allowing the axle to contact the oil pan and crush the transmission lines. I am sure the transmission had trouble maintain proper pressure and cooling with the restricted flow.
I checked on the price of new lines but the Jeep dealer wanted $170 for the set. I decided to recover the lines from the donor Jeep. It took a while working on the cold wet ground but I finally worked the lines out intact saving all the plastic connectors.
With both transmission on the floor beside each other, I started sorting out the differences in the 92 vs 94 wiring. It turned out he only difference was the speed sensor for the speedometer drive. I planned to change it any way due to possible differences in the speedometer drive gear. It turned out both used the green gear so that would not have been a concern. However, I had to make the swap to have compatible wiring connectors.
After slightly modifying my lift table, I set about reinstalling the transmission. I use a floor jack and a pole under the oil pan to help align the engine with the transmission and it slipped in easily. After installing the two large side bolts, I lowered the assembly slightly to install the two inverse torx bots on the top.
Next I installed the starter and exhaust pipe and the good transmission mount. After raising the assembly close to its proper place I installed the torque converter bolts and replaced the inspection plate.
Jenny’s Jeep is fitted with a transfer case drop to reduce drive line vibration caused by her three inch lift. The drop uses longer bolts and spacer blocks to mount her cross member.
I noticed that her cross member was twisted so I replaced it with the one from the donor Jeep. This one was also pretty beat up from off road abuse but at least it did not have a twist.
As I tightened the bolts I found one of them was stripped out in the unibody. Rather than try a more complicated repair, I found a long all thread bolt and cut off the head to make a stud. I then welded the stud in place in the unibody. Having a stud here actually makes bolting the cross member in place much easier as it keeps the spacer from sliding out on that side.
I welded up her muffler where the tail pipe was broken out. Once it was all in place I set it down and attached the wires and installed the dip stick tube. I then reattached the battery.
A quick test drive showed there was no delay in uptake to drive or reverse unlike the previous transmission. It was well within the 1.2 second spec for engagement even cold.
I headed out of the driveway for a road test. All went fine until I got onto the pavement. It simply refuse to switch out of first gear. I drive a lot of different driving options but to no avail.
Back in the shop, I started reading the trouble shooting guide in Factory Shop manual. failure to shift our of first was not one of the possible failure modes listed in the book!
I next started following the test procedure. The first step was to check for mechanical operation of the transmission. This step involves disconnecting the transmission computer and shifting manually. I dug under the passenger side dash and disconnected the controller.
A test drive showed the transmission functioned perfectly in manual mode. All gears engaged properly. I then plugged back in the computer and it stayed in first gear.
Assuming I had somehow damaged the computer or maybe it was not as compatible between different years as I had been told, I removed the computer from the donor Jeep and connected it to Jenny’s Jeep.
It still stayed in first. Completely stumped, I took a break and posted my question to the XJ list. A reply from Dave had me checking the throttle position sensor, and speed sensor inputs. I saw that the computer used these two inputs to decide when to shift.
The throttle position sensor tested out to within specs. And I assumed that since the speedometer worked, that the speed sensor must work also. However, after some more reading in the shop manual, I noticed there were in fact two speed sensors.
Testing it was a bit difficult due to access to the wires so I first decided to test the one on the floor. Once I figured out where to connect the test leads I saw the sensor made two pulses per revolution of the drive shaft.
When I connected my test leads to the one in the Jeep, it was constantly on and did not change like it was supposed to. I was on to something now.
The biggest trouble was that this sensor is located under a bracket that holds the transmission to the transfer case and holds the shift linkage. It is locate just about the cross member and on top of the transmission.
Access meant supporting the transmission, removing the cross member and lowering the assembly enough to remove the bracket and get to the sensor. Eventually, I accessed the sensor and as I removed it to swap it for the good on, I saw the problem.
The wires had been damaged by the shift linkage when the grommet popped out sometime ago. I guess moving the wires around made then contact in the bare spots as the transmission had been working fine before I pulled it out.
With the replacement sensor in place and all the metal parts bolted back up, I took it for another test drive. This time it shifted perfectly.
I swapped out a few more parts from the donor Jeep like the fan shroud and seat cushions and delivered it back to Jenny. She seemed very happy to have her Jeep back. Especially now that she does not have to wait ten to fifteen minutes from the time she cranks it until she can drive it.
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