XJ Torque Converter Swap For Mileage And Power
From the May, 2012 issue of Jp
By Pete Trasborg
We embarked upon our ’98 Cherokee project during a time of astronomically high gas prices. Our goal initially was to build it to go off-road while not losing any on-road commuter-type mileage. We’ve stayed pretty close to the original plan, but over the last year or so we’ve been underwhelmed by the performance we were seeing.
The first step (after disconnecting...
The first step (after disconnecting the battery, of course) is to support the transmission and T-case. If you have an aftermarket skidplate like we do, you won’t be able to disconnect any of the vital components until it is out of the way. However, the skid supports the transmission and T-case, so before removing it all willy-nilly, put something under the T-case output to support the drivetrain. If you are doing this at home, a jackstand on the T-case output is usually the best way to go.
The transmission was getting too hot. Downshifting only made things worse. Then we started getting codes that the torque converter wasn’t locking up. Now, we knew the torque converter was hurting. We’d been hearing that death rattle every time we took the Jeep wheeling, and with 245,000 miles on the original transmission and torque converter, it was no big surprise.
But was a full transmission rebuild necessary, or was our torque converter the sole culprit as we suspected? We figured a torque converter swap could be done in a day. However, living 20 miles from the nearest parts store, and with no other Jeeps on hand if something went wrong in the driveway, we decided to enlist some expert help. We took the Jeep and the new torque converter down to Jeeps R Us in Laguna Hills, California. The crew had the install done in one morning, and we were back on the road before afternoon rush hour hit.
Once you’ve got the skidplate...
Once you’ve got the skidplate out of the way, you are free to pull the driveshafts off the T-case. We are still running the stock driveshafts, so the front one unbolts from the T-case at the CV joint. The rear shaft unbolts from the differential and then just pulls out of the slip yoke on the T-case. Fasten the front shaft up with a bungee cord or zip ties, and be careful not to lose the U-joint caps off of the rear shaft when you lay it out of the way. Larry Garcia was the main wrench on our Jeep that day; he discovered that the rear pinion seal was leaking so he ordered and installed a new one. That would have been a long bike ride to the parts store for us.
The results? Our suspicions were confirmed. Our gamble to change only the torque converter paid off this time around. We immediately noticed a seat-of-the-pants improvement in power, which the dyno verified. However, we were surprised to see that our power improvement didn’t translate into any increased mileage at the pump. So if your converter is chattery, your Jeep sluggish off the line, or your fluid temperature is inexplicably climbing, an inexpensive torque converter swap could buy many more miles for your automatic before a full rebuild is necessary.
If your exhaust still crosses...
If your exhaust still crosses under your engine behind the oil pan, you are going to have to disconnect it from the header/manifold and lower it. The first step to lowering the exhaust is to remove exhaust hanger at the transmission mount. Once that is loose, disconnect any O2 sensors you have in the downtube, and then unbolt the downtube from the manifold. Soaking the bolts at the manifold with penetrating lube can help loosen them; if you live in the rust belt or your Jeep has lived in the rust belt, you are going to want to buy new bolts, nuts, washers, and lock washers before you start the job.
One of the things that a lot...
One of the things that a lot of us forget when doing this type of work is to completely disconnect the wiring. Usually we end up testing the tensile strength of one or two wires. Garcia showed us that the easiest way to pull the electrical connections to the transmission and T-case in this Jeep is to disconnect these two plugs that can be found about halfway up the firewall.
You will also want to remove...
You will also want to remove the tranny cooler lines from the passenger-side of the transmission. Be sure to drain the transmission first. Garcia actually drained the transmission while he was removing the driveshafts, and by the time he got to this point the lines were mostly empty. Still, mostly empty isn’t entirely empty, and the few ounces of ATF left in the lines will make a big puddle. An old water bottle can be used to catch the rest of the fluid.
If your transmission has one,...
If your transmission has one, you will need to remove the kickdown cable. On the AW4 the easiest way to do that is to remove it at the engine end. Start at the throttle body and work back towards the transmission. In our case, there was a clip at the throttle body, a plastic retainer at the throttle linkage bracket, a plastic clip on top of the engine, and a plastic washer that attaches to a stud in the firewall. Once all that was disconnected, we were able to pull the cable down under the Jeep, ensuring that it wouldn’t get snagged on anything when the transmission came out.
Once you’ve removed all electrical,...
Once you’ve removed all electrical, fluid, and vent lines and cables you are ready to pull the transmission off the engine. But wait, if this is your first automatic transmission removal, you probably don’t know that the torque converter is bolted to the flexplate. Sure, you could pull the transmission without removing the four bolts that hold the torque converter in, but it makes the removal much more difficult and messy.
The first time you pull an...
The first time you pull an ’80s or ’90s Jeep transmission out of the Jeep, you’ll find these little buggers. They are external Torx bolts and located way up at the top of the bellhousing. While it is possible to pound a 3⁄8-inch, 12-point socket onto them, you might want to make your life easier by picking up an E14 socket before you start the procedure. If someone pounded a 12-point socket on them in the past, you will see the damage when you take these bolts out; you might want to replace them with regular hex head-bolts.
Here, Garcia compares the...
Here, Garcia compares the new stock-spec Omix-Ada torque converter on the left to our old burnt unit on the right. Even though Omix-Ada makes good parts, it is always a good practice to make sure there are no differences between the original and replacement part. For the converter, check for things like height, overall diameter, the flexplate-side bolt pattern and bolt size, and the OD of the sealing surface where the converter slides into the transmission. There is nothing worse than getting the transmission back in and discovering something doesn’t line up or fit.
There were two parts we didn’t...
There were two parts we didn’t think of before we started this job. One was a new element for the B&M auxiliary filter, which we were able to get from the parts store. The other was the input seal on the transmission. Unfortunately, the parts store didn’t have it in stock and since we needed the Jeep on the road that day, we couldn’t wait. Garcia inspected our existing seal and it was still soft, the spring was still in it, and there were no cracks in the rubber. So, we lucked out and were able to re-use the old seal. Do yourself a favor, though—pick up this seal and whatever filter or filters you will need before you start.
Always add fluid to the torque...
Always add fluid to the torque converter to keep the transmission from running dry at startup. It goes without saying that you should replace all the old fluid with new. Jeeps R Us isn’t a dedicated transmission shop, so they didn’t have a fluid reclamation/recirculation machine. Instead, Garcia blew out the transmission cooler lines with compressed air. The entire system was refilled with a total of 8 quarts of Royal Purple Max ATF, including the quart that was put into the torque converter. After that is filled, carefully slide it onto the input shaft without forcing the converter and keep in mind the input seal. Then reassembly is the opposite of removal.
The blue curves show the dyno run we did during our tire weight power shootout(baseline) and the orange curves show a similar run with the only change being the torque converter. You can see how we picked up almost 11hp and 14 lb-ft of torque at peak. More important than those peak numbers is the area between the before and after power curves. This is what our butt-dyno measures and is really noticeable in day-to-day driving.