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T18 Transmission Rebuild

Posted in How To: Transmission Drivetrain on March 24, 2017
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Most manual transmissions have the shifter mechanism incorporated into the top cover. This top cover is easily removed and all of the guts of the transmission are installed through this opening–hence the term, “top loader.” Most top loaders have a similar layout, so this article will give you a good idea of what you are getting into if you are considering any transmission work on a Jeep up to 1986. We are going to rebuild one of the beefiest manual transmissions you can put into a Jeep, the top-loader Borg-Warner T18.

The Borg-Warner T18 transmission is famous for its strength and durability in the truck and off-road world and was built for quite a few Ford trucks, IH vehicles, and Jeeps. With or without an adapter (depending upon which version of the T18 you find—Ford or Jeep), it’s compatible with GM, Ford, and AMC engines. It features an iron case, a 6.32:1 “granny” first gear, and is direct-drive in fourth gear. Extremely strong, but with good highway and trail manners, it’s adaptable to essentially all of the Jeep transfer cases from ’66 to ’91.

In general, the IH versions of this transmission are not desirable for swapping into a Jeep due to some unique components that make this version prohibitively expensive to adapt. As well, some versions of the T18 were a “close ratio” and only had a 4.02:1 First gear, and the less desirable First gear ratio makes it hard to justify doing the swap. The best places to find a “wide ratio” 6.32:1 T18 is in Full Size Jeeps (FSJ), like a J-truck or Wagoneer, and just about any Ford truck from ’66 to ’91.

We worked with a Ford T18 transmission to rebuild and swap into our Jeep (because it was much easier to find and a cheap buy from our local classified ads), and it’s the next best thing to the ’77-’79 Jeep CJ T18. It came with the old style Dana 300 adapter, but the adapter was cracked, and that helped us get it for a great price.

Each of these options has some obstacles. The Ford version of the T18 has the correct input shaft length but needs a bellhousing adapter as well as a rear case adapter and different main shaft to mate to a Jeep transfer case. The T18 found in FSJs had varying lengths of input shafts that require long adapters between the bellhousing and transmission that make it difficult for use in short-wheelbase Jeeps. Fortunately, Novak Adapters offers the right parts to convert these two T18s to fit a wide variety of Jeep vehicles. If you find a 4.02:1 FSJ T18, there are no parts available to convert it for a short wheelbase Jeep. The bonus with the FSJ transmission is that they came with Dana 20 Jeep transfer cases bolted to them, so swapping them into a CJ is simple.

Then there is the Holy Grail of Jeep T18s. Found in ’77-’79 CJs was a T18 from the factory with the correct input shaft and a Dana 20 transfer case bolted to it. If you can find one of these, buy it! It is worth a few extra bucks since it has all of the right stuff to bolt right into a CJ. Be careful of the ’76 CJ T18, though: it only had the 4.02:1 first gear.

The T18 in this article is a Ford version that was bought on the cheap via the local classifieds. It already had an early version of a Novak Jeep Dana 300 adapter installed, but the mounting plate was cracked. That was not a problem because the plan was to mate it to a Dana 18 transfer case anyway. A phone call to Novak Adapters helped properly identify this T18, and the correct rebuild kit and Dana 18 adapter were soon on their way. So without further babbling, here are the highlights of the rebuild.

The letters and numbers near the PTO port (driver side) of our cheapo-find T18’s case helped identify it.
The Novak kits came with everything we needed, including excellent instructions for the rebuild kit and the adapter kit. We highly recommend you read the instructions before opening any items or taking the transmission apart. Having a good idea of the order of operations will save you a lot of time by not having to do things twice.
We removed the top cover and inspected the guts of the transmission before calling Novak for the rebuild kit and adapter, that way if any of the gears look rusted or pitted, we could order replacement parts too. To get started, the front and rear bearing retainers were removed, exposing the main bearings. A thin drift was then used to drive out the roll pin holding in the reverse shift lever, and then the reverse shift lever was removed.
Once the C-style snap ring was removed from the front bearing, a flathead screwdriver was used to pull the bearing out a little bit. The bearing is not moving on the shaft here, you are actually beginning to slightly separate the input shaft from the main shaft. This is to gain enough room to get a bearing puller on the input bearing.
A three-jawed puller had to be modified to fit on the input bearing. The heads on the bearing side of the arms were ground flat and then a tooth was cut into each head. A small tie-down strap was used to hold the arms in the snap ring groove of the bearing, and then it was pulled off without too much effort. After removing the snap ring, an un-modified two-jaw puller made quick work of the rear bearing.
Now that the front and rear bearings had been removed, we separated the input and main shafts. The roller bearings inside the relief of the input shaft will be replaced with new bearings from the rebuild kit. We pushed the input shaft forward as far as it would go, and pulled the main shaft as far back as it would go. The main shaft lifted out easily, but if yours doesn’t, don’t force it! A little finesse may be required. You don’t want to damage anything.
Starting from the front of the main shaft, we removed the snap ring and then carefully slid the third gear clutch hub assembly, synchro, and third gear off the main shaft. One of the most important parts of a rebuilding a transmission is to keep all of the parts in order the way that they came out and off, as well as the proper orientation. One trick we learned to lay fresh cardboard on the workbench so notes can be written on the cardboard. Little black arrows written below each part show which direction each piece goes.
Working from the back of the main shaft, we removed the snap ring and then carefully removed the first gear with the first-and-second gear clutch hub as an assembly (seen sitting on work bench to the left removed). We then removed the second gear from the main shaft (seen still on the shaft).
We suggest wrapping the first-and-second-gear clutch hub assembly in a rag before removing the first gear-slider so the detent balls and springs do not fly across the floor. Notice there are no detent balls in this picture (we found them later). It’s also important that the three grooves in the synchro ring (gold) and the three rectangular shifting plates that are part of the clutch hub are properly aligned during reassembly, as failure to do so could damage your newly rebuilt transmission.
For comparison, we lined up the old main shaft (top), with the new main shaft (bottom) that will allow the rebuilt Ford T18 transmission to mate right up to the Jeep Dana 18 transfer case.
Our first step in reassembly was replacing the detent balls and springs in the first gear selector assembly. Take your time and be careful, you don’t want to slip and have those little balls catapult across the shop and then have to order new ones from Novak.
Reassembly was a breeze because we paid close attention to how it all came apart. The front half of the main shaft was completely reassembled, and then the new second gear synchro was put into place. The First gear and first-second gear clutch assembly was slid into place, and the snap rings installed. Bearing grease was used to hold the roller bearings in place inside the recess of the input shaft, the new syncho put in place on the input shaft, and then the input shaft and main shaft were joined again.
Now that the main shaft and input shaft were back together, we could focus on the removing the countershaft and cluster gear. We used a brass drift to knock out the counter shaft so that the cluster gear can be removed. When removing the cluster gear, we kept track of the thrust washers, where they went, their order, and orientation. These thrust washers are specially designed to allow oil to flow into the counter shaft bearings.
The Novak transfer-case adapter is made of high-grade aluminum. This particular adapter requires one of its necessary four mounting-bolt holes be drilled and tapped into the T18 transmission case. We test-fit the adapter on the T18 transmission case so that the location for the new hole could be marked with a center punch, then the transmission case was set up in a drill press where the new hole drilled. We then hand-tapped it.
We replaced all of the roller bearings inside of the cluster gear and used bearing grease to hold the roller bearings in place. There are two layers of bearings on each side of the counter shaft and thrust washers between the layers.
Again, we use a little grease to hold the outer thrust washers to both ends of the cluster gear. The order and orientation of the thrust washers on both ends of the cluster gear are important. The grooves on these washers allow oil to flow to the roller bearings inside the cluster gear. Notice the alignment feature at top of one of the outer thrust washers in this photo.
The boss for each end of the cluster gear is inside each end of the transmission case, and they are different. We made sure that the outer thrust washers on the ends of the cluster gear were matched with the correct case boss. You do not want to put them on the incorrect side. You may find it easier to use a little grease to hold those thrust washers onto the boss’ to ensure proper alignment and drop the cluster gear in separately. As long as they are in the right place in the proper orientation, it doesn’t matter if you stick them to the boss’ or to the cluster gear for installation.
Once the cluster gear was in place, we inserted the countershaft, lightly tapping with a brass hammer as needed. The trick here is to not displace any of the roller bearings inside of the cluster gear as you are installing the counter shaft. If you do, simply remove the cluster gear, reset the roller bearings, and try again. We got it on the second try. We also cleaned the front counter shaft bore and added a tiny bit of black RTV to help seal the case before tapping the countershaft into place. We also dapped a bit of black RTV on to the countershaft bore on the other end of the case once the countershaft was installed.
A new countershaft keeper is included in the rebuild kit from Novak. It keeps the countershaft and reverse idler shaft from falling out and also keeps them from rotating. The roller bearings rotate on the shaft while the shaft remains stationary.
The rebuilt input shaft was first slid into its place in the transmission case. Then, we slid the rebuilt main shaft into its place. This was a delicate operation that required patience. If you use force to get the main shaft into the correct position, gear teeth can be damaged. Clearances were tight, but it did go in with careful manipulation.
We carefully slid the tip of the main shaft into the recess of the input shaft. This step was a little tricky, as we didn’t want to displace any of the roller bearings in the end of the input shaft. A displaced roller will damage your transmission during bearing press.
We double-checked that the three relief cuts on the fourth-gear synchronizer on the input shaft were properly aligned with the shift blocks on the front of the main shaft. If these are not properly aligned, they will break when you press the front and rear bearings into place.
We were on the homestretch now, but didn’t want to get cocky, so we double-checked all of our work up to this point before pressing the bearings into place. We added the oil slinger for the front bearing, and made sure the slinger was placed in the correct orientation.
A hand-operated hydraulic press was used to press the front and rear main bearings into place. Do not attempt to hammer them into place, as the bearings can be damaged. The snap rings were put onto the bearings so that they would not travel farther than intended. It didn’t take a great amount of force to seat the bearings, but if the jack handle on the press gets difficult to pull down on, stop, pull the transmission out, and double-check everything again.
After the main bearings are successfully pressed into place, rotate the transmission by hand in all of the gears. It should flow freely and evenly. If the gears seem locked up when you try to turn it by hand, don’t panic. The cone shapes of the synchros tend to stick to the mating surfaces during the press operation. A very gentle pry with a flat screwdriver can easily free up the stuck synchros.
We reinstalled the reverse shift lever and the new roll pin to complete the assembly.
The top cover was bolted back on to the case (both of which had been cleaned up and given a coat of fresh black spray paint during the rebuild process) after the front and rear bearing retainers were outfitted with their seals and torqued to the proper specification. There was a great sense of satisfaction once it all was completely back together and positioned between the frame rails behind the new V-8. Now, if only we could get some time to work on the axles.

Sources

Novak Conversions
Logan, UT 84321
877-602-1500
http://www.novak-adapt.com

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