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T-90A Transmission - Black Box No More

Trenton McGee | Writer
Posted October 1, 2006

Rebuilding a T-90 Three-Speed Tranny at Home

Many experienced off-roaders won't think twice about tearing down an axle to fix a broken axleshaft or even pulling down their rig's engine to change a worn-out timing chain or swap in a hottercam. But when it comes to the internals of transmissions and transfer cases, something about these mysterious black boxes sends the majority of them running for the hills, or at least to their local off-road shop where they'll shell out big bucks to fix a problem rather than crack open what seems like a Pandora's Box. But we're here to tell you it doesn't have to be that way.

Using ourselves as guinea pigs to prove our point, we tore down and rebuilt a T-90A three-speed transmission from a '47 Jeep CJ2-A using a master rebuild kit and some extra items sourced from Novak Conversions. While Editor Rick Pw and perhaps a few of our readers have been through hundreds of T-90s, it was the author's first time inside any manual transmission. As such, it was a lifesaver having Novak's extraordinarily detailed instructions on hand along with an exploded view of the tranny. Novak's master rebuild kit includes everything you need to do a quality job, and the instructions saved us from ourselves more than once. While the T-90 is one of the simplest trannies on the planet (no special tools are needed to do the job), its basic construction is a good primer for many other three- and four-speeds. What follows are the highlights of the rebuild process along with a few tips should you be brave enough to venture into the depths of your own gear jammer. In the end, we had all three forward gears (plus Reverse!), no extra parts, and a little extra money to spend on other upgrades.

Novak's master rebuild kit is one of the most complete on the market and includes bearings, a new Second gear (not shown), a hardened cluster shaft, synchros, thrust washers, gaskets, and all the small parts you need to complete the rebuild. We popped the top on the tranny before calling Novak and noted the First-Reverse gear was hosed along with the Reverse idler, so Novak recommended replacing them along with the cluster gear (large gear in photo). The reason for this whole exercise was a wasted mainshaft, but we scored a serviceable used mainshaft from a buddy for a six-pack of Corona.

Start with a clean workbench and a T-90 that has been freed from the vehicle. In most applications you'll need to pull the top cover before dropping the tranny out of the vehicle. Separating the transfer case is a bit odd and is further complicated if it's equipped with an overdrive, so read the instructions first. Before beginning, take a good look at the internals to see if anything is obviously wrong. In this case, the First-Reverse gear was badly rusted and the Reverse idler gear had several chipped teeth. Also note the molasseslike sludge in the bottom of the case, indicating contaminated oil.

Remove the snap ring from the front bearing along with the two 12-point 5/16-inch bolts from the front of the case that hold an oil collector (A). Next, remove the retaining plate on the cluster and idler shafts (B) on the back of the case; don't worry if you mangle it, as a new one is provided. Next, drive the cluster shaft (C) rearward out of the case; don't drive it forward or it will damage the case. The cluster gear and all its needle bearings will drop to the bottom of the case. Leave them there for the time being.

Remove the rear bearing, retaining plate, and spacer, then grab the mainshaft and pull it rearward out of the case. You will hear more needle bearings fall, but that's OK. The mainshaft, First-Reverse gear, Second gear, and synchro hub will all come out of the case together. Note that the shift fork groove in the First-Reverse gear faces the front of the case.

Since we didn't have a shop press on hand, we reinstalled the front bearing snap ring and used a brass drift to drive the input shaft inward, thus separating it from the front bearing (it only has a light press fit). Note that you'll need to fish out the oil collector (arrow) first to avoid damaging it. If a previous installer left this oil collector out, source a new one before putting the tranny back together as it plays an important part in oiling the front bearing. With the input shaft out, you can remove the cluster gear from the bottom of the case.


Novak Conversions
Logan, UT 84321
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