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T-90A Transmission - Black Box No More

Rebuilding a T-90 Three-Speed Tranny at Home

Photography by Trenton McGee

The last portion of the disassembly involves removing the synchro hub from the mainshaft by removing its snap ring. Take note of how the synchronizers, three shift pawls or "dogs," and springs all go together. Clean and thoroughly inspect the case and all of the components that will be reused. Check the case carefully for cracks. Any pitting, chipping, or galling on the gears, shafts, or case means it's time to order replacements.

While waiting for a coat of paint on the case to dry, we assembled the needle bearings in the new cluster gear. There are a total of 88 needle bearings, six small spacers, and one large split spacer that all must be stacked inside the cluster gear bore. If that sounds tedious, that's because it is. Avoid the urge to use wheel-bearing grease to hold the needles in place during assembly; Novak claims the grease can repel gear oil for quite some time and prevent the rollers from getting adequate lubrication. We used petroleum jelly instead and took another gem of Novak's advice by cutting a piece of 31/44-inch OD tubing (arrow) and inserting it in the cluster gear bore to help hold all those needles in place during assembly.

Aside from the needle bearings, the trickiest portion of the installation is assembling the synchronizer hub. The two small wire springs install in both sides of the hub and must engage the three synchronizer pawls (also commonly called shift dogs). Then, while holding all three plates with your fingers, slide the synchronizer sleeve (the part the shift fork engages) over the plates to retain them. When done correctly, it should look like what is shown. Also, the three recesses in the brass synchronizers must line up with the plates when installed. Now you can assemble the Second gear and synchronizer hub on the mainshaft.

Carefully place the cluster gear (A) in the bottom of the case along with its outer thrust washers, and loop a piece of wire under it so that you'll be able to lift it when it's time to install the cluster shaft. Position the oil collector (B) in the case as well, but leave it loose for the time being. Press the new bearing on the input gear (C) and install it in the front of the case. Now you can stack the 14 supplied needle bearings (D) inside the input gear bore using petroleum jelly. Note that it's necessary to install the last bearing on end.

With everything ready to go, insert the mainshaft with the synchro hub, Second gear, and First-Reverse gear in the case from the rear and gently insert the nose of the mainshaft in the input gear bore. Be sure that the brass synchronizer that goes between the hub and the input gear is properly indexed and not bound on the input gear. While holding the assembly, install the rear bearing retainer, spacer sleeve, and rear bearing in the case.

Gently lift up the cluster gear and insert the cluster shaft through the back of the case. It should slide easily until the tip reaches the front of the case. Check the cluster gear bore frequently as you slide in the shaft; if one needle bearing gets dislodged, you'll have to start over. Tap the cluster shaft the remaining distance and install the retaining plate, then reinstall the bolts for the oil collector.

If all goes well the finished product should look like what is shown here. Double-check that there aren't any needle bearings in the bottom of the case, then check your work by manually shifting the tranny into each gear. Remember that you'll have to hold light pressure against the back of the mainshaft to keep the rear bearing seated as you test the gears, and it's a good idea to loop a piece of wire through the hole in the back of the mainshaft to keep it seated until you wrestle the tranny back into the Jeep. Though we probably won't be tearing into a late-model five-speed any time soon, we're no longer leery of what goes on inside this black box.

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