Last Updated November 12, 2005                                                 You can find the rest of my web pages here

Sorry, if you wanted the Model 18 Transfercase Rebuild Guide you will need to go to: Here

In my search for detailed instructions for rebuilding a T-90 I found there was little in the way of helpful information available. I did find a local transmission guru to answer some of my hardest questions. Since I considered the service manual to be inadequate for a beginning rebuilder, I bought a T-90 and practiced taking it apart and putting it back together again. I have practiced it so many times now that I've lost count, so I feel somewhat qualified to pass on what I have learned. (I have successfully rebuilt over ten T-90s since I first posted this guide) If you wish to follow these instructions, you will need to manufacture the tools listed below. If you prefer to use the heavy grease method of assembling the cluster gear, please feel free to do so. Just skip the instructions that require special tools and figure it out for yourself using an illustrated parts breakdown (IPB). I found that my hands are far too big to do that type of work so I made the special tools I describe below to assist me. These procedures should work for every top shifted T-90. I know there are some step variations with the side-shifted models but I haven't incorporated those into this guide. Use these instructions at you own risk. Even though over fifty T-90s have been rebuild using them, there are still probably a few glitches left to fix. It will be very beneficial for you to learn the names of all of the parts from an IPB. I also recommend that you keep your old parts and practice assembling the transmission before you do the final rebuild. Good luck, I hope you have as much fun as I did.

As other people use these instructions and provide me with feedback I will post their comments. Merl was my first guinea pig and he, Rick Grover (http://www.public.asu.edu/~grover/willys), Frank Woods, Dr. Vern, Mike, Paul and numerous others have provided some great feedback. Matt Clark was nice enough to provide me with a typo corrected copy of this page.  I have also taken the liberty of taking a quote from one of Richard Needham's WillysTech postings about sealed bearings. Below are a couple of web links to the CJ-3B web site that show the T-90 illustrated parts break down.

http://www.film.queensu.ca/CJ3B/Photos/Parts/Transmission.gif

http://www.film.queensu.ca/CJ3B/Photos/Parts/TransmissionCutaway.gif

Dr. Vern - First, I'd highly suggest pre-ordering the usual replacement parts. After disassembling mine, I had some trouble getting the parts in a timely manner. In the several weeks that passed, I forgot much about how it all went together. Just by pulling the top cover, you could inspect most of the major parts without much disassembly.

Merl - My T90 rebuild is finally done, and I must say that it went along much easier than I had expected. I used Rick's rebuild guide and a blowup picture for part name reference, never even looked at the shop manual for instructions on the rebuild. Overall, I'll give Rick's manual a hearty recommendation. I'm doing this from memory so I hope I'm not leaving anything out, but here are the more notable points and observations that I encountered...

Mike Harris wrote: Joe Van Slyke & I got together Sunday to rebuild his T90, it seemed to go well but had a few, if not problems at least some questions. Joe also got my thumb a good one w/ the ball peen, proof that it's better to have an assistant so's you have someone else's thumb to hit! :-)

 A separate section at the end of this instruction covers the Shift Tower. You can get there quickly by clicking Here.

Merl - Make sure you test fit the dowel through the front and rear holes of the case prior to assembling the cluster gear, sanding was required in my case.

2b. Tool B is manufactured using a length of 1" diameter metal electrical conduit. Cut it to 2 3/4" long with a hacksaw. It must be cut straight and any burs removed. Note: Do not use plastic conduit because it is the wrong size. 

Merl - Look for conduit labeled 3/4". You might have to buy a long piece, but it's dirt-cheap. Exact measurement of the electrical conduit tools is not critical. Within 1/4" inch of Rick's measure is OK, but do make sure there are no burs on the end of the tool.

Pair of flat bladed snap ring pliers . Round tipped pliers will not work.

Frank - Get the right tool to install the snap rings. The small stiff one on the front, the main-drive-gear snap ring, is a pain in the ers. Jabbed my finger with it trying to pry it out the first time.

2b. Remove transfer case bottom cover .

2c. Remove the cotter pin, nut and washer. (You may notice in the picture that the two gears do not mesh. That's because they are not a matched set. The intermediate gear is for a 26-tooth output and the output gear shown is a 29-tooth. They don't even fit together enough to install the intermediate shaft in the transfer-case. I just set it in place so the view would look close to what you would see if you were just opening up the case. If you have difficulty removing the nut you can wedge a hardwood block or brass drift between these two gears to lock them into position. Once the nut and washer are removed the main gear can be removed from the main shaft. If it sticks two thin wooden wedges can be tapped in between the rear bearing and main-gear to pop it loose.)

2e. To hold the mainshaft in place until removal is desired, install the front two shift tower screws back into their holes. Loop a heavy piece of wire under and behind the second speed gear and tightly wrap it around each of the two screws .

2f. Remove the transmission to transfer case bolts . There is one bolt that is somewhat hidden on the opposite side from the first bolts. It is on the front side of the transfer-case. Make sure to remove this bolt or you could crack the T-90 case trying to force them apart.

2h. Remove the three screws from the main drive gear bearing retainer..

2j. Remove the two twelve point/socket head screws that hold the oil collector to the case. (The oil collector can not be removed at this time so move it out of the way of the main drive gear as needed.)

2n. Slide the mainshaft complete with the front synchronizer blocking ring backwards, then tilt the front end upward to clear the cluster gear and slide it out of the case through the rear opening. (Some T-90s have the counter shaft locking plate installed over the top of the rear-bearing adapter. This will prevent the rear-bearing adapter from being removed. If this is the case on your T-90 you will need to remove the locking plate as described in step 2o - 2q prior to removing the mainshaft. This may prove to be difficult due to the limited space for accessing the reverse idler gear shaft with the mainshaft installed. In this case brute force applied to the locking plate may be required.)

2o. Using Tool A or a brass drift, gently tap the countershaft toward the rear of the transmission about 1/2".

2r. Using tool A drive the countershaft out of the cluster gear.

Rick Grover - When you say to drive the counter shaft out, it should be driven out to the rear. The front hole is a few thousandths smaller that the back hole. Driving it out the front would be much harder and could stretch the front hole.

2t. Tap the main drive gear forward and out of the case.

2y, Using tool E drive the reverse idler gear shaft out the back of the case. (This must be done from inside the case. Caution: do not attempt to drive the shaft into the case from the rear as this can damage the shaft and the case. Remove the reverse idler gear from the case. Some people have found it necessary to use a bent piece of rebar to drive the reverse idler gear out of the case. Use as little force as you can to prevent damage. Whatever you do, don't drive the shaft into the case.)

Mike Harris wrote: Reverse idler was a bear. We pounded it out using all-thread since it was long & flexible enough to get around the slight bend from the front of the case to the shaft.

(Danny M. has provided us with an alternative method of removing the reverse idler shaft. Use a 4 inch C-Clamp, a 3/8" drive 1/2" socket and a 3/8" drive 3/4" deep-well socket. Install the C-Clamp as shown with the 1/2" socket against the inside end of the idler shaft and with the deep-well socket slid over the outside end of the shaft. It took a good bit of pressure and a couple of taps on the threaded end of the "C" Clamp. Then you tighten it again and tap it again until the inside end of the C clamp bottoms out. Once it breaks free it can easily be driven out the rest of the way with your drift)

2aa. Hold the main drive gear by the bearing and gently tap the small end of the shaft onto a board until the bearing slides down and off the gear shaft .

Rick Grover - An alternative is several taps with the brass hammer. Worked for me. :-)

2cc. Slide the clutch sleeve off of the clutch hub, making sure not to drop the three synchronizer plates . (Collect the synchronizer plates and put them off to one side for inspection.)

2dd. Using flat edged snap ring pliers remove the clutch hub snap ring.

2ee. Remove the clutch hub from the mainshaft. (You may find that the clutch hub will not want to slide off the main shaft after you have removed the snap ring. Holding onto the clutch hub while gently tapping the mainshaft with a brass hammer will usually coax it off. Warning - years of the clutch sleeve sliding on the clutch hub can cause very sharp edges to develop. Use caution when handling the sleeve and hub.)

2ff. Remove the synchronizer springs from the hub.

2jj. Remove the rear bearing from the mainshaft. If necessary, stand mainshaft on its tail end an use the 1^st/Reverse gear like a slide hammer to drive the rear bearing off the shaft .

2kk. If you have the large hole bearing adapter, remove the snap ring from inside the bearing adapter. (You can not use snap ring pliers to remove this snap ring. A flat bladed screwdriver works just fine. Hook it under the notch in the ring and pry the ring out. Place the bearing on the front end of the mainshaft again use a slide hammer action to drive the bearing from the adapter.

1. The main Drive Gear bearing should be replaced if the center wobbles in the cage, grinds when spun or makes a squealing noise. I recommend changing it anyway. This bearing may be changed with a sealed bearing but some things need to be changed if you do this. Whatever bearing you choose, make sure that it has the groove as shown in the picture. This is where the front bearing snap ring sits and it is used to hold the bearing in place.

Richard Needham - Well I made it out to the shop and found the bearing number for the front of the T-90 with the seal. It's a SKF bearing but any good auto parts store should be able to cross reference to another brand.

I tried to locate the bearing that Richard used but was unable to find it. I did some local research and found this sealed bearing.

MRC brand Part #208-SZZG

I found them at Purvis Bearing in San Antonio (210) 299-1010. They cost $31.25 (At the time I authored this July 2000) and they had them in stock. They said they would mail order them to credit card customers. They also said to leave the seals installed on both sides because the bearings were designed to run for over 100,000 miles without servicing.

Update: (Nov 2005) Mike Harris has reported paying $48.86 plus tax for his bearing at the Purvis Bearing in Austin and I recently paid about $51 out the door here in SA.  These beings have gone up a lot in 5 years.

2. The front Bearing Washer should be replaced if bent or scored. Most of them I have removed have looked like the one on the right. A new one should look like the one on the left.

3. On the Main Drive Gear (Referred to by some as the Input Shaft) inspect the pilot-bearing race for scoring and pitting. Inspect all oil passages to insure they are clear. The inside diameter can be checked by measuring the diameter of the pilot shaft on the Mainshaft adding this size to the twice the diameter of a new pilot needle bearing. The sum of these diameters should be within .001" of the inside diameter of the Main Drive Gear pilot bearing race. An easier way to check this is to install new bearings in the race and insert the mainshaft into the bearing. There should be virtually no wobble of the shafts. If this fit is loose it will cause the pilot bushing in the engine crankshaft to wear out quickly. Check the gear teeth and blocking ring teeth for signs of wear and breakage. The beveled surface the blocking ring rides on should be smooth and free of cracks or pits . If any of these items is damaged you should replace the Main Drive Gear.

Long Shaft and Short Shaft Main Drive Gears have been identified as being different in more ways than just length. The long shaft has an oil hole drilled from the inside of the pilot-bearing race to the other side of the front main bearing race. It is the dark spot in the bottom as shown in the picture. It is easier to see in this photo taken from the other side. If you install a sealed bearing during installation, you must seal this hole or the transmission will leak.

4. Countershaft gear Oil Collector should be examined for cracks and dents. If damaged replace it. Many people recommend leaving this assembly out of the transmission, but I recommend against this. The Oil Collector retains oil around the front end of the Countershaft Cluster Gear. This feeds oil into the needle bearings. In the event that you ran low on oil the collector would continue to feed oil onto the bearings. The Oil Collector will also help to prevent the oil from foaming at high speeds. Note the difference between the old oil collector and the new one. The new one at the bottom is not as good as the old one and will require trimming the edge to get it to fit without dragging on main-gear. If you choose to buy a new oil collector make sure you are ready to trim it if necessary.

5. The synchronizer blocking rings should be inspected for broken teeth and worn mating surfaces. The mating surfaces that fit against the Main Drive Gear and Second Speed Gear should have small grooves machined into them with raised surfaces that come to points between the grooves and should be free of cracks and chips . When installed on the Main Drive gear and Second speed gear there should be a gap where the arrow is . I believe the gap should be at least 0.010" wide. I don't have any documentation to back that up, just my minor experience with these things. The blocking ring should not fit all the way down over the mating surface. If the rings are damaged or if the grooved surface is contaminated with chunks of metal they should be replaced. I've tried to dig those particles out of there and it isn't worth the effort.

Merl - Inspection was also easy, just so long as you know what these things are *supposed* to look like. For example, I stated that my synchros looked good...*wrong*. I made this assumption without actually making a side-by-side comparison to new synchros. Turns out that while my 2nd gear synchro was ok, the 3rd gear was badly worn. Take your mainshaft assembly completely apart and take a good close look at everything. With everything apart take your synchros and put them on the beveled edge of the 2nd speed gear and the input gear. If either the beveled edge of the gear is worn or the rear or inside of your synchro is worn replacement is needed. As Rick suggests, you might as well just go for new synchros, they're cheap.

6. The Clutch Sleeve should be inspected for cracks and pits. Inspect the inside splines for sharp edges and burs. These can be removed with a file or crocus cloth. After cleanup, it should still fit snugly on the clutch hub. If not replace it and the clutch hub.

Rick Grover - The burrs on the inside of the clutch slider were pretty bad on mine. I worried about them and whether or not to replace it, but finally did as you recommended, filed them off with a fine file and emery cloth.

7. The Clutch Hub should be inspected for sharp edges and burs on the splines. Caution should be used when handling a used hub as it could have very sharp edges. Using a file or crocus cloth, remove any burs. Check fit on the Mainshaft and inside the Clutch Sleeve for snug fit. If it does not fit both pieces snugly, replace it.

8. The Second Speed Gear should be inspected for broken or worn teeth. Examine the blocking ring surface area for scoring. Check for snug fit on main shaft. If it does not fit properly or if teeth are damaged replace the gear.

9. 1^st/Reverse sliding gear will take severe abuse due to its not having a 1^st/Reverse synchronizer. Examine for broken or excessively worn teeth. Rounded and shaved teeth can still be used but gears with broken teeth should be replaced. Note the severely chipped tooth in the photo. Check for snug fit on mainshaft. If not replace the gear.

10. The Rear Main Bearing should be replaced if the center hub fits loosely in the cage. Note that this bearing does not have a snap ring groove like the front bearing does. I also recommend changing this one regardless.

11. Inspect the Mainshaft for cracks, chips and excess wear of the splines. Measure the mainshaft pilot shaft to determine if, with new roller bearings installed, it will be within .001" of the inside diameter of the Main Drive Gear. If not replace it. If this fit is loose it will cause excessive wear on the engine crankshaft pilot bushing.

12. The Countershaft Gear Set (Known by most as the Cluster Gear) should be examined for cracks and broken teeth. Because the 1^st/Reverse gear rides well up onto the 1^st gear ring on the Countershaft Cluster Gear , you can have as much as 3/8" of wear to the 1^st gear ring without affecting the gear's operation. Small chips and sharp edges should be dressed with a file. With new Countershaft Washers, and bearings installed, the cluster gear should have no wobble on the countershaft. The easiest way to detect inside wear on the cluster gear is to run your finger inside and feel the surface. If you can feel ridges inside the gear, it is worn and should be replaced.

13. The Countershaft should fit very tightly into the case. It should also have no perceptible grooves or ridges worn into the bearing surface. These shafts are cheap so do yourself a favor and replace it.

14. The Reverse Idler Gear will have worn teeth. These should be dressed with a file to eliminate small chips or sharp edges that could be broken off and left inside the transmission. Check the fit on the Idler Shaft for wobble. The gear has a bronze bushing that should look like this . If it doesn't fit well or is missing large sections of teeth it should be replaced.

Frank - Buy your small parts kit from:

Four Wheel Drive Hardware   USA/Canada 1-800-333-5535
Int'l 1-330-482-4924 or 1-330-482-5560
Fax 1-330-482-5035
www.4wd.com
Columbiana, OH

It's the best.

Dr. Vern - Did any of the later model T90's use a neoprene lip seal at the front? On mine, the front seal was a flat cork washer sandwiched against the face of the bearing by the bearing retainer. The bearing that I removed (original?) was shielded, but not sealed, on both sides. The shields were probably enough to slow the flow of oil to the point that the cork washer could handle it.

Jason@MileHiJeep - We have new T-90 bearing retainers that are machined to accept a metal/neoprene seal. When our tech rebuilds our T-90's, he said that he polishes the input shaft to give a better sealing surface.

Rick - If you are not installing a sealed bearing I highly recommend buying these parts from Jason at Mile High Jeeps.

Rick - Before ordering your new parts you should evaluate the expense involved with doing your rebuild.  When I first wrote this guide (1998), a complete rebuild of a T-90 with new bearings and seal ran about $125 and it still does.  A new T-90 came in between $500 and $700, so adding in another $200 worth of parts to your list still made sense.  In the last year the price of new T-90s has dropped dramatically.  You can buy a new T-90 without the shifter today (Dec 2000) for $400.  If your rebuild is going to cost you $300 in parts then you might want consider buying one of these trannys instead.  Therefore, you should do a careful inspection of your parts prior to ordering new parts to determine what you will need.

Merl - I have to *highly* recommend Rick's technique using the electrical conduit. After I cut the tool A, B, C, and D and finally understood the way Rick's method works, I put newspaper on our kitchen table, got my 6 & 8 year old boys to count out 4 piles of 22 needle bearings each, gave them a cup of grease and let THEM put the thing together. Of course I supervised to make sure everything was going in the right order, but the fact that my 6 year old did most of the work should tell you how easy these tools make it (plus, my boys had a good time with the grease).

Mike Harris: The dowel/electrical conduit for the countershaft needle bearing assy made a fussy job easy. This "tool A, tool B, Tool C" cha-cha-cha is the way to go. Don't do it the conventional way unless you want to make yourself nuts trying to hold four rows of needle bearings in with grease (with both 6-7/8"-long index fingers), using the other hand to hold the countershaft, your other hand to hold the plastic hammer, leaving your other hand free to hold the shop light to watch yourself catch a needle bearing with the countershaft & drive it sideways into the case.

Mike Harris: We heated the front & rear bearings by putting in a Ziploc and putting the bottom end of the Ziploc into boiling water - boil-in-bag-bearing, yum. This got the bearings hot enough that I don't think freezing was needed.

Make sure the snap ring groove is forward or you will have to do it again. This bearing had to be removed and installed the right way. If you think I did it just for the photo, you don't know me very well. :-)

Merl - Make sure you grease the middle spacer...I forgot. But, I was able to put a little light oil in the lube hole in the middle of the gear so I didn't take it all back apart.

Frank - I didn't use any of slick Rick's tool tricks. I'm wondering if someone else can verify if this works:

4i. Place the Countershaft Cluster Gear into the case with the large end to the front. It will just lay in the bottom for now.

4j. Place the Oil Collector in position in the case. Do not install the screws at this time. You will note on the left side of the photo some extra parts that your T-90 doesn't have. This is the shift mechanism for the side shift tranny. You can build a side shift T-90 to be a top shifted T-90.

Frank - Don't forget to install the oil collector in the right order because it won't go in last like I thought it would. Unless you want to practice disassembly/assembly one more time.

4k. Install the Main Drive Gear into case from the front. The bearing snap ring will rest against the front of the case.

Dr. Vern - I found it easier to install the pilot bearing rollers before installing the main drive gear. I have a magnet on a stick that worked great for handling those teeny little rollers, too. Things got pretty slick using assembly lube.

Dr. Vern - Keep in mind when you put the main drive gear and its bearing in the front of the case, you will have to back it out partway later. Since I did the sealed front bearing mod, I decided to seal between the big snap ring and the case too. When I had to back out the bearing and shaft as required, the sealer had partially set and came apart in globs. I had to scrape it clean and reseal it. So if you plan to seal it like I did, wait until just before installing the bearing retainer to add the sealer. I also cut a piece from the snap ring of the old bearing, and used it to fill the gap in the new bearing's snap ring. Hopefully this will help me get a better seal without that big gap. If you are not replacing the bearing, a piece of thin metal the appropriate size would work just fine. If you are using the stock front seal and open bearing, this will not be needed.

4l. Install the countershaft through the cluster gear from the rear of the case. It may be necessary to stand the case on its end to get the thrust washers to align with the countershaft. Take your time and don't use too much force to insert the countershaft. If it isn't going in, then washers aren't aligned properly. It's ok to gently tap the end of the shaft with a brass hammer but any more force than that is too much. As the countershaft slides in, Tool A will slide out. Let Tool A fall out on its own if possible. This will help keep the thrust washers aligned. Make sure the locking plate slot that is cut into the shaft is at a 90-degree angle to the case hole for the Reverse Idler Gear Shaft. Do not install the shaft all the way or you will not be able to install the locking plate. As per the manual, once installed, the cluster gear should have between .012" and .018" of clearance. This should be obtained using thrust washer shims. I've never seen one that had that much clearance. They usually have less than .005" clearance and I haven't had any trouble with them.

Dr. Vern - The rear countershaft thrust washer gave me fits when it was time to lift the gear into place to install the countershaft. It kept staying down, not lining up. Then I looked at how the keyed tabs were oriented. I had them aligned vertically at first. When I turned the gear 90 degrees so the key tabs were horizontal, the thrust washer did not slip down as I lifted the gear into place.

4n. If you have the shim identified by Merl and you wish to use it, install it on the mainshaft now. I feel these were only used to compensate for worn parts, so with all new bearings and blocking rings you should not need them.

4o. Install the second speed gear onto the mainshaft with the blocking ring mating surface pointing forward.

4p. Place the rear blocking ring on the second speed gear.

4q. Install the synchronizer springs into the clutch hub. They should be installed in opposite positions with one in the front and one in the rear. One end of each spring should fit into the same synchronizer slot. I have no idea why they are installed like this but every old transmission manual I have been able to find shows the springs installed this way. If you installed them the other way, I don't think it would hurt but why fight 50 years of experience?

4s. Install the clutch hub snap ring.

4t. Heavily grease the synchronizer plates and hold them in place while installing the clutch sleeve over the hub. There are three slots in the blocking ring that the synchronizer plates must fit into to install. Make sure the shift fork groove is to the rear of the mainshaft. It can go on the other way, but it will prevent you from installing the shift tower later.

4v. If you have the large-hole bearing adapter you will now install rear bearing in rear bearing adapter and install snap ring. This bearing is also a press fit and can be tapped in using a brass drift.  If you have the small hole adapter the bearing will just sit in an shallow relief in the adapter.

Merl - The only other problem I had during assembly was getting the rear bearing pressed onto the mainshaft prior to inserting the mainshaft into the case. I tried Rick's 2" PVC pipe technique, but it tends to shoot small shards of plastic off into the bearing.

I wound up using a blunt nose chisel on the inner race, a tap on the chisel with a hammer at 90 degree increments around the bearing race did the trick. It should be noted at this point that even though Merl had success using a steel punch to drive the bearing on, this is not a recommended practice. On occasion I have been known to hammer steel on steel. Sometimes this has met with success but on occasion I have had less than positive results. Rick's recommendation below should be followed.

Rick Grover - Brass hammer taps worked for when I did my T-90, I never hit anything with steel. Get a brass hammer and/or a brass punch. They are about $10 each. They get all dinged up and even shed little brass flakes sometimes, but they do not scratch or mark the machined steel surfaces.

4kk. Tap shafts into case until the locking plate is held firmly in place. ** See note at bottom of assembly guide

Dr. Vern - The front bore of the countershaft is known for leaking. The end of the shaft is about 1/16" inside the case when fully assembled. I plan to put some sealer in there when I bolt the transmission to the bellhousing. The flat surface of the bellhousing will sandwich the sealer in place. Naturally you don't want to use too much, but just enough to fill that cavity. I'll let you know how it works after I get the jeep back on the road.

Merl - Oh, and one last thing. While you've got your transmission output gear off (you've got to have it off to separate your TC and transmission), count the number of teeth on that sucker. You never know when you're going to run across a used Warn OD at a decent price and wouldn't you just HATE to miss out because you didn't know or guessed wrong?

** Rick - On the last T-90/Model 18 rebuild I encountered a new problem. I installed the locking plate from the bottom instead of the top. When I bolted the T-case to the T-90, the locking plate interfered with the mating and I had to pull it all back apart to swap the plate. Make sure you check this fit before applying gaskets and sealer. Another guy was rebuilding his IH Scout T-90 and had the same problem. His info is printed below.

Gary- Major lesson learned last night. There's already some added comments in your text regarding the locking plate that secures the reverse idler shift shaft and the cluster gear shaft. On IH Scout using the T90/T18 combo, the locking plate MUST be installed from the top, so that it is a right-side up "T". I put mine in from the bottom, put gasket shellac on all the gaskets and cranked everything down tight. When I filled both with the requisite 6 pints of gear oil and started the engine, I had a puddle on the floor pretty quickly. Tried quick fixes like shellac on the threads of the bolts that join the T18 and T90, but still had good flow. Took the two units apart last night and found that the locking plate is interference with the fit. Kinda like slipping a dime between the mounting surfaces.

Dr. Vern- During assembly, the shaft locking plate on the rear must be correctly positioned to fit into a recess on the front of the T-case. Rick's guide mentions this, and how one guy had the plate keep the T90 and T-case from pulling together correctly. I used the gasket as a template and traced the outline of the recess with a magic marker. When the two shafts were still protruding about an inch, that is when I fit the locking plate into the shafts' grooves. That allowed me to keep everything in correct alignment as I drove the shafts all the way in. 

Rick - Even with a correctly aligned locking plate it is possible for the plate to interfere with the T-case installation.   This will cause one of two things to happen.  Either the tranny and T-case will leak terribly through an unsealed gasket or the tranny will bind up and not turn.   The binding is caused by the T-case cocking the Rear Main Bearing.  The solution to this problem is to trim the locking plate with a file or grinder to make it fit inside the hole in the T-case.

Dr. Vern - I felt like I had discovered the cure for cancer or something when I finished the rebuild. It was not hard at all. It is just a matter of following the steps in the correct sequence. Being familiar with all the names of the parts helped, too, as you read the instructions.

Dr. Vern - Since you must have the shift tower off when removing or installing the T90, I'd suggest taping a piece of cardboard across the open case. I think I'd cry if some crud from under the body fell in during the installation.

Rick - Here's new bit of information for you.  Tom Jacoby's tranny went together beautifully and worked fine until it was bolted to the T-case.  Once it was bolted up everything bound up tight and was very hard to turn.  This sounds a lot like the binding locking plate mentioned above and therefore that was inspected and ruled out.  In the end the cause of his problems stemmed from the bearing spacer being too thick (0.031") for his tranny.  This forced the Mainshaft forward too far when the T-case was installed against the tranny.  On most T-90s this thick a spacer would not have been a problem but on his the other parts had larger tolerances too and they combined together to create an assembly that was too long to fit the case.  If you encounter this problem you may need to find a thinner spacer.  A new spacer that was 0.021" thick worked just fine for Tom.

Thanks to Ron Cox and Reed Cary I have been able to add the Shift Tower rebuild instructions to this guide. Without their help this would not have been possible. Thanks guys. In the research that we have done it has come to light that there are two different shift towers available for the T-90 transmission. One is in the M-38 and looks like this. It was designed to be waterproof and seems to have a more rugged design. The second one I call the other T-90 shift tower and it looks like this. It's is possible that the M-38 shifter was used in other military jeeps as well, if so please let me know and I will add them to the list.

Remove shifter fork pins from the second and high-speed shifter-fork and the low and reverse speed shifter-fork. In some shifters this is a split pin and in others it will be a hollow pin that is staked in the end. The split pins can simply be driven out with a pin drift but the staked pins must have the staked end drilled off first. Place both shift rails into the neutral position.

The M-38 shift tower will have two 3/8-inch countersunk head pipe plugs at the rear of the shift rod rail holes. Remove these. For other models this is N/A.

Verify that the rods are both still in the neutral position. Drive the second and high-speed gears shifter rail to the front until the rail hole expansion plug can be removed. Carefully slide the shifter rod forward while rotating the shift lever notch in the rod toward the bottom of the tower. Do not allow the notch to pass the poppet ball while it is pointed toward the top or the poppet ball and spring will become trapped in the notch. If this happens you can force the poppet ball back into the hole by rotating the shaft with a pair of vise-grips. Caution: as the rod slides past the poppet ball, the natural tendency is for the ball to shoot out. Cover the hole with a rag. Remove the rail and the second and high-speed gears shift fork.

Drive the low and reverse speed gears shifter rail to the front until the rail hole expansion plug can be removed. This rail does not have the notch to worry about so it should be a little easier to deal with. Caution: as the rod slides past the poppet ball, the natural tendency is for the ball to shoot out. Cover the hole with a rag. Remove the rail and the low and reverse speed gears shifter fork.

This leaves the removal of the shift lever. This procedure is totally different between the M-38 and other T-90 transmissions.

M-38: Unscrew the shift tower cap from the shift tower and remove. Slide shift lever out of the shift tower.

Other T-90s: Turn the shift tower upside down and lock into a vise if possible. It worked pretty well for me sitting in my lap. Start at the top of the spring and using a large screw driver gently pry the spring over each spring retaining dog one at a time. My first idea was to use a pair of vise-grips and rotate the spring from the case. This can be done but it is very hard on the spring and chews up where the vise-grips bite. It only takes about 2 minutes to do it with the screwdriver and it's much easier on the spring. Once the spring is removed, slide the shift lever out the bottom of the tower.

Now clean and inspect the shift tower case for cracks, stripped threads (For M-38) or damage of any kind. Any cracked or otherwise damaged units should be replaced or repaired.

Replace the gearshift lever if it is excessively worn or bent.

M-38: Replace the gearshift shift tower cap if it is bent or has stripped threads.

Other T-90s: Replace shift lever retaining ring if it is bent or broken.

Replace the second and high speed gears shifter-rail and second and high-speed shifter fork if they are excessively worn, or if they are bent or distorted. Any burs should be removed.

Replace the low and reverse speed gear shifter-rail and low and reverse speed shifter fork if they are excessively worn, or if they are bent or distorted. On one of the ones I inspected, there was a groove cut in the shift rail where the poppet ball rode. Any burs should be removed.

M-38: Replace the 3/8-inch countersunk head pipe plugs if the threads are stripped. Replace the gearshift lever support spring if it is cracked or distorted.

Replace the poppet balls and poppet ball springs if they are worn, broken, or distorted. I recommend replacing them anyway.

M-38: Install shift-lever back into the shift tower and secure with gearshift shift tower cap.

Other T-90s: Turn shift tower upside down and install shift lever into the tower make sure the positioning pin seats in the notch on the shift lever ball. Slide spring down over the shift lever and pop the spring over the retaining dogs one notch at a time with a large screw diver. This took me about 20 minutes the first time I did it, but now I can do it in about 2 minutes. Just don't loose patience with it.

Make sure the shift lever is to the inside of the rail before installation. Insert poppet ball spring and poppet balls into gearshift control housing on the low and reverse speed gears side. Insert the low and reverse speed gears shifter shaft into the gearshift control housing from the rear. If you have difficulty getting the shaft to go in more than about 3 inches inspect the interlock pin to make sure it is out of the way. Slide the low and reverse speed gears shifter fork onto the rail Note: it is easy to put this fork on backwards if you aren't careful. When it is properly installed the fork should fall evenly in the middle of the shift tower. Depress the poppet ball and poppet ball spring, using a blunt shaft (Do not use a sharp tipped instrument like a screwdriver or a nail.) and slide the rail in over the poppet ball to the second groove. This is the neutral position.

Make sure the shift lever is to the inside of this rail also before installation. Insert poppet ball spring and poppet balls into gearshift control housing on the second and high-speed gears side. Insert the second and high-speed gears shifter rail into the gearshift control housing from the rear. If you have difficulty getting the shaft to go in more than about 3 inches inspect the interlock pin to make sure it is out of the way. By now the interlock pin must fit into the detent notch in the low side rail. Note: This interlock pin is not like the one on the model 18 transfer-case. If you remove this pin it will allow the transmission to shift into two gears at the same time. This would effectively destroy a T-90. DO NOT REMOVE THE PIN. Slide the second and high-speed gears shifter fork onto the rail. Note: it is easy to put this fork on backwards if you aren't careful. When it is properly installed the fork should fall evenly in the middle of the shift tower. Depress the poppet ball and poppet ball spring, using a blunt shaft and slide the rail in over the poppet ball to the second groove. This is the neutral position.

Situate the shift lever so that it falls in between both the Low shift fork and the High shift notch. Secure both shifter forks onto the shifter shafts with shifter fork pins. For those with staked pins, flange the ends of the gearshift fork pins with a center punch.

M-38: Install 3/8-inch countersunk head pipe plugs in ends of gearshift control housing.

Place a small amount of sealant around the new gearshift rail hole expansion plugs into shifter shaft holes in the front end of gearshift control housing. If there is enough room in the ends of the rear shaft holes of your shifter, I recommend installing these plugs there too.

There has also been some interest in installing a reverse light switch in the shift tower. A write-up for this can be seen here.