T90 Transmission Tech Tips

Damage to Look For

T90Piet Versleijen: Last autumn while driving my 1956 CJ-3B through the fields and forests of the Peel (a small region in the Netherlands between Brabant and Limburg) a strange squeaking noise came from the gearbox. After about ten minutes it disappeared, but then the shifting between the third and second gear wasn't as smooth as before. This, plus occasionally popping out of the second gear, told me that something was wrong there!

After pulling the gearbox and the transfer case from the Jeep anddismantling the gearbox, I discovered some extensive damage inside.
The three synchronizer plates were missing (I found them in the drainedoil from the gearbox). After comparing them with new ones I could see that they were totally worn. See a new and old one side by side (40K JPEG).

The blocking ring from the 3rd gear was also very worn. Here are the new ring (left) and old ring (right):

Blocking ring

Here are some more photos of damaged parts I found (40K JPEGs):

  • This picture shows the main shaft. Clearly visible is the worn shaft end where the pilot bearing was running, and where the clutch hub has left its mark.
  • On the other end of the shaft are the worn spots from the (29 tooth) output gear.

  • This picture shows the washer from the output gear. Obviously the gear had some endplay to cause this.
  • The bearing spacer that's mounted just ahead of the rear main bearing shows some visible wear. During the rebuild I had to make a new one and had to adjust the thickness from 7 mm to 5.25 mm for the right amount of endplay for the new parts.
  • Some of the roller bearings out of the countershaft had some damage. Also badly damaged were the thrust washers at the front and back of the countershaft.

After reassembly and checking, the transmission and transfer case went back under the Jeep for testing on the road. Not a easy job with no lifting tools other than a hydraulic car jack. At first the shifting was a bit tight, but after a few kilometers things are getting better and all the problems from before the rebuild are gone. -- Piet

Here are some questions and answers from the CJ-3B Bulletin Board, dealing with the T90 transmission.

Grinding Gears on Downshift

Ken began: "I bought a project that someone else started. He had removed the tub and bought many new parts; I took it from there. After three years, I have a drivable 3B less the body. In driving it around the yard I only noticed one issue. When down shifting into second, I have a bit of a grind. Afterwards, I realized that it had been in low range so I figure that it is more prone to grinding and hoping that's why. I pulled the cover, but saw nothing obvious. Any thoughts?"

Maxx advised: "I wouldn't look too deeply into the downshift issue. There are many gears in play; a lot of reciprocating mass involved. My Jeep is twitchy about downshifting in 4-wheel low. I give the clutch a little extra time between shifts out of habit."

Oldtime said: "You made an excellent choice in testing the running gear and drive train before installing the body. Remove the shift tower again. Look specifically at the main-shaft blocking ring. There are three synchronizers located evenly around it. These synchronizers are about one-inch long about 3/16 inches wide and about 3/16 inches tall. These synchronizers are stamped from flat stock, so they will be hollowed on the bottom side. Now that you have identified the synchronizers, take a closer look. The ends of the synchronizers should have a tab of metal extending down and over both ends. If these end tabs are broken off, you have just found a common problem with the T-90. This problem arises about every 100 thousand miles of T-90 operation. If the synchronizers are intact and have no hairline cracks on the ends, then follow the advice of Maxx."

Ken added: "I pulled the shifter and looked for what you mentioned. Everything looks right. While I was doing the rebuild, I noticed that the synchronizer on the front end had a tendency to drag sometimes. The input shaft was new and the bearing surface was not as smooth as the original. I tried polishing the surface where it rides and I thought that it was okay. When I had the tower off after driving it, I noticed that it still seemed to drag a bit. I don't know if this is the cause and if it is, will it work itself out? I am inclined to let it go as Maxx suggested and if I need to later, I will pull the transmission."

Oldtime responded: "I would drive the 3B in first gear with transfer case in neutral with the tower removed. Use the original stick shift to change gears. You can run through the gears and see them work, but be careful that you don't get two gears at one time. Second gear should not grind. Your clutch may not be disengaging fully. Does the input shaft cease to spin nearly immediately when the clutch is depressed? If not, this is your problem and here are some possible causes: input pilot too tight in the flywheel bushing, rust on the flywheel, worn disk or a rusty or worn pressure plate."

Loose Bearings

Curtis Weddle: "I removed the tranny from my '54 3B and have found that there is approximately 1/4" free movement of the splined transmission input shaft at its tip. I have a very strong hunch that this is not normal, but perhaps it is. Should there be any play at this location? Has anyone had bearing problems this bad with the T-90?"

Tim Salkeld: "I can go one better, I found that after driving my new CJ-3A for one month, the tranny locked in 3rd gear. When I removed it all of the bearings from the front race were on the bottom of the case along with what was left of the inner race. The input shaft was locked to the mainshaft, second and third syncro rings were stripped and the oil slinger on the secondary shaft looked like a bumper in a demo car."

"Lesson 1: learned that any slop in the input shaft will likely cause one to replace most of the internal parts if left long enough.

"Easy enough to check and replace the bearings. Likely if you have that much movement you also have a leaking front oil seal."

Jason: "I was in the same boat as Tim. My T90 seemed to be fine until the motor seized up. We pulled the motor and I am currently rebuilding it but the tranny is another story. The input shaft bearing was missing about half of the balls so I had about 2 inches of play to start with. Then upon further investigation the roller bearings between the input and output shaft were all at the bottom of the case just like Tim's. That addes another inch! The third gear synchro block ring is completely chewed up and cracked in one place. I am in the process of rebuilding this too. I suggest doing the comparatively small amount of labor to fix the freeplay before you end up like us!"

Curtis: "Well, I suppose that that's a lesson. I figured that so much slop would be unacceptable. The transmission seems to shift well (stationary - I've never driven the vehicle: it was not functional when I purchased it). Gear changes are crisp, and it feels as if the 2nd and 3rd synchronizers are in place and functional. The oil seal theory sounds pretty reasonable. These will almost certainly need to be replaced. The T-90 and Spicer 18 are reputed to be bulletproof; I'd say that they would have to be to survive the vehicle's previous owner."

Terry Fairchild: "Check the pilot bushing in the engine before re-assembling. In all likelihood that is what initially caused the tranny bearings to head south."

See also T90 Pilot Bushing Removal on CJ3B.info.

Input Shaft

Curtis Weddle: "I got the T-90 apart yesterday, and was able to examine all of the suspect components. The input bearing actually seems to be in good condition. Output bearing is a little rough, but doesn't have a great deal of slop. Apparently, all of the play at the pilot of the input shaft (it was really around 1/8"; I exaggerated in my consternation at what I thought to be excessive free movement) is due to wear on the mainshaft-input shaft needle bearing. Have any others had this problem? It doesn't seem that the shaft would be entirely secure with this small bearing providing the only support for the mainshaft-input shaft juncture, but it apparently does. Are the needle bearings in this location free? I would suspect so."

Reed Cary: "All bearings are cheap in comparison to your time and energy. Replace any you have the slightest doubt about. If you feel unsure, replace it...."

Jim Sammons: "They are tough transmissions. Replace the bearings and put it back together. Unless it is worn slap out it should give good service. You may want to replace the synchronizers if worn. Sometimes they are bad about jumping out of second gear. Check to be sure there isn't a lot of wear on it (second gear) so you don't have to tear it down again. When you get it back together it should be a tighter tranny with new bearings, and shouldn't give problems."

Countershaft Bearings

Curtis: "I had resolved to get the transmission stripped today, and proceeded to extract the countershaft without the aid of tool "W-151" or whatever it is called, which substitutes for the shaft in retention of the free needle bearings and their spacers. All bearings are in the countershaft gear set hub, and I have the Jeep service manual which illustrates their order of assembly, so the only real concern is dealing with their tedious reassembly once the new tranny parts are ordered and the case has been hot tanked. Since I have gotten a bit anxious, and caused myself more trouble than was probably necessary, I was wondering if some of my ignorance could be redeemed by installation of new countershaft needle bearings. Is this often a concern? It would seem that most would avoid the task out of dread for putting the countershaft back together."

Curtis: "The reverse idler in my T-90 has its teeth on the meshing face rounded over at the sides (along the "V") and angled backwards at about 45 degrees. Are these teeth supposed to be square? The majority of each tooth is uniform, but the described nonconformity is apparently either the result of wear, or a design feature which facilitates smoother transition to reverse. The first and reverse gear is shaped similarly, but the angle is not as severe. The synchronizer teeth also exhibit this geometry to a smaller degree. Should these components be replaced? Is this acceptable wear, or should this cause concern for the secure and reliable operation of the transmission if the gears are retained?"

Jason: "The wear you are describing sounds all too familiar. Replacing the gears or not all depends on how big your wallet is. I am rebuilding the same tranny at school and my teacher says that those gears would be unacceptable in a passenger car because they would make way to much noise. But if you're concerned about noise in your 3B you better get another vehicle! I have chosen to use the worn gears anyway because of a lack of funds (a college student's budget doesn't leave much room for extra parts!) if you've got the money go for it. That tranny will last forever if you replace everything. Think about how long those gears were used (30 or 40 years) and the amount of wear they have. If they're new they'll last that much longer."

Jim Sammons: "That is normal wear. Folks don't always stop all the way when shifting from forward to reverse, hence the wear on the gears. If it doesn't jump out of gear don't worry about it. Since the synchronizers are made of brass, I would replace them. Speed shifting is hell on these trannys, and it usually gets second gear. If the previous owners did this you may want to replace second. A good way to tell is the synchros will be worn bad and the face edge of second will have the teeth worn off badly."

Transmission Noise At Light Throttle

Josh Driver: "I read the other posts on grinding, but mine is not the same. It does not happen while the motor is torquing (going up hill or when you have your foot in it) and it doesn't happen when you are off the throttle and de-accelerating. It happens when cruising with only light throttle on flat ground... 20-30 mph, not at 35-40 mph (where I guess the motor is torquing more). Kind of a guttural gggggggg sound."

Eric Lawson: "First, before anything else, check the drive shaft's U-joints and slip joint. They may need some grease. Next grab the yoke on the transmission and try to wobble it up and down. Next do the sameto the pinion gear on the rear axle. Both 'wobble tests' should produce no wobble. While you are at it, try the same thing on the driveshaft's slip joint. Again, no wobble is good.

"Now for stinky part. Drain the axle, remove the cover and look at the gears. There are plenty of magazine articles showing what good gears should look like. Now for the even-more-stinky part. Hold onto the ring gear to prevent it from turning, and lightly turn the pinion (transmission in neutral, parking brake off). You should feel a definite click as you move the pinion, and you may see a very slight amount of movement, but not too much... (Oh yes, the engine should be off for all of this. I couldn't resist that. :-)"

Tranny and T-caseGeorge Romond: "Another good possibility would be the noise coming from the transfer case. The intermediate gear in the transfer case has a large shaft with needle bearings inside it. The intermediate gear may chatter inside the transfer case with light-to-no-load conditions, and cause a similar noise. On a hard load it usually will quiet down due to the force exerted on it. This shaft, rollers and gear can be dropped out of the transfer case while still in the vehicle. I would recommend studying the manual first before doing this, so you get the idea of what you're up against. You would inspect the shaft for wear. Often the shaft gets ridges in it that act like speed bumps for the needle rollers to cause the chatter/noise. Also over the years there were three different diameters of center shafts. I believe 3/4, 1" and 1 1/8"."

David L. Rust: "I have the same problem with my '53 CJ-3B. I am getting ready to tear open the tranny, transfer case and clutch area. I am curious if you found out anything. I removed the floor panels and drove around and it is REALLY LOUD. Kind of scary, like something is getting ready to break. My noise is a heavy rattling sound -- if I release the gas (unloading the drive train still in gear) it gets loud, and I can aggravate the noise by taking it out of gear, letting the clutch out and revving up the engine (still rolling along). I cannot get the noise when I am stopped and running up the rpm's. Last year I rebuilt the tranny with a couple of new gears, blocking rings etc... and did not have any problems. I have had a nagging problem of not being able to downshift without grinding, but I am not sure if it is normal or not for this vintage drive train."

Reed Cary: "Immediate reaction: U-joints. You might check your driveline first, before tearing into anything more serious."

David: "I replaced all the U-joints last summer. I looked them all over and they are tight and greased, all fine. I have the transfer and tranny apart on my bench at work. I hate to say that all looks good so far, nothing obvious. I think that I have too much forward and aft play on the 2nd and 3rd gear shaft. I am not sure if this play can be adjusted or not -- I didn't see anything in the maintenance manual about it. I also noted that the oil collector has worn spots on both sides about halfway through the thickness -- it does not look like it would be what I was hearing. I wonder if this wear is a result of too much fore and aft play. All the gears turn smoothly and look good, there was no substantial metal in the oil, just a little brass from the blocking rings. Considering the amount of noise this was making I expected to find something really banged up. So now I am really stumped. Has anyone had a problem with bent shifting forks? If so, what was the problem leading to their replacement?"

"I will look at it for a couple more days. If I cannot find anything I will change all the seals and gaskets, and anything else that looks like it needs replacing, then put it back together and hope the problem is fixed. I wish I'd found something obvious. It is such a pain doing this without finding anything."

Reed: "Please note, I am no expert in this area. I have rebuilt one T-90. That is it. But I have read about problems concerning reinstallation of the oil-thrower. I, myself, made some notes about its reinstall (as I also noticed some wear) and (I've forgotten what now) had to think matters over. I seem to remember noise problems from folks' complaints. What can I say? It is a tinny thing, which could be a real noisemaker, if it constantly wore against a gear."

"The end play on the main shaft is a typical T-90 problem. Most folks consider bearing wear to be the culprit, so rebuild accordingly. The symptom is usually popping out of 2nd gear while not under load, as in motor-braking. This doesn't sound like your problem. (And there is a quick fix for that, anyway, without tearinginto the whole of it.)"

David: "This is the deal. Two summers ago I rebuilt the tranny with a new synchro-assembly and a couple of gears, bearing set, etc... Going into second and third gears sometimes would grind (50% of the time) and would not grind if I double clutched. I did not know at the time if this was typical or not. Further research told me it wasn't normal. So I tore it apart last summer and went all through it and everything looked good! (I have not rebuilt any other tranny). Once I put it together there was no improvement.

"This summer the noises got much worse! So last week apart it came again. I brought it down to Brian's 4WD in Connecticut so he could take a look (I needed someone who knows what he was looking at!) It turned out that the original synchro-assembly that I installed two years ago was manufactured wrong! The gear that slides over the shaft was about an eighth of an inch shorter than it was supposed to be! Brian replaced the part and went through the rest of the tranny and found everything looked fine. I just put the tranny and transfer back in today and it works GREAT. I can shift without grinding! I can also down shift, something that I never could do before. I believe that all that slop in the gears was the culprit. The lesson I learned after yanking the tranny and transfer three times in two years is to make sure the parts you put in are OEM and not the foreign look-alikes! Brian said he had run into a bad batch of new synchro-assemblies but now has good stock again."

Thanks to all the contributors. -- Derek Redmond

Elsewhere on the web, see:


See also The Novak Guide to the Borg-Warner T90 and Rebuilding the T-90.

Return to Tech Tips on CJ3B.info.

FacebookVisit CJ3B.info on Facebook.

CJ3B Home | Contents | Search | Links | Bulletin Board

Last updated 6 March 2009 by Derek Redmond redmond@cj3b.info
All content not credited and previously copyright, is copyright Derek Redmond