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T90 Issues - Time To Rebuild?

Discussion in 'Early CJ5 and CJ6 Tech' started by kenb, Sep 13, 2020.

  1. Sep 13, 2020
    kenb

    kenb Member

    Detroit
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    Hello,

    My Jeep is running a T90 behind a F134. I have 5.38 axles and a Saturn overdrive on the D18.

    Lately I've noticed two issues with the transmission. First is the second gear synchronizer. Occasionally when the transmission is warm I'll get some gear clash shifting from first to second. This only happens if I try to shift quickly, usually attempting to merge with traffic. It's not an issue when I'm driving normally. So I don't know if this is normal or a sign that the synchronizer is getting worn. I'm using Sta-Lube 85w-90 GL-4 gear oil.

    The second issue is with the transmission popping out of second gear. This only happens under specific circumstances. I noticed it driving in town. If I shift into second and just let it idle along (approaching a red light) if will sometimes pop out of gear. I've never seen the issue when accelerating or climbing a hill where the gear is "loaded". When this happens the shift lever doesn't move all the way to neutral. I need to move to neutral and reselect the gear otherwise it clashes.

    So, I don't know if these issues are something that would be solved by a rebuild. I hate to tear the whole thing down if it's not necessary. On the other hand if these issues are signs maintenance is due I would rather go through it this winter than have it get really bad next summer.

    If anyone had thoughts they are appreciated.

    Thanks,
    Ken
     
  2. Sep 13, 2020
    timgr

    timgr Eppur si muove. 2020 Sponsor 2019 Sponsor

    Medford Mass USA
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    The clash means the blocking rings are worn out. These are brass rings that act like clutches between the gears, to match the gear's speeds so they slide together with no clash. Blocking rings wear out, and can be replaced. A T-90 has two, one on second and one on third. Into third is a lazy shift compared to second, so second always wears more.

    Coming out of second most likely means the bushing inside second gear is worn out. This too is a common sign of wear. The worn bushing allows the gear to skew on the main shaft. This pushes the synchronizer hub away from the gear and the transmission pops into neutral. My understanding - you replace the gear to fix this. They are available.

    You cannot do much to a manual transmission unless it's on the bench where you can take it apart. Whether you call it repair or rebuild, it's pretty much the same amount of work.
     
  3. Sep 13, 2020
    kenb

    kenb Member

    Detroit
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    Thanks for the reply. Sounds like a good winter project. If I'm reading Novak's website correctly, a new second gear comes with their master rebuild kit.

    Now, I need to decide if I should do anything with the D18 while it's out and separated....
     
  4. Sep 13, 2020
    Glenn

    Glenn Kinda grumpy old man Staff Member

    Apopka, Fl
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    You definitely should go through the transfer case too. The intermediate shaft is susceptible to wear and generally goes bad before anything else.
     
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  5. Sep 13, 2020
    kenb

    kenb Member

    Detroit
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    OK cool, thanks for the reply. My theory is "do it once, do it right" so I'll go through the D18 too.
     
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  6. Sep 13, 2020
    Keys5a

    Keys5a Sponsor

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    X2 on the second gear's bushing being worn, causing it to pop out of gear on deceleration. Thats also likely part of your syncro/clash when shifting into 2nd gear. Be sure to get a quality replacement 2nd gear. There are NOS originals still available out there from some of the military Jeep parts places. These are by far the best.
    Yes, while things are pulled down, the transfer case intermediate shaft should be at least be removed and inspected for wear, as well as the thrust washers.
    -Donny
     
  7. Sep 13, 2020
    Ol Fogie

    Ol Fogie 74 cj5 304, 1943 mb 2020 Sponsor

    Jasper Georgia
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    Many years ago when I was a teen my older brother had a 53 model 3B .the T-90 would jump out on hold back every time, but never when pulling. Being chief cook, bottle washer and jeep mechanic I pulled the trans and done a rebuild, second gear bushing was worn some and the brass blocking rings some wear too. replaced main shaft bearings and main drive pilot bushing, and needle brgs. counter shaft brgs and thrust washers. Reinstalled, helped a little but still the same problem. :banghead:,:study:. Re checked shift tower assy, synchronizer shift sleeve, blocking rings all looked perfect. Humm and double humm. So what I did was I drained the oil and with he shift tower removed I jacked up the rear wheels, so I could watch what was happening. I slid the synchronizer sleeve in 2nd gear and started the engine. On acceleration all was well, as soon as you released the gas peddle and the torque reversed the synchronizer assy was separating. There was a lot of end play in the main shaft (not the main front drive)separating blocking ring from the shift sleeve. When the torque reversed the helical cut gear pushed the whole main shaft assy to the rear toward the rear main shaft bearing and away from the 2nd gear synchronizer disengaging 2nd gear.
    There is steel spacer (about 3/16 in thick) on the the rear main shaft between the rear bearing and the reverse gear slide boss. This spacer gets worn allowing excessive end play in the shaft. What I did was make a shim thick enough to remove ALL of the end play except about .005 to .010. I measured this with the two cases bolted together. This stopped the main shaft from moving rearward when the torque reversed.
    Problem fixed, never did jump out of second gear again. That old T-90 out lasted two rebuilds of the F-134 engine. I have repaired two other T-90's successfully doing this. See item #22 in the pic below, this is the spacer. The shim I made was put between the rear brg and the original spacer #22.

    upload_2020-9-13_16-48-24.jpeg upload_2020-9-13_16-48-24.jpeg
     
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  8. Sep 13, 2020
    kenb

    kenb Member

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    Thanks for that explanation. I'll have to take a close look when I get it apart.
     
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  9. Sep 13, 2020
    timgr

    timgr Eppur si muove. 2020 Sponsor 2019 Sponsor

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    Interesting. You would expect the Borg-Warner 3-speeds to have an end-play spec, but AFAIK there is none. Assumes the OAL of all parts is correct? Certainly a important measurement.
     
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  10. Sep 13, 2020
    Keys5a

    Keys5a Sponsor

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    I fully agree with Ol Fogie's assessment regarding endplay of the mainshaft. I have addressed the other end to help control end float. Excess movement of the input shaft also kick second gear out on decel. Dry assemble the nose of the mainshaft into the input shaft w/rollers in place and see how much play there is. A little wear on the nose of the mainshaft and a little wear on the inside bore of the input shaft can add up to a very loose fit even with new rollers.
    I have added shims to the input shaft (used to come in small parts kit back in the day) behind the input shaft bearing to take up excess movement of the mainshaft, effectively the same as shimming the T/C end as Ol Fogie suggests. I've placed these shims along with the oil slinger behind the bearing, but you have to make sure you can still get a snapring on the input shaft outside the bearing. Also be sure to select the thickest snapring when installing the syncro hub on the mainshaft (I guess the small parts kits have about 3 thicknesses?).
    I seem to remember shooting for maybe under .003" endplay for the mainshaft?
    -Donny
     
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  11. Sep 13, 2020
    Ol Fogie

    Ol Fogie 74 cj5 304, 1943 mb 2020 Sponsor

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    Yeah, I have one of the original jeep service manuals for the cj-2, cj3, cj3b. and it never said anything about end play there. All of the ones that I have worked on had a huge amount of slop there,I am talking .050 or more. Why I am not sure, I don't think the steel spacer could ever wear that much. I made a shim from another one of the factory steel spacers. First I would take a measurement between the rear bearing and the factory spacer with the trans and transfer case bolted together. Sometimes it would be almost 1/16 of an inch. I would then face down a new spacer to get it close and reassemble, check, and then use a surface grinder to make final tolerance adjustments. As Donny said I also used two oil slingers behind the front bearing on one trans that had excessive slop. One thing for sure it worked very well, it always fixed the problem.
     
  12. Sep 13, 2020
    Ol Fogie

    Ol Fogie 74 cj5 304, 1943 mb 2020 Sponsor

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    You need to check the clearance before you start disassembly to see how much shim you will need. Once the trans and transfer cases are separated the rear bearing will not be tight enough in it's bore to give an accurate measurement.
     
  13. Sep 14, 2020
    kenb

    kenb Member

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    I found a seller of an OEM second gear as Donny suggested. Does anyone know where Novak gets their second gear and other parts? I was planning to get their kit for transmission and transfer case.
     
  14. Sep 14, 2020
    timgr

    timgr Eppur si muove. 2020 Sponsor 2019 Sponsor

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  15. Sep 14, 2020
    Keys5a

    Keys5a Sponsor

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    QTM (Quarter Ton Military in north GA) is getting new 2nd gears made in Japan, not the same ones as the Omix one. It may be a good part, but I haven't tried that one, yet.
    I have bought used take-off 2nd's from QTM, but that was several years ago. I think his selection has been picked over by now, but the one I got was essentially new. He used to have barrels of them.
    -Donny
     
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  16. Sep 14, 2020
    nickmil

    nickmil In mothballs.

    Happy Valley, OR
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    Remember to always check the clearances with the rear output bearing and transfer case input gear installed as it pulls the mainshaft into the proper location.
     
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  17. Sep 14, 2020
    Ol Fogie

    Ol Fogie 74 cj5 304, 1943 mb 2020 Sponsor

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    X2 that is very important. That is the ONLY way you will be able to get an accurate measurement of total end play between the rear bearing and the spacer. When you contact Matt at QTR for a new 2nd gear be sure to ask him for an extra spacer(#22 in the diagram) you may need it to make yourself a shim.
    Replacing the 2nd gear and it's bushing may help somewhat. But in my experience the most success was achieved by eliminating the shaft end play.
     
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  18. Sep 15, 2020
    kenb

    kenb Member

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    I'm not going to fully understand what end play I'm measuring until I can look at it. If I remove transmission and transfer case as a unit can I measure this on the bench, or will this need to be done in the vehicle?
     
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  19. Sep 15, 2020
    Ol Fogie

    Ol Fogie 74 cj5 304, 1943 mb 2020 Sponsor

    Jasper Georgia
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    Yes you will need to remove the trans and transfer case together as one unit. Drain the oil from both cases before you remove them from the jeep. When you have it removed keep both of the cases bolted together. First place the T-90 shift lever in neutral and remove the shift tower bolts(6) and remove the tower assembly. Then reach inside and slide the big 1st/reverse gear forward as far as possible. You will then be able to see the spacer (#22) sitting inside the bore of the big round plate(#15). Use a screwdriver or similar tool to push the spacer back against the big rear bearing. You will see that there is space between the front face of the spacer and the shoulder on the main shaft where the 1st/reverse gear slide splines are. That is where you will need your new shim to stop the back and forth movement of the main shaft.
    First though as Donny said you will need to completely disassemble the main shaft, remove the pilot needle bearings from the rear of the main drive gear/shaft and check those for wear and replace if necessary all as Donny outlined in his post. Then install your new 2nd gear/bushing on your main shaft. Then you can reassemble the main shaft back into the transmission case and bolt up to your transfer case. Then install the transfer case drive gear and nut.
    Now you can take that measurement of the back and forth movement between spacer and the shoulder on the main shaft to determine how much shim thickness you will need.
    I know this sounds like a lot to understand but when you get it on the bench where you can see it, things should become easy to see just how it all works.
     
  20. Sep 16, 2020
    kenb

    kenb Member

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    Thanks for the well thought out explanation. I'll probably start gathering parts soon and do the work over winter.
     

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