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Shift Problems.

Often what feels like a shift in TH125 is really the TC locking or unlocking. If there is a problem with the TC lock then it can feel like you've lost a gear. Does the problem happen with the TC lock plug disconnected?

Does the problem happen at the 1-2 shift, the 2-3 shift or both? If it is only one shift then you very likely need a shop to work on it. You can try the stuff below but don’t be surprised if nothing helps.

First of all make sure that the transmission fluid is at the right level. Over or under fill will both cause shift problems. What condition is the fluid in? If it’s turned light or even clear then it’s oxidized and you might want to try changing the fluid and filter before taking it for repairs. If it’s brown to black or smells different from new fluid then the transmission may have fried a clutch. You could try changing fluid but you should probably take it to a shop to be checked out.

The next item to check is the Throttle Valve Cable, which runs from the throttle linkage on the engine to the top of the transmission. This cable IS NOT a “kick down” cable like many people are familiar with. It works with an internal governor to control all transmission shift points. If this cable is binding or out of adjustment you will have shift problems.

Another thing that happens is a passage inside the valve body gets blocked with a flake of dirt or sludge. This can affect one shift or the whole transmission. You can try one of the cleaning products that you add to the fluid. Some people have reported good luck with these. Depends on just what’s blocking the passage if it will work or not. If this fixes your problem then do a fluid and filter change to get the rest of the dirt out.

Another possibility, although rare, is that the filter has failed or come unsealed inside the tranny. The result is that the fluid is picked up higher in the transmission. This can have the same result as low fluid.

Does the problem happen at the 1-2 shift, the 2-3 shift or both? If it is only one shift then you very likely need a shop to work on it.