Okay, before I make assumptions and go by what everyone is telling me, I need some help.

My D16z6 is not letting the 3rd gear go in. every other gear goes in fine, reverse i have to rev it a little to get it in without grinding, but 3rd won't go in at all... What could the problem be?

 

Possible you have a bent fork. Odd that you have to rev it a bit to get into reverse.

 

Is that the only problem that it could be? Is there any way to diagnose this ****? I don't want to buy a new transmission on monday, and it could end up being something else..

 

i gotta s20 ex/si tranny sittin' around

 

Is the MTF low? When was it last replaced?
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Please place simple technical questions directly into the thread title -- Title edited.



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No, but if it goes into every other gear fine then either way it's an internal transmission issue.

Pull the transmission and take it apart. There is no crystal ball for this stuff. If you work on the same stuff day in and day out yes after a while you can take an educated guess and usually be right but every once in a while you'll see something totally new.

There is something internally wrong with the transmission, if you're just planning to replace rather than rebuild then you wont be wasting your money unless you buy a junk replacement tranny.

 

Low MTF wont usually cause issues with 3rd Ron, normally what you will see is the transmission wants to pop out of 5th gear.