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Anyone seen my Fifth gear? I think it fell off!


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So I was driving home from work yesterday in my 79 620. It kept popping out of fifth gear. The last time It did it and i put it back in..fifth gear wasn't there any more. Thoughts? Looks like I'm in the market for another 5 speed!

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I beleave there is a nut on the rear shaft that might have come loose, but I could be wrong.

Inside the tranny? What are those things like to take apart


Wayno is correct .. this is exactly what I was going to type.

7earlier 280z 5spd's are notorious for this. Big main-shaft nut on the rear works itself loose ....

Nissan later reversed the thread pitch .. on the later 5spd's .. to prevent this from happening.


pop off tail-housing ... not to bad ... I can't remember exactly as it's been a while since I've had to tighten one and my memory isn't so good these days.

30-something mm shaft nut ? ... can't remember it's been a long time ... might have to make a wrench or dedicate an adjustable one if one can't be found.

Someguys spin it back on and tighten with loc-tite

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Order a rear seal #32136-U0100 only $5 and only seconds to change while the tail is off. Good drip insurance. Grease it before putting the tail back on. This will prevent tearing it or a dry start up.


You should be able to do this without draining it.... unless it needs to be changed.



Just forward of the shifter is that 'bolt'. remove it and the springs inside and save...



This is what causes the shifter to to jump into the 3/4 position when in neutral. You have to pull the shifter towards you to get in the 1/2 shift gate and push away to get the 5th/rev gate.




Remove the 10mm bolt and key, and pull the speedometer pinion straight out.




Your '79 may have these two switches in the tailstock. Neutral switch just forward of the shifter with two yellow wires on it. The other (top gear switch) is lower down and to the right also with two yellow wires. Just remove and keep so they go back in the same positions.


Stand the tranny up on two lengths of 2x4 to keep the nose out of the dirt and remove the case bolts around the adapter plate. Twist the shifter over to the left or driver's side , and tap case upward with a soft hammer. Have someone hold the adapter plate to avoid separating it from the bottom (front) case.


You're half way there.




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I made a extension socket for building those transmissions. I cut a snap-on socket in half and welded a piece of 1.5" tubing in between, then I can hit the nut with my air gun. Always use red loctite on the threads and be sure to check for end play after you've tightened it all up. If the thrust washer is worn a bit, you can accidentially over tighten the nut and loose all your endplay. I've done this too! You end up welding the gears together by friction. You can also hit the thrust washer on a belt sander to make it fresh again.

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I would say so. The gear can't 'fall off' the mainshaft. It's simply just been pushed maybe 1/2" to the rear and just out of range of the shift fork. Because reverse is on the same fork just ease it in and out of reverse when using it to avoid jostling 5th. Otherwise treat it as a 4 speed.... which is what 5 speeds are really... with an extra gear added.


If the nut should back off all the way it's possible that the speedometer may stop working.

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