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mouse240z

280zx gearbox jumps out of 5th?

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G,Day all.

 

I have a problem with my series 1 280zx 5 speed jumping out of 5th gear.It also crunches into 5th as well.

Thought it might be a broken syncro ring?

 

Any help would be great! Thanks Kevin.

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i had it in my 260z it was the nut on the main shaft had come loose, it requires gearbox pull down to tighten though, since then it has not jumped out, on another note i would change the springs and ball bearings for the selectors first. you will notice 2 bolts in the middle of the box underneith and one on the side this also helps and cost about $30 to replace

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If you end up pulling it apart to tighten the nut, order a new nut for it. Apparently they are a locking, 1 use item. I had a gearbox rebuilt at a shop and the nut came lose twice, once on 500 klm trip straight after getting the box back and then again a couple of months later. After the shop had to pull it apart on their dime for a 3rd time they worked it out ;)  The nut was something like $10 or $20.

 

Can't confirm 100% if this is correct but that's what they told me!

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Yes, you are right. The nut will need replacing.

Surely there is a kit available?

 

My springs and ball detents were fine and it was still jumping out and notchy. But definately try it first. Could save a lot of time!

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I haven't done it, but I'm led to believe that it is good practice to use a second nut on the main shaft as a lock nut.  That should prevent it coming loose.

 

The guys with more box experience than I should be able to verify.  (Sheldon - ready set go!)

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I haven't done it, but I'm led to believe that it is good practice to use a second nut on the main shaft as a lock nut.  That should prevent it coming loose.

 

The guys with more box experience than I should be able to verify.  (Sheldon - ready set go!)

I actually didn't want to gloat about my escapes with my box........ But.

I had custom nuts made at Hollinger, where it was rebuilt. It had 2, one acting as a lock nut. But didn't know if it was customary to do so. I just went with the experts advice.

While it was all apart. Every gear had chamfers put on the edges also. Something else they advised.

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The main offender is the mainshaft nut that retains 5th gear, which is to the rear of the centre plate (the other four gears are in front of the centre plate). The sleeve for selecting 5th gear also has the straight cut reverse gear teeth on the outside of it. That is why 5th and reverse gear problems associated with the mainshaft nut can occur together.

 

The mainshaft nut, along with the counter shaft nut (holds one of the reverse gears) are both designed to be 'staked' to the shaft. That is, after you 262 loctite them and torque them up, you use a pin punch to deform the skirt on the nut into the groove in the shaft. This prevents it coming undone.

 

The practice of double nutting the mainshaft nut involves machining the skirt off the old nut in a lathe, (which cannot be used twice due to the skirt being damaged during the removal process), and then doing that one up first and follow it up with a second nut which you do up VFT behind the first one. This process was developed by the Nissan Rally team many years ago. I have done it with mixed results....I have still had them come undone, and personally favour the factory configuration. One of the problems with double nutting is it moves the second nut too far back to engage the staking groove, so if the nuts do come loose there is no 'last line of defence' via the stake to prevent the nut coming right off and fifth gear drifting back down the main shaft.

 

The other thing to look at is the detents that have been mentioned earlier (the ball and spring in the centre plate). These usually work pretty well from the factory, but you can increase the spring tension a little via plugs between the nut and spring.

 

Finally, wear in the reverse gears can cause tapering on the teeth that creates thrust while driving (in reverse) and can cause them to jump out of reverse gear. The fifth gear problem is more likely to be a mainshaft nut/excessive end float on 5th gear problem.

 

Cheers

 

Jamo

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