78 Z, stock, may have later model tranny installed. It jumps out of 1st and 5th gear, does this sound like an easy fix? ie something is just loose like a nut on the end of a shaft? Thoughts?

More than likely it has bad synchros and possibly worn gears.

Only easy if you know tranny repairs.

My Z is a 70' but it has a later model tranni in it. After I put it in, it would also jump out of 1st and 5th until............. I trimmed the sheet metal where the shifter comes through and I'm still able to use the stock boot.

Usually your rubber boot wiggles it out of gear. Most likely an easy fix.

Also check you shifter bushings for wear. Excess vibration from worn bushings can also cause it to "jump out of gear"

JM2C,

Dave.

The tranny in my 71 only jumps out of second; and only when I am decelerating. I had rebuilt it awhile back for a destroyed countershaft bearing. There was no visible damage to anything else, and it was free of any debris internally. Any ideas? I have another tranny that just needs some seals and gaskets, so I will be getting that one ready and doing a swap soon. Then I will dismantle the 'jumper' and see whats up.

i have the same problem! jumps out of second...really annoying me.

I don't have shop manual here at work and haven't dived into a datsun tranny yet. This is based on past experience when working on other manual boxes. There is usually a spring and detent ball for each shift rail. These keep the tranny in the selected gear as well as preventing another unused gear from accidentally vibrating into engagement. You might look into replacing these simple items assuming that the tranny shifts properly otherwise.