4th gear problem

[Greendust]

I found a 74 Duster for sale. It has a 318 w/340 heads, 4 speed and 323 posi. The seller told me it jumps out of 4th gear when you let off the accelerator at over 50 mph. Can anyone tell me what causes this and what is the remedy?

 

[mguner]

First thing I would do is make sure the shifter linkage is in good condition and adjusted properly. If somebody has been into the transmission the could have left out the detent block rod or something else.....

 

[teringer]

this could be many things, wore out pilot bushing letting the inputshaft move out of alinement, blocking rings wore out, input shaft inner or outer bearings very lose shift fork problem and the list goes on and on.too much play in the mainshaft, linkage issues,

 

[jtkaaa07]

When it pops out on deceleration , most of the time is a worn slider shoe key or hub which is what holds it in gear. The other suggestions could be possible, but more then likely it's a slider shoe key or hub problem

 

[jtkaaa07]

 

[jtkaaa07]

There about $10 on eBay or available from Brewers Performance

 

[AJ/FormS]

I can tell you exacticly. Never lift!
Ok but; the clutch teeth on the front of the gear are chipped off, and so are the matching teeth on the slider. I used to fix these all the time. Hundred and hundred of 'em.
Guys sometimes think it's the struts, but it's not.The struts only have one job; to carry the brass into the brake-cones.
There is a good chance this started with worn shift forks not driving the slider far enough, or a sloppy bearing; but most likely abuse; whether from ignorance or somebody just didn't care, I cannot say.
I doubt there are any shops that will fix those gears for you tho, and that's a shame, cuz it's pretty easy.
Jumping outta 4th is unusual tho, but I'm surprised it is cuz that particular gear is way out there and hard for the slider to reach.
The gear is super easy to fix, but you will probably have to replace the synchronizer or at least the slider. A full rebuild is,of course,recommended; but mine has gone for many thousands of miles on all used parts including gaskets and seals. I just love that dinosaur.