[Wayne]

can anyone specifically give me a hint as to why my 4th gear pops out when i hit a bump?

 

[baz]

you have a weak detent spring in the box which is not locking it in place
you can live with it or have the box rebuilt
a lot cost saved if you can live with it

 

[Glenn M]

Any difference in the answer if transmission pops out of reverse but all forward gears ok?

 

[nobody]

I've seen worn synchro gears and a bad detent button do it too.

 

[GTJIM (R.I.P.)]

Internal .. or Extenal

First check for external problems like a colapsed gearbox and/or rubber monting. Then check the adjustment of the gear lever linkage to be sure that the gearbox moving about under the "bump" loading is not just operating the linkage and "popping" the 4th gear out manually.

Internal problems usually centre upon high milage wear - syncro detents and such - which are usually caused by the looseness (wear) in the bearing in the input shaft that the front end of the tailshaft spins in for the intermediate gears. In 4th this wear allows the main shaft to wobble around and "walk" the syncro slider back off the input shaft.

 

[BQS4]

I would also check to see if the 4 bolts holding the trans to the bellhousing are tight. I had several 4-spds jump out of gear because these 4 bolts were loose.

 

[jlthunder]

Low on Oil

I agree with BQS4. I had a loose trans to bell housing bolt. The oil leaked out the front seal to a low level and 4th gear would pop out when I let up on the gas. Check your oil level and make sure all bolts are tight.

Warning, don't overtighten since the bellhousing is aluminum and it will strip out.

Check for signs of oil leakage at the front of the bellhousing and rear imput shaft. It might be time for a rebuild or a used replacement.

 

[73Manta72gt]

easy fix..maybe

My tranny jumped out of gear. when I replaced the stock rubber shift boot with a soft leather one the problem went away...couldt be worth a try to remove the shift boot and see if that helps...might get a few more miles out of it.

 

[baz]

My tranny jumped out of gear. when I replaced the stock rubber shift boot with a soft leather one the problem went away...couldt be worth a try to remove the shift boot and see if that helps...might get a few more miles out of it.

bad idea the boot is there to stop fumes from getting in to the cab