Bob,
I had this problem about 15 years ago after Rich Chrysler restored my BJ8. The
transmission would pop out of 4th gear when, "letting off the accelerator pedal
in the middle of an acceleration; letting off the accelerator pedal to engine
brake," which is from my notes at the time. After disassembling the gearbox and
carefully examining everything, his diagnosis was:
"The cause of the slipping out of 4th is due to two things, each of which might
not have caused the situation by itself, but combined to cause problems.
The 3rd/4th speed gear selector fork shows a lot of wear on both sides where it
pushes against the shifter hub in both directions. Also, there is wear on the
3rd/4th gear internal synchro hub. This is the sliding assembly preloaded with
the 3 sets of springs and balls.
To replace the offending parts will require: 1 selector fork, and 1 3rd/4th
synchro hub assembly"
I had some other work done on the gearbox at the same time, which included
replacing the layshaft, reverse gear/idler and the 4 caged needle roller
assemblies for the laygear.
After all this was done, it never popped out of 4th gear again, no matter how
much coasting or engine braking I applied.
John
On May 19, 2017 03:15:22 PM Bob Spidell wrote:
> My gearbox is popping out of 4th and 4th/OD, usually coasting in gear
> downhill, but sometimes randomly. Anyone know what the typical cause(s)
> of this are?
>
> My guess? My rebuilt engine has (much) more compression, and the
> 'reverse torque' from coasting it causing something to flex or buckle in
> the box.
>
> TIA,
>
> Bob
>
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