jumping out of 2nd gear

Stock 66 cj5, f head, 3 speed, pops out of 2nd gear on compression about 70% of the time. Sometime back I read on here about that problem and the fix but I have tried the search function with every combo I can think of with no luck. Any suggestions?

 

Very common problem, time to drop the tranny and do a rebuild, almost all of the Jeeps I've had over the years suffered from this.

 

That symptom is speciffically addressed (popping outta second) in the Universal Shop Manual. Mine's on loan or I'd post the page. Look in the trouble shooting section of the tranny trouble shooting and it will give you things like endshake on that shaft.

 

From the T90 rebuild guide:

When I rebuilt my T90, I got the master rebuild kit from Herm (it contained a new 2nd gear):

http://www.hermtheoverdriveguy.com/id3.htm

 

The info that EricM posted is absolutely correct. There is more that can cause this however. Worn teeth on the inside of synchronizer sleeve where they engage those teeth on the gear, a worn second gear bushing, worn input and output bearings allowing the shafts to walk back and forth, a loose transfer case input gear nut, or worn detent springs or shafts in the shifter top. Worn forks can also cause this as they won't allow the synchro sleeve to engage the gear fully. Most likely is a worn bushing or worn teeth on the gear or synchro sleeve. A good time to freshen up the transmission.

 

Most common cause by far is broken synchronizer plates.

6-26-07
Concerning the fact that your tranny pops out of 2nd, I advise the following:
Remove the shift tower cover to inspect the inside of your transmission.
Note the gear oil lube quantity.
Now look closely at your synchronizer clutch hub.
This is positioned at top on the front of the mainshaft.

http://www.film.queensu.ca/CJ3B/Photos/Parts/Transmission.gif

Inspect the synchronizer blocking ring teeth for excessive wear. (brass ring)
The rear blocking ring teeth in particular must be sharply edged.
If one side is worn down this will be the notable cause of your concern.

Also on this hub there are 3 blocking plates.
These small blocking plates are about 1 inch long and 1/4" wide.
They have a cross section like a formed channel (not seen when installed}
This simply means they are hollow inside.
The front and rear ends of these plates are folded down.
Take particular note here!
If these folded down "tabs" are broken off you have just discovered another
major cause of your shift problems. These synchronizer shifting plates are
often the first thing to go out on an original tranny.

I would estimate that you will need an overhaul gasket set plus synchronizer
blocking rings (brass gears) and plates as an absolute minimun.
The synchronizer clutch hub itself is normally fine.

A complete tranny overhaul is the realistic approach if you find the
synchronizer plates or something else to be obviously defective upon visual
inspection. These trannys are very basic and easy (for me) to rebuild.
A tranny rebuild will require the fabrication of only 1 special tool.
A countershaft gear bearing pilot.

 

My to do list will start with an inspection and go from there, based on what I find. Thanks for all the responses!

 

Mine was popping out of second with a full rebuild (replaced 2nd gear and all). Turns out I had to 'bend' the 2/3 gear shift fork a bit in the vice to get it to engage 2nd gear further.

It would pop out of second at the slightest decel in 2nd. After bending it just a little at a time and testing it, I can downshift hard in second and it won't pop out.

I only went this route because the trans internals were all new.