'67 cj5: grinds and won't stay in first gear

I have a '67 cj5 with a v6 and a three speed transmission that has trouble staying in first. If I put it in first and try to go, the transmission makes a loud grinding noise and it pops out. If I try to hold it in first, it just makes a lot of grinding noise. It doesn't do this in any of the other gears.

I just replaced the transmission fluid and it's at the appropriate level. What should I look for first when trying to fix this?

 

I suggest that you remove the floor panel and then remove the top of the transmission (6 bolts) and take a look inside. If you have a telescoping magnet (use to retrieve dropped screws), fish around in the bottom of the transmission and see if you come up with chips, roller bearings and such. Sounds to me like time for trans rebuild. The t-90 transmission doesn't have synchro in first gear, and drivers often grind the gear when going from 2nd to first, which catches up with you after a while. Most don't know how to double clutch or come to complete stop before going from 2nd to first. Let us know what you find.

 

A '67 with a V6 would have a T-86 (if it's stock) which doesn't exactly have a sterling reputation for durability...

 

The T-86 is basically a T-90, updated a little to work with the V6.

If you have a T-86 that has major issues, likely your best option is to replace all the internal parts with T-90 parts. You cannot mix T-90 and T-86 parts, but you can build a T-90 with a T-86 case, and have a functionally identical transmission to the original T-86. Herm sells these transmissions http://hermtheoverdriveguy.com/?page_id=1415 if you do not want to source the parts and do the assembly work yourself.

Yep - first thing to do is look down inside. Pull the floor cover and take the transmission top off. I would drain the oil so I could see better. You can pour it back in the open top when you are done looking.

Just a FYI - there is very little you can do to a manual transmission with it in the car, other than look. You can repair shifter problems, and you can change the oil ... not much else. Likely it's coming out, for replacement or repair. Compared to most cars and trucks, this is an easy job in a CJ - if that's any consolation.

 

So I finally had time to pull the cover off and look inside. It looks clean, but when you move the lever into first gear, it'll move into a position, and then you can move it a little further, but it won't stay there. I'm hoping this is the problem, because when you move the lever that extra little bit, the shift fork moves a decent amount. In order to fix this, would it be a new fork, or new shift rail? or both?

also, the cover that I took off said t-90c, so I'm assuming its a t90 and not a t86 as most everything on the jeep is original, but I'm not positive.

 

That's a T-86. The spiral splines on the main shaft and angled teeth on the sliding gear are specific to the T86. That's why the gears won't mix with the T90.

If you have a cast in T90C on the top cover, it's just because the T86 and the T90 use the same raw casting.

You can take the shift top apart. There should be an exploded drawing in the FSM. Check that all the detent balls and springs are intact, and that the shift rails are in good condition. There may be a small parts kit for the shift top - if you can't find one easily, ask Herm or R&P.

 

First and reverse sliding gear is toast, broken teeth.
Better look underneath the gear; the cluster gear is most likely damaged too.

 

I see a T86 in your pictures. The spotting feature is the spiral cut splines on the mainshaft for the 1st and reverse slider gear.
I also see a badly abused set of teeth on the 1st gear side of that slider gear. I doubt that your problem is with either the shift fork or the shift rail. Relatively little wear takes place on those parts except for the tips of the shift forks where they engage into the slot of the slider.

I would contact Herm for parts availability. Just as a guess, your countergear is also damaged from the engagement of the 1st gear slider. Look down below those chipped teeth at the gear teeth that mate to them for damage to the countergear. If it is also damaged I would expect that your transmission must have a complete rebuild.

Parts for a T86 are hard to find and expensive. You can put a complete set of T90 gears in a T86 case, thats what a lot of T86 owners end up doing.

Don