Haven't driven the car, yet...It's parked for the night, but I got it to go into 6th doing the method Billman suggested.

Any insight into why it did that? How did I burr up the 5-6 collar when I didn't use it?

 

I dont know the failure mode of this yet. You are not the first to lose 6th after a track day. I have a guy coming here at the end of the month with the same issue, and he can not get it in 6th at all. He had just finished a track session as well.

I know of at least two others besides him with the same problem, from tracking the car, and was able to cure it completely by the above method.

Did at any time on the track you attempt to go into 3rd, accidentally touch fifth with the shifter, then let off and make the 3rd gear shift?

Be honest and I can determine the failure mode

 

I do remember catching 5th one session coming out of a 2nd gear corner.

Is that it? Really? lol

 

It happened to me once, after a track day (2nd time on the track, only did 3 track days and it's now over 3 years ago).
Only used 2-3-4-5 on the track.
6th came back after some force and was fine the whole way back home.

As far as I can tell by looking at some pics (of my trans insides) and the service manual, 5th and 6th only share a synchro hub and sleeve.
5th and 6th have their own single synchro ring.
(1 & 2 and 3 & 4 have double synchro rings.)

So if it shifts normally into 5th, one could think the sleeve, hub (5th gear side of them) and 5th synchro are all fine.
Everything slides, the shift linkage is ok too.
That leaves 6th synchro.
How do you damage it by not using it?
How do you get a burr on a synchro teeth by not using it?

This is 5th & 6th gear / synchro set with 5th (almost fully) selected.

 

Just pulled a trans apart with a locked out 6th gear after a track day. Here's the deal:

5th and 6th share a synro sleeve, and a syncro hub. The syncro sleeve slides one way OVER the syncro hub to engage 5th, and slides the other way to engage 6th.

The problem is actually not a 6th gear problem. Its a 5th gear problem. The trans cannot fully come out of fifth gear, even though it may seem like it does.

The syncro sleeve gets its teeth mashed over on the 5th gear side. Since it is already on the 5th gear side of the hub, it will go into 5th.

When you go to shift to 6th, the mashed syncro sleeve teeth on the fifth gear side do not let the sleeve pass over the hub to 6th gear. The burrs hang up on the 5th gear side of the hub. If the burrs are light, you can force it into to 6th gear. Once on the road, USING 5th and 6th gear under full load will flatten the burrs and cure it usually 100%.

How does this happen? Skip shifting. Whether intention or accidental, the single cone 5th and 6th gear syncros have little braking power over the mainshaft compared to the double cones in gears 1-4th. That's a syncro's only function: to slow down or speed up the mainshaft to the speed of the countershaft that is being turned by the rear wheels of the car...to syncronize

On the track, if you are wide open in second, and accidentally move the shifter into the fifth gear gate, you burn the crap out of the teeth. The speed variation is too great between the synro sleeve and 5th gear.

If you have done all you can to force the shifter and it will not go, disassemble the trans and replace FIFTH gear, and the 5th-6th syncro sleeve and hub set.

Close inspection will reveal salvageable parts. This trans ONLY needed the synro sleeve.

 

Well put. It's long documented not to skip shift for this reason.

 

I feel very fortunate to be a member of this forum. We have some smart, dedicated people here that give up their knowledge and time freely to help others (me) whom otherwise wouldn't have a clue. Thank you.

 

Billman, you're great as usual!!!

 

Recently bought the car, I was also missing 6th. Thanks Billman, worked like a charm!
Also thanks SpitfireS for the picture

 

Just buy a 5 speed knob. Way less trouble.