3.8 Moss box not synchronizing 3rd

This box was rebuilt a couple years ago with new 2nd/3rd gears, new 3rd/4th synchro assembly (both inner and outer), new layshaft cluster gear and new needles. Since then 3rd speed has been unusable. It’s out now and I’m trying to get as much useful information as possible before I tear into it further tomorrow.

My suspicion is that the fellow who did the work either assembled the synchro parts in the wrong orientation, or he slid them onto the shaft in the wrong orientation. There is also the remote possibility that 3rd gear or the synchro sleeves are just bad parts.

This is how it’s behaving. Screen left is the front of the box and 4th gear, right is towards 3rd gear. Note how it behaves differently.

Am I correct in my understanding that as the fork pulls the synchro back towards the gear, the syncho should spin up, before it finally pulls the outer operating sleeve off of the detente on the inner synchro sleeve to engage with 3rd gear? This is what it does when I shove it forward toward 4th gear. But there is zero friction when it is slid back.

Are there any other tests or checks I should perform before tearing it down to find this or other problems? I haven’t noticed any issues with 1st, 2nd or 4th.

Yes, that is what should happen.
Your post is several days old and I see you got no comments. So it never worked since the rebuild? From what you show, it does seem something is clearly preventing the sleeve from moving onto the synchro and then over the 3rd gear locking teeth. It does not even seem to be trying to engage.
Since you indicated it would be apart by now, where you able to find the problem? I am curious what you may have found. Is it solved?


Yes I did find it, the synchro sleeve was installed the wrong way around. It looked very much like the illustration in the manual, but it didn’t quite match the description. The side with the taller boss was facing backward and was interfering with the locking ring on 3rd gear. It’s all apart and cleaned up now and I’ll start building it back up when some supplies arrive. The gearbox magic has been greatly demystified in the process.


That is good to hear.

I find it supremely gratifying when I not only end up the problem solved, but I’ve actually learned something as well.

Unfortunately not all my projects work that way, solutions or knowledge.

A perfect late Nov day in Texas, 70 degrees and sunny. I seized the opportunity to repaint the box after thoroughly washing it out last night.

I also did my best to scrub out the top and and the shift fork assembly with spray cleaners, brushes, compressed air, pipe cleaners and q-tips, then relubed the slides with new Redline fluid using a syringe. Hopefully the Jaguar gods will forgive me for not completely disassembling it, but some cans of worms simply aren’t worth opening. It’s clean and operating very smoothly.