Do I put in new synchro rings
 

Just acquired a 40 to 48 side shift three speed to get a good cluster for a rebuild into a 39 box. Took it all apart to find it in pretty good shape. Slight rust on 1st reverse slider. Cleaned up well.

The synchro rings look really good. I am resisting putting made in China pepro parts if originals are serviceable.

Re: Do I put in new synchro rings
 

If the grooves inside the cone area are still present and the teeth have good sharp points where they engage, I would use what is there. If you have NOS OEM synchro rings then you wouldn't be gambling on the parts if you wanted to change.

Re: Do I put in new synchro rings
 

There is a gap between synchro and gear sideways...when that closes up it stops working.
So the size of the gap is a hint how worn it is.

Re: Do I put in new synchro rings
 

The gap between the brass synchro blocker ring and the gear part of the syncho is important. Since the blocker ring acts as a brake for the gear, it need to have enough meat on it to work properly. This ink is what Mac VanPelt had to say about the gap.
https://www.fordbarn.com/forum/showt...3599&showall=1

If it still has a good gap, use it. If not pitch it. Mac tries to get the best parts and he is aware of the reproduction blocker rings that don't fit right. I purchase my parts from him since he's a lot less likely to sell me a paper weight.

Re: Do I put in new synchro rings
 

Fred @ Southside Obsolete (Barnfind08) has them NOS for a very reasonable price. While apart, I'd suggest replacing them.

Or, contact Mac VanPelt or Michael Driscoll. They will ensure the ones they sell you are correctly sized.

Re: Do I put in new synchro rings
 

The last new synchro rings I bought came from Third Generation Automotive. They looked good and work well in my '35 transmission rebuilt last year using a later '46-'48 gear set.....an amazing improvement in shifting, and no more popping out of 2nd gear!!

*Note of clarification...I mentioned where I purchased brass synchro rings above in case the OP wants to buy good quality new parts. However, this had little, or no affect in eliminating popping out of second gear as some other posts assumed this is what I was saying.
The popping out of second occured with the original '35 gears no matter what I did trying to prevent this. The elimination of this problem occured when later '46 to '48 gears were installed and spacings of gears and other components were set to original specifications as outlined in MacVP's Book. Also, during this rebuild I used the original '35 shifter top and shift lever with special fork assemblies made to properly shift the later gear assembly,.....so, there were no better detents in this shifter top to help prevent jumping out of second gear. Just thought I should clarify this.
I probably now have ~3,000 miles on this transmission conversation, and shifting is a remarkable improvement over what it was with original '35 gears.

Re: Do I put in new synchro rings
 

Maybe I need to look into changing mine. Pops out of 2nd when going down hill, have to hold the shifter to prevent.

Re: Do I put in new synchro rings
 

That may not be a blocker ring problem. It's more likely a wear problem but blockers can get problematic. Thrust slack is taken up by snug fitting parts with the counter shaft and the main shaft as a whole. If things wear too much, the thrust load can push it out of gear. Even a worn 2nd gear bushing could be at fault. They like to do that when the load reverses and thrust changes such as letting off the throttle & engine braking in 2nd.

Re: Do I put in new synchro rings
 

End play is crucial here (hopefully Mac VP will jump in). From what I gather after having my arms elbow deep in one for the past few weeks, too much end play will make this condition happen. Blockers are certainly a part, but so are the metal "shims" and thrust washers and the overall condition of the bushings, gears, thrust surfaces of the case, etc. Another place to look is the detent in the tower. Not likely the sole cause, but could be adding up as part of the problem.