Technical 39 trans slips out of 2nd on deceleration

My trans slips out of 2nd gear when slowing down. It doesn't "pop"out it's more of a gradual slide out of gear. This trans has been gone through, bearings, synchros and hub, gearset was real nice to begin with. Only thing I didn't replace we're the rails and detents in the shift tower. They didn't look worn. I took the detents out and cleaned the holes out etc but I didn't take the rails out (probably should have) so I may not have seen any bad areas. Think that might be the problem?

 

I would be looking at your syncro assembly as the culprit..When you say gone thru,,explain,new parts or just cleaned up?

 

I've heard complaints about the new replacement sincro's doing just that. Have not had first hand issues myself. Will be interesting to hear from the hands on guys.
The Wizzard

 

Second gear thrust washers can make it do that, and the sychro parts.

 

Snychro collar dog wear will do that even with new snyc' rings

 

New bearings, thrust washers, synchros and hub from VanPelt. I didn't know what hub I needed so I actually sent the complete gearset to Mac so he could fix me up with the right hub instead of trying to figure out what I needed over the phone. Boxed it all up and asked him to send it back with the right parts, which I know he did, he's the man.

 

Hmmm....a problem that's plagued hot rodders and roundy-round racers for 60+ years.
I had found that the thrust was the big fix, early on...of course, worn synchro hub was a main culprit.
Rebuilt transmissions also did it when driven harder than normal, hence the 'hook' in the middle of the dash in rods and roundys.
Hot Rod John has a double-detent shaft and kit for this problem, "when all else fails"...
(Plainjane on the Bay) He's been at this for about 40 years.
Good kit, it works.

 

Yeah i had a 66 goat with a m22 that did the same thing, new bearings, synchros and still did it, i got use to it.
Just finished working on a 65 goat and it does the exact same thing, other than that the trans feels great.

 

Yeah like I said, all that is new stuff. I've seen flathead johns rails in eBay and thought about getting a set when I was doing the trans. Maybe nows the time.

 

A worn pilot bearing/bushing will cause that also.

 

FYI: his user ID on eBay is

plainjane038

just incase anyone else reading this thread needs a set. Also, he says, "it's not a cure for popping out of 2nd gear, but it helps".

 

That is new also.

 

When I bought my '40 coupe in 1959 it had a metal hook on the dash. My '39 tranny popped out of 2nd gear too. I took the car back to the guy and he showed me how to put the shift lever into the hook. What'd I know---I was 17.

 

a tarp strap will also work..

 

Anytime the old 3-speeds have play somwhere inside, the chance of gear disengagement increases. If it has all new bearings and the synchros are new with a good fit on the tapers, I'd look real close at the end play in the countershaft cluster gear or any looseness in the second gear sleeve or wear surface(inner ID). Many of these old gearboxes have a lot of wear on the thrust face at the back of the countershaft. The thrust washer surfaces have to be in good condition of they will wear right back out. As was mentioned before too, the bearing inside the input gear that pilots the mainshaft and the pilot bearing in the flywheel have to be good too or the shafts get some wobble induced into them under load. Stiffening up the shifter will help as mentioned but it won't correct the problems.

 

one of mine had a slightly bent selector fork when I adjusted it a bit no more probs ,does it feel like its going all the way into 2nd gear

 

I built this .080" bronze thrust washer to take up the back and forth play out of the main shaft, it seemed to me without it 2nd gear would only be about half engaged. and be sure to use the correct original type shoulder bolts to bolt on the top shifter housing, with regular full threaded bolts the top cover can move around quite a lot.

 

I too would suggest checking the bushing or needles between input and output shaft, and also tightening up on the end-play of the countershaft.

Just a little extra slop in the thrust washers there causes tons of thrust on the helical cut gears. That forces the counter shaft in one direction and the output shaft in the other, slightly separating and misaligning the syncro dogs.

*POP*

 

Whoa! The top cover's not doweled down?

Shoulder bolts are a cheap alternative to dowels IMO. They're not nearly so accurate.

 

Nope, no dowel pins to hold the top cover in position. Just the six bolts ( see the photo).

 

I get the bronze shim mod. I've seen some transmissions pop out because the shafts were simply loose in the gearcase. I've also seen them pop because a pilot was actually bent and it was throwing the mainshaft alignment off.

<EDIT... Did anyone mention to check for a bent or worn shift fork? I had to build up the shift fork on my Plymouth because it was half worn off.

 

I am running Hotrod Johns shift rails and stronger detent springs with longer detent balls , I like the positive shift , my trans was rebuilt there is no hint of jumping out of second cheers David

 

Thanks everyone for the input. I think I can live with it for the rest of the short hot rod season we have here in Michigan. Lots of good things to look at this winter. I'll tear it down and see what's goin on. Thanks again everyone.