Tranny Input Needed am at a loss!!!

[SpiderJim]

Two months ago I replaced all synchros and a shift select lever in my 81 FI transmission along with the leaky oil seals. Once open everything actually looked in superb condition. In fact the old synchros measured out the same as the new which I replaced anyway.

So here is the issue. Prior to replacing seals and the above I had no issues other than oil leaks from a ten year storage. Shifting was good and hardly any noise from the tranny except what is normal with these older designs. After putting 150 miles on it popped out of fourth which I thought was a mis-shift. Did a fifty mile trip the other day and it began popping anytime I had loaded the fourth gear. A little pressure on the stick and it stayed in gear.

So I removed and opened it up and noticed that the new shift selector fork is on 3+4 where the problem is. Before breaking down I double checked all bearings, synchros and anything that could cause a problem. No play, leaks or weird stuff. Gears turned nice with no grating or friction etc. I removed the 3+4 gear selector fork and measured the contact shoulder against the older original that is installed on 1+2 gears. The new one that I purchased from one of our suppliers to my surprise was 0.025 Thinner than the old original that showed a little wear but no ridging /gauling etc. The so called new one hardly has any wearing shoulder and is nothing like the old one in quality and weight.

I need expert help here. Can this be the issue? My understanding is the shift fork contacts the slider then engages the synchro which engages the gear until being moved the opposite way. The detent lever and ball holds the whole lot in gear until a change of gear. The only other thing that I noticed is the detent ball springs have two in red and one in green. The green was located in the center position that is also 3+4th gear. Any suggestions to what can cause the fourth to pop out when synchros are new the detent ball is solid and bearings seem to be like new? Also had vibration in the lowe stick and yes, all is tight?

P.S I called the supplier to inform them of the skinny assed shifter fork in case they had a bad batch and was told... Jeeze never had complaints before and that was it. I was thinking to purchase a rebuilt one off them for $1250.00 but figure if they use the same crap in what they build and sell then maybe not worth the risk. So decided just to rebuild this one again and if necessary replace everything with OEM parts and not third world.

[So Cal Mark]

is there any end play in the output shaft?

[azruss]

worn shift forks are classic for popping out of gear. this is why you dont ride the shifter with your hand. dont know what to tell you about the detent balls. still have the old shift fork around?

[SpiderJim]

As I recall I had no end play on the output shaft. I have it all stripped for inspection now. All of the bearings seem remarkably tight with zero play when using my fingers to check. The only thing that looks suspicious is that skinny assed shifter fork that I replaced which is on fourth gear which is causing me the problem. I'm taking the whole unit to the machine shop today to have an expert check the bearings. I will also order an OEM shift fork to replace the suspect one along with anything that the shop says that I need. I will also replace the springs and sliders regardless.

What usually causes this to happen?

[So Cal Mark]

the two problems I see are excessive end play and worn sliders/forks

[SpiderJim]

the two problems I see are excessive end play and worn sliders/forks

Thx for the input Mark... I did reassemble the output shaft to retest and the end play is super tight and very smooth with no wobble etc. Except for the 4th gear shaft that springs out until bell housing installed. The shifter fork was new with only 150 miles on it but like said is 0.025 under what the old used one was. So I have ordered new detent springs, bearings, sliders, hubs etc to see if that resolves the issue along with an OEM shift fork from a different vendor than before. The actual shifter rods are in like new condition with zero wear. I'm at a loss?

[Kingme2]

Jim, how did things get resolved?

Was the other shifter fork "more robust", from the 2nd vendor?