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Hi everyone, Just getting back to the forum. Last projects went very well. New problem if someone can help. I cant get into 3 & 4 gears. 1 & 2 + rev. go in good. any suggestions, Want to drive this summer... thanks in advance vinnytruck

Does your truck have the older 88950 or the newer NP420 transmission?

I'd start by taking the top cover off of the transmission, and checking the shift rails and tower. It could be in the gears, but I'd start with the top end.

thanks for the reply ELWOOD, I took the cover off found the rails were stuck.??? I am now taking them apart. I will let you know what I find, thanks again Vinnytruck

There is a lockout system that prevent two rails from moving if a third is not centered. Prevents putting the vehicle into two gears at once and blowing it up. If a spring or plunger in that is damaged, it can lock a rail up. Full service procedure is in the Body and powertrain manual.

THANKS just me, your input hepled BUT... freed up rails thought that was it BUT I dont know how this happened. The syncro plates and rods are all bent. Will replace. Does anyone have a idea how this had happened, just like to know so I dont do anything wrong. P.S. truck wont make 4th july but its comming along. I would love to post a photo once done.( there is a rainbow and a nice story about this truck but cant write till finished ) THANKS TO ALL VINNYTRUCK

vinnytruck wrote:THANKS just me, your input hepled BUT... freed up rails thought that was it BUT I dont know how this happened. The syncro plates and rods are all bent. Will replace. Does anyone have a idea how this had happened, just like to know so I dont do anything wrong. P.S. truck wont make 4th july but its comming along. I would love to post a photo once done.( there is a rainbow and a nice story about this truck but cant write till finished ) THANKS TO ALL VINNYTRUCK

What are the "synchro plates"? And by "rods" do you mean one or more of the shift rails in the top cover? Those would need some serious force to be bent.

If you can post photos of the damaged parts, that would be really helpful.

Only thing I can think of that would bend the rods on the synchro plate would be the input shaft lock nut coming off and then the synchro snap ring shearing. This would let the synchro slide forward and bind.
I just took apart a free core transmission and the lock nut was spun off, the main shaft was ruined and the synchro's were destroyed.

just me wrote:Only thing I can think of that would bend the rods on the synchro plate would be the input shaft lock nut coming off and then the synchro snap ring shearing. This would let the synchro slide forward and bind.
I just took apart a free core transmission and the lock nut was spun off, the main shaft was ruined and the synchro's were destroyed.

Ahh...the stub spacer stand offs on the synchro halves.

elwood, this is what I purchased: NOS early synchronizer assembly the halves and pins (4) were bent on my truck. (NP420) maybe this helps, dont know why they bent and got distorted. also changed seal. whats your thoughts??? thanks so much VT

All you describe points straight toward the classic issue with these transmissions. The forward snap ring being broken, forced off the main shaft, or the most common cause, the snap ring groove broken off the main shaft. In the early trans, this lets everything from second gear forward on the main shaft slide forward out of place. First symptom is generally grinding and jumping out of 3rd gear. What you have described is the typical later stages of the problem. Based on the info you have offered, sounds like you are nearing the time when the unit self destructs; I've seen a few where only the case was salvageable.

MSR, thanks for the reply. Are you saying I did the wrong thing in purchasing the syncho assembly? all other parts look fine. Please get back to me, I am ready to put the top plate with the rods back on. VT

What he is saying is that that is just one of the cascading failures of an improperly set up trans or one that has had other failures.
I was given a core trans. It was pulled out of a truck the guy had been driving, he swapped in an automatic because he couldn't drive a stick any longer due to knee surgery. To eliminate down time, I do engines, trans, transfer and different as assemblies and fully build one then do a swap old to new when i have time. Since I'm building an engine, time for a trans, too. Opened up the core expecting it to be chewed but operable. ( I have all new internals in case something was trash )Wrong. I don't know how he was driving it. The front retainer nut was backed all the way off and was just captured by the front bearing retainer. The snap ring was a pretzel. There was only one 'tab' left to locate it on the main shaft. The synchro hub gear was worn .200 and the shims were extruded out.
Case you s good, castings are good. Cluster is serviceable, but I have a new one. I'm sure this was just a grenade with the pin pulled and he was lucky he swapped when he did. Don't know how he drove and shifted it!

vinnytruck wrote:MSR, thanks for the reply. Are you saying I did the wrong thing in purchasing the syncho assembly? all other parts look fine. Please get back to me, I am ready to put the top plate with the rods back on. VT

Feel free to give me a call, I'll fill you in with details of what typically happens with all this and tell you some things to look for. This is not to say you are sitting on a grenade with the pin pulled, but by all means be aware of this common issue and check it out thoroughly while you are into it. Shop phone 704-474-4683. We are here all day, but less than full crew because of Holiday, no one in the office to answer the phone. Just leave a message if there is no answer, I'll call you back.

Thanks Charles, Will do.

Hello Vinny, This is Bill, the guy from Middletown who helped you with your truck. I see you're still working on it. I moved last year to South Carolina. You can email me at billsil@atlanticbb.net