Truck wont shift into 3rd or overdrive... any ideas

[AlexK5]

I was driving my 90 K5 down the highway, and I got off to get gas and after the truck shifted down out of third it would not shift back up into the higher gears. I still have R,N,1,2. hits about 25mph and then just revs without shifting.
I have checked the transmission governor and that seems to be in good shape.

Has this happened to anyone else? Any ideas on what this might be?

 

[rockin kw]

Sungear stripped out it sounds like. Had it happen on two different transmissions.

 

[AlexK5]

Ive never heard of a sungear. is that something that can be fixed without replacing the whole trans?
any idea what causes that?

 

[rockin kw]

It's the case around the clutches I believe. Stamped steel part. Splines strip out. Have to disassemble the trans to replace. There is a upgrade that I put in called to beast. Better part and heat treated splines.

 

[AlexK5]

ok. thanks for the help man.
was your truck having the same issues? that fixed it?

 

[Fastereddie]

When you say it revs instead of shifting to third, does it keep accelerating in second or does it free rev like neutral?

 

[AlexK5]

It free revs in neutral.
If I leave the truck in 2nd it will go up to 30-35mph but thats where 2nd tops out. If I have it in drive it will go up to about 25mph and rev like its trying to change gear but just stay in neutral.

When you say it revs instead of shifting to third, does it keep accelerating in second or does it free rev like neutral?

 

[AJs72K5]

Sounds familiar. Thinking one of the clutches let go. But, I'd page @Greg Ducato

 

[Fastereddie]

the 3-4 clutch is not working. But why? The 3-4 clutch pack is the most prone to fail but usually they start slipping first. Not just quit instantly. If it was the sunshell you would have third and no reverse. Maybe the valve body has a hangup.

 

[AlexK5]

Thanks.
what do you need to do to fix that? Will I need a new clutch or a new trans?

the 3-4 clutch is not working. But why? The 3-4 clutch pack is the most prone to fail but usually they start slipping first. Not just quit instantly. If it was the sunshell you would have third and no reverse. Maybe the valve body has a hangup.

 

[Vombrown]

With a 3-4 slippage like that the end result is a transmission rebuild. No matter what you are going to need to pull it and go through it to fix any of the issues mentioned. It doesn't sound like something that is going to be corrected with an adjustment or pan drop. Sorry....

 

[AlexK5]

If I am going to rebuild my Trans should I be looking into any upgrades while I'm at it. Any suggestions on better parts or should I just have the original one rebuilt?

 

[Vombrown]

As was mentioned earlier a "beast" sun gear, upgrade clutches and a towing shift kit wouldn't hurt any.

 

[AlexK5]

cool. thanks. Im going to look into those parts.
thanks for the help/suggestions everyone

 

[Fastereddie]

There are numerous upgrades. Depends on what you expect to do with it. The biggest killer of 700r4 is towing in overdrive and putting on bigger tires and not gearing lower. For behind a stockish 350 I would at least put a hd reaction shell and a shift improvement kit. There is also a better 3-4 apply piston setup. I think its out of a later 4l60e. And obviously use a good kit and clutches/steels

Vombrown beat me to it. I was making mac n cheese.

 

[Greg Ducato]

While you are gathering parts, pick up a new reverse input drum, yours will be warped from the band slipping in fourth.