I recently rebuilt the tranny in my 99 silverado I have put about 1000 miles on it with no problems it has shifted fine and never sliped but today I left the house and it will shift through 1st 2nd fine but when it shifts to third it just goes into neutral more or less and I have nothing. Also when setting still and you shift to D you hear ( what sounds like) the clutches tighten up. So since I am just a self taught mechanic and only have a few trannies under my belt I would like to get some of you experts advice.

 

I would guess you have a 3-4 clutch issue actually kinda sounds like if this happened suddenly that the snap ring broke out of the input drum for the 3-4 clutch

 

yea it ran fine the day before i had just gotten back from a 225 mile road trip and it ran fine on the trip. parked it and now this.

I cant work on it for a few days so if anyone else has any ideas let me know.

 

can anyone tell me if it could be a valve body issue or a band problem

 

The band would only affect 2nd and 4th , Where the 3-4 clutch would affect 3rd and 4th, I cant think of any valve body issue that would cause a neutral on the 2-3 shift . Sorry