Hi, My name is Scott and I'm new here. Thanks in advance for any help.
My son just replaced the transmission in his 92 K1500. TH700R4.
The truck now has a vibration as soon as you drop it in gear. It's almost like it's causing the motor to miss badly but it immediately smoothes out when you take it out of gear. I crawled under it to see if I could see anything out of the ordinary but the only thing I can see is a 1-2 inch nipple on the drivers side of the transfer case the looks like a vacuum line should be attached. Any ideas as to what the heck could be causing this?

 

That is probably the modulator valve, and yes a vacuum hose goes to it. That is really just for shifting, and I doubt it would be a vibration cause, but there is more than likely a vacuum line unhooked.

 

thank you Kevin. Is the modulator valve inside the transmission?
(edit) Is this something that should show up on a diagnostic?

 

Valve is external, and no it won't show IT as a dtc, but again, you have a vacuum hose running around somewhere that will affect the engine.

 

Thanks again Kevin. I'll let you know what I find.