I have an '89 K1500 Cheyenne 4x4 with a tired 305 and the 5-speed manual HM-117 transmission. I am rebuilding a '98 350 Vortec to replace the 305, and think that I should upgrade the transmission for the Vortec's increased power and tourqe. I don't plan to drive this truck hard, but reliability and the ability to pull a trailer is essential.
Can anyone suggest a transmission upgrade that will bolt right in??
Any reply greatly appreciated, Thank you, Kevin

 

Do not believe there is a bolt in upgrade. Also I don't recall if the NV3500 has a higher torque capacity than your current trans. The NV4500 can handle much more but has a separate bell housing and takes a different input gear on the transfer case.

Now what I looked up shows the HM-117 to be a 4speed manual.
If you have a 5spd it is something else.
Do you know what your RPO code is?

 

Dan, thank you for your reply.
I made an error in my initial post. The transmission is in my truck is the HM-290 RPO MG5 (NOT the HM-117). My understanding is that the HM-290 is rated for 300 ft-lbs of tourqe. Maybe it can handle the Vortec, as I don't drive hard. Currently the transmission is working fine and there have never been problems with it.
I don't mind if I have to change the transfer case.
I'm hoping that there is a Chevrolet or GMC truck out there, any model year, that I can salvage the transmission (and transfer case if needed) and bolt them into my 1989 chassis.

 

Those transmission are sensitive to having the proper quality fluid in them.
I'd recommend draining and filling it now if you don't know the maintenance history.

 

Thanks for that Dan, I do know the transmissions service history; I've driven the truck daily for roughly the last 15 years and the transmission fluid is correct.
Chances are the transmission will be fine behind the rebuilt Vortec, but I would prefer to put in a transmission that's known to be tough.