90 K3500 4 speed transmission upgrade options (5spd)

[rcb1]

On my 90 k3500 the 4 speed (3spd w/granny) falls out of second if you don't hold it, particularly going up hills. I think I'll pull it and repair whenever it needs a new clutch. But, it also go me to thinking about putting a 5 speed in it so it can handle highways a little easier. At 60 the 350 is really humming. I'd like a little more casual highway driving. Is there a good sturdy 5 speed I should be preparing or is the 4 speed as tough as it comes?

 

[Chewy1576]

An NV4500 will be about the easiest swap you can find. I almost had one of the early ones with the granny first gear for $300 to swap with my SM465 but I was a little too late with my phone call. From what I understand, the Chevy bell housing will bolt directly to an SBC block, the early version also has an external slave cylinder that will use the same hydraulic line as the SM465, same (a little bit longer but only by 1/8" which is negligible really) input shaft, and same output shaft so the NP241 transfer case will bolt right to it. If your K3500 is like my K2500, the VSS is also in the transfer case, so you won't have to worry about the speedometer. May need to modify the transmission crossmember slighty for the NV4500 but I'm not sure.

 

[someotherguy]

Just watch out; while the NV4500 is truly a tough transmission, a large number of them out there with significant miles also have at least a few bad synchros. I know I've driven enough of them where the 2-3 (actually 1-2 when you rule out low gear starts) grinds badly. If driven like this for any real amount of time then the whole trans needs to be rebuilt and you're looking at grand, easy.

If they have the original carbon-fiber synchros and have been run with the incorrect lube (Castrol Syntorq, sold under GM and Dodge labeling) then the synchros can become damaged. People don't want to pay $20+ /qt for 4 qts of fluid, so instead they wreck their trans...

Richard

 

[rcb1]

Thanks for the info! I'm mainly a mopar guy, but my father gave me this truck in exchange for replacing the motor in his k1500 (diesel). I don't know all the do's and do not's of chevy's yet. This is actually the first one I've ever owned... though I was quite fond of our suburban in the 80s.