The Stovebolt Site Forums The Shop Area General Truck Talk NAPCO question 3.9 axles

Hello,
I am looking to put a NAPCO system in my 59 Apache stepside. The gear ratio is 3.9. Can anyone tell me if that will run at highway speeds when matched to a 3 speed with overdrive? My son will be doing much of the mechanical work on this project. Hope I have explained my question so that it is understandable. Thanks, Ken in NY

a 59 w/ the stock 3.9 ratio can run 60-65 w/ no problems

considering the NAPCO's all came w/ the 4spd, and the transfer case suits that, I think it's likely you wouldn't be able to switch the setup to the 3spd - might inquire at this NAPCO site

Bill

The only other gear ratio available for your current 3.90:1 setup is a 3.38:1 ratio. These gears have been back ordered for quite some time now, but I think the wait is over! I was able to aquire a set from Golden State Truck parts and they said they had just got them in when I called. It's quite pricey though, ~$400 for the gears and ~$200 for the complete install kit. Those were the prices for just one axle and I believe you would have to both axles on a 4x4 truck (Ouch). I think I would just learn to drive slower. I know what you mean about driving at highway speeds though. I have 54 GMC with a 261, SM420 4-spd, and 3.90:1 rear gears and the engine really revs at 55MPH. That is why I am changing my rear gears this weekend. I want to be able to drive my rig to some out of state shows this summer and I would like to cruise at 65MPH. Good luck with your project.

Jim

The old three speed overdrives were 30% overdriven so behind a 3.90 that gives your a final drive ratio of 2.73. Anything in the high 2's makes a good highway cruiser but is near the edge if loaded or in hilly terrain and forget trailer towing in OD.

I have 57 Chevy that I installed a Napco setup in. It originally had 3.90 gears, but since one ring & pinion set was chipped, I replaced both axles with 3.38 gears from Patricks (very helpful & he gave me a discount on the seccond set since I ordered both at once). I have a 3spd overdrive trans installed. So far so good, but I really haven't driven it much since I'm re-doing the body. Some people suggest that 3.38 gears with a the 3spd overdrive is way too tall for a rock climbing NAPCO. My logic is that I won't be doing any rock climbing and I don't have to put it in overdrive unless I want to (e.g., highway cruising). In any case, I'll find out how it works, but it seems to me that if you're not worried about extreme off-road conditions the set-up should be reasonable. I have a modified 261 in it now, I've decided to go to a 283 V8 sometime soon, so that may help mitigate the gearing even more. As they say, it's my truck, my time & my money; I'll make it the way I want it.