Montana transplant with 79 K10

[planecycle]

Well hello all ya`ll - I've moved from my home states of Oregon and Washington to Montana with my 1979 K10 short bed.

Just before the move my camshaft was diagnosed with flat cams and it was suggested I look at dropping in a crate motor. Using a little time and effort I swapped the camshaft for a CompCams RV model and I'm quite pleased with the results in the engine's idle, torque, and sound.

The move created a new issue for me however. The speed limits here in Montana are 75mph in most areas and I'm geared optimally for 55mph. My setup is Chevy 350 to SM465 / NP205 to 3.73 gears running 235/75R15 tires. Cruise RPM is about 3300rpm at freeway speeds which is too high for comfort and any semblance of fuel economy, not to mention the lack of power when it is time to pass.

I'll be looking through these forums for guidance on gear ratio swaps. What I seem to have learned so far is that I'll need different axles because the carriers are different if I want to go to a 3.42, 3.08, or even lower. I don't believe I'll need to "upgrade" my axles to Dana 60's or the like as the existing use of the truck includes daily driving around town for errands and hauling reasonable loads of materials on occasion. It sees a moderate amount of camp hauling and pulling a boat during the summer. Sadly, I also commute about 8 hours each way every two weeks on the freeway though, which is were I'll end up wearing this engine out.

Ok, cheers.

[Don5]

The carriers are the same from 3:73 on down. You can change the gears to 3:42 or 3:08's and use your existing carrier. It is when you go to 4:10's that the carriers have to be changed out. You could always put a lift on it too. A lot easier than swapping gears too.

BTW-Welcome from the western part of WVA!

[planecycle]

Hey thank you for the clarification. When I did the cam swap I was able to find a LOT of literature both in my manual and online to set me at east doing the job myself. I haven't yet unearthed this level of information about axle gearing. After sleeping on this thought for a few nights I started wondering if I shouldn't just get myself a 5 speed so I have overdrive applicable to both axles instead of tearing into both ends of my truck. With the knowledge that I can swap gears I might just do the rear end first at 3.08s and see if I'm happy with it. If I am I could get the front gears swapped out before winter hits and I'd be ready for the snow again. BUT if I'm not happy with 3.08s I could try going one way or the other. The 3.08s should get me right about 2600 rpm at 75mph all else being the same as now.

BTW, I have a diverse technical background that began with farm machinery and moved on up to military jet mechanic and then to technical school for Instrumentation and controls... but I've only recently felt comfortable attempting my own deep maintenance. Forums such as this one add a lot of leverage to a person like me when the search button and my thought process line up. Thank you everybody who positively contributes to this knowledge base!

[zieg85]

Welcome from NW Indiana.  Pondering the same change on my C-30.  4.56 gear does not make even 55 feel good...

[Irish_Alley]

dodge uses 3.55 in its cummins truck (or at least they did for a while) granted they have all that low power but i think it makes most speeds feel better

[Tazman]

Welcome from AZ.