Rear gears

[Longhorn Man]

a 350/TH350 should already have the 4.10 gears (assuming still stock) and as said, that's about the best you'll get. There used to be an aftermarket gear, I think it was a 3.90, but it's safe to say you'll never find one.
The RPMs do seem high, and while Tim is right, you can just live with it, and they were in fact built to run on the freeway @ 70MPH... however, it does wear the engines faster, and does consume more fuel on most vehicles.
I would recomend either adding an overdrive trans, or swapping to a later rear end with more reasonable gearing. The reality is, putting a 3.73 gear rear end will drop the RPMs quite a bit and you can still haul/drag anything you want. If you have the truck grossed out or overloaded more often than not, then you should probably keep the gearing, but if running empty/lightly loaded, then I would recomend an upgrade. My daily driver C/30 has the same gearing, and I am swapping the rear end for a 14 bolt with 3.73 gears, with any luck, it'll be in there this summer.

[factorystock]

Originally Posted by Longhorn Man

The reality is, putting a 3.73 gear rear end will drop the RPMs quite a bit and you can still haul/drag anything you want.

Good all around ratio for a 3/4 ton that still occasionally hauls. But, the 64,000K question is why GM never offered this ratio on C 20's during this era? Ford did offer this ratio on Dana 3/4 ton rear axles during this era. Its water under the bridge now, but it does make you wonder.

[special-K]

Originally Posted by factorystock

Good all around ratio for a 3/4 ton that still occasionally hauls. But, the 64,000K question is why GM never offered this ratio on C 20's during this era? Ford did offer this ratio on Dana 3/4 ton rear axles during this era. Its water under the bridge now, but it does make you wonder.

GM didn't offer the 3.73s but did offer 3.54s in Dana60s and they haul just fine behind an automatic. My '72 was used as a 5th wheel hauler by the original owner I got it from.

[Andyboy]

Sorry guys I got under the truck and the tranny is a th400, dont know if that makes a difference. I'll run it tomorrow and check the RPM's again. Thanks for all this info guys.

[Stocker]

No problem, and no difference..... both have direct 1:1 output ratio in high gear.