What gearing to go to.

[firedoger]

I’m looking to change my gearing in my 72 K5. It currently has 3:08’s in it. I’m running 33x13.5r15 Nitto’s. Drive train is 400 sbc with TH350. Should I run 3:73 or 4:10’s. This is a street queen will never see the dirt. Mainly local driver. At some point I plan on LS swap it.
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[Richard]

My 72 originally had 373's and 31 inch tires, stock TH350 trans. The rpm was a bit high for me. Around 2500+ if IIRC. If not planning on adding an OD trans with the swap I would go no more than the 373's. Would go 4.10's if planning an OD trans. My engine trans and axle swap with 37" tires and 5.13 gears should put me just over 2k on the highway. Right about where my 94 is. Comfortable at highway speeds with power still available. Great milage will never be attainable in these heavy old trucks with brick wall aero dynamics. All we can get is better performance with a bit more economy than 10 mpg.

[DeadheadNM]

I have 33” tires, th350, 350 sb, and 3.73s. Works well driving in and around town.

[hemi43]

3.73's with a TH350, or 4.10's with a 700R or 4L60.

[firedoger]

Originally Posted by hemi43

3.73's with a TH350, or 4.10's with a 700R or 4L60.

Thx for the replies. I do plan on putting a 6.0 or 6.2 with a 4l80 in it. That’s probably 3 or 4 yrs away.
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[Mike C]

My ‘72 Jimmy has 4.10 and an SM465 with 35” tires while my sons has 3.73 and TH350 with 35’s. Because of the converter, both trucks turn about the same rpm on the road. And the combo of 35’s, 3.73, and TH350 has the factory speedometer more accurate than anything else I own! Originally a 3.08 geared truck, I think 3.73 ideal for a TH350 equipped with 33-35” tire.

[kwmech]

Originally Posted by hemi43

3.73's with a TH350, or 4.10's with a 700R or 4L60.

^^^This....any towing in the future will require different, but it's just a street vehicle. 4.10s with the 4l60 takes the ratio in overdrive back to the 3.08 (2.90)