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**tdangle** · 01-09-2019, 11:16 AM

I believe when these trucks were built the highway speed limits where about the 5+same as they are today. 65/70. I just verified it, Nixon lowered the speed limits to 55 in 1974. I know my dad drove my truck at 70+ all the time with the 4.10 gears TH350 and a 350 engine. Never seemed to bother anyone then. It's just what trucks did then. Fast forward to today and everyone is used to 2K engine speed at 75+ and much better sound isolation. If you want to lower the hwy RPM an overdrive unit might just be the way to go.

01-09-2019, 11:16 AM	#5
tdangle Senior Member Join Date: Mar 2005 Location: Jurupa Valley, Ca Posts: 1,209	Re: HO52 Rear Axle for general use I believe when these trucks were built the highway speed limits where about the 5+same as they are today. 65/70. I just verified it, Nixon lowered the speed limits to 55 in 1974. I know my dad drove my truck at 70+ all the time with the 4.10 gears TH350 and a 350 engine. Never seemed to bother anyone then. It's just what trucks did then. Fast forward to today and everyone is used to 2K engine speed at 75+ and much better sound isolation. If you want to lower the hwy RPM an overdrive unit might just be the way to go. __________________ Terry 1970 Custom Camper/C20 , GM Crate 350/7004R, Dana 60, factory AC