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Old 09-28-2010, 11:25 PM   #1
LilD
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Low gear or trans or both?

The 70 C20 I just bought revs to the moon at highway speeds. It was a 6 cylinder to begin with but now has a V8. The trans is the original 4speed with the "granny" gear. I was told that the 6 cylinder trucks had a lower gear ratio in the rear end to make up for some low end grunt. So is it the gear in the rear end or the trans that has too low of a gear or a combination? It sucks not being able to enjoy a cruise down the highway and watching the speedo needle and gas gauge needle meet.
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Old 09-28-2010, 11:38 PM   #2
Husker
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Re: Low gear or trans or both?

Probaly the rear end, I have a 6 with 373's and it sucks the fuel going anything ver 50. The transmission in 4th is probaly 1:1.
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Old 09-28-2010, 11:42 PM   #3
Stocker
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Re: Low gear or trans or both?

Fourth gear is 1:1 ratio, so lacking an overdrive, you can blame the low rear diff gears -- and yes, they are probably quite low on any older 6-cyl 3/4T truck. I'd guess at least 4.10, maybe 4.56, and possibly even lower.
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Old 09-28-2010, 11:47 PM   #4
treveiger
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Re: Low gear or trans or both?

Its probably a sm465 with a low rear end and the final gear in the sm465 is 1:1. I have a 69c20 with probably a 4:10 or 4:11 rear end at least and im sure thats what you have if not lower to make up for the v6.
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Old 09-29-2010, 12:36 AM   #5
Jacfourteen
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Re: Low gear or trans or both?

My truck had the 305 v6 originally and it has a granny 4 and 4.56 gears. This combo with 31" tall tires is spinning about 3000 rpm at 60 mph. I plan on swapping to a 3.73 rear gear and an ovedrive tranny (Maybe an NV4500, not sure yet). Then I'd be around 1800 rpm with a little shorter tire at 60 mph.
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Old 09-29-2010, 10:01 AM   #6
LilD
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Re: Low gear or trans or both?

When I went to look at the truck the p.o. told me he thought the rear gears were 4:56. Driving it I would be inclined to agree. Ive read several threads involving swapping rear ends so maybe Ill take that route and kill two birds with one stone. Driver freindly gears and 5 or 6 lugs.
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