Help Picking new gears - The 1947 - Present Chevrolet & GMC Truck Message Board Network

oteixeira · 11-05-2002, 11:43 AM

Hi all,

I have a friend at work that has a '70 K-10 that was originally a 292 I-6 with a 4 speed crawler. He has done a "few" mods over time and it is now a 8" lifted 4x4 with 38s, and a 427. He left in the original 4 speed and axel gears.

The first question is based on the original setup what should his gears be from the factory? The second is what would you recomend for it? In 4th gear at 65 (a true 65), he is at 2K on the tach.

Any help is appreciated...

Orlando

crazy longhorn · 11-05-2002, 11:59 AM

I would say you need a 4.56 or 4.88 gear with the 38" tires. that will require a carrier change, as stock was likely a 3.07(3 series carrier). check this link for math to see what you want for rpms on the hyway..... http://www.smokemup.com/auto_math/index.php

ckhd · 11-05-2002, 03:21 PM

The standard ratio for a '70 K10 six w/a 4-speed is 3.73. Are you sure that it's 2000? Could it be about 2150? If you do the math with what you give, then the rear is around 3.50 (3.54). If you do the math for 2150rpm, then it's 3.73.

3.07 was an optional ratio. They would have had to specify just a 3.07 ratio, or it would have come with a 307 with a 4-speed, a 350, or a 396 with a t-400.

3.54 was also an optional ratio.

Since it was originally a six, it would have had to be ordered specifically as a 3.07. Check the glovebox.

crazy longhorn · 11-05-2002, 04:02 PM

Oops, checking the math I come up with the same figures.....it sounds like 3.54s run 64 mph @ 2000 rpms on 38s.....

11-05-2002, 11:43 AM	#1
oteixeira Registered User Join Date: Jan 2001 Location: Middlesex, NC Posts: 231	Help Picking new gears Hi all, I have a friend at work that has a '70 K-10 that was originally a 292 I-6 with a 4 speed crawler. He has done a "few" mods over time and it is now a 8" lifted 4x4 with 38s, and a 427. He left in the original 4 speed and axel gears. The first question is based on the original setup what should his gears be from the factory? The second is what would you recomend for it? In 4th gear at 65 (a true 65), he is at 2K on the tach. Any help is appreciated... Orlando __________________ 70 C-20 Custom Camper Build thread: http://67-72chevytrucks.com/vboard/s...d.php?t=300251

11-05-2002, 03:21 PM	#3
ckhd Registered User Join Date: Oct 2000 Location: St. Johns, Arizona Posts: 2,660	The standard ratio for a '70 K10 six w/a 4-speed is 3.73. Are you sure that it's 2000? Could it be about 2150? If you do the math with what you give, then the rear is around 3.50 (3.54). If you do the math for 2150rpm, then it's 3.73. 3.07 was an optional ratio. They would have had to specify just a 3.07 ratio, or it would have come with a 307 with a 4-speed, a 350, or a 396 with a t-400. 3.54 was also an optional ratio. Since it was originally a six, it would have had to be ordered specifically as a 3.07. Check the glovebox. __________________ my 2¢ - t.i.o.l.i. Bowen 1968 K20 fleet 1969 K10 swb fleet 1972 K10 Suburban 1972 C10 lwb step 1992 K1500 'burb 1995 K2500 'burb 1997 C1500 'burb 1999 K1500 2000 K1500 'burb Why do I own so many Suburbans?

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11-05-2002, 11:59 AM	#2
crazy longhorn Fabricate till you "puke" Join Date: Jun 2002 Location: Ill Posts: 9,402	I would say you need a 4.56 or 4.88 gear with the 38" tires. that will require a carrier change, as stock was likely a 3.07(3 series carrier). check this link for math to see what you want for rpms on the hyway..... http://www.smokemup.com/auto_math/index.php

11-05-2002, 04:02 PM	#4
crazy longhorn Fabricate till you "puke" Join Date: Jun 2002 Location: Ill Posts: 9,402	Oops, checking the math I come up with the same figures.....it sounds like 3.54s run 64 mph @ 2000 rpms on 38s.....



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