Transfer Case - The 1947 - Present Chevrolet & GMC Truck Message Board Network

mitch23 · 07-24-2003, 06:36 PM

Could anyone please tell me how to determine my transfer case and also my gear ratio for a 85 GMC K1500?

*mike reeh* · 07-24-2003, 08:17 PM

it will be an NP208 aluminum case, chain driven, 2.61:1 low range..

if you're talking about axle gear ratio, well thats different.. you have to look it up on your RPO list or take the diff cover off of the axle and count teeth.. probably something like 3.08 or 3.42 or maybe 3.73

mike

ChevyThunder67 · 07-24-2003, 10:51 PM

How you count the teeth is fairly simple. Just take off the the diff cover and make a mark at one of the teeth on the ring gear( big gear). Start from the mark and count all of the teeth on the ring gear. Next, count the pinion gear teeth ( front of the diff housing gear). Finally, take the number of teeth on the ring gear divided by the teeth on the pinion gear and that will give you your gear ratio.

Westley

rockman20 · 07-25-2003, 08:36 AM

Probably stupid question here, but if you had a NP208 transfer case with the 2.61:1 range and 3.42 gears in the axles, does that mean you are running 6.03:1 when you have it in low range?

Jonboy · 07-25-2003, 05:03 PM

Actually, it would depend on which gear the trans is in. First gear with a 700R4 is 3.06:1. Taking that, multiplied by the transfer case low of 2.61:1, multiplied by the axle ratio of 3.42 gives a crawl ratio of 27.31:1. I am pretty sure that is how it is figured. Conversely, in 2High, 4th gear (.70) and 3.42 the effective gear ratio is 2.39:1.

07-24-2003, 06:36 PM	#1
mitch23 Registered User Join Date: Jul 2003 Location: Venice, FL Posts: 1	Transfer Case Could anyone please tell me how to determine my transfer case and also my gear ratio for a 85 GMC K1500?

07-24-2003, 10:51 PM	#3
ChevyThunder67 Registered User Join Date: Jun 2003 Location: Las Vegas, NV Posts: 12	How you count the teeth is fairly simple. Just take off the the diff cover and make a mark at one of the teeth on the ring gear( big gear). Start from the mark and count all of the teeth on the ring gear. Next, count the pinion gear teeth ( front of the diff housing gear). Finally, take the number of teeth on the ring gear divided by the teeth on the pinion gear and that will give you your gear ratio. Westley __________________ 2000 Dodge 2500 diesel 1992 Jeep Cherokee 1976 Chevy K20 smallblock 1967 Chevy C10 smallblock 1974 Chevy Nova 2dr.

07-25-2003, 08:36 AM	#4
rockman20 "The dude abides" Join Date: Apr 2003 Location: North Dakota Posts: 472	Probably stupid question here, but if you had a NP208 transfer case with the 2.61:1 range and 3.42 gears in the axles, does that mean you are running 6.03:1 when you have it in low range? __________________ RockMan 1993 Chevy Silverado C3500 1 ton dually 1994 Honda Civic 1969 Oldsmobile Cutlass S 1953 IH Farmall Super M New to the fleet: 1992 Subaru Loyal

07-25-2003, 05:03 PM	#5
Jonboy Slots go on anything! Join Date: May 2003 Location: Richardson, TX Posts: 5,957	Actually, it would depend on which gear the trans is in. First gear with a 700R4 is 3.06:1. Taking that, multiplied by the transfer case low of 2.61:1, multiplied by the axle ratio of 3.42 gives a crawl ratio of 27.31:1. I am pretty sure that is how it is figured. Conversely, in 2High, 4th gear (.70) and 3.42 the effective gear ratio is 2.39:1. __________________ 1974 Jimmy- 5.3/4L80e/NP241

07-24-2003, 08:17 PM	#2
mike reeh 5 day ban, learn to behave. Join Date: Nov 2002 Location: san diego, ca Posts: 684	it will be an NP208 aluminum case, chain driven, 2.61:1 low range.. if you're talking about axle gear ratio, well thats different.. you have to look it up on your RPO list or take the diff cover off of the axle and count teeth.. probably something like 3.08 or 3.42 or maybe 3.73 mike



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