identifying rearend ratio? - The 1947 - Present Chevrolet & GMC Truck Message Board Network

gabet40 · 02-11-2005, 06:19 PM

is there anyway to find out your rearend ratio without opening it up?

Vince M · 02-11-2005, 08:42 PM

Depending on what rear end you are talking about and if the gears are original....the truck12 bolt has a number/letter code stamped into the top of the passenger side axle tube between the center casting and the brake backing plate. Post it here if you find one and somebody can decode it for you.

71RestoRod · 02-11-2005, 08:47 PM

If you have an open diff:

Take the truck out of gear, jack up one wheel.. align your yolk with some point of reference.. spin your tire two full revolutions and count the number of revolutions the yolk makes. If it goes just past three revolutions than it's a 3.08, three and three quarter revs is a 3.73, just past four revs is a 4.11... you get the idea.

If you have a stiff posi or a locker you can do the same thing with both wheels jacked but you will only need to spin the tire once making sure the opposite side spins the same amount. If you want a more accurate reading, spin the tire two or three times and divide the driveshaft revolutions by the number of spins.

You can actually get a very close read with this method.

Longhorn Man · 02-11-2005, 10:20 PM

Why not pop the cover off and see how much metal is in the oil...maybe drain the 20 year old oil out and put fresh oil in it.

02-11-2005, 06:19 PM	#1
gabet40 Registered User Join Date: Dec 1999 Location: Modesto, CA Posts: 565	identifying rearend ratio? is there anyway to find out your rearend ratio without opening it up? __________________ Current owner of 2016 2500 Silverado Midnight Edition. Former owner of: 69 1/2 ton, change from long/fleet to short/fleet, shaved door handles, shaved tailgate, 4/6 drop, power windows, 700r4 72 blazer, 350 with Holley Commander 950 DFI, crane energizer cam, 350 tranny, dual sanderson blockhuggers/magnaflow exhaust

02-11-2005, 08:42 PM	#2
Vince M Senior Member Join Date: Apr 2000 Location: Orlando, FL Posts: 1,076	Depending on what rear end you are talking about and if the gears are original....the truck12 bolt has a number/letter code stamped into the top of the passenger side axle tube between the center casting and the brake backing plate. Post it here if you find one and somebody can decode it for you. __________________ ............................................................ 68 Chevy CST SWB w/LS1, carb & 700r4. Golden Anniversary clone with a few improvements.

02-11-2005, 08:47 PM	#3
71RestoRod Registered User Join Date: Sep 2003 Location: Evergreen, CO Posts: 492	If you have an open diff: Take the truck out of gear, jack up one wheel.. align your yolk with some point of reference.. spin your tire two full revolutions and count the number of revolutions the yolk makes. If it goes just past three revolutions than it's a 3.08, three and three quarter revs is a 3.73, just past four revs is a 4.11... you get the idea. If you have a stiff posi or a locker you can do the same thing with both wheels jacked but you will only need to spin the tire once making sure the opposite side spins the same amount. If you want a more accurate reading, spin the tire two or three times and divide the driveshaft revolutions by the number of spins. You can actually get a very close read with this method.

02-11-2005, 10:20 PM	#4
Longhorn Man its all about the +6 inches Join Date: Jan 2001 Location: Hilliard Ohio Posts: 2,690	Why not pop the cover off and see how much metal is in the oil...maybe drain the 20 year old oil out and put fresh oil in it.



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