Rearend diff question. - The 1947 - Present Chevrolet & GMC Truck Message Board Network

GobbleStalker · 09-16-2010, 09:07 PM

Is there any way to tell the gearing in the rear end without taking it appart. Also I do not know if it is posi or not. Truck is running but not well enought to burn the tires. Motoer getting ready for a rebuild. Any help is appreciated.

Thanks
Kev

ChevLoRay · 09-16-2010, 09:37 PM

With it jacked up, or on a rack....mark a reference point on the tire (or remember where you started)..then turn the tire one full revolution while you count the number of times that the rear u-joint turns. If the tire turns one time and the u-joint turns just a hair over 4 turns, it's probably a 4.11.

jcis4me · 09-16-2010, 09:49 PM

So if the drive shaft turns 3 times? 3.08?
Thanks
Marty

raycow · 09-17-2010, 02:27 AM

Close, but no cigar.

Put matching marks on the pinion yoke and differential housing. Jack one rear wheel off the ground, put the transmission in neutral, and the parking brake off. Turn the wheel exactly TWO revolutions and count how many times the driveshaft turns, estimating any fractional turn as closely as possible. That number is your axle ratio.

If the wheel is difficult or impossible to turn, you may have posi. In that case, jack both rear wheels off the ground and turn either of them only ONE revolution. Count the driveshaft turns the same way as for an open rear.

Ray

09-16-2010, 09:07 PM	#1
GobbleStalker GobbleStalker Calls Join Date: Aug 2010 Location: Port Hope, Ontario Posts: 653	Rearend diff question. Is there any way to tell the gearing in the rear end without taking it appart. Also I do not know if it is posi or not. Truck is running but not well enought to burn the tires. Motoer getting ready for a rebuild. Any help is appreciated. Thanks Kev Last edited by GobbleStalker; 09-16-2010 at 09:08 PM.

09-16-2010, 09:37 PM	#2
ChevLoRay Old Skool Club Join Date: Jun 2001 Location: Benton, AR "The Heart of Arkansas" Posts: 10,880	Re: Rearend diff question. With it jacked up, or on a rack....mark a reference point on the tire (or remember where you started)..then turn the tire one full revolution while you count the number of times that the rear u-joint turns. If the tire turns one time and the u-joint turns just a hair over 4 turns, it's probably a 4.11. __________________ Member Nr. 2770 '96 GMC Sportside; 4.3/SLT - Daily driven....constantly needs washed. '69 C-10 SWB; 350/TH400 - in limbo The older I get, the better I was.

09-16-2010, 09:49 PM	#3
jcis4me Registered User Join Date: Aug 2010 Location: Jersey shore Posts: 115	Re: Rearend diff question. So if the drive shaft turns 3 times? 3.08? Thanks Marty

09-17-2010, 02:27 AM	#4
raycow Registered User Join Date: Mar 2003 Location: San Francisco, CA USA Posts: 2,454	Re: Rearend diff question. Close, but no cigar. Put matching marks on the pinion yoke and differential housing. Jack one rear wheel off the ground, put the transmission in neutral, and the parking brake off. Turn the wheel exactly TWO revolutions and count how many times the driveshaft turns, estimating any fractional turn as closely as possible. That number is your axle ratio. If the wheel is difficult or impossible to turn, you may have posi. In that case, jack both rear wheels off the ground and turn either of them only ONE revolution. Count the driveshaft turns the same way as for an open rear. Ray



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