a why question on my rear axel - The 1947 - Present Chevrolet & GMC Truck Message Board Network

john_doe · 03-12-2005, 08:52 AM

Hi, I was changing tires on my 71 3/4 4X4 when I got questioning how the rear axel works. If my passenger tire is off the ground it spins freely forward turning the driveshaft also. But when I lift both tires off the ground the passenger tire goes forward and the drivers tire goes backwards. I know it's a petty issue but I would like to know. And just wanted to say this website has helped alot. Thanks everyone.

Sweet72 · 03-12-2005, 09:37 AM

The 4 spider gears in the diff. carrier allow one axle will rotate opposite the other with no "load" on one of the tires. If you really want to know how it works, and you probably shoud do this anyway...Get a few quarts of gear oil and a new inspection cover gasket and pull the cover off. The rear tends to get pretty nasty inside over time. If it's a limited slip diff., ask for some "limited slip additive" at your parts store and add before filling with gear oil.

**JIMs70GMC** · 03-12-2005, 10:59 AM

You have what's refered to as an "open differential". It's acting as it should. If you had a traction adding device then it would behave differently, i.e. with one wheel off the ground it would be difficult to spin the tire with tranny or transfer case in neutral, you have to overcome the friction of the disc(posi) or force the locking diff to disengage.

Sweet72 · 03-12-2005, 08:45 PM

Worn clutches in a limited slip (positraction) diff will act like an open diff. so the only way to be sure is to remove the cover.

03-12-2005, 08:52 AM	#1
john_doe Registered User Join Date: Sep 2004 Location: Western New York Posts: 37	a why question on my rear axel Hi, I was changing tires on my 71 3/4 4X4 when I got questioning how the rear axel works. If my passenger tire is off the ground it spins freely forward turning the driveshaft also. But when I lift both tires off the ground the passenger tire goes forward and the drivers tire goes backwards. I know it's a petty issue but I would like to know. And just wanted to say this website has helped alot. Thanks everyone.

03-12-2005, 09:37 AM	#2
Sweet72 Registered User Join Date: Nov 2003 Location: Alexandria, VA Posts: 1,534	The 4 spider gears in the diff. carrier allow one axle will rotate opposite the other with no "load" on one of the tires. If you really want to know how it works, and you probably shoud do this anyway...Get a few quarts of gear oil and a new inspection cover gasket and pull the cover off. The rear tends to get pretty nasty inside over time. If it's a limited slip diff., ask for some "limited slip additive" at your parts store and add before filling with gear oil. __________________ '72 GMC SWB C1500 Custom, frame-off in progress. 383 SBC, 9:1CR, Comp Cams XE262H, Scat internal balanced crank, Eagle SIR 6" rods, Keith Black dish pistons, Dart Iron Eagle 72/180 heads, Weiand Stealth intake, Stewart stage I water pump, Holley 4bbl vac sec, TH350 with B&M Shift Improver Kit. 12 bolt positraction.

03-12-2005, 10:59 AM	#3
JIMs70GMC user # 2756 Join Date: Jun 2001 Location: Chesapeake, Virginia Posts: 4,612	You have what's refered to as an "open differential". It's acting as it should. If you had a traction adding device then it would behave differently, i.e. with one wheel off the ground it would be difficult to spin the tire with tranny or transfer case in neutral, you have to overcome the friction of the disc(posi) or force the locking diff to disengage. __________________ 1970 K25, 8' stepside bed 350/465/205 44 up front, 60 in the rear 4.10s rolling on 33" Dunlop MTs 1986 K5, 350/465/208 Dana 60/14 bolt from a cucv 36" Super Swampers TSL/SX 1983 K20 w/ CUCV axles, 350/700R4/208 sitting on 37" Goodyears 1986 M1031 6.2 diesel, TH400/NP205 locker in the rear and a LS in the front, all stock for now..... 1986 K30, 350/400/205 dana 60 and 14 bolt. I kept the drivetrain. Body/bad and chassis are gone. 1981 K30, 350/465/205 dana 60 and dually 14 bolt. Has a G80, and a flat bed. Going to replace the flat bed. 1985 K20, 350/400/208 10 bolt and SF 14 bolt. I wonder where I can find some 1 tons. Hmmmmm

03-12-2005, 08:45 PM	#4
Sweet72 Registered User Join Date: Nov 2003 Location: Alexandria, VA Posts: 1,534	Worn clutches in a limited slip (positraction) diff will act like an open diff. so the only way to be sure is to remove the cover. __________________ '72 GMC SWB C1500 Custom, frame-off in progress. 383 SBC, 9:1CR, Comp Cams XE262H, Scat internal balanced crank, Eagle SIR 6" rods, Keith Black dish pistons, Dart Iron Eagle 72/180 heads, Weiand Stealth intake, Stewart stage I water pump, Holley 4bbl vac sec, TH350 with B&M Shift Improver Kit. 12 bolt positraction.



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