Differential code - The 1947 - Present Chevrolet & GMC Truck Message Board Network

knuckledragger · 11-06-2010, 09:29 PM

I tried searching for a code list,but did not find any.My diff has trr w3641 stamped on the rt tube.I would like to know what year and ratio.Thanks in advance for the help.
Dan

knuckledragger · 11-06-2010, 09:47 PM

I found pauls gmc site and the code for the 68 is tr = 3.07.Is it possible this is a 3.07?

swamp rat · 11-07-2010, 02:30 AM

Don't know about the C10 but in my 3/4 ton i could have one of 2 maybe 3 different rearends in it, do you know which rearend you have? 10 bolt? Dana 60?

Jack the back of the truck up (use jack stands) and spin one tire on a slip diff or both tires on a posi and count the revolutions of the driveshaft per 1 turn of the wheel, mark it with chalk or wax crayon if nessasary, or like i did and put a scratch in the grime

knuckledragger · 11-07-2010, 09:37 AM

It is a 12 bolt.I bought it out of the truck to do a drop in 5 lug conversion.So I do not know what year it is either.

raycow · 11-07-2010, 11:33 AM

It is very possible you have a 12 bolt with 3.07 gears. This was a factory option. You can verify the ratio without taking off the cover.

Jack one rear wheel off the ground, put the transmission in neutral, and the parking brake off. Put matching marks on the pinion yoke and differential housing. 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.

As for year, if you have coil springs and want a bolt-in swap, look for a large cast lug for the panhard bar on the upper right side of the center section. If it has this lug and takes 5 hole wheels, it is a 71 or 72 rear. If no lug, it is 73-up and will require welding on the mounts for the trailing arms and an aftermarket panhard bar.

Ray

67Mach1 · 11-13-2010, 08:11 PM

Dan,

That rear end came from a 71 Chevy that was a factory 402/400 truck.

Hope that helps.

Thomas

knuckledragger · 11-13-2010, 08:55 PM

Well ,I guess it will be happy behind my 402/350!It does appear to be a 3.07.Thanks,Thomas.
Dan

11-06-2010, 09:29 PM	#1
knuckledragger Registered User Join Date: Aug 2010 Location: Hutto,Texas!! Posts: 160	Differential code I tried searching for a code list,but did not find any.My diff has trr w3641 stamped on the rt tube.I would like to know what year and ratio.Thanks in advance for the help. Dan __________________ 65 c-10 swb,bbw,step,402/t350,sold!! 1979 c10 Silverado,250,auto,gonna have a 3/5 drop,and twice pipes!Sold Bought the wife a 84 gmc short step

11-06-2010, 09:47 PM	#2
knuckledragger Registered User Join Date: Aug 2010 Location: Hutto,Texas!! Posts: 160	Re: Differential code I found pauls gmc site and the code for the 68 is tr = 3.07.Is it possible this is a 3.07? __________________ 65 c-10 swb,bbw,step,402/t350,sold!! 1979 c10 Silverado,250,auto,gonna have a 3/5 drop,and twice pipes!Sold Bought the wife a 84 gmc short step

11-07-2010, 02:30 AM	#3
swamp rat Registered User Join Date: Oct 2007 Location: Spanaway Posts: 8,451	Re: Differential code Don't know about the C10 but in my 3/4 ton i could have one of 2 maybe 3 different rearends in it, do you know which rearend you have? 10 bolt? Dana 60? Jack the back of the truck up (use jack stands) and spin one tire on a slip diff or both tires on a posi and count the revolutions of the driveshaft per 1 turn of the wheel, mark it with chalk or wax crayon if nessasary, or like i did and put a scratch in the grime __________________ Mike. Swamp Rat build thread : http://67-72chevytrucks.com/vboard/s...d.php?t=595019 72 3/4T 4X4 4" BDS Lift 33" BFG's

11-07-2010, 09:37 AM	#4
knuckledragger Registered User Join Date: Aug 2010 Location: Hutto,Texas!! Posts: 160	Re: Differential code It is a 12 bolt.I bought it out of the truck to do a drop in 5 lug conversion.So I do not know what year it is either. __________________ 65 c-10 swb,bbw,step,402/t350,sold!! 1979 c10 Silverado,250,auto,gonna have a 3/5 drop,and twice pipes!Sold Bought the wife a 84 gmc short step

11-07-2010, 11:33 AM	#5
raycow Registered User Join Date: Mar 2003 Location: San Francisco, CA USA Posts: 2,454	Re: Differential code It is very possible you have a 12 bolt with 3.07 gears. This was a factory option. You can verify the ratio without taking off the cover. Jack one rear wheel off the ground, put the transmission in neutral, and the parking brake off. Put matching marks on the pinion yoke and differential housing. 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. As for year, if you have coil springs and want a bolt-in swap, look for a large cast lug for the panhard bar on the upper right side of the center section. If it has this lug and takes 5 hole wheels, it is a 71 or 72 rear. If no lug, it is 73-up and will require welding on the mounts for the trailing arms and an aftermarket panhard bar. Ray __________________ Live more responsibly. Eat lower on the food chain. Eat vegetarians. Last edited by raycow; 11-07-2010 at 11:33 AM.

11-13-2010, 08:11 PM	#6
67Mach1 Senior Member Join Date: Nov 2005 Location: Round Rock, TX Posts: 1,100	Re: Differential code Dan, That rear end came from a 71 Chevy that was a factory 402/400 truck. Hope that helps. Thomas __________________ Soon to be selling all but one, or two... Depends on what the Boss has to say....... 67 GMC Shortbed 454 Project more junk and most of it is for sale

11-13-2010, 08:55 PM	#7
knuckledragger Registered User Join Date: Aug 2010 Location: Hutto,Texas!! Posts: 160	Re: Differential code Well ,I guess it will be happy behind my 402/350!It does appear to be a 3.07.Thanks,Thomas. Dan __________________ 65 c-10 swb,bbw,step,402/t350,sold!! 1979 c10 Silverado,250,auto,gonna have a 3/5 drop,and twice pipes!Sold Bought the wife a 84 gmc short step



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