68 Chevy C10 Rear End Gears? - The 1947 - Present Chevrolet & GMC Truck Message Board Network

jsbo1968 · 01-18-2015, 11:15 AM

Can anyone tell me what this rear end code is? NF3896838
My Truck was Orig a 6Cyl, W/3 Speed on the Column. It revs pretty high when driving. Feels like it needs to shift again. I want it to be for daily driving mostly and sometimes (very little) on the highway. Motor now is a SB350 w 3 Speed Auto. No Overdrive. I have searched my Door Tag w/ no luck. And the glove box tag didn't have any gear info.

Thanks for any help. JB

**LockDoc** · 01-18-2015, 11:59 AM

-

Probably a 4.10. I don't think that is the correct number for decoding it.

Check out this thread I posted a while back.

http://67-72chevytrucks.com/vboard/s...d.php?t=578793

I would recommend reading the whole thread because there are different locations for the code letters/numbers depending on which axle assembly you have.

LockDoc

Mike C · 01-18-2015, 12:27 PM

If it doesn't specify anything different on the SPID it is most likely 3.73.

PanelDeland · 01-18-2015, 02:37 PM

I would agree with Mike C. The standard ratio for the 3 speed trans was 3.73 but options were available from the factory. If you have the original SPID and it's not listed , it's probably 3.73. If you want to know for sure. Put it on stands and mark the wheel and the driveshaft and turn one or the other. You will see how many turns of the driveshaft equals how many turns of the tire. There's always the chance it was changed at some point in the last 40+ years.

R.L. · 01-18-2015, 07:49 PM

Quote:

Originally Posted by PanelDeland

I would agree with Mike C. The standard ratio for the 3 speed trans was 3.73 but options were available from the factory. If you have the original SPID and it's not listed , it's probably 3.73. If you want to know for sure. Put it on stands and mark the wheel and the driveshaft and turn one or the other. You will see how many turns of the driveshaft equals how many turns of the tire. There's always the chance it was changed at some point in the last 40+ years.

Great point, I think if it's not a posi you will need to turn both rear wheels to get a good reading, 4 spins of the driveshaft to just over one turn of the tires = 4.10. I tried to determine my rear end's ratio and came up with something crazy till I found out about this.

Mike C · 01-18-2015, 07:55 PM

Correct, if it's an open diff the spider/side gears can screw up the math. I think they are 2:1, so if it's open, lift one tire, mark the driveshaft, turn the tire until the driveshaft has made a full rotation then divide by 2.

Most of these old trucks are probably due for a gear lube change anyhow, so pull the cover and visually confirm what gear ratio you have. Then refill with fresh lube. Your truck thanks you.

frankslagoon · 01-19-2015, 02:58 AM

Man, do yourself a favor and just pull the cover and take a look. then you know for sure . It's probably 3:73 but, the second thing I do after lookin under the hood is see whats in the rear diff.

01-18-2015, 11:15 AM	#1
jsbo1968 Registered User Join Date: Dec 2014 Location: Beaumont, Texas Posts: 11	68 Chevy C10 Rear End Gears? Can anyone tell me what this rear end code is? NF3896838 My Truck was Orig a 6Cyl, W/3 Speed on the Column. It revs pretty high when driving. Feels like it needs to shift again. I want it to be for daily driving mostly and sometimes (very little) on the highway. Motor now is a SB350 w 3 Speed Auto. No Overdrive. I have searched my Door Tag w/ no luck. And the glove box tag didn't have any gear info. Thanks for any help. JB

01-18-2015, 11:59 AM	#2
LockDoc The Older Generation Join Date: Aug 2006 Location: Montezuma, Iowa Posts: 25,773	Re: 68 Chevy C10 Rear End Gears? - Probably a 4.10. I don't think that is the correct number for decoding it. Check out this thread I posted a while back. http://67-72chevytrucks.com/vboard/s...d.php?t=578793 I would recommend reading the whole thread because there are different locations for the code letters/numbers depending on which axle assembly you have. LockDoc __________________ Leon Locksmith, Specializing In Antique Trucks, Automobiles, & Motorcycles (My Dually Pickup Project Thread) http://67-72chevytrucks.com/vboard/s...d.php?t=829820 -

01-18-2015, 12:27 PM	#3
Mike C Registered User Join Date: Dec 1999 Location: Austin, TX, USA Posts: 7,727	Re: 68 Chevy C10 Rear End Gears? If it doesn't specify anything different on the SPID it is most likely 3.73. __________________ 44 Willys MB 52 M38A1 64 Corvette Coupe 68 Camaro 'vert LT1 & TH700 69 Z/28 355 12.6's @110 69 Chevy Short Step 4 1/2"/7" drop 72 Jimmy 4WD 4spd 4" & 35's 02 GMC 2500HD 4x4 Duramax

01-18-2015, 02:37 PM	#4
PanelDeland I am a Referee of life. Join Date: Jun 2000 Location: Greensboro N.C. Posts: 13,992	Re: 68 Chevy C10 Rear End Gears? I would agree with Mike C. The standard ratio for the 3 speed trans was 3.73 but options were available from the factory. If you have the original SPID and it's not listed , it's probably 3.73. If you want to know for sure. Put it on stands and mark the wheel and the driveshaft and turn one or the other. You will see how many turns of the driveshaft equals how many turns of the tire. There's always the chance it was changed at some point in the last 40+ years. __________________ The 47-present Chevrolet and GMC Truck Message Board Network,it's owners,moderators,members,and associates of any type should not be held responsible for my opinion. You can't fix stupid,not even with duct tape. "My appearance is due to the fact that "GOD" does punish you for having too much fun!" Barrett-Jackson has perfected alchemy,they make rust into gold! "You can lead a horse to water but you can't saddle a duck" "Cleverly disguised as a 'Responsible Adult' "Sometimes your Knight in shining armor is just a retard in tinfoil"

01-18-2015, 07:55 PM	#6
Mike C Registered User Join Date: Dec 1999 Location: Austin, TX, USA Posts: 7,727	Re: 68 Chevy C10 Rear End Gears? Correct, if it's an open diff the spider/side gears can screw up the math. I think they are 2:1, so if it's open, lift one tire, mark the driveshaft, turn the tire until the driveshaft has made a full rotation then divide by 2. Most of these old trucks are probably due for a gear lube change anyhow, so pull the cover and visually confirm what gear ratio you have. Then refill with fresh lube. Your truck thanks you. __________________ 44 Willys MB 52 M38A1 64 Corvette Coupe 68 Camaro 'vert LT1 & TH700 69 Z/28 355 12.6's @110 69 Chevy Short Step 4 1/2"/7" drop 72 Jimmy 4WD 4spd 4" & 35's 02 GMC 2500HD 4x4 Duramax

01-19-2015, 02:58 AM	#7
frankslagoon Registered User Join Date: Jan 2014 Location: Wasilla Alaska Posts: 537	Re: 68 Chevy C10 Rear End Gears? Man, do yourself a favor and just pull the cover and take a look. then you know for sure . It's probably 3:73 but, the second thing I do after lookin under the hood is see whats in the rear diff.

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