Gear ratios used in 67-68 2wd's? - The 1947 - Present Chevrolet & GMC Truck Message Board Network

glock35ipsc · 02-22-2004, 12:41 PM

Sorry, posted this in the wrong forum earlier.

I have a 68 2wd LWB, 3 speed on the column, and it originaly had a V-8 (not sure what size though). Short of pulling the diff cover, I was trying to figure out the ratio.

I tried the tire-to-pinion count, but that was weird.....1 full spin of the tire netted 1.8 turns of the pinion. I could not find a tag, or any stamping on the tubes (to much junk built up).

I will pull the diff cover someday, just wondering if anyone had an idea of what GM threw in there back then.

dwaite72lnghrn · 02-22-2004, 12:55 PM

The most accurate way with out pulling the cover would be to tape a string to the driveshaft and chalk a line next to the tape, Mark the tire at the ground with chalk, Have a friend watch the tire chalk mark, move the truck forward till the mark hits the ground again, count the number of times the string wraped the drive shaft. this will be your ration.
When you just lift the truck with open diff. the far side might not turn at the same rate which means the spiders are eating the revs that should have been going to the drive shaft this won't be the most accurate way.

Bowtie67 · 02-22-2004, 12:55 PM

If you haven't pulled the cover, it's not a bad idea, this way you can change the gear libe and put some nice new gearl oil in afterwards just for GP. WHo knows how long it's been since it was changed. Guesing by rotation is really not the best way. Count ring and pinion teeth or get the number off of the ring gears, then divide the two. 10/39 = 3.90

Longhorn Man · 02-22-2004, 02:09 PM

I vote for pulling the cover and doing it that way. If the oil is original, (pretty likely) then it is less than 50% effective acording to our oil lab we use at the shop.
You didn't mention if this is a C/10 or a C/20, but I'll asume you are talking about the C/10 in your signiture...
the book is kinda funny reading, but I think it says 3.07 with v-8/auomatic, and 3.73 with V-8/manual.

cobb_ben · 02-22-2004, 03:38 PM

Yeah just pull the cover, to check ratio, they're usually marked on the ring the numbers of the ration like 11/43 or what ever. Plus changing the oil is cheap insurance. Make sure you get a gasket.
Ben

glock35ipsc · 02-22-2004, 10:33 PM

Um, I know how to pull the cover and find out what I have, what I am wondering is what GM put in these truck in 1968? What different ratios were available? Oh yeah, it's a C10.

Longhorn Man · 02-22-2004, 10:35 PM

3.07, 3.73, and 4.11 if it came with over drive.

glock35ipsc · 02-23-2004, 01:20 AM

Thanks, Longhorn Man!! That's what I was hunting for. I suspect these are 3.07's.

jimfulco · 02-23-2004, 02:43 AM

Jack up ONE back tire & then count the driveshaft turns it takes to get TWO tire revolutions. That's your ratio. This is only for open rear ends.

lukecp · 02-23-2004, 11:01 AM

1.8x2=3.6, so you proably have a 3.73 ratio

MrGoodpliers · 02-23-2004, 11:20 AM

3.73's would have been standard for this truck with a 3 speed. If nothing is listed on the glovebox option sheet and the truck is original, I would assume 3.73 single track.

02-22-2004, 12:41 PM	#1
glock35ipsc Next project: 1970 K10 Join Date: Feb 2004 Location: Fort Collins, Colo 80524 Posts: 6,685	Gear ratios used in 67-68 2wd's? Sorry, posted this in the wrong forum earlier. I have a 68 2wd LWB, 3 speed on the column, and it originaly had a V-8 (not sure what size though). Short of pulling the diff cover, I was trying to figure out the ratio. I tried the tire-to-pinion count, but that was weird.....1 full spin of the tire netted 1.8 turns of the pinion. I could not find a tag, or any stamping on the tubes (to much junk built up). I will pull the diff cover someday, just wondering if anyone had an idea of what GM threw in there back then. __________________ *Bob* 1970 Chevy K10 LWB "Goldie" 350/TH350 *next project!!* 1981 Chevy C10 LWB 355/TH350 - My son's truck LS SWAP FORUM! Tons of LS swap info here! PLEASE CLICK HERE TO SUPPORT THE GREATEST BOARD ON THE NET! CLICK HERE FOR THE FAQ INDEX by KRUE

02-22-2004, 12:55 PM	#2
dwaite72lnghrn Registered User Join Date: Jun 2002 Location: central pa Posts: 1,525	The most accurate way with out pulling the cover would be to tape a string to the driveshaft and chalk a line next to the tape, Mark the tire at the ground with chalk, Have a friend watch the tire chalk mark, move the truck forward till the mark hits the ground again, count the number of times the string wraped the drive shaft. this will be your ration. When you just lift the truck with open diff. the far side might not turn at the same rate which means the spiders are eating the revs that should have been going to the drive shaft this won't be the most accurate way. __________________ 72 longhorn c30 502BB/th400/fact air/4.11rear/ custom camper 72 bug(the better half's) under reconstruction 2009 HHR aqua blue 71 GMC k20 350/sm465 2009 Chevy hd3500 6.6 Victory Red crew cab dually Dave & Jeanne

02-22-2004, 03:38 PM	#5
cobb_ben Registered User Join Date: Feb 2004 Location: Fort Leonard Wood Mo Posts: 299	Yeah just pull the cover, to check ratio, they're usually marked on the ring the numbers of the ration like 11/43 or what ever. Plus changing the oil is cheap insurance. Make sure you get a gasket. Ben __________________ '69 Chevy C10 400sb-350 crank 400 destroker!!! 377 2.02 dart pro1 alum.heads msd, holley db hooker pro-comps-3in exh. 3 spd. saginaw-3.73posi Flat Bed...want Reg bed...trades?

02-22-2004, 10:33 PM	#6
glock35ipsc Next project: 1970 K10 Join Date: Feb 2004 Location: Fort Collins, Colo 80524 Posts: 6,685	Um, I know how to pull the cover and find out what I have, what I am wondering is what GM put in these truck in 1968? What different ratios were available? Oh yeah, it's a C10. __________________ *Bob* 1970 Chevy K10 LWB "Goldie" 350/TH350 *next project!!* 1981 Chevy C10 LWB 355/TH350 - My son's truck LS SWAP FORUM! Tons of LS swap info here! PLEASE CLICK HERE TO SUPPORT THE GREATEST BOARD ON THE NET! CLICK HERE FOR THE FAQ INDEX by KRUE

02-23-2004, 01:20 AM	#8
glock35ipsc Next project: 1970 K10 Join Date: Feb 2004 Location: Fort Collins, Colo 80524 Posts: 6,685	Thanks, Longhorn Man!! That's what I was hunting for. I suspect these are 3.07's. __________________ *Bob* 1970 Chevy K10 LWB "Goldie" 350/TH350 *next project!!* 1981 Chevy C10 LWB 355/TH350 - My son's truck LS SWAP FORUM! Tons of LS swap info here! PLEASE CLICK HERE TO SUPPORT THE GREATEST BOARD ON THE NET! CLICK HERE FOR THE FAQ INDEX by KRUE

02-22-2004, 12:55 PM	#3
Bowtie67 Registered User Join Date: Jan 2004 Location: NH Posts: 2,266	If you haven't pulled the cover, it's not a bad idea, this way you can change the gear libe and put some nice new gearl oil in afterwards just for GP. WHo knows how long it's been since it was changed. Guesing by rotation is really not the best way. Count ring and pinion teeth or get the number off of the ring gears, then divide the two. 10/39 = 3.90

02-22-2004, 02:09 PM	#4
Longhorn Man its all about the +6 inches Join Date: Jan 2001 Location: Hilliard Ohio Posts: 2,693	I vote for pulling the cover and doing it that way. If the oil is original, (pretty likely) then it is less than 50% effective acording to our oil lab we use at the shop. You didn't mention if this is a C/10 or a C/20, but I'll asume you are talking about the C/10 in your signiture... the book is kinda funny reading, but I think it says 3.07 with v-8/auomatic, and 3.73 with V-8/manual.

02-22-2004, 10:35 PM	#7
Longhorn Man its all about the +6 inches Join Date: Jan 2001 Location: Hilliard Ohio Posts: 2,693	3.07, 3.73, and 4.11 if it came with over drive.

02-23-2004, 02:43 AM	#9
jimfulco Registered User Join Date: May 2003 Location: Shreveport LA Posts: 3,170	Jack up ONE back tire & then count the driveshaft turns it takes to get TWO tire revolutions. That's your ratio. This is only for open rear ends.

02-23-2004, 11:01 AM	#10
lukecp Formerly yellow72custom Join Date: May 2001 Location: Austin, TX Posts: 7,531	1.8x2=3.6, so you proably have a 3.73 ratio __________________ '72 Chevy C10 Mild 350/TH350/3.07. Ochre/White. Old high school ride. '70 GMC C2500 '62 327 4bbl/SM465/4.56-geared Dana 60. White/White. Project or parts truck. '97 Saturn SL DD. 1.9/5-speed. 40+ highway mpg

02-23-2004, 11:20 AM	#11
MrGoodpliers Registered User Join Date: May 2002 Location: Gainesville, Georgia Posts: 704	3.73's would have been standard for this truck with a 3 speed. If nothing is listed on the glovebox option sheet and the truck is original, I would assume 3.73 single track. __________________ We made Oklahoma a little after 3, Randy & his brother Bob & my old GMC...



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