gears in the rear - The 1947 - Present Chevrolet & GMC Truck Message Board Network

bac1755 · 01-14-2009, 03:23 PM

I have a 71 gmc 1/2 ton. i have a 350 with a stock 350 trans and 275-60-15 tires on it, I have no idea what gears i have in the rear but am wanting to put someting new in. does anyone have some advise on a good ratio.

lts70 · 01-14-2009, 03:40 PM

We need to know what Ratio you currently have to go from there. It is easy to find out. You can look on the top of your passenger side axle tube and find a stamped code that will have the info needed to see what you have. If you get the code PM me and I will let you know what you have. Or you can put a piece of tape on you tire and on your drive line. Have some one turn the tire on rotation and count how many times the driveline goes around. If it is just over 3 times you have a 3.07, 3-1/2, you have a 3.41, 3-3/4 you have 3.73 and so on. Hope this helps.

We also need to know if you want more top end or more low end. You can't have both unless you get an overdrive.

chevy_mike · 01-14-2009, 03:42 PM

It depends on what you are planning to do with it. Are you planning to haul things, just cruise around, mainly freeway driving, city street driving, drag racing, etc? Are you keeping the tranny or will you replace it with an overdrive tranny?

Without knowing what you have and knowing what you want to do, it's really hard to recommend anything.

Longhorn Man · 01-14-2009, 05:24 PM

you should have a 3.07 gear, and running right about 2500 RPM @ 65 mph.

bac1755 · 01-15-2009, 02:20 AM

I will have to get out and see if i can find the stamp on the axle tube. I plan on the truck being in town some highway use.

I have been thinking about putting an over drive trans in it but dont know yet.
should i wait on the rearend till i figure that out?

**LockDoc** · 01-15-2009, 02:29 PM

-
There are several ways to tell your current ratio. The one I usually use is the letters stamped on the housing. That way if the rearend has ever been replaced it will still give you the correct ratio. I have included a couple of pictures that show the location of the letters. (use the first two or three letters) When you have the code go to the following web site and look it up in the axle section. (you have to select the year of your truck) If you're not sure if it's the original rear end you can just check all of the years.

http://www.americanclassic.com/paint.htm

Another good way is to take the cover off of the rear housing and look at the numbers stamped on the gears. The good thing about using this method is that you put fresh gear oil in the rear end to replace the 40 year old oil that is in there now. Below are the numbers for the different ratios. The last two numbers in each row are the ones that will be stamped into the gears.

Rear Axle Ratios

Ratio 2.56:1 - Tooth Combination 41,16
Ratio 2.73:1 - Tooth Combination 41,15
Ratio 3.07:1 - Tooth Combination 43,14
Ratio 3.08:1 - Tooth Combination 40,13
Ratio 3.08:1 - Tooth Combination 37,12
Ratio 3.31:1 - Tooth Combination 43,13
Ratio 3.36:1 - Tooth Combination 37,11
Ratio 3.42:1 - Tooth Combination 41,12
Ratio 3.55:1 - Tooth Combination 39,11
Ratio 3.73:1 - Tooth Combination 41,11
Ratio 4.10:1 - Tooth Combination 41,10
Ratio 4.11:1 - Tooth Combination 37,9

LockDoc

01-14-2009, 03:23 PM	#1
bac1755 Registered User Join Date: Jan 2009 Location: Denison, Texas Posts: 245	gears in the rear I have a 71 gmc 1/2 ton. i have a 350 with a stock 350 trans and 275-60-15 tires on it, I have no idea what gears i have in the rear but am wanting to put someting new in. does anyone have some advise on a good ratio.

01-14-2009, 03:40 PM	#2
lts70 1970 Daily Driver Join Date: Jun 2007 Location: Glenns Ferry IDAHO Posts: 1,038	Re: gears in the rear We need to know what Ratio you currently have to go from there. It is easy to find out. You can look on the top of your passenger side axle tube and find a stamped code that will have the info needed to see what you have. If you get the code PM me and I will let you know what you have. Or you can put a piece of tape on you tire and on your drive line. Have some one turn the tire on rotation and count how many times the driveline goes around. If it is just over 3 times you have a 3.07, 3-1/2, you have a 3.41, 3-3/4 you have 3.73 and so on. Hope this helps. We also need to know if you want more top end or more low end. You can't have both unless you get an overdrive. __________________ It's not truly yours if you didn't build it yourself or if you don't do your own maintenance. Last edited by lts70; 01-14-2009 at 03:43 PM.

01-14-2009, 03:42 PM	#3
chevy_mike Never Ending Projects Join Date: Jul 2006 Location: San Diego, CA Posts: 3,836	Re: gears in the rear It depends on what you are planning to do with it. Are you planning to haul things, just cruise around, mainly freeway driving, city street driving, drag racing, etc? Are you keeping the tranny or will you replace it with an overdrive tranny? Without knowing what you have and knowing what you want to do, it's really hard to recommend anything. __________________ . 1965 C10 Panel, Tiki Express http://www.67-72chevytrucks.com/vboa...d.php?t=506580 SOLD 1968 Chevy C10, Long, Fleetside, Hot Rod Hauler http://67-72chevytrucks.com/vboard/s...d.php?t=313233 SOLD 1965 Chevy C10, Long, Fleetside, Hot Rod C10 http://67-72chevytrucks.com/vboard/s...d.php?t=415702 SOLD We were given two ears and one mouth for a reason... listen twice as much and speak half as often...

01-14-2009, 05:24 PM	#4
Longhorn Man its all about the +6 inches Join Date: Jan 2001 Location: Hilliard Ohio Posts: 2,690	Re: gears in the rear you should have a 3.07 gear, and running right about 2500 RPM @ 65 mph.

01-15-2009, 02:20 AM	#5
bac1755 Registered User Join Date: Jan 2009 Location: Denison, Texas Posts: 245	Re: gears in the rear I will have to get out and see if i can find the stamp on the axle tube. I plan on the truck being in town some highway use. I have been thinking about putting an over drive trans in it but dont know yet. should i wait on the rearend till i figure that out?

01-15-2009, 02:29 PM	#6
LockDoc The Older Generation Join Date: Aug 2006 Location: Montezuma, Iowa Posts: 25,818	Re: gears in the rear - There are several ways to tell your current ratio. The one I usually use is the letters stamped on the housing. That way if the rearend has ever been replaced it will still give you the correct ratio. I have included a couple of pictures that show the location of the letters. (use the first two or three letters) When you have the code go to the following web site and look it up in the axle section. (you have to select the year of your truck) If you're not sure if it's the original rear end you can just check all of the years. http://www.americanclassic.com/paint.htm Another good way is to take the cover off of the rear housing and look at the numbers stamped on the gears. The good thing about using this method is that you put fresh gear oil in the rear end to replace the 40 year old oil that is in there now. Below are the numbers for the different ratios. The last two numbers in each row are the ones that will be stamped into the gears. Rear Axle Ratios Ratio 2.56:1 - Tooth Combination 41,16 Ratio 2.73:1 - Tooth Combination 41,15 Ratio 3.07:1 - Tooth Combination 43,14 Ratio 3.08:1 - Tooth Combination 40,13 Ratio 3.08:1 - Tooth Combination 37,12 Ratio 3.31:1 - Tooth Combination 43,13 Ratio 3.36:1 - Tooth Combination 37,11 Ratio 3.42:1 - Tooth Combination 41,12 Ratio 3.55:1 - Tooth Combination 39,11 Ratio 3.73:1 - Tooth Combination 41,11 Ratio 4.10:1 - Tooth Combination 41,10 Ratio 4.11:1 - Tooth Combination 37,9 LockDoc Attached Images __________________ Leon Locksmith, Specializing In Antique Trucks, Automobiles, & Motorcycles (My Dually Pickup Project Thread) http://67-72chevytrucks.com/vboard/s...d.php?t=829820 - Last edited by LockDoc; 01-15-2009 at 02:36 PM.



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