A rear end question - The 1947 - Present Chevrolet & GMC Truck Message Board Network

Boise69 · 01-18-2007, 05:24 PM

Today I was under my truck cutting out my old rotted muffler...

I tried the "mark the driveshaft and spin the tire" trick to see what gears I have... the drive shaft turned 1.5 times to 1 revolution of the tire. what does that mean? whats my gears

Next question: my axle seems to be aftermarket, here are the numbers next to the cover... CN1 (upside down) K138 on the driver side and L3 stamped on the pass side. what do i have?

thanks

BowTieOgre · 01-18-2007, 05:53 PM

Quote:

Originally Posted by Boise69

Today I was under my truck cutting out my old rotted muffler...

I tried the "mark the driveshaft and spin the tire" trick to see what gears I have... the drive shaft turned 1.5 times to 1 revolution of the tire. what does that mean? whats my gears

Next question: my axle seems to be aftermarket, here are the numbers next to the cover... CN1 (upside down) K138 on the driver side and L3 stamped on the pass side. what do i have?

thanks

I know when I pulled my rearend out I counted each half revolution of the diff to each full revolution of the tire. It came out to a little less than 4 so I think I have a 3.73 and it sounds like yours might be a 3.08 if that is possible. Maybe someone will sound off to confirm.

FYI my rearend was a non posi.

Solver · 01-18-2007, 06:23 PM

Only way to tell ratio by axle numbers is to get the numbers off the top of the axle tube passenger side. takes a little wire brushing to see them but they are there. with those we can tell you what it originally had in it.

jimmydean · 01-18-2007, 06:47 PM

Mine says right on the glove box sticker "3.73 Gear ratio" or something

msgross · 01-18-2007, 06:52 PM

mine doesn't say it but it has 3.73's. My front axle had a tag on one of the bolts and the back axle will have numbers on the ring gear (but you have to take the diff cover off) never hurts to change oil anyway! Once you have those numbers there is a chart with the teeth count that will answer your question without a guess...

1969k10stepside · 01-18-2007, 06:55 PM

On the ring gear look for these numbers,compare the numbers to ones listed below to find ratio.Example:41,11 on the ring gear means 3:73s.

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

Longhorn Man · 01-18-2007, 06:59 PM

with an open diff, don't you need to turn the wheel twice?
That would come out to a 3.07, which is what comes in a small block/auto truck.

**WorkinLonghorn** · 01-18-2007, 07:11 PM

I'd say you have 3.07 or 3.08. Mine has a little stamped metal tag attached to the lowest bolt that says 41:11 3.73-1 .

Boise69 · 01-18-2007, 07:16 PM

OK, i'll check tomorrow when i'm back under there and look for these numbers you speak of. i'll even pull the cover off and look in there too. any recomendations on gear lube to fill it back up with and how much does it take??

msgross · 01-18-2007, 07:55 PM

depends on your rear end and diff cover.... 90W gear oil and 2 qts for a stock 12 bolt but confirm that number first.

Dowdy · 01-18-2007, 07:56 PM

If you have a 3.07, which I have, can you put 3.73 gears in that housing? I was told at a car show by some guys who had the same trucks, that you could not.

Boise69 · 01-18-2007, 07:59 PM

well this will be interesting. i'll tackle this tomorrow. It has a chrome cover with 12 red bolts

msgross · 01-18-2007, 08:25 PM

drive it around before you empty the oil... better when it a little warm look for chunks of metal in the oil...small shavings are common. I looked in the service manual for capacities and it says "as required"...go figure. Check your operators manual or a haynes manual... good luck. DOn't forget to pick up oil and a new diff seal, little rtv couldn't hurt either

Boise69 · 01-18-2007, 08:48 PM

torque values on the cover?

msgross · 01-18-2007, 09:28 PM

service manual says 20 ft lbs... like an oil pan drain plug...!

mnunn454 · 01-18-2007, 10:07 PM

Quote:

Originally Posted by Dowdy

If you have a 3.07, which I have, can you put 3.73 gears in that housing? I was told at a car show by some guys who had the same trucks, that you could not.

Assuming it's a truck 12-bolt rear end, short answer is "No".
However, you can put 3.42's in it.

Reason is 3.73's and numerically higher R&Ps take a different (a #4) carrier while yours (if it's a 3.07) take's a #3 carrier. What you can do is use a ring gear spacer with a 3.73 on your carrier. Another option is buy a "thick" ring and pinon gear set that will do the same thing. These are fine for stock applications but may not be for high performance/racing apps.

Let us know what you find out tomorrow (besides the fact that hypoid gear lube stinks).

Longhorn Man · 01-18-2007, 11:05 PM

Don't use straight 90 weight. Get 80/90 gear lube, and if you have the money, get synthetic. 10 times better than the conventional oil.

chopper103in · 01-19-2007, 01:12 AM

fill it up to the bottom of the fill hole

Boise69 · 01-19-2007, 12:53 PM

Quote:

Originally Posted by chopper103in

fill it up to the bottom of the fill hole

chopper you need to make a drive up to rockford with that truck to talk and compare trucks!! oh and help me too

bobthecop · 01-19-2007, 01:12 PM

I was gonna say, fill it 'til it starts running out, let run 'til it quits. It's full. BG makes a great synthetic gear lube, look for a shop that carries BG products. I don't think any auto parts stores carry them. Just repair shops.

chopper103in · 01-19-2007, 04:39 PM

Quote:

Originally Posted by Boise69

chopper you need to make a drive up to rockford with that truck to talk and compare trucks!! oh and help me too

we will have to do that when the weather gets warm and the roads are clean

01-18-2007, 05:24 PM	#1
Boise69 The Hammer Man Join Date: Oct 2006 Location: Wilmington, NC Posts: 864	A rear end question Today I was under my truck cutting out my old rotted muffler... I tried the "mark the driveshaft and spin the tire" trick to see what gears I have... the drive shaft turned 1.5 times to 1 revolution of the tire. what does that mean? whats my gears Next question: my axle seems to be aftermarket, here are the numbers next to the cover... CN1 (upside down) K138 on the driver side and L3 stamped on the pass side. what do i have? thanks __________________ Boise69. Bought in Boise ID and its a '69 ___________________________________________ 1969 Chevy C-10 SWB 350/400 - drivable project www.americanhammer.com 2013 MBZ Sprinter customized 2005 MBZ Sprinter Van 2004 Land Rover Discovery 2001 Yamaha Road Star 1997 MBZ E420 1989 Ferrari Mondial T Last edited by Boise69; 01-18-2007 at 05:25 PM.

01-18-2007, 06:52 PM	#5
msgross Registered User Join Date: Jul 2006 Location: Central PA Posts: 12,201	Re: A rear end question mine doesn't say it but it has 3.73's. My front axle had a tag on one of the bolts and the back axle will have numbers on the ring gear (but you have to take the diff cover off) never hurts to change oil anyway! Once you have those numbers there is a chart with the teeth count that will answer your question without a guess... __________________ The Garage: 1968 K-10 SWB - "Project Money Pit" 1996 Z-71 - "huntin rig" 1969 C-10 LWB (SOLD) "Project flip that truck or else" 1993 Passport, F@rd 1-ton (SOLD)"Project Cousin Eddie" My Garage Build "The 1,000 footer"

01-18-2007, 06:55 PM	#6
1969k10stepside Registered User Join Date: Mar 2006 Location: USA Posts: 21,019	Re: A rear end question On the ring gear look for these numbers,compare the numbers to ones listed below to find ratio.Example:41,11 on the ring gear means 3:73s. 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 Last edited by 1969k10stepside; 01-18-2007 at 07:00 PM.

01-18-2007, 06:59 PM	#7
Longhorn Man its all about the +6 inches Join Date: Jan 2001 Location: Hilliard Ohio Posts: 2,690	Re: A rear end question with an open diff, don't you need to turn the wheel twice? That would come out to a 3.07, which is what comes in a small block/auto truck.

01-18-2007, 07:11 PM	#8
WorkinLonghorn Senior Member Join Date: Dec 2006 Location: Studio City, Calif. Posts: 2,887	Re: A rear end question I'd say you have 3.07 or 3.08. Mine has a little stamped metal tag attached to the lowest bolt that says 41:11 3.73-1 . __________________ '69 GMC C2500 Custom Camper, 8 1/2' bed, New GM 350, NP 435 Close Ratio 4spd. Trans., 3.73 Dana-60 open.Camper and Trailer wiring, PS, PB, AC, tach , three gas tanks, stereo speakers, 2nd owner, Work-Truck supreme.

01-18-2007, 06:23 PM	#3
Solver Registered User Join Date: May 2000 Location: Storm Lake, Ia Posts: 1,449	Re: A rear end question Only way to tell ratio by axle numbers is to get the numbers off the top of the axle tube passenger side. takes a little wire brushing to see them but they are there. with those we can tell you what it originally had in it. Attached Images __________________ 1972 Cheyenne Super 20 LWB-Blue 1972 Cheyenne Super 10 LWB-Black 1972 Cheyenne Super 10 LWB-Red 1972 Cheyenne Super 10 LWB-green 1972 GMC 4x4 LWB-White 1971 Cheyenne 10 LWB-Ochre 1971 Cheyenne 20 Longhorn-Copper 1971 Cheyenne 20 Longhorn-Black 1969 Custom 10 LWB-lt blue 1968 GMC 3/4 ton-green 1968 1/2 ton swb stepside-silver 1967 Chevrolet CST 10 LWB-green 1967 Chevrolet custom 20 LWB-Maroon

01-18-2007, 06:47 PM	#4
jimmydean Registered User Join Date: May 2005 Location: Beaverton, OR Posts: 3,728	Re: A rear end question Mine says right on the glove box sticker "3.73 Gear ratio" or something

01-18-2007, 07:16 PM	#9
Boise69 The Hammer Man Join Date: Oct 2006 Location: Wilmington, NC Posts: 864	Re: A rear end question OK, i'll check tomorrow when i'm back under there and look for these numbers you speak of. i'll even pull the cover off and look in there too. any recomendations on gear lube to fill it back up with and how much does it take?? __________________ Boise69. Bought in Boise ID and its a '69 ___________________________________________ 1969 Chevy C-10 SWB 350/400 - drivable project www.americanhammer.com 2013 MBZ Sprinter customized 2005 MBZ Sprinter Van 2004 Land Rover Discovery 2001 Yamaha Road Star 1997 MBZ E420 1989 Ferrari Mondial T

01-18-2007, 07:55 PM	#10
msgross Registered User Join Date: Jul 2006 Location: Central PA Posts: 12,201	Re: A rear end question depends on your rear end and diff cover.... 90W gear oil and 2 qts for a stock 12 bolt but confirm that number first. __________________ The Garage: 1968 K-10 SWB - "Project Money Pit" 1996 Z-71 - "huntin rig" 1969 C-10 LWB (SOLD) "Project flip that truck or else" 1993 Passport, F@rd 1-ton (SOLD)"Project Cousin Eddie" My Garage Build "The 1,000 footer" Last edited by msgross; 01-18-2007 at 07:56 PM.

01-18-2007, 07:56 PM	#11
Dowdy Registered User Join Date: Dec 2006 Location: Oviedo, Florida Posts: 11	Re: A rear end question If you have a 3.07, which I have, can you put 3.73 gears in that housing? I was told at a car show by some guys who had the same trucks, that you could not.

01-18-2007, 07:59 PM	#12
Boise69 The Hammer Man Join Date: Oct 2006 Location: Wilmington, NC Posts: 864	Re: A rear end question well this will be interesting. i'll tackle this tomorrow. It has a chrome cover with 12 red bolts __________________ Boise69. Bought in Boise ID and its a '69 ___________________________________________ 1969 Chevy C-10 SWB 350/400 - drivable project www.americanhammer.com 2013 MBZ Sprinter customized 2005 MBZ Sprinter Van 2004 Land Rover Discovery 2001 Yamaha Road Star 1997 MBZ E420 1989 Ferrari Mondial T

01-18-2007, 08:25 PM	#13
msgross Registered User Join Date: Jul 2006 Location: Central PA Posts: 12,201	Re: A rear end question drive it around before you empty the oil... better when it a little warm look for chunks of metal in the oil...small shavings are common. I looked in the service manual for capacities and it says "as required"...go figure. Check your operators manual or a haynes manual... good luck. DOn't forget to pick up oil and a new diff seal, little rtv couldn't hurt either __________________ The Garage: 1968 K-10 SWB - "Project Money Pit" 1996 Z-71 - "huntin rig" 1969 C-10 LWB (SOLD) "Project flip that truck or else" 1993 Passport, F@rd 1-ton (SOLD)"Project Cousin Eddie" My Garage Build "The 1,000 footer" Last edited by msgross; 01-18-2007 at 08:25 PM.

01-18-2007, 08:48 PM	#14
Boise69 The Hammer Man Join Date: Oct 2006 Location: Wilmington, NC Posts: 864	Re: A rear end question torque values on the cover? __________________ Boise69. Bought in Boise ID and its a '69 ___________________________________________ 1969 Chevy C-10 SWB 350/400 - drivable project www.americanhammer.com 2013 MBZ Sprinter customized 2005 MBZ Sprinter Van 2004 Land Rover Discovery 2001 Yamaha Road Star 1997 MBZ E420 1989 Ferrari Mondial T

01-18-2007, 09:28 PM	#15
msgross Registered User Join Date: Jul 2006 Location: Central PA Posts: 12,201	Re: A rear end question service manual says 20 ft lbs... like an oil pan drain plug...! __________________ The Garage: 1968 K-10 SWB - "Project Money Pit" 1996 Z-71 - "huntin rig" 1969 C-10 LWB (SOLD) "Project flip that truck or else" 1993 Passport, F@rd 1-ton (SOLD)"Project Cousin Eddie" My Garage Build "The 1,000 footer" Last edited by msgross; 01-18-2007 at 09:32 PM.

01-18-2007, 11:05 PM	#17
Longhorn Man its all about the +6 inches Join Date: Jan 2001 Location: Hilliard Ohio Posts: 2,690	Re: A rear end question Don't use straight 90 weight. Get 80/90 gear lube, and if you have the money, get synthetic. 10 times better than the conventional oil.



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01-19-2007, 01:12 AM	#18
chopper103in Registered User Join Date: Dec 2006 Location: sycamore,il Posts: 163	Re: A rear end question fill it up to the bottom of the fill hole

01-19-2007, 01:12 PM	#20
bobthecop Senior Member Join Date: Nov 2006 Location: Yukon Oklahoma Posts: 2,647	Re: A rear end question I was gonna say, fill it 'til it starts running out, let run 'til it quits. It's full. BG makes a great synthetic gear lube, look for a shop that carries BG products. I don't think any auto parts stores carry them. Just repair shops. __________________ Happiness is towing your "new" truck home. 1972 C-10 1982 GMC (parts truck??) 1969 c10 parts truck 1969 C-10 ( my sons) 1992 Silverado 4X4 (now the boys truck)(now mine again) 2002 Tarus (my wife loves that car)

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