Gears - The 1947 - Present Chevrolet & GMC Truck Message Board Network

chevykid1969 · 09-07-2003, 08:37 PM

I am thinking of going to a posi. What would be good gears for the streat. I have a 327 wit a th350 tranny. Thanks

jmanz69 · 09-07-2003, 08:42 PM

3.73 would be best, 4.10 is pretty high for running on the street. What year is your truck, it might already have 3.73 gears. They were pretty common for the pre-71 trucks. Then just buy a 4 series posi carrier, and have it installed professionally. It really isn't something you can do very well on your own. There are a lot of tolerances that need to be measured.

Good luck

chevykid1969 · 09-07-2003, 09:08 PM

I have a 69 that org had a straight six. i was told that it probally had4.10/4.11 gears in it.

jmanz69 · 09-07-2003, 09:11 PM

Only way to tell is to pop the cover off and count the number of teeth on the ring and divide that by the number of teeth on the pinion gear. Probably need new oil anyway.

chevykid1969 · 09-07-2003, 09:15 PM

sorry but this might sound dumb. To do this i just take the bolts out count the teeth on what and what and then where do i put the oil. Ok i know this sounds stupid but i dont know much about that end of my truck.LOL

jewels. · 09-07-2003, 09:24 PM

there is a ring gear and a pinion gear inside the rear end.... it should be pretty visible..... the ratio of the two gears is your gear ratio.....

if you open the rear end, you can also read on the side of the ring gear (i believe), and the ratio should be imprinted on the side of the gear (if you hate counting teeth)...

if you are too lazy to do either of those, try this (this is what i did)... jack up the end of the truck, and turn one of the rear wheels a full turn. as you turn the rear wheel one complete turn, count the number of rotations of the drive shaft. BTW, use a piece of chalk to mark the tire and the driveshaft (it makes counting much easier)..... then do a little math....

here is how mine turned out:

1 turn of rear tire = 1-7/8 turn of driveshaft (or 1.875 turns)

2 wheels x 1-7/8 = 3.75 (which is approx 3.73)

thus, my rear gear ratio is 3.73.
if you think you have a 4.10 rear gear ratio, your driveshaft will turn just over two complete rotations for each single rotation of a rear tire (4.10 / 2 = 2.05 drive shaft turns)

hope this helps.
good luck!

jewels.

truckster · 09-07-2003, 09:29 PM

To get into the diff, put a pan under the housing and take out all the bolts on the cover. It will probably start leaking 90w as soon as you take out the bottom bolts. Use a new gasket to put the cover back on (some people use silicone, but I like using a gasket), and make sure you put the cover back on in the same position (it's really easy to get them upside-down if you've got an Eaton). Once you've got it bolted up, just pull the access plug (it's about halfway up on the cover and has either a square 1/2 in recess or a square knob on it) and fill it with 90w until it reaches the bottom of the plug hole. If you find you have a posi in there, you'll also need a friction modifier additive from GM.

jmanz69 · 09-07-2003, 09:40 PM

If you have a 12 bolt (non-round cover) you will find the fill plug on the front side of the housing, near the top. Fill as described above and your set. The ratio will be printed on the side of the ring gear as a tooth count. It will appear as 41:11. This is the ring gear tooth number (41) and the pinion gear tooth number (11). This combo would be 3.73. 4.10 I think is 41:10.

BTW, the oil will stink really bad when you dump it out, so be sure to catch it in a pan, you don't want it on you. It takes a while for the smell to come out of your clothes and skin.

09-07-2003, 08:37 PM	#1
chevykid1969 Registered User Join Date: Apr 2003 Location: Knightdale,North Carolina Posts: 377	Gears I am thinking of going to a posi. What would be good gears for the streat. I have a 327 wit a th350 tranny. Thanks

09-07-2003, 09:24 PM	#6
jewels. Registered User Join Date: Jul 2001 Location: Munster, IN Posts: 1,100	there is a ring gear and a pinion gear inside the rear end.... it should be pretty visible..... the ratio of the two gears is your gear ratio..... if you open the rear end, you can also read on the side of the ring gear (i believe), and the ratio should be imprinted on the side of the gear (if you hate counting teeth)... if you are too lazy to do either of those, try this (this is what i did)... jack up the end of the truck, and turn one of the rear wheels a full turn. as you turn the rear wheel one complete turn, count the number of rotations of the drive shaft. BTW, use a piece of chalk to mark the tire and the driveshaft (it makes counting much easier)..... then do a little math.... here is how mine turned out: 1 turn of rear tire = 1-7/8 turn of driveshaft (or 1.875 turns) 2 wheels x 1-7/8 = 3.75 (which is approx 3.73) thus, my rear gear ratio is 3.73. if you think you have a 4.10 rear gear ratio, your driveshaft will turn just over two complete rotations for each single rotation of a rear tire (4.10 / 2 = 2.05 drive shaft turns) hope this helps. good luck! jewels. __________________ 68 C10 Red Step 350 my first child & main focus 58 3200 Apache LWB Step the upcoming project

09-07-2003, 09:29 PM	#7
truckster Registered User Join Date: Jan 2001 Location: Orem, Utah Posts: 8,021	To get into the diff, put a pan under the housing and take out all the bolts on the cover. It will probably start leaking 90w as soon as you take out the bottom bolts. Use a new gasket to put the cover back on (some people use silicone, but I like using a gasket), and make sure you put the cover back on in the same position (it's really easy to get them upside-down if you've got an Eaton). Once you've got it bolted up, just pull the access plug (it's about halfway up on the cover and has either a square 1/2 in recess or a square knob on it) and fill it with 90w until it reaches the bottom of the plug hole. If you find you have a posi in there, you'll also need a friction modifier additive from GM. __________________ I have sworn upon the altar of God, eternal hostility against every form of tyranny over the mind of man. - Thomas Jefferson

09-07-2003, 08:42 PM	#2
jmanz69 Careful, they attack... Join Date: Aug 2001 Location: Waterford, MI, USA Posts: 1,107	3.73 would be best, 4.10 is pretty high for running on the street. What year is your truck, it might already have 3.73 gears. They were pretty common for the pre-71 trucks. Then just buy a 4 series posi carrier, and have it installed professionally. It really isn't something you can do very well on your own. There are a lot of tolerances that need to be measured. Good luck

09-07-2003, 09:08 PM	#3
chevykid1969 Registered User Join Date: Apr 2003 Location: Knightdale,North Carolina Posts: 377	I have a 69 that org had a straight six. i was told that it probally had4.10/4.11 gears in it.

09-07-2003, 09:11 PM	#4
jmanz69 Careful, they attack... Join Date: Aug 2001 Location: Waterford, MI, USA Posts: 1,107	Only way to tell is to pop the cover off and count the number of teeth on the ring and divide that by the number of teeth on the pinion gear. Probably need new oil anyway.

09-07-2003, 09:15 PM	#5
chevykid1969 Registered User Join Date: Apr 2003 Location: Knightdale,North Carolina Posts: 377	sorry but this might sound dumb. To do this i just take the bolts out count the teeth on what and what and then where do i put the oil. Ok i know this sounds stupid but i dont know much about that end of my truck.LOL

09-07-2003, 09:40 PM	#8
jmanz69 Careful, they attack... Join Date: Aug 2001 Location: Waterford, MI, USA Posts: 1,107	If you have a 12 bolt (non-round cover) you will find the fill plug on the front side of the housing, near the top. Fill as described above and your set. The ratio will be printed on the side of the ring gear as a tooth count. It will appear as 41:11. This is the ring gear tooth number (41) and the pinion gear tooth number (11). This combo would be 3.73. 4.10 I think is 41:10. BTW, the oil will stink really bad when you dump it out, so be sure to catch it in a pan, you don't want it on you. It takes a while for the smell to come out of your clothes and skin.



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