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

truckminded · 12-15-2006, 02:47 PM

Hey everybody, right now I have a open diff. w/373's. I bought a complete rear end w/limited slip but it has 307's.do you think I should just put the whole rear end in and run the 307's? would I notice any differance?

soulman67 · 12-15-2006, 04:04 PM

yep, the 307's will lower your highway rpms, which will probably get you better mileage. It will be a little slower on take off, which depends on your engines power. It might just slow you 0-60 time a half second to a whole second maybe more if your engine is weak.

Rick Mills · 12-15-2006, 05:59 PM

Oh you'll see a big difference. Especially light to light.
If you're doing a lot of city driving you may not notice much change in the gas mileage, but highway driving will improve.

Longhorn Man · 12-15-2006, 06:23 PM

highway revs will seem almost like an overdirve... if i remember right, 65 is right at 2400 RPM with 28 inch tall tires.

truckminded · 12-15-2006, 08:41 PM

I am real happy with the way it is now. I dont want to loose power out of the gate.I think I'll wait and find sombody to show me how to put the eaton in my carrier & use my gears.MY truck is 72 1/2 ton gmc 5 lug, the other rear end is 72 1/2 ton chevy 5 lug. Theese should trade right I dont know why but the chevy looks smaller.mabey I am seeing things again.

BCOWANWHEELS · 12-15-2006, 10:35 PM

It Will Be A Dog On Takeoff And A Super Dog If You Tow Or Haul. And Your Speedo Will Be Off Also.

*wolfthing2000* · 12-15-2006, 10:35 PM

4.56 would be loads better for take off!!!

Just kiddin!! I had 3.07s in a 76 with 350 and 350 and it was perfect with 32 inch all terrains (4x4) Not a dragster for sure off line but it was a good all around gear.

GREASEMONKEY72 · 12-15-2006, 11:33 PM

i have a 72 with stock 350 (175hp i think) and 350 tranny and 31s(thats what it says on the sidewall) with the 3.07s and mine runs fine and if i had more hp it would drag fine ofcourse thats on the street but still, and if urs is a DD the 3.07s will actually be an improvement

-steven

68C15 · 12-15-2006, 11:44 PM

I would go with the 307's as well. mine works great around town and on the highway with 29" tires. the posi may be a bad isea on snowy/iced roads.

ChevyCrazy67 · 12-16-2006, 12:04 AM

If all your after is not losing anything off the line don't go with the 307s

bryanw1968 · 12-16-2006, 12:27 AM

3.40 is a great gear in IMHO. I had that setup in my '78/stroker truck and loved it. Right now I'm running a 3.73 and pull about 3200RPM to do 70MPH and it is KILLING me on gas.

crazy longhorn · 12-16-2006, 10:46 AM

Quote:

Originally Posted by truckminded

I am real happy with the way it is now. I dont want to loose power out of the gate.I think I'll wait and find sombody to show me how to put the eaton in my carrier & use my gears.MY truck is 72 1/2 ton gmc 5 lug, the other rear end is 72 1/2 ton chevy 5 lug. Theese should trade right I dont know why but the chevy looks smaller.mabey I am seeing things again.

You cant swap the gears from 3.07 to 3.73 without a carrier swap, the 3.07 is a 3 series carrier (gears 2.76-3.42), & the 3.73 is on a 4 series carrier (3.73-4.56). You can get AFTERMARKET 3.73 gears that will fit the 3 series posi that you have tho. IMO, a 3.42 gear would give the best of both worlds, less rpm on the hyway, but also good takeoff. Best of luck,

L

12-15-2006, 02:47 PM	#1
truckminded Junior Member Join Date: Dec 2006 Location: sacramento Posts: 54	Gears Hey everybody, right now I have a open diff. w/373's. I bought a complete rear end w/limited slip but it has 307's.do you think I should just put the whole rear end in and run the 307's? would I notice any differance? Attached Images

12-15-2006, 04:04 PM	#2
soulman67 Randy churchill Join Date: Apr 2003 Location: Pearsall, Tx Posts: 356	Re: Gears yep, the 307's will lower your highway rpms, which will probably get you better mileage. It will be a little slower on take off, which depends on your engines power. It might just slow you 0-60 time a half second to a whole second maybe more if your engine is weak. __________________ 1983 GMC K2500 6.2 diesel 4" lift on 35x12.50 tires 2008 GMC 2500HD 6.6 diesel 3" lift on 315 75 16X10 2003 Jeep Rubicon 4.5" short arm lift 1985 Jeep CJ7 30k in parts and still adding up

12-15-2006, 05:59 PM	#3
Rick Mills Senior Member Join Date: Dec 2003 Location: Colorado Posts: 351	Re: Gears Oh you'll see a big difference. Especially light to light. If you're doing a lot of city driving you may not notice much change in the gas mileage, but highway driving will improve. __________________ The Fastor Pastor '68 swb, 447 BBC/ 6-71 Weiand, Dual 950 Bigs Carbs/ 2 1/2" Header tubes - 4" collectors/ M-21 4speed: '70 swb; TH-400 - bagged & shaved. Looking for new engine or parts. Wife - Original {A Real Classic!}

12-15-2006, 06:23 PM	#4
Longhorn Man its all about the +6 inches Join Date: Jan 2001 Location: Hilliard Ohio Posts: 2,690	Re: Gears highway revs will seem almost like an overdirve... if i remember right, 65 is right at 2400 RPM with 28 inch tall tires.

12-15-2006, 08:41 PM	#5
truckminded Junior Member Join Date: Dec 2006 Location: sacramento Posts: 54	Re: Gears I am real happy with the way it is now. I dont want to loose power out of the gate.I think I'll wait and find sombody to show me how to put the eaton in my carrier & use my gears.MY truck is 72 1/2 ton gmc 5 lug, the other rear end is 72 1/2 ton chevy 5 lug. Theese should trade right I dont know why but the chevy looks smaller.mabey I am seeing things again.

12-15-2006, 10:35 PM	#6
BCOWANWHEELS Registered User Join Date: Nov 2006 Location: KINGSPORT,TN. Posts: 3,035	Re: Gears It Will Be A Dog On Takeoff And A Super Dog If You Tow Or Haul. And Your Speedo Will Be Off Also.

12-15-2006, 10:35 PM	#7
wolfthing2000 Account Suspended Join Date: Oct 2004 Posts: 1,276	Re: Gears 4.56 would be loads better for take off!!! Just kiddin!! I had 3.07s in a 76 with 350 and 350 and it was perfect with 32 inch all terrains (4x4) Not a dragster for sure off line but it was a good all around gear.

12-15-2006, 11:33 PM	#8
GREASEMONKEY72 Registered User Join Date: Aug 2006 Location: Bakersfield,CA Posts: 7,893	Re: Gears i have a 72 with stock 350 (175hp i think) and 350 tranny and 31s(thats what it says on the sidewall) with the 3.07s and mine runs fine and if i had more hp it would drag fine ofcourse thats on the street but still, and if urs is a DD the 3.07s will actually be an improvement -steven __________________ -steven Alte Seele S.S. "Allison" '72 C/10 LWB 350SB/TH350 - DD PITBULL IS NOT A CRIME Last edited by GREASEMONKEY72; 12-15-2006 at 11:46 PM.

12-15-2006, 11:44 PM	#9
68C15 blood type; Retumbo Join Date: Jan 2004 Location: next to my reloading bench Posts: 10,269	Re: Gears I would go with the 307's as well. mine works great around town and on the highway with 29" tires. the posi may be a bad isea on snowy/iced roads.

12-16-2006, 12:04 AM	#10
ChevyCrazy67 Senior Member Join Date: Dec 2005 Location: Dothan Alabama Posts: 2,604	Re: Gears If all your after is not losing anything off the line don't go with the 307s __________________ Kevin 1967 C-10 swb fleetside 1968 C-10 stepside 1999 Z71- sons dd 1999 2wd silverado-my dd 2003 Tahoe- wifes dd

12-16-2006, 12:27 AM	#11
bryanw1968 Senior Member Join Date: Jul 2006 Location: Leander, Texas Posts: 850	Re: Gears 3.40 is a great gear in IMHO. I had that setup in my '78/stroker truck and loved it. Right now I'm running a 3.73 and pull about 3200RPM to do 70MPH and it is KILLING me on gas.



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