typical rearend ratios? - The 1947 - Present Chevrolet & GMC Truck Message Board Network

streetstar · 06-09-2008, 11:49 AM

my truck is a 69 and has a 307 with a th350 -- no other options listed on the SPID related to perf./towing/posi-trac. etc. -- so i assume it has base model, peg leg gears--

i do know that this can vary, but does anybody have an idea of what typically was installed in the rearend of a combo like this?

(its rainy today and i'm bored, but i dont feel like rolling in the mud to pull the diff cover today)

reason is i will be doing a 700r4 conversion sooner rather than later, and trying to determine if i will need to change the diff gears too

sameyrasmea72 · 06-09-2008, 01:17 PM

If it was a 373 it would list it on the option list. I would say it is a .307

Longhorn Man · 06-09-2008, 04:58 PM

3.07 was standard in a small block/automatic tranny 2 wheel drive truck.
You'll want to swap that out if going with an overdrive

Patg · 06-09-2008, 05:30 PM

mine has a 307 in it and it was a no option truck. When I put a 700r4 I discovered you need to change the gears. The RPM are low for around town and if you have alot of hills around you will see you do not have enough power when in overdrive.
IT has been recomended to install 341 grears at least or 373's. If you want real tire burning go with 373

streetstar · 06-09-2008, 07:22 PM

Thanks for the info fellas -- after calling a few tranny shops, i have almost decided to just rebuild the th350 and keep it rockin down the highway.

The shops no longer have stacks and stacks of 700r4 cores laying around and i can get the th350 done for 500 bucks.

I figure for a truck that i intend to leave mostly stock and drive less than 2 or 300 miles a month, it might be less aggravating to fix it as is

Zoerb · 06-10-2008, 05:40 AM

does anyone know if you can swap over the 3.73's into a 3.07 housing and use the 3.07's posi unit?

Classic69 · 06-10-2008, 10:01 AM

I got 4.56 gears in mine. That's what was in the truck when I bought it. It orginally had an inline 6 and a 3-speed manual tranny. Takes off like a bat outta hell off the line, but screams like a banshee on the highway with the SBC 327/TH350 combo I have in it now.

Longhorn Man · 06-10-2008, 04:40 PM

did you count the teeth for that 4.56, or you going by RPMs?

06-09-2008, 11:49 AM	#1
streetstar Registered User Join Date: May 2007 Location: Moore, Oklahoma Posts: 2,396	typical rearend ratios? my truck is a 69 and has a 307 with a th350 -- no other options listed on the SPID related to perf./towing/posi-trac. etc. -- so i assume it has base model, peg leg gears-- i do know that this can vary, but does anybody have an idea of what typically was installed in the rearend of a combo like this? (its rainy today and i'm bored, but i dont feel like rolling in the mud to pull the diff cover today) reason is i will be doing a 700r4 conversion sooner rather than later, and trying to determine if i will need to change the diff gears too __________________ Are you retired too? Nonsense! I'm in my prime

06-09-2008, 01:17 PM	#2
sameyrasmea72 Senior Member Join Date: Aug 2003 Location: Lubbock, Texas Posts: 2,443	Re: typical rearend ratios? If it was a 373 it would list it on the option list. I would say it is a .307 __________________ 72 Cheyenne Super 80 Silverado Blazer 2wd

06-09-2008, 04:58 PM	#3
Longhorn Man its all about the +6 inches Join Date: Jan 2001 Location: Hilliard Ohio Posts: 2,690	Re: typical rearend ratios? 3.07 was standard in a small block/automatic tranny 2 wheel drive truck. You'll want to swap that out if going with an overdrive

06-09-2008, 05:30 PM	#4
Patg Registered User Join Date: Nov 2005 Location: Nevada Posts: 7	Re: typical rearend ratios? mine has a 307 in it and it was a no option truck. When I put a 700r4 I discovered you need to change the gears. The RPM are low for around town and if you have alot of hills around you will see you do not have enough power when in overdrive. IT has been recomended to install 341 grears at least or 373's. If you want real tire burning go with 373 __________________

06-09-2008, 07:22 PM	#5
streetstar Registered User Join Date: May 2007 Location: Moore, Oklahoma Posts: 2,396	Re: typical rearend ratios? Thanks for the info fellas -- after calling a few tranny shops, i have almost decided to just rebuild the th350 and keep it rockin down the highway. The shops no longer have stacks and stacks of 700r4 cores laying around and i can get the th350 done for 500 bucks. I figure for a truck that i intend to leave mostly stock and drive less than 2 or 300 miles a month, it might be less aggravating to fix it as is __________________ Are you retired too? Nonsense! I'm in my prime Last edited by streetstar; 06-09-2008 at 07:23 PM.

06-10-2008, 05:40 AM	#6
Zoerb Registered User Join Date: Dec 2005 Location: Wasilla Alaska Posts: 73	Re: typical rearend ratios? does anyone know if you can swap over the 3.73's into a 3.07 housing and use the 3.07's posi unit? __________________ 2017 Tahoe Premier - Daily '99 Silverado 2500 Wife's whip- 2020 Equinox Premier

06-10-2008, 10:01 AM	#7
Classic69 Love That '69 Join Date: Oct 2007 Location: Sherwood Park, Alberta, Canada Posts: 360	Re: typical rearend ratios? I got 4.56 gears in mine. That's what was in the truck when I bought it. It orginally had an inline 6 and a 3-speed manual tranny. Takes off like a bat outta hell off the line, but screams like a banshee on the highway with the SBC 327/TH350 combo I have in it now. __________________ *I AM CANADIAN!!!!!* 1969 Chevy C/10 Truck - SBC V8, TH-350, 3.73 Posi, 1000W Rockford Fosgate Stereo System, B&M Megashifter, GT Grant Steering Wheel, Dual Magnaflow Exhaust System, Dynomax Headers, Lowered 1" Front & 3" Rear, Front/Rear Sway Bars, Racing Seats, 6000K HID Headlights 2008 Chevy Colorado LT - 3.7L I5, 4 Speed Automatic, Crew Cab, 4X4, Z71 Off-Road Package, "Ground Effects" Package, K&N Cold Air Intake, Supermod PTB, Magnaflow Exhaust w/ Resonator, 500W Kenwood / Rockford Fosgate Stereo System, Custom LED Lighting, 6000K HID Low's / High's, Blackcat Customs Gauges / Needles, Carbon Fiber Interior Accents, KrFabs 2" Lift Shackles / Torsion Bar Crank with Rancho RS5000 Shocks, Superskids Skid Plates

06-10-2008, 04:40 PM	#8
Longhorn Man its all about the +6 inches Join Date: Jan 2001 Location: Hilliard Ohio Posts: 2,690	Re: typical rearend ratios? did you count the teeth for that 4.56, or you going by RPMs?

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