Gear Ratio Question - The 1947 - Present Chevrolet & GMC Truck Message Board Network

Ole Blue 68 · 02-01-2006, 05:08 PM

I'm running a stock Saginaw 3 speed and all the info that I've found on it says the gear ratio runs from 2.56 in first gear to 1:1 in third gear which is pretty darn tall.

A mild-performance 350 is just about dropped in my truck and I'll probably go with shorter gears. (swapping the trans is not an option right now). Is that just a matter of swapping out the ring and pinion? If so, how hard of a job is it to do in a home garage without any power tools? Also, what ratio would you all recommend?

John

farside847 · 02-01-2006, 07:13 PM

Probably a 3.08 rear would work nice. From what I hear it is not very easy to do for a weekend warrior, so I decided to have a pro do it.

MrC1 · 02-01-2006, 07:51 PM

All non-overdrive trannys are 1:1 in top gear.

You didn't mention what rear you've got, but they all pretty much require use of power tools to rebuild. The pinion nut comes to mind as the biggest culprit needing quite a bit of torque to remove. Also, if you've not done one before you may want to pay someone to do it. This is one of those jobs you just don't figure out by tearing it apart and throwing it back together.

dwaite72lnghrn · 02-01-2006, 08:48 PM

I would say first is, What RPMs do you want to run in? Second, How mild a 350 do you have? Stock or near stock? Third what rear do you have now?
I don't think that 3 speed will hold up if you start dropping the hammer at 3-4 grand. So you might be putting something in anyway. The ratio of your 3 speed covers about the same as all 4 speeds(granny low excluded because it is not syncrod) they just give you more inbetween gears. Autos cover the same except for the 700r4 which has a lower 1st. JMO

**VetteVet** · 02-01-2006, 09:00 PM

Here is a website with the info you want plus a ton more. The ratios are on the first page.

http://images.google.com/imgres?imgu...lr%3D%26sa%3DN

Ole Blue 68 · 02-02-2006, 01:03 AM

Thanks for the good feedback and the good questions raised.

The engine's going to be modded and I'm hoping to hit 300hp at the wheels(we'll see). As far as the rear goes, it's just the stock rear (14 bolt, 10.5 inch?) with six lug axles. Even with the old motor, I could get some nasty launches out of first gear but it's not very practical and a lot of times I don't even bother with first. I want something that's still gonna give me good low end torque but not feel like I'm tearing the thing apart. So I was thinking a 3.08 might be the way to go just as Farside is suggesting.

It's also good to know that I might be in over my head if I tried it so I will leave it to an expert.

dwaite- you bring up a good point about the 3 speed holding up and I have the same concerns but since I just dropped a good chunk of change on the engine, I'm gonna have to keep my fingers crossed that the old Saginaw holds out for a while.

Bill72BB · 02-02-2006, 12:21 PM

This chart shows you your RPM at 60 mph for different gear ratio's and tire size . Hope it helps .

Ole Blue 68 · 02-02-2006, 02:24 PM

Huge help, thanks Bill!

02-01-2006, 05:08 PM	#1
Ole Blue 68 Registered User Join Date: Aug 2005 Location: Philly Posts: 1,140	Gear Ratio Question I'm running a stock Saginaw 3 speed and all the info that I've found on it says the gear ratio runs from 2.56 in first gear to 1:1 in third gear which is pretty darn tall. A mild-performance 350 is just about dropped in my truck and I'll probably go with shorter gears. (swapping the trans is not an option right now). Is that just a matter of swapping out the ring and pinion? If so, how hard of a job is it to do in a home garage without any power tools? Also, what ratio would you all recommend? John

02-01-2006, 07:13 PM	#2
farside847 Registered User Join Date: Feb 2005 Location: Bay Area, California Posts: 995	Re: Gear Ratio Question Probably a 3.08 rear would work nice. From what I hear it is not very easy to do for a weekend warrior, so I decided to have a pro do it. __________________ 1971 Chevy C10 Shortbed Stepside, 307v8 3-on-the-tree

02-01-2006, 07:51 PM	#3
MrC1 Dork For Days Join Date: Aug 2005 Location: Dallas Posts: 407	Re: Gear Ratio Question All non-overdrive trannys are 1:1 in top gear. You didn't mention what rear you've got, but they all pretty much require use of power tools to rebuild. The pinion nut comes to mind as the biggest culprit needing quite a bit of torque to remove. Also, if you've not done one before you may want to pay someone to do it. This is one of those jobs you just don't figure out by tearing it apart and throwing it back together. __________________ 1972 C20, 402/700R4 - My first classic truck, bought in September 2005. 85% transformed from "Farm" to "Cool" status! 1970 Dodge Challenger 440, 4sp (my other toy) 12.67 @ 117 MPH, with a pathetic 2.022 60' 2007 Dodge Charger SRT-8 2008 Cadillac CTS All-American garage, baby!

02-01-2006, 08:48 PM	#4
dwaite72lnghrn Registered User Join Date: Jun 2002 Location: central pa Posts: 1,525	Re: Gear Ratio Question I would say first is, What RPMs do you want to run in? Second, How mild a 350 do you have? Stock or near stock? Third what rear do you have now? I don't think that 3 speed will hold up if you start dropping the hammer at 3-4 grand. So you might be putting something in anyway. The ratio of your 3 speed covers about the same as all 4 speeds(granny low excluded because it is not syncrod) they just give you more inbetween gears. Autos cover the same except for the 700r4 which has a lower 1st. JMO __________________ 72 longhorn c30 502BB/th400/fact air/4.11rear/ custom camper 72 bug(the better half's) under reconstruction 2009 HHR aqua blue 71 GMC k20 350/sm465 2009 Chevy hd3500 6.6 Victory Red crew cab dually Dave & Jeanne

02-01-2006, 09:00 PM	#5
VetteVet Msgt USAF Ret Join Date: Jan 2005 Location: Kalamazoo, Michigan Posts: 8,717	Re: Gear Ratio Question Here is a website with the info you want plus a ton more. The ratios are on the first page. http://images.google.com/imgres?imgu...lr%3D%26sa%3DN __________________ VetteVet metallic green 67 stepside 74 corvette convertible 1965 Harley sportster 1995 Harley wide glide Growing old is hell, but it beats the alternative.

02-02-2006, 01:03 AM	#6
Ole Blue 68 Registered User Join Date: Aug 2005 Location: Philly Posts: 1,140	Re: Gear Ratio Question Thanks for the good feedback and the good questions raised. The engine's going to be modded and I'm hoping to hit 300hp at the wheels(we'll see). As far as the rear goes, it's just the stock rear (14 bolt, 10.5 inch?) with six lug axles. Even with the old motor, I could get some nasty launches out of first gear but it's not very practical and a lot of times I don't even bother with first. I want something that's still gonna give me good low end torque but not feel like I'm tearing the thing apart. So I was thinking a 3.08 might be the way to go just as Farside is suggesting. It's also good to know that I might be in over my head if I tried it so I will leave it to an expert. dwaite- you bring up a good point about the 3 speed holding up and I have the same concerns but since I just dropped a good chunk of change on the engine, I'm gonna have to keep my fingers crossed that the old Saginaw holds out for a while.

02-02-2006, 12:21 PM	#7
Bill72BB Thats the Hillbilly way Join Date: Jul 2001 Location: Torrance,Ca Posts: 5,980	Re: Gear Ratio Question This chart shows you your RPM at 60 mph for different gear ratio's and tire size . Hope it helps . Attached Images __________________ BILL Torrance Calif 90504 Member DUF Club Member Old Farts Club 72 3/4ton Custom Camper BB402/400 trans Dynomax Cerama-coat headers , Hei distributor ,Edelbrock 1411 air,ps,pb,leafsprings ,98 chevy 60/40 seat,S10 shoulder belts tilt,3.54 Dana 60 rear. 16" Eagle wheels with LT265/75 16 tires,Gaylord Lid,H4 headlights with 100W relay conversion. " If I knew I was going to live this long I would have taken better care of myself " Marriage changes passion...suddenly you're in bed with a relative. A GUY'S PRAYER.... Lord, I pray for a nympho with huge boobs who owns a liquor store and likes to fish and hunt and has a Harley .Amen ,

02-02-2006, 02:24 PM	#8
Ole Blue 68 Registered User Join Date: Aug 2005 Location: Philly Posts: 1,140	Re: Gear Ratio Question Huge help, thanks Bill!



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