Tranny & Rear end ratios - The 1947 - Present Chevrolet & GMC Truck Message Board Network

tfen2001 · 06-07-2010, 11:47 PM

I have a '64 C10 with 292 cubes. The truck tops out at 50-55 mph so I'm looking for help on how to get more top end out of her. I pulled the diff cover to determine the ratio and found it is a 3.73 ratio. At some point I'd like to drop in a 350 with a manual 4 speed. This maybe a dumb question but upgrading to a 350 4-speed won't change the top end speed, right? So, I'll need to go to a lower ratio in the rear end, right? That being said, I think this may be a 12-bolt posi but I'm not sure how to ID a posi. There are some small coil type springs in the carrier. I haven't been able to find any pics that would show whether this is a posi or not. With the rear wheels off the ground, both wheels spin in the same direction - does that mean anything? Thanks for the help.

apachedaddy · 06-08-2010, 12:17 AM

From what you wrote that is a posi.. But that matters not if you want to go to a higher gear you will have to change out the diff any way. 3:73 is the highest gear that will bolt to your current diff. Series 3 or 4 are what I think they are called. So to change the gears you’re looking at a new diff with new gears to make the change. Plenty of threads on here on the subject just do a search and they will pop up. Hope this helps you out.

raycow · 06-08-2010, 01:20 AM

Another way would be to keep the rear you have now and replace your transmission with one that has overdrive. This might be less work and money than buying a new posi and gears and paying someone to set it up.

That's what I did in my 60 because I couldn't find a rear with better gears that would have installed without welding. I used a 5 speed out of an S-10 and would recommend the same if you have a 4 speed now. If you have a 3 speed, you can get a 3 speed with overdrive that will almost be a bolt-in.

Ray

old cruiser · 06-08-2010, 05:27 AM

You could also change wheel / tyre diametre

tfen2001 · 06-08-2010, 11:07 PM

Wow! You guys are fantastic! I'm new to the forum having just bought my '64 last summer and tinkering with it since then. I appreciate all the helpful advice and comments. Finding this forum makes a hobby that much more fun. I'll search as noted and thanks again for your thoughts.

06-07-2010, 11:47 PM	#1
tfen2001 Registered User Join Date: Mar 2010 Location: Littleton, Co Posts: 2	Tranny & Rear end ratios I have a '64 C10 with 292 cubes. The truck tops out at 50-55 mph so I'm looking for help on how to get more top end out of her. I pulled the diff cover to determine the ratio and found it is a 3.73 ratio. At some point I'd like to drop in a 350 with a manual 4 speed. This maybe a dumb question but upgrading to a 350 4-speed won't change the top end speed, right? So, I'll need to go to a lower ratio in the rear end, right? That being said, I think this may be a 12-bolt posi but I'm not sure how to ID a posi. There are some small coil type springs in the carrier. I haven't been able to find any pics that would show whether this is a posi or not. With the rear wheels off the ground, both wheels spin in the same direction - does that mean anything? Thanks for the help.

06-08-2010, 12:17 AM	#2
apachedaddy Registered User Join Date: Feb 2008 Location: pooler, GA Posts: 213	Re: Tranny & Rear end ratios From what you wrote that is a posi.. But that matters not if you want to go to a higher gear you will have to change out the diff any way. 3:73 is the highest gear that will bolt to your current diff. Series 3 or 4 are what I think they are called. So to change the gears you’re looking at a new diff with new gears to make the change. Plenty of threads on here on the subject just do a search and they will pop up. Hope this helps you out. __________________ 66 short wide fleet sbw = Gave to my best friend 66 short wide fleet bbw

06-08-2010, 01:20 AM	#3
raycow Registered User Join Date: Mar 2003 Location: San Francisco, CA USA Posts: 2,454	Re: Tranny & Rear end ratios Another way would be to keep the rear you have now and replace your transmission with one that has overdrive. This might be less work and money than buying a new posi and gears and paying someone to set it up. That's what I did in my 60 because I couldn't find a rear with better gears that would have installed without welding. I used a 5 speed out of an S-10 and would recommend the same if you have a 4 speed now. If you have a 3 speed, you can get a 3 speed with overdrive that will almost be a bolt-in. Ray

06-08-2010, 05:27 AM	#4
old cruiser Registered User Join Date: Mar 2010 Location: Camperdown Vic Australia Posts: 230	Re: Tranny & Rear end ratios You could also change wheel / tyre diametre

06-08-2010, 11:07 PM	#5
tfen2001 Registered User Join Date: Mar 2010 Location: Littleton, Co Posts: 2	Re: Tranny & Rear end ratios Wow! You guys are fantastic! I'm new to the forum having just bought my '64 last summer and tinkering with it since then. I appreciate all the helpful advice and comments. Finding this forum makes a hobby that much more fun. I'll search as noted and thanks again for your thoughts.



Register or Log In To remove these advertisements.

Register or Log In To remove these advertisements.