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

ThatOneBlue67 · 04-03-2007, 07:44 PM

Hi everybody! I was wondering if someone could tell me what the common rear end gear ratio is for a 1967 half ton truck that had a 250 inline six and standard 3 speed transmission.

I now have a 350 w/ 700R4 and I think the rear end is too low for the speeds I'm trying to reach. Someone mentioned to me that if I make a rearend that low try and go 90, it'll "go out" on me. Right now she tops out at about 85-90. I'd like to hit those speeds, but without worrying about blowing my motor. What rear end gearing would you suggest for my combination?

Where can I find an entire rear exle with this new gearing that bolts up to rear trailing arms fo my 1/2 ton? Probably no where I imagine. Can I just get a ring and pinion setup out of a Cmaro axle or something and put them in my 12-bolt truck housing? IS that hard to do?

Thankyou for all of your input. The new overdrive works great, but using an old, inline six rearend for freeway use is freaking me out.

Longhorn Man · 04-03-2007, 07:53 PM

you should have a 3.73... which is perfect for use with an overdrive tranny.
Do you have a tach? You should only be doing 2000 to maybe 2250 at 60 MPH.... right in the good part or the powerband on a small block, yet low enough to get more than 10 MPG

sdkid · 04-03-2007, 07:55 PM

There is a code on the label in the glovebox door if its still legible. My '68 250/3 spd had a 3:08 gear. I've seen several with 3:73. I don't know what other factory ratios were available.

msgross · 04-03-2007, 08:46 PM

I just pulled a 3.73 w/posi from the junkyard for $35. It came from a 69 with trailing arms and coils, inline six. I would start searching, swapping gears will cost you $$$$ not counting labor $$$$ to do.

Longhorn Man · 04-04-2007, 05:44 AM

sd, your 3.07 was listed on the spid, right? That means it was an option... if there is no listing, then an inline with a 3 speed manual, would automaticly get a 3.73.

sdkid · 04-04-2007, 09:02 AM

Not sure, the spid was illegible.

ThatOneBlue67 · 04-05-2007, 12:49 AM

Sweet, then it is a 3.73 Yes, my RPM sits at about 2,000 RPM doing 65. My complaint is the fact that my truck only does about 85 to 90. But, oh well. Its a truck, not a Camaro. I'll just lower it next...

Longhorn Man · 04-05-2007, 05:49 AM

even without the overdrive, you should be able to do 100+ MPH. EASY.
Time to find out why your (probabaly) engine isn't pushing hard enough.

ThatOneBlue67 · 04-05-2007, 06:03 PM

Yeah... no kidding. I don't actually have a speedometer hooked up (sending gear is too small) but someone clocked me at 80. Maybe they were wrong. I'll jus have to get it fixed and go off my own.

THe motor actually does not want to go passed a certain RPM range (think it's 3000) BUT only in 4th gear. I've had it passed that in other gears.

msgross · 04-05-2007, 06:05 PM

you can find someone with a GPS to give you a good reading.

JAKES 68GMC · 04-05-2007, 08:30 PM

Quote:

Originally Posted by msgross

you can find someone with a GPS to give you a good reading.

Yeah, like a cop!

**WorkinLonghorn** · 04-05-2007, 09:52 PM

If you do have 3.73 (and it kinda sounds like you do) then with 31 inch tires you should be going about 60 at 2500 RPM,72 at 3000,84 @ 3500 and 96 at 4000 RPM.Forget overdrive. 4000 Rpm is where a stock '69 350 gets it top NET horsepower (200HP). I don't know what motor yours has,but 4000 will not "blow up" any healthy 350.Mine goes to 5000 on a regular basis,and if it had a different cam would happily go to 5500.

04-03-2007, 07:44 PM	#1
ThatOneBlue67 I survived Dead Man's Curve. Join Date: Apr 2006 Location: The Nine-Five-687 Posts: 389	Rear end question Hi everybody! I was wondering if someone could tell me what the common rear end gear ratio is for a 1967 half ton truck that had a 250 inline six and standard 3 speed transmission. I now have a 350 w/ 700R4 and I think the rear end is too low for the speeds I'm trying to reach. Someone mentioned to me that if I make a rearend that low try and go 90, it'll "go out" on me. Right now she tops out at about 85-90. I'd like to hit those speeds, but without worrying about blowing my motor. What rear end gearing would you suggest for my combination? Where can I find an entire rear exle with this new gearing that bolts up to rear trailing arms fo my 1/2 ton? Probably no where I imagine. Can I just get a ring and pinion setup out of a Cmaro axle or something and put them in my 12-bolt truck housing? IS that hard to do? Thankyou for all of your input. The new overdrive works great, but using an old, inline six rearend for freeway use is freaking me out. __________________ "The people should not be afraid of their government. The government should be afraid of it's people." "The Hurricane" 1967 Chevrolet C10 350 Eight Cylinder, 700R4 BowtieOverdrive *Cherry Bomb...* Disturbing the Peace Since 1968.

04-03-2007, 07:53 PM	#2
Longhorn Man its all about the +6 inches Join Date: Jan 2001 Location: Hilliard Ohio Posts: 2,693	Re: Rear end question you should have a 3.73... which is perfect for use with an overdrive tranny. Do you have a tach? You should only be doing 2000 to maybe 2250 at 60 MPH.... right in the good part or the powerband on a small block, yet low enough to get more than 10 MPG

04-03-2007, 07:55 PM	#3
sdkid Registered User Join Date: Sep 2004 Location: Pierre SD Posts: 1,533	Re: Rear end question There is a code on the label in the glovebox door if its still legible. My '68 250/3 spd had a 3:08 gear. I've seen several with 3:73. I don't know what other factory ratios were available. __________________ I think the world needs a drink... Help somebody...If you can....VanZant We're not wrong, we're not sorry, and its probably gonna happen again. That's the truth about men. Tracy Byrd Member# 13924 '70 c10, 350/350 '68 c10 250/4spd '68 c10 no eng/trans fac ps/pb/ac/at (future father/sons project) '48 Chevy Loadmaster

04-03-2007, 08:46 PM	#4
msgross Registered User Join Date: Jul 2006 Location: Central PA Posts: 12,201	Re: Rear end question I just pulled a 3.73 w/posi from the junkyard for $35. It came from a 69 with trailing arms and coils, inline six. I would start searching, swapping gears will cost you $$$$ not counting labor $$$$ to do. __________________ The Garage: 1968 K-10 SWB - "Project Money Pit" 1996 Z-71 - "huntin rig" 1969 C-10 LWB (SOLD) "Project flip that truck or else" 1993 Passport, F@rd 1-ton (SOLD)"Project Cousin Eddie" My Garage Build "The 1,000 footer"

04-04-2007, 05:44 AM	#5
Longhorn Man its all about the +6 inches Join Date: Jan 2001 Location: Hilliard Ohio Posts: 2,693	Re: Rear end question sd, your 3.07 was listed on the spid, right? That means it was an option... if there is no listing, then an inline with a 3 speed manual, would automaticly get a 3.73.

04-04-2007, 09:02 AM	#6
sdkid Registered User Join Date: Sep 2004 Location: Pierre SD Posts: 1,533	Re: Rear end question Not sure, the spid was illegible. __________________ I think the world needs a drink... Help somebody...If you can....VanZant We're not wrong, we're not sorry, and its probably gonna happen again. That's the truth about men. Tracy Byrd Member# 13924 '70 c10, 350/350 '68 c10 250/4spd '68 c10 no eng/trans fac ps/pb/ac/at (future father/sons project) '48 Chevy Loadmaster

04-05-2007, 12:49 AM	#7
ThatOneBlue67 I survived Dead Man's Curve. Join Date: Apr 2006 Location: The Nine-Five-687 Posts: 389	Re: Rear end question Sweet, then it is a 3.73 Yes, my RPM sits at about 2,000 RPM doing 65. My complaint is the fact that my truck only does about 85 to 90. But, oh well. Its a truck, not a Camaro. I'll just lower it next... __________________ "The people should not be afraid of their government. The government should be afraid of it's people." "The Hurricane" 1967 Chevrolet C10 350 Eight Cylinder, 700R4 BowtieOverdrive *Cherry Bomb...* Disturbing the Peace Since 1968.

04-05-2007, 05:49 AM	#8
Longhorn Man its all about the +6 inches Join Date: Jan 2001 Location: Hilliard Ohio Posts: 2,693	Re: Rear end question even without the overdrive, you should be able to do 100+ MPH. EASY. Time to find out why your (probabaly) engine isn't pushing hard enough.

04-05-2007, 06:03 PM	#9
ThatOneBlue67 I survived Dead Man's Curve. Join Date: Apr 2006 Location: The Nine-Five-687 Posts: 389	Re: Rear end question Yeah... no kidding. I don't actually have a speedometer hooked up (sending gear is too small) but someone clocked me at 80. Maybe they were wrong. I'll jus have to get it fixed and go off my own. THe motor actually does not want to go passed a certain RPM range (think it's 3000) BUT only in 4th gear. I've had it passed that in other gears. __________________ "The people should not be afraid of their government. The government should be afraid of it's people." "The Hurricane" 1967 Chevrolet C10 350 Eight Cylinder, 700R4 BowtieOverdrive *Cherry Bomb...* Disturbing the Peace Since 1968.

04-05-2007, 06:05 PM	#10
msgross Registered User Join Date: Jul 2006 Location: Central PA Posts: 12,201	Re: Rear end question you can find someone with a GPS to give you a good reading. __________________ The Garage: 1968 K-10 SWB - "Project Money Pit" 1996 Z-71 - "huntin rig" 1969 C-10 LWB (SOLD) "Project flip that truck or else" 1993 Passport, F@rd 1-ton (SOLD)"Project Cousin Eddie" My Garage Build "The 1,000 footer"

04-05-2007, 09:52 PM	#12
WorkinLonghorn Senior Member Join Date: Dec 2006 Location: Studio City, Calif. Posts: 2,883	Re: Rear end question If you do have 3.73 (and it kinda sounds like you do) then with 31 inch tires you should be going about 60 at 2500 RPM,72 at 3000,84 @ 3500 and 96 at 4000 RPM.Forget overdrive. 4000 Rpm is where a stock '69 350 gets it top NET horsepower (200HP). I don't know what motor yours has,but 4000 will not "blow up" any healthy 350.Mine goes to 5000 on a regular basis,and if it had a different cam would happily go to 5500. __________________ '69 GMC C2500 Custom Camper, 8 1/2' bed, New GM 350, NP 435 Close Ratio 4spd. Trans., 3.73 Dana-60 open.Camper and Trailer wiring, PS, PB, AC, tach , three gas tanks, stereo speakers, 2nd owner, Work-Truck supreme.



Register or Log In To remove these advertisements.

Register or Log In To remove these advertisements.