Rear ratio change !!!!
Thread Starter
Racer
Joined: Sep 2004
Posts: 482
Likes: 1
From: Brandon Manitoba
Rear ratio change !!!!
I just removed the rear end from my 80 and I am going to be getting rid of the 3.07 ratio. I am back and forth between the pros and cons of a 3.55 and a 3.74. Once I make my chioce I know that I must also change a gear in my automatic tranny to correspond to the new ratio. Where can I purchase this gear and will they know the appropriate part for my chosen ratio ? Thanx Brent
Instructor
Joined: Feb 2005
Posts: 147
Likes: 0
OK.......If U don't plan on putting in an O/D trans & if U plan on driving it alot at high speeds, You'll be working your engine to a slow death. If your set on upping that ratio.....go with the 3:55. It's gonna bump up your R's to approx. 800 more at about 65mph. This will be hard on your engine if it stays stock or if it's got high milage. However, a mildly massaged motor casn handle the extra R's. Good Luck! 
Drifting
Joined: Oct 2004
Posts: 1,496
Likes: 1
From: Lafayette Louisiana
Originally Posted by bams12
I just removed the rear end from my 80 and I am going to be getting rid of the 3.07 ratio. I am back and forth between the pros and cons of a 3.55 and a 3.74. Once I make my chioce I know that I must also change a gear in my automatic tranny to correspond to the new ratio. Where can I purchase this gear and will they know the appropriate part for my chosen ratio ? Thanx Brent
Drifting
Joined: Oct 2004
Posts: 1,496
Likes: 1
From: Lafayette Louisiana
Originally Posted by cruzzin-style
I think he's refering to the speedo gear to have the speedometer & odomoter correct. That would be my guess. 
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Melting Slicks
Joined: May 2004
Posts: 2,002
Likes: 17
From: Inlet Beach, FL
If it's Speedometer Gears you're talking about Dr. REBUILD has them in his catalog. 1961-1981 are listed so you might be in luck.
I know they have a website, but I can't find the URL in the catalog. Try typing "Dr. REBUILD" into your search engine. Or you can call them at (203) 366-1332 for tech and product assistance.
I know they have a website, but I can't find the URL in the catalog. Try typing "Dr. REBUILD" into your search engine. Or you can call them at (203) 366-1332 for tech and product assistance.
Race Director
Joined: Jan 2003
Posts: 15,175
Likes: 86
From: State of Confusion
Assuming you are running 27" tall tires (255/60R15), I'm figuring (with your current 3.07s) you are turning just over 2500 RPM at 60 MPH:
with 3.55s, it'd be just over 2900, and with 3.73s, it'd be almost 3100.
with 3.55s, it'd be just over 2900, and with 3.73s, it'd be almost 3100.
Pro
Joined: Feb 2003
Posts: 582
Likes: 0
From: Ashaway RI
Check out smoke em up.com. There is a section to figure out what RPMs you will be running with different gear ratios. Check out bowling and grippo to see how many tooth gear you will need. Your local Chevy dealer can order whatever tooth gear you need.
