Topic: Re: Gear Ratios
in Forum: C3 Driveline Components
Already a Member?
Click Here to Login
Not yet a Member?
Click Here to Register for Free!
Ok Feet, here's how to check the rear end gear ratio:
Get rear of your Vette up on two jack stands.
Place the trans in Neutral.
Put chalk marks at the 6:00 position on the inside of your rear tires.
Put a chalk mark on the bottom of your rear U-Joint or driveshaft.
Then, by hand, carefully rotate the driveshaft and count the turns it makes until the rear tires make exactly one revolution.
The number of turns of your driveshaft will equal your rear end gear ratio.
Is this something you can do?
John
BTW, if you really have a 4.56 rear gear ratio, you should be able to take off from a dead stop in 3rd. or 4th gear without too much trouble. I had a 4.88 rear for awhile and 4th gear was like an "All purpose gear". The first 3 gears were not all that necessary for just cruising.
1973 BB 4-Speed Coupe Project Car
2009 Z06 Mostly Stock
SPONSOR AD:: (Our Sponsors help support C3VR)
Lifetime MemberModerator
Duncanville, TX - USA
Joined: 11/8/2003
Posts: 20214
Vette(s): #1-1974 L-48 4spd Cp Med Red Metallic/Black deluxe int w/AC/tilt/tele./p/w-p/b/
Am-Fm/map light National/Regional/Chapter NCRS "Top Flight"
#2-1985 Bright Red/Carmine Cp.L-98/auto
Member: NCRS, NCRS Texas, Corvette Legends of Texas
VETTERBOB said: Definitely 3:55.i run them with my T 400 auto. Rpm matches.
I think that should tell the tale....
Without knowing the tire diameter, there's no way to calculate the ratio from just RPM/MPH. Jacking it up and spinning the tires, and counting the driveshaft revolutions will get you just about as close as you can without actually looking at the gear set.
There are only a certain number of ratios that will fit into the stock(original) diff housing. In this case, I think the 3.55 is all that would work, without changing the diff carrier. The 3.70 and 4.11 ratios that were available for the year took a specific carrier that would only be used for those two ratios. However, we also do not know if any of the stuff has been changed, so really, it's a crap shoot, and we're all just guessing....well...everyone except Bob, who happens to have the 3.55 gears, and turns the same RPMS at the same MPH....
Joel Adams
C3VR Lifetime Member #56 
My Link 
(click for Texas-sized view!) NCRS
"Money can't buy happiness -- but somehow it's more comforting to cry in a CORVETTE than in a Kia"
20111115155328r.jpg)
My stock Silver Ann and the Pace car both with the L-82, 4 speed and 3.70 tachs 3500 somewhere between 60 -65. I'll pay closer attention next time I'm out.
Maybe you got the 4.10 if doing 3500 right at 60mph. Converting to 4 spd they may have wanted that extra get up and go.
|UPDATED|4/15/2014 2:35:25 AM (AZT)|/UPDATED|
Maybe you got the 4.10 if doing 3500 right at 60mph. Converting to 4 spd they may have wanted that extra get up and go.
|UPDATED|4/15/2014 2:35:25 AM (AZT)|/UPDATED|
Lifetime MemberHot Springs, AR - USA
Joined: 4/24/2004
Posts: 3236
Vette(s): 69 Conv #'s match 427, TKO-600/.64, 3.36HD-Posi, HT, T/T, PS, PB, PW, SP, Leather, Comp XE264HR & Roller Rockers & Lifters, Air-Gap RPM intake, Holley St Av 770 VS, MSD 6AL+Dist+Blaster SS, K&N, Jet-Hot Hooker Side-Pipes, Steeroids, Al Rad, Spal Fans
JohnRR said: Ok Feet, here's how to check the rear end gear ratio:
Get rear of your Vette up on two jack stands.
Place the trans in Neutral.
Put chalk marks at the 6:00 position on the inside of your rear tires.
Put a chalk mark on the bottom of your rear U-Joint or driveshaft.
Then, by hand, carefully rotate the driveshaft and count the turns it makes until the rear tires make exactly one revolution.
The number of turns of your driveshaft will equal your rear end gear ratio.
Is this something you can do?
John
BTW, if you really have a 4.56 rear gear ratio, you should be able to take off from a dead stop in 3rd. or 4th gear without too much trouble. I had a 4.88 rear for awhile and 4th gear was like an "All purpose gear". The first 3 gears were not all that necessary for just cruising.
Adding a little more precision Make a chalk mark on the driver shaft where it stops Using a sewing tape to measure the distance between the two marks and divide by the circumference to get the fractional portion. Example. If the the circumference is 5". And your final mark is 1.9" past your starting mark you would have a 3.36, 2.6 =3.55, 3.5"= 3.70. Actually even better in centimeters.
in Forum: C3 Driveline Components
SPONSOR AD: (Our Sponsors help support C3VR)