NSW Corvettes

Technical Tips => Transmissions - Differentials => Topic started by: DA383 on October 13, 2009, 03:33:44 PM

Title: Diff ratio ?
Post by: DA383 on October 13, 2009, 03:33:44 PM

does any body know how to work out diff ratio or if there is any numbers on the out side of the diff other than dismantling the diff

Title: Diff ratio ?
Post by: Reklaw on October 13, 2009, 03:48:40 PM

Hi DA383. What year model is your car? I found the following on a yankee web site. There's probably a similar table for whatever model you have.

"You will need to check under the rear differential for the ratio code :
1970 Corvette (Late 1969) Axle Ratios

Code Ratio Application
CAK 3.36 Standard (350)
CAL 3.08 Standard (350)
CAM 3.36 Positraction (350)
CAN 3.55 Standard(350)
CAO 3.70 Positraction (350)
CAP 4.11 Standard (350)
CAS 3.70 Standard (350)
CAT 3.08 Heavy Duty Positraction (454)
CAU 3.36 Heavy Duty Positraction (454)
CAV 3.08 Standard (454)
CAW 3.08 Standard (454)
CAX 3.36 Heavy Duty Positraction (454)
CAY 2.73 Positraction (454 Turbo-Hydra-Matic)
CAZ 3.55 Heavy Duty Positraction (454)
CFA 3.70 Positraction (454)
CFB 4.11 Heavy Duty Positraction (454)
CFC 4.56 Heavy Duty Positraction (454)
CLR 3.36 Standard (454)

It will be located on the bottom of the differential."

Title: Diff ratio ?
Post by: Reklaw on October 13, 2009, 03:52:52 PM

Here's another site to check out (assuming yours is a C3)
http://www.corvettec3.ca/axle.htm

Title: Diff ratio ?
Post by: DA383 on October 13, 2009, 04:07:33 PM

Thanks very much for your quick response, my car is a C3 1978 vin no match indy pace car.

Title: Diff ratio ?
Post by: gtc on October 13, 2009, 11:52:32 PM

According to "Corvette by the Numbers", the 1978 rear axle code takes the format: XX Y 999 Z

where:

XX is diff ratio, where: OK=3.08; OM=3.36; OH=3.55; OJ=3.70

Y is assembly plant, where B=Buick; C=Buffalo NY; D=Cadillac; G=Detroit Gear & Axle;  K=McKinnon Industries; M=Pontiac of Canada; O=Oldsmobile; P=Pontiac; W=Warren MI

999 is day of year, where 218 = August 6, 1978

Z is shift number, where 1=first; 2=second; etc

Title: Diff ratio ?
Post by: DA383 on October 14, 2009, 08:42:06 AM

Thanks all I have found the letters on the bottom of the diff

Regards
Dennis Anderson

Title: Diff ratio ?
Post by: RHD.68.l89 on October 14, 2009, 05:42:42 PM

The code on the diff does not necessarily give the ratio inside. a PO may have changed the ratio.
You may have to jack up the rear end (both wheels) and count the rotations of the wheels to get one turn of the tailshaft.