Jerapais 69

Need some help guys. My L36 came with an M21 close ratio and a G95 RPO which means "rear economy". ALL listed on the tank sticker. Any literature I've seen states that ONLY the turbo-hydromatic auto trannys could have a highway intended 2.73:1 rear end gear ratio.
Either this is very rare or something is wrong. Guy before me put a '63 3.70 in it. Anyone ever hear of this? is it possible? If not, the tank sticker is wrong!

Gordonm

The economy gear for the M21 was a 3.08. The economy for the turbo 400 was the 2.73 gear. So yours should have the 3.08 in it.

Jerapais 69

Agree but does RPO G95 not mean 2.73:1? M21, G95, all on tank sticker. But after G95, all I can read is the word "rear".

garage-ghost

According to the gm specification guide G95 means 3.55 ratio.

http://www.gmheritagecenter.com/gm-h...t-Corvette.pdf

69 Chevy

2.20:1 first gear ratio coupled with a 2.73:1 differential has got to equal clutch slippage no matter how much torque the BB engine has. I doubt the factory allowed this combo.

Mike Ward

An M21 with a 2.73:1 couldn't get out of it's own way going downhill. All my documents indicate that G95 is the RPO for the economy diff but does not specify which numerical ratio.

Your car came with a 3.08 but the previous owner did you a favour by putting in a 3.70

Jerapais 69

Thx for all the help boys. J

Alwyn678

gbvette62

According to the 69 Corvette sales brochure, the economy ratio with the L-36 and a close ratio 4 speed, was the 3:08. 69 L-36's with the wide ratio 4 speed, and/or air conditioning, came with the 3:08 standard, and no economy rear was offered. 69 L-36 automatics came with a 2:73 rear, when the economy rear was ordered. Positraction was required when the economy rear axle ratio was ordered.

As far as installing a 63 3:70 rear in a 69, it is possible, but I'm not sure this would be an upgrade. The 63-64 rear is different internally, from the 65-79 rears. It is not as strong, and very few parts are available for it.