heavyduty or std. axle?

[Tom S.]

I have figured out with the help of several people on the message board that I have a 4:11 ratio and I found the tag on the storage comp. and rear axle stating it was a posi. How do I identify it as a heavy duty or std? Also what year model carriers will fit the 69.I want to gear it up so that I can do some road trips.Also what do you think about going to a 3:08 or 3:36? I would appreciate any and all input.

Thanks Tom

[Mark #28455]

Re: heavyduty or std. axle?

heavy duty means big block - had the bolt on caps for the U joints instead of the U bolt type and FB code on the case. Just because you have the sticker in the car doesn't guarantee the car had positraction as they put those stickers in every car, but the 4.10 ratio was only available in a posi. You can swap in any differential from '63 to '79 (they all look the same and are cast iron) but the '63 - '64 are internally less desirable. '70 and newer are all posi rears. You must also look at the input yoke on the rear as there are two sizes. The 1969 4 speed cars used the smaller one which was only used on stick cars till about 1971. If you get the larger yoke, you'll need to get a special U joint to adapt it. The 3.08 and 3.36 are nice "driver" ratios and are cheap and easy to get. The 3.55 is a nice all around performance gear.

[Duke W.]

Re: heavyduty or std. axle?

There is no such thing as "standard" and "heavy duty" rear axle assemblies.
As previouslly pointed out, big blocks have "cap type" side yokes versus "strap type" on small blocks. The OE internals were the same for BBs and SBs.

Current replacement limited slip differential assemblies are available from Eaton (original clutch type ) or Auburn (cone type) for all '63 to 79 Corvette rear axles. There are two case sizes depending on ring and pinion ratio - one for 2.73 to 3.70, and another for 4.11 and up.

Current aftermarket replacement ring and pinions are available with 31 spline drive pinions. If installed in 63-64 carrier with original 17 spline drive pinions, a later 31 spline companion flange will be required. There are two 31 spline companison flanges sized for two different u-joint diameters, which were discussed in a recent thread.

Choosing axle ratio is subjective. A 4.11 with a CR trans is like a five speed without fifth. A 3.08/CR trans is like a five speed without first. WR trans versions usually work well with lower numerical gears, but have a big gap between third and fourth gears.

If you spend more time on road trips than drag strips, you will probably come to appreciate "taller" (lower numerical) final drive gears.

Duke

[Tom S.]

Re: heavyduty or std. axle?

Mark and Duke
Thanks for your response. Would auto salvage yards be a good place to start a search for a different carrier? I want to keep the 4:11 I have for the future resale,so I don't want to really change the gears out.But I would like to get it geared a little better. Thanks IN ADVANCE.

Tom

[Mark #28455]

Re: heavyduty or std. axle?

Unless your local salvage yard has Corvettes, you're not likely to get parts there. Try Contemporary Corvette in Bristol, PA they ship mall over the country. Expect UPS to be about $60 to $80.

[John G.]

Re: heavyduty or std. axle?

I bought a '72 3:08 pumpkin from Dave's Auto Wrecking, located in Placentia, CA. Price was $400 and included the side yolks. I figure to use the 3:08 on long road trips, especially between CA and WA. The 4:11 gear presently in my car is great for anything other than steady state freeway driving. A few more mpg wouldn't hurt either .. ! ..