66 L79 Convertible - Rear Axle Question

[Scott V.]

Hi

I recently purchased a numbers matching L79 convertible 4 speed that underwent a frame off restoration 12 years ago. I am waiting for the car to be transported to me. The current owner says the car has a 3:08 posi rear that is original to the car as far as he knows. The engine, VIN, transmission numbers all match but I do not have the numbers from the rear.

Everything I am seeing shows that rear option was not available in 1966 with the L79. I'm thinking it would more likely have been the 3:55 gearing and maybe the current owner is incorrect.

Does anyone know if it would have been possible to order that 3:08 rearend with the L79?

Thanks

Scott

[Mark F.]

Re: 66 L79 Convertible - Rear Axle Question

Hi I recently purchased a numbers matching L79 convertible 4 speed that underwent a frame off restoration 12 years ago. I am waiting for the car to be transported to me. The current owner says the car has a 3:08 posi rear that is original to the car as far as he knows. The engine, VIN, transmission numbers all match but I do not have the numbers from the rear. Everything I am seeing shows that rear option was not available in 1966 with the L79. I'm thinking it would more likely have been the 3:55 gearing and maybe the current owner is incorrect. Does anyone know if it would have been possible to order that 3:08 rearend with the L79? Thanks Scott

Hi Scott,

Welcome to the Technical Discussion Board (TDB)...

The GM Heritage Center "Hobby Kit Book" for '66s does not show a 3:08 available on an L79.
See page 18 of 105 of the pdf file when it opens up - which has the Power Teams chart...

https://www.gmheritagecenter.com/docs/gm-heritage-archive/vehicle-information-kits/Corvette/1966-Chevrolet-Corvette.pdf

good luck with your purchase!

[Duke W.]

Re: 66 L79 Convertible - Rear Axle Question

For '66 L-79 was available with either the CR or WR four speed, and neither transmission choice offered a 3.08 axle. You can find all the details in the 1966 Corvette Vehicle Information Package that you can download from the GM Heritage Web site.

You should also procure a '66 Assembly Instruction Manual, Chassis Service Manual, and Chassis Overhaul Manual.

Once you get the car you can check the axle code to determine the original axle ratio and check that the date is appropriate for the car's build date, but that doesn't mean the axle or R & P was not replaced at some point.

Assuming, the installed speedo gears are correct for the installed axle ratio and it has tires close to the original's 775 revs/mile:

Axle ratio = revs @ 60/775

Duke

[Harry S.]

Re: 66 L79 Convertible - Rear Axle Question

The ordering dealership could have COPO'd the car or installed the gears upon arrival. I would not worry about it until you get the car. Check the stamping for the ratio and the date.

[Gary B.]

[Scott V.]

Re: 66 L79 Convertible - Rear Axle Question

For '66 L-79 was available with either the CR or WR four speed, and neither transmission choice offered a 3.08 axle. You can find all the details in the 1966 Corvette Vehicle Information Package that you can download from the GM Heritage Web site.

You should also procure a '66 Assembly Instruction Manual, Chassis Service Manual, and Chassis Overhaul Manual.

Once you get the car you can check the axle code to determine the original axle ratio and check that the date is appropriate for the car's build date, but that doesn't mean the axle or R & P was not replaced at some point.

Assuming, the installed speedo gears are correct for the installed axle ratio and it has tires close to the original's 775 revs/mile:

Axle ratio = revs @ 60/775

Duke

The ordering dealership could have COPO'd the car or installed the gears upon arrival. I would not worry about it until you get the car. Check the stamping for the ratio and the date.

Thanks all, I think it is most likely the 3:36 as that appears to be the standard ratio offered with the 4 speed and L79. Its not a highly optioned car or as noted someone has changed the gears in the past. Attached pictures of the car since we all like pictures

[Mark F.]

Re: 66 L79 Convertible - Rear Axle Question

Hi Scott,

Make sure he gives you the spare tire tub (unless he just had it out for the photos)...
nice looking car!
enjoy...

[Timothy B.]

Re: 66 L79 Convertible - Rear Axle Question

Beautiful car, Scott

[Scott V.]

Re: 66 L79 Convertible - Rear Axle Question

Just to provide a final update on the car. I have received it, as good as I had hoped. Back to the axle ratio, it has a very faint AO stamp with 14 66 date stamp so likely original to the car and originally 3.70 gears. However based on confirmation from the PO and my speed/RPM calculations here (https://www.angelfire.com/fl/procrastination/rear.html) it has a close ratio M21 and 3.36 gears.

[Duke W.]

Re: 66 L79 Convertible - Rear Axle Question

'66 L-79 with M-21 had a standard 3.70 axle with 4.11 optional. 3.36 was standard with m-20 and 3.55 was optional

The speedometer is set up for 760 revs/mi tires so:

Axle ratio = Revs @ 60/760

[Scott V.]

Re: 66 L79 Convertible - Rear Axle Question

'66 L-79 with M-21 had a standard 3.70 axle with 4.11 optional. 3.36 was standard with m-20 and 3.55 was optional

The speedometer is set up for 760 revs/mi tires so:

Axle ratio = Revs @ 60/760

That matches up I see 2500 rpm at 60mph so someone swapped in 3.36 gears at some point.

[Eric P.]

Re: 66 L79 Convertible - Rear Axle Question

Scott,
Not only do we like seeing the pictures, but we also really like seeing new members especially with their Corvettes at NCRS meets.

Welcome to the NCRS, as you can see from your first post there is a wealth of knowledge in this membership.

Great looking '66!
Eric Patty