1972 LT-1 Differential / Rear Axle types

[Michael C.]

I just had my 1972 LT-1 with A/C judged at Nationals and was told my differential / side yokes were not typical. They use the U-Bolts to attach to the half-shaft U-Joints. I was told they should be the Big Block HD variety, which use Caps and Bolts instead of the U-Bolts to attach to the half-shafts.

I researched this issue in the AIM for 1972 and compared some build sheet codes I have for 1972 LT-1's and a ZR-1, and this is what I came up with:

The AIM calls out the Diff. Carrier Assy. as "GV4" -- P/N 3969582 on page UPC 4 - Sheet A2, and shows the U-Bolt attaching hardware for the side yokes.

Near the LS5 Big Block section, it calls out the Diff. Carrier Assy. as "GS4" -- P/N 3993476 on page UPC GS4 - Sheet A1, and shows the Caps and Bolts attaching hardware.

A survey of some 1972 build sheets yielded the following:

Early LT-1 serial 278 Build Date: 8/?/71 Rear Axle Code: 2VGS410 Gear Ratio: 3.70

LT-1 Coupe Build Date: 5/15/72 Rear Axle Code: 2VGV4AA Gear Ratio: 4.11

"Last ZR-1" serial 26476 Build Date: 7/?/72 Rear Axle Code: 2VGV4AA Gear Ratio: 4.11

LT-1 A/C serial 26683 Build Date: 7/20/72 Rear Axle Code: 2VGV7AA Gear Ratio: 3.55

This information suggests that the U-Bolt type yokes/differentials were used on many LT-1's in 1972, and that not all had the GS4 type yokes.

Can anyone shed some light on this? I believe my Differential and yokes to be original to my car which I have owned since 1991.


Thanks!

[Edward J.]

Re: 1972 LT-1 Differential / Rear Axle types

Mike, A few years ago at a Fla. regional there was a 301 mile 72 ZR1 a member sent me some photos of the car and there is a pic of the rear half shafts with bolt in caps, I really have no VIN on the car.

[Kevin G.]

Re: 1972 LT-1 Differential / Rear Axle types

The tank sticker from my 20942 05/10/72 built LT-1 AC car sheet reads 2VGV7AA 3:55 ratio.

I'm going to side with the chassis judges on this one.

[Michael C.]

Re: 1972 LT-1 Differential / Rear Axle types

Kevin, you don't say, but I assume from your post that your car has Caps and Bolts?

If so, then maybe what I need to know is what, if anything, these axle codes on the build sheet signify. I understood from the AIM that a "GV" rear end had the U-bolt hardware, and a "GS" rear end had the caps and bolts as I explained above.

Apparently this might be incorrect. So, Does anyone know what these axle build sheet codes signify?

[Joe L.]

Re: 1972 LT-1 Differential / Rear Axle types

I just had my 1972 LT-1 with A/C judged at Nationals and was told my differential / side yokes were not typical. They use the U-Bolts to attach to the half-shaft U-Joints. I was told they should be the Big Block HD variety, which use Caps and Bolts instead of the U-Bolts to attach to the half-shafts.

I researched this issue in the AIM for 1972 and compared some build sheet codes I have for 1972 LT-1's and a ZR-1, and this is what I came up with:

The AIM calls out the Diff. Carrier Assy. as "GV4" -- P/N 3969582 on page UPC 4 - Sheet A2, and shows the U-Bolt attaching hardware for the side yokes.

Near the LS5 Big Block section, it calls out the Diff. Carrier Assy. as "GS4" -- P/N 3993476 on page UPC GS4 - Sheet A1, and shows the Caps and Bolts attaching hardware.

A survey of some 1972 build sheets yielded the following:

Early LT-1 serial 278 Build Date: 8/?/71 Rear Axle Code: 2VGS410 Gear Ratio: 3.70

LT-1 Coupe Build Date: 5/15/72 Rear Axle Code: 2VGV4AA Gear Ratio: 4.11

"Last ZR-1" serial 26476 Build Date: 7/?/72 Rear Axle Code: 2VGV4AA Gear Ratio: 4.11

LT-1 A/C serial 26683 Build Date: 7/20/72 Rear Axle Code: 2VGV7AA Gear Ratio: 3.55

This information suggests that the U-Bolt type yokes/differentials were used on many LT-1's in 1972, and that not all had the GS4 type yokes.

Can anyone shed some light on this? I believe my Differential and yokes to be original to my car which I have owned since 1991.


Thanks!

Michael------


You left out a VERY important and relevant piece of information. What is the axle code for your car? This is the code STAMPED on the bottom of the carrier housing.

[Michael C.]

Re: 1972 LT-1 Differential / Rear Axle types

Joe,

My Code reads AAW 179 E 2

[Joe L.]

Re: 1972 LT-1 Differential / Rear Axle types

Joe,

My Code reads AAW 179 E 2

Michael------


Your axle code of "AA" denotes a 3.55:1 axle ratio unit. The "AA" coded 3.55:1 was the only 3.55:1 axle used for 1972. Consequently, it would have been used for both big blocks and small blocks and, thus, I fully expect it was configured for use with cap-and-bolt u-joint retention.

On the other hand, though, I just don't understand why someone would have serviced this rear end with u-bolt type stub axles rather than the cap-and-bolt.

[Paul O.]

Re: 1972 LT-1 Differential / Rear Axle types

Michael

What type of fastening system is used on your drive shaft u-bolts or bolt and straps/caps and bolts. If they are u-bolts for me that would bring up the question is the rear drive train original to the car. As you have stated you have owned the car since 1991 in the 19 years before your ownership many thing could and did happen. Have you checked the date of the differential and cover? If so what are the dates? When we judge a car we judge to a standard of normal factory production (NFP). If your car is non-typical production it is the owners responsibility to to prove that variation from NFP.

[Joe L.]

Re: 1972 LT-1 Differential / Rear Axle types

Michael

What type of fastening system is used on your drive shaft u-bolts or bolt and straps/caps and bolts. If they are u-bolts for me that would bring up the question is the rear drive train original to the car.

Paul------


It would be interesting to know but the only way the car could use u-bolt attachment for the driveshaft u-joints would be if a conversion u-joint or modified driveshaft was also used.

[Paul O.]

Re: 1972 LT-1 Differential / Rear Axle types

Joe

I agree but stranger things have been done before. We need to have all the information before a good judgement can be made. But even then we as a whole do not have information before 1991 on what may or may not have happened to this car.

[Kevin G.]

Re: 1972 LT-1 Differential / Rear Axle types

Mike,

You're right. Sorry, I did forget to include that it does caps and bolts. I'd be interested in hearing of a documented LT-1 example with U bolts?

[Michael C.]

Re: 1972 LT-1 Differential / Rear Axle types

Paul and Joe,

Thanks for your help on this, and Paul, I did indicate the stamping on the diff carrier was AAW 179 E 2

I can't answer the driveshaft yoke question until Tuesday when I can get under the car again, but I believe the shaft to be original as well. All these components had about 20 years worth of rust on them when I pulled and restored them in 1995, and I didn't alter anything on the Diff, or change the driveshaft.

It may be a mystery which cannot be solved, but can anyone tell me some good reasons to change out the side yoke stub axles besides a few judging points? If the U-Bolt type axles could severely affect the safety and/or performance of the car, I'd probably have enough reasons to replace them with Cap and Bolt types.

Thanks to all...

Mike

[Joe L.]

Re: 1972 LT-1 Differential / Rear Axle types

Paul and Joe,

Thanks for your help on this, and Paul, I did indicate the stamping on the diff carrier was AAW 179 E 2

I can't answer the driveshaft yoke question until Tuesday when I can get under the car again, but I believe the shaft to be original as well. All these components had about 20 years worth of rust on them when I pulled and restored them in 1995, and I didn't alter anything on the Diff, or change the driveshaft.

It may be a mystery which cannot be solved, but can anyone tell me some good reasons to change out the side yoke stub axles besides a few judging points? If the U-Bolt type axles could severely affect the safety and/or performance of the car, I'd probably have enough reasons to replace them with Cap and Bolt types.

Thanks to all...

Mike

Mike------


There is no functional reason for you to change the stub axles. The u-bolt stub axles will work just fine. I believe some u-bolt stub axles were used for 1970 LT-1. I know, for sure, they were used for 1969 L-46 (which had about the same power and torque as 1972 LT-1). They were also used for ALL 1963-67 small blocks, regardless of horsepower.

I'm still not 100% convinced that they're not original to your car. The primary, if not only, reason for replacement of stub axles is wear on the inner ends of the axle shafts. Unless this car accumulated a lot of miles in the period before you owned it, I just don't see why this would have become necessary.

[Paul O.]

Re: 1972 LT-1 Differential / Rear Axle types

Mike

Should have stated casting dates for those parts are they also dated correctly for the car.

[Gary R.]

Re: 1972 LT-1 Differential / Rear Axle types

Mike------There is no functional reason for you to change the stub axles. The u-bolt stub axles will work just fine. I believe some u-bolt stub axles were used for 1970 LT-1. I know, for sure, they were used for 1969 L-46 (which had about the same power and torque as 1972 LT-1). They were also used for ALL 1963-67 small blocks, regardless of horsepower.I'm still not 100% convinced that they're not original to your car. The primary, if not only, reason for replacement of stub axles is wear on the inner ends of the axle shafts. Unless this car accumulated a lot of miles in the period before you owned it, I just don't see why this would have become necessary.[/COLOR]

I agree with Joe, ....... those axles are fine. I have yet to see one break at that point and I see a lot of abused vette diff's. My son sheared the inner & outer solid spicer 1350 joints last year on his 75 st/strip car but that was hard use.