1972 LT1 - Question

[Greg Y.]

I recently purchased a 1972 convertible LT1. I got the car with its original window sticker, Corvette Order Copy and Protecto-Plate as well as the original dealer order sheet. The car was ordered with the ZW4 wide-ratio transmission and 3.55 "standard" rear gears per the dealer order sheet. The Corvette Order Copy and the Protecto-Plate (as well as the matching rear-end in the car) reflect that the car was equipped with a 3.70 rear ratio, which I understand from the Powertrain chart to be the "performance" rear axle ratio for the M-20, wide-ratio transmission in the 1972 Corvette LT1. My question relates to the fact that this rear-axle ratio is not mentioned on the window sticker as a ZQ9 "Performance Axle Ratio" option or called out in any way on the window sticker, I was thinking that the 3.70 ratio would have been annotated on the window sticker. Is there a chance that it was somehow missed or is there another reason why this would not have been annotated on the window sticker? Thanks in advance for any thoughts or ideas.

[Bill C.]

Re: 1972 LT1 - Question

I'm not an LT-1 expert by any means ---
but I always thought that when you moved into the 3.70 /4.11 rears the cars were equiped with a M-21.
Someone told me that 3.55 was that pivot point for a M20/M21, depending on the engine combo....

The window sticker will show the 3.70 upgrade on it - as well as the Protecto-Plate.

seems kind of strange that there is different info on the documents...

[Jerome P.]

Re: 1972 LT1 - Question

For what it is worth, my '72 LT1 has air conditioning and is equiped with the following original rear end: (I understand an LT1 W/AC did not have an option for any gear other than the 3.55:1 and the M20 transmission)

AAW143 1E
AA = 3.55:1 Corvette positraction axle
W = Warren, MI plant
143 = Day of year: May 22, 1972
1 = Shift
E = Positraction Source: Eaton

I would think if it had the 3.70 gears it would be listed on all the doc's. Who knows why things happen.

Sounds like you found a great car.

[Mike E.]

Re: 1972 LT1 - Question

Greg--
I recently documented 3 different late 71 LT-1 cars, all two owner, all with less than 30,000 miles. The latest of the three, 36 cars from the end of production, has a 3.70 in it that is dated right for the car, etc., but the tank sticker says 3.55. FWIW
By the way, there's an article on the three with all the dates, etc., coming in a future Restorer.

[Mike G.]

Re: 1972 LT1 - Question

i was always told the stock gear for the lt1 was a 370. if you ordered an optional rear end you could get a 355 or a 411. my 72 lt1 has a 370 and so does my 70 lt1. dont know about the 72 lt1 ac car since there were so few.

[Terry M.]

Re: 1972 LT1 - Question

Both Jerome and Mike Green are right about rear differential chouces (or lack of choice in the case of C60).

[Greg Y.]

Re: 1972 LT1 - Question

Thank you all for your thoughts and input. Mike I would guess that if both of your cars have the 3.70 rear gear that you have M-21's in both, unless they were ordered with optional gears. From my understanding and refering to the Powertrain charts of the time, the LT1 could be had with either the M-21/3.70 combo or the M-20/3.55 combo at no charge. When a customer ordered the M-20 with either 3.36 (Economy) or 3.70 (Performance) or with the M-21 3.55 (Economy) or 4.11 (Performance) then these gears were considered optional ratios per either transmission and should be annotated as such. I also have a 1972 LT1 with factory a/c and it does have the M-20 with 3.55 combo and as Terry states, that was the only way it could be ordered from what I understand. My question related to the fact that on the dealer order sheet (filled out at the dealership by the ordering customer or dealer order person, in the case of my convertible by the individual personally ordering the car), it states that the "standard" ZW4 wide-ratio M-20 was ordered and the 3.55 rear ratio was also annotated on the order sheet, one of the standard combinations available. Yet the car was built with a 3.70 rear ratio, which is confirmed by both the Corvette Order Copy and the POP (the date on the rear matches the POP) and thus I was wondering why it would not be annotated on the Window sticker. I guess as most people contemplate, it just happened and who knows why.

[Mike G.]

Re: 1972 LT1 - Question

correct, both cars have m21