Rear axle gearing for 1971 LT-1

[Mark Chance]

I'm considering purchasing a 1971 LT-1. Can anyone tell me what the rear axle ratio options were for the 71 LT-1?

Thanks,
Mark

[Joe L.]

Re: Rear axle gearing for 1971 LT-1

Mark-----

With a wide ratio 4 speed (M-20), the standard ratio was 3.55:1. Optional ratios with this transmission were 3.36:1 and 3.70:1.

With the close ratio 4 speed (M-21), the standard ratio was 3.70:1. Optional ratios were 3.55:1 and 4.11:1.

The actual rear axle ratio installed in the car, assuming that the current differential carrier case is original to the car AND still has its original gears within it, will be coded in a stamping found on the bottom of the case, just forward of the cover. There will be a series of characters and the original ratio will be a 2 alpha character code beginning with "A" or "L".

[Mark Chance]

Re: Rear axle gearing for 1971 LT-1

Joe -

Thanks much for the info. The differential housing is off a 1972 (the rest of the numbers match and the owner has no idea why the differential housing isn't original - could it possibly have come off the assembly line this way)?

The car has a M21 close ratio. Was there a specific ratio the LT-1 engine with the M21 4 speed should have (3.70:1)? Again, thanks.

Mark

[Joe L.]

Re: Rear axle gearing for 1971 LT-1

Mark-----

The standard ratio for LT-1 and M-21 was 3.70:1. But, such a combination could have been optionally equipped with either the 3.55 or the 4.11.