Two questions here really. I found production numbers of:

49,213 Base Corvette Sport Coupes built in '77

41,231 with auto
2,060 with manual

These totals don't add up to 49,213.

First question is why the difference of 5,922? Maybe the numbers I found are not accurate? Either way it would seem that the 4 speed is a pretty low production number.

Second question is what type the original 4 speed in a '77 would be? Is it a close ratio - what brand etc.

Thanks in advance for any info

Adam

 

The 2060 are with optional M21, the missing 5922 cars had the M20 box.

 

Revised

Can anyone tell me a way to identify (other than driving it) the difference between a wide and close ratio trans?

Thanks,
Adam

 

Adam

This gets a little lengthy and you can conclude there is no easy answer so I share much of what I've concluded on the subject. And I assume your asking about a method that could be used without pulling the transmission and counting gear teeth. Actually there are two methods...last character in the production code and the broadcast code.

The Muncie four-speeds used through 1974 included a letter for the "ratio code" in the production code but in 1975 Borg Warners were equipped in Corvettes. There is some dispute in what I've read whether the last digit in the B/W production code is shift or ratio code. But if its ratio code it would be interpreted as this

1 = M20
2 = M21

In terms of broadcast codes, tranny broadcast codes were used to call out a particular four-speed and installed on a vehicle. I have worked out those codes for 1978 but have yet to find a build sheet or low-mileage 1977 with the codes still visible on four-speed transmissions. I've attached a link to an article that may offer some background that can help you identify what to look for on four-speeds of 1977. Note that in the article I refer to the last digit in the numerical code as the "shift" code. At the time I wrote this, there was conflicting sources of what this code meant and I haven't looked at enough four-speeds to determine the correct meaning. But the code is off an M21 four-speed it reconciles nicely.

I do know that the M38 automatic was code AM in 1977 but that doesn't help you. In 1978, that code was STL...so you understand they changed from year to year.

The Fourspeeds of 1978

 

Thank you for posting that info...good stuff!

I didn't realize that there wasn't a cut and dry method for this. After reading this I'm guessing it's a M20 due to the fact the car is a L48. It could have been changed out at some point I'm sure. I'll look into it closer in the next couple of days.

Adam

 

Build sheet or window sticker would be easiest method...if available but have assumed they are not available...so we tick down to other methods.

Keep us posted