Looking at a 79 L82 4 speed car. I know the M21 was only available if you ordered the L82. Was there another 4 speed trans that came with the L82? How can I tell which one the car has? Thanks.

 

The base M20 wide ratio 4 speed.

M20s are stamped A on the tranny case. M21s are stamped with a B.

 

Thanks, Mike. Much appreciated.

 

In 79, a Borg Warner was installed not a Muncie. You need to check what transmission is in there.

http://pontiacpower.org/BW.htm

 

That is correct. My 1975 L-82 has a Borg Warner M21 origianal numbers for the car.

The first gear ratio was indicated by a 2-digit (paint?) code on the main case below the side cover. "HS" is a 2.64:1 wide ratio, and "HW" is a 2.43:1 close-ratio.

And I think (?) the Muncie to Borg Warner occurred around 1974.

 

As Mike wrote, the M20 was the base four-speed while the M21 was the option, both of which are the Borg Warner. However, what is stamped on the case is the broadcast code that is M20 = UH while the M21 = UK. Not sure about that A, B which I believe was the metal tag stamp on Muncies...in which case, ignore that. A buildsheet will also document what was installed in 1979 along with the window sticker.

Here's a photo of what to look for. This is from a 1979 March/April car. This 79 has an L82 M20 and you can see part of the green stamp and outline of the UH code

Just checked the 1973-74 NCRS technical manual and the Muncies did use the A,B in the assembly/date code while B/W used digits. 1973-74 last year for Muncie and first year for B/W.

 

what are the gear ratio differences of M20 and M21?

 

Base 4-speed ratios for 1979
2.64:1 1.75:1 1.34:1 1.00:1

Optional close ratio 4-speed ratios for 1979 (RPO M21)
2.43:1 1.61:1 1.23:1 1.00:1

The close ratio 4-speed was available ONLY with the L82 engine option. It had ZERO cost. Given the production numbers in 1979 I suspect that nearly all of the cars with the L82 engine and manual transmission were built with the M21 option.

 

At Bloomington Gold (last year) and this year at NCRS, we've judged a low mile 1979 with L82 M20 which is where that photo above was taken...very nice car!

 

I've wondered about that myself. This is the best estimate I've come up with, which I think is pretty close.

Based on the numbers I've compiled for over 2,000 1979 Corvettes, I estimate that about 10% of L48 cars left the factory with a 4-speed—but about 40% of L82 cars left so equipped. So the manual transmission was much more popular among the L82 crowd than with L48 buyers. That's interesting, but not surprising.

Taking this a little further, and according to Chevrolet records, there were 14,516 L82 Corvettes built in 1979. So 40% of 14,516 = 5,806 Corvettes that probably had the combination of L82/4-speed out of 53,806 total Corvette production. That's only about 11% of the cars that year.

Furthermore, Chevrolet records indicate that there were a total of 4,062 close-ratio 4-speeds installed. Since we know that all close-ratio gearboxes went into L82 cars, that leaves us with 5,806 - 4,062 = 1,744 estimated L82 cars that had the wide-ratio 4-speed.

So the breakdown estimate for 1979 would be...

L82/M21 = 4,062 -- about 70% of the L82/4-speed cars.
L82/M20 = 1,744 -- about 30% of the L82/4-speed cars.

Clearly, the close-ratio 4-speed was certainly the more popular choice for L82 buyers, but 30% of these buyers opting for the wide-ratio is far from meager.

Perhaps many of the wide-ratio buyers were attracted to the lower first gear of 2:64, rather than 2:43, for quarter mile/drag racing. The close-ratio buyers probably appreciated keeping 3rd and 4th gear closer together (less RPM drop during frequent shifting) to enhance and smooth out road-race type of driving.

Just speaking for myself, I like the M21 gearing.

That's my take.

--------------------------
1979 L82 M21 FE7
Classic White / Doeskin

 

Thanks for posting this update! I love 79s, and 4-speeds, though I had to buy two different Corvettes to get both in my garage.

I'd humbly suggest that the correlation is reversed, and the L82 was much more popular among 4-speed enthusiasts than the L48, with the transmission being more fundamental to the overall appeal of the car.

It could just be me, though.

 

any thoughts what mine is?
cannot find ant codes above, 79 L82

 

Let us try to determine which you have; close-ratio or wide-ratio 4-speed?

We really need to see the column to the left of your tank sticker remnant, shown in your pic above (post #12), which would show the transmission installed. Unfortunately, nature has long ago destroyed that portion of your sticker.

Significantly, though, I can barely see that your car had the 3.70 rear axle installed, as most L82 cars did. That doesn't answer your question, but if your sticker showed 3.36 rear axle, we could conclude your car had the wide-ratio 4-speed installed at the factory.

Noteworthy, according to Chevrolet records, 428 of the L82 buyers opted for both the wide-ratio 4-speed AND the 3.36 rear axle. In your case, we must continue our effort to answer your question.

Looking at your undercarriage pics, your transmission case no longer has the ink stamp (broadcast code) showing close or wide-ratio, as is explained, with an example shown, in post #8 above. With the gearbox installed, that is the only visible marking GM utilized to indicate close- or wide-ratio. That code was very helpful for assembly workers at the time, but my ink stamp is long gone as well. Thank you, hunt4cleanair for that pic. I wondered what that stamp might have looked like.

If you ever remove your 4-speed, the input spline would, I believe, have 2 rings around it to indicate a close-ratio unit.

Arguably, the most practical way to answer your question is by testing its function by following a simple procedure like the one I provide below. Such a test does require you to have a reasonably accurate speedometer and tachometer. I am also assuming you still have your 3.70 rear axle and still running about a 27.5 inch diameter (225/70-15) tire. Both are indicated on your tank sticker.

Drive out onto a highway, preferably with little traffic, and bring the car up to 70 mph, shift into fourth gear, and hold that speed while noting your RPM. Your tachometer should be reading about 3100-3200. This is true for either close- or wide-ratio boxes because fourth gear is the same for both; direct drive (1:1).

Note: If you are running at, say, 2900 RPM, then something is a bit off—but that's no problem—just adjust all numbers below down by about 200 RPM. It is the relative difference that is important here, as we shall see.

While holding that 70 mph speed, downshift to third gear, and note the increase in RPM. If you are now at about 3900-4000 RPM, then you have the close-ratio M21 transmission (due to the 1.23 third gear). If, instead, your engine is now running about 4200-4300 RPM, then you have the wide-ratio gearbox (due to the 1.34 third gear).

I hope this is helpful.

---------------------------
1979 L82 M21 FE7
Classic White / Doeskin

 

For $50 you can find out what was in there when it was made. I assume your partial vin is on your Borg Warner? since you are not the original owner it could have been changed but the odds I think are in your favor of being unmolested.

Contact GM Heritage for a copy of the invoice. It will look similar to mine:

 

Thank you, Bikespace.

There is no doubt some 1979 C3 buyers desired a 4-speed as their priority. But C3 sales statistics clearly show that L82 engines were far and away more appealing to buyers than 4-speed gearboxes.

Relatively few C3 buyers opted for 4-speeds in 1979; amounting to less than 20% of the cars. That is quite low for a choice that cost nothing.

In contrast, the L82 option was very expensive, adding $565 to the base price of a $10,220 new C3 in 1979. So it cost, by itself, more than 5% of the base price—yet about 28% of the buyers still opted to pay for it.

Consider also that, even among the L82 crowd, most (about 60%) of them chose the automatic transmission, according to my compiled data.

The manual transmission is far more popular today, now that C3 cars tend to be owned for their vintage/hobby appeal, rather than used as daily drivers.

Speaking for myself today, I love the 4-speed in my '79, and wouldn't want anything else.
But years ago when I was driving a '76 C3 as a daily driver, I appreciated the automatic.

---------------------------
1979 L82 M21 FE7
Classic White / Doeskin

 

99 percent sure original
build sheet or invoice? Pretty cool site..will ask for Christmas!
http://www.gmmediaarchive.com/?page=2

 

You want the invoice.

Can't get the build sheet that I know of.

And here is where the build date of the transmission is and the partial vin:

 

Thanks to all for sharing here. As a 79 L-82, M21 car owner, I find all of this very interesting.

 

thank you for this resource..it took about 24 hours for them to take my fifty bucks..
it confirmed all my options..confirmed i have close ratio transmission...confirmed me as second owner story from original owner indianapolis and i have about 30600 miles from summer purchase at 28900 original miles..it adds up..happy camper, ..
here it is!
also makes sense why i have 78 interior color for a 79..very early build

 

Interesting dealer owner as i never heard of baker in indy but moved here in 96 from mi.

I grew up in the used-car end of the business in downtown Los Angeles,” he says while looking back on his career. “My dad was probably one of the best auto wholesalers in L.A. But he played the horses and drank. He was abusive. He and my mother divorced when I was 10.”

Baker lived in foster homes, then served in the Korean War. He saw heavy fighting, later telling an interviewer “I counted nine different times when I figured I’d be killed.”

When he returned home to Los Angeles, he had no intention of getting into the car business. But a general manager at Frank Taylor Ford talked him into it. “I became the top salesman.”

Baker later served as a troubleshooter who was assigned to ailing dealerships to turn them around. He mastered the art of managing several stores at once.
In 1966, he finally got his own store, Bob Baker Chevrolet in Indianapolis. Twelve years later, he moved back to California. Why? “You can’t take California out of a boy who grew up there. But Indiana was very good to me.