terrystrand

Corvette didn't want to IMO let people know that in the mid seventies the THD400 that had been a Corvette standard auto trans 'forever' suddenly magically disappeared and was replaced by the THD 350 !!! What year did the Vette switch away from the 400? That info does not seem easily found. I've looked

Thanx.

lvmyvt76

76 had the 350

terrystrand

Hard to find out this info...for example these specs don't identify the trans in a '75:


RPO Description Price Production

L82 350ci. 205hp engine $336 2,372
M21 4-spd, Close Ratio Manual Trans. avail. only with L82 $0.00 1,057
M40 Turbo Hydra-Matic Auto. Trans. $0.00 28,473

terrystrand

Why it is confusing:

MV4 76 86 TRANSMISSION.3-SPO AUTO (THM350C)
MV9 76 87 TRANSMISSION,3-SPO AUTO (THM200C)
MW9 76 88 TRANSMISSION,4-SPD AUTO (THM200-4R)
MX0 82 88 MERCHANDISING OPTION ONLY-DO NOT CATALOG
MX1 82 88 MERCHANDISING OPTION ONLY-DO NOT CATALOG
MX2 76 84 TRANSMISSION,3-SPO AUTO (THM350C)
MX3 76 81 TRANSMISSION,3-SPO AUTO (THM350C)
MX5 82 83 TRANSMISSION,3-SPD AUTO (THM350C)
MX6 85 86 TRANSMISSION,4 SPD MAN (MUNCIE)
MY1 76 87 TRANSMISSION,4-SPO MAN (MUNCIE)
MY6 76 88 TRANSMISSION,4-SPD MAN (NEW PRUutbb)
MY7 76 86 TRANSMISSION,5-SPD MAN (ISUZU)
MY8 76 86 TRANSMISSION,4-SPD MAN (MUNCIE)
M08 82 84 TRANSMISSION,4-SPD MAN (BORG-WARNER)
M11 76 81 SHIFT,FLOOR
M15 76 81 TRANSMISSION,3-SPO MAN
M16 76 81 TRANSMISSION,3-SPO MAN
M17 76 87 TRANSMISSION,4-SPO MAN (MUNCIE)
M18 76 83 TRANSMISSION.4-SPD MAN (BORG-WARNER)
M19 76 88 TRANSMISSION,4-SPD MAN (MUNCIE)
M20 76 88 TRANSMISSION,4-SPO MAN (MUNCIE)
M21 76 81 TRANSMISSION,4-SPO MAN
M24 76 83 TRANSMISSION,4-SPO MAN (BORG-WARNER)
M26 76 85 TRANSMISSION,4-SPD MAN (MUNCIE)
M27 76 81 TRANSMISSION,4-SPD MAN
M29 76 81 TRANSMISSION,3-SPD AUTO (THM200)
M31 76 85 TRANSMISSION,3-SPD AUTO (THM250C)
M32 76 81 TRANSMISSION,3-SPD AUTO (THM325)
M33 76 81 TRANSMISSION,3-SPO AUTO (THM350)
M34 76 83 TRANSMISSION,3-SPO AUTO (THM125)
M38 76 81 TRANSMISSION.3-SPO AUTO (THM350)

Jeffs82c3

Not sure when the th400 was dropped, but 1982 was the first year of the 700r4 (overdrive) in the corvette...

'75

In '77 L82 was the last Corvette with the TH400.

77 L48 had TH350

76 L82 TH400

76 L48 TH350

75, Th400 was the only auto offered

TimAT

M38 is TH 350
M40 is TH 400
MD8 is 700-R4

hunt4cleanair

Yes!

Only the L82 in 76/77 were equipped with the heavy-duty THM400 (Turbo Hydra-Matic). The lower-powered L48 received the THM350 and in 1978, the THM350 was equipped with either the L82 or L48.

The THM, or RPO M40 was a heavy-duty three-speed automatic transmission and had a long run by Corvette sales standards serving as a transmission mainstay from 1968 through 1977 through both thick and thin. The THM 400 had earned a reputation for heavy-duty work seeing duty on Rolls-Royces, Jaguars, Chevrolets and the GM fleet since 1965. In 1968, THM 400 was introduced to compliment the heavy-duty needs of the Mark IV.

terrystrand

Great summary...this info is almost impossible to find...no, it IS impossible to find in the dealer/company brochures. I've tried many times to find answers to this simple question. As I suspected, the M40 was gradually phased out, and the 1975 Vette was the only year you could be SURE of getting that THD400. As mentioned in 1975 the 400 was dropped in the L48, and by 1978 you couldn't even get the 400 in the L82 !!!! Pretty sneaky of them in view that Chevy never mentioned it in any of their sales brochures. Here the 400 is shown in the '77! with no mention of the 350. This is what I mean by sneaky. http://1-4u-computer-graphics.com/1977-specs.htm

terrystrand

So in summary is it accurate to say that ONLY in 75 could you be sure that you got the 400. And by 78 you can be sure that you got ONLY the 350. IN between those two years you got ONLY the 400 with the L82 and ONLY the 350 with the L48?

Thank You.

Easy Mike

Yes and No. The TH400 was the only automatic tranny for 68-74, so those model years can be included in your statement.

terrystrand

Yes...I should have clarified that I was interested in the 75 through 78 years when the switcheroo was going on. I appreciate it..thanx!

I found only one reference to the phasing out on a Vette site which said ''A new, lighter 350 is offered for 76..." as if they were some kind of engineering advance. 350 is a fine trans, but they sort of snuck it in without much advertisement. I had a '78 and thought that the 400 came with the L82...I was wrong.

hunt4cleanair

The switheroo!

Well GM Chevrolet did the same thing with the four-speed in the 78/79 when the L48 was called out. The Muncie cast iron four-speed was the base M20 when L48 was equipped. But when L82 was ordered, the buyer got the Borg Warner T10 four-speed. The M21 was the option. To this day, L48 M20 owners are surprised when they must tend to their four-speed for repairs and learn its the Muncie cast iron box and parts are extremely hard to find...no one knew it was out there!

See Muncie Four-Speed: What makes your M20 work?

terrystrand

CLEANAIR... Now THAT'S a fantastic, detailed article on the trans 'switcheroo'. Very complete sorting out of what's what, which would be hard to find in the Vette literature, internet sites, brochures, reference stats, etc. Thanx, bro!