Sales of General Motor's small cars have been so strong five of its U.S. midwest plants had to report to work this week - losing half of their traditonal summer shutdown - in order to keep up with booming demand.

GM's growing success in the small and mid-size car segments has been overshadowed by the historic consumer stampede out of pickup trucks and SUVs in recent months. Less well known is that many of those buyers are only crossing the showroom floor.

"We've had lots of people focussing on what's happening to our trucks, but it's a market shift," said David Paterson, vice president of GM Canada Ltd. "They're shifting to our cars and crossovers, and that's good news for us.

The plants that had to work during their vacation are mostly building cars - the Chevrolet Cobalt, the Pontiac G5 and G6, Chevrolet Malibu, Saturn Aura - plus a trio of crossovers, the GMC Acadia, Buick Enclave and Saturn Outlook. Cadillac sales are also up.

"We're having trouble keeping up with our sales of sub compacts, too," Paterson said - particularly the Korean-built Chevrolet Aveo.

The U.S. plants that had to report to work this week, the first vacation weeks they have worked in many years, included plants in Orion Township, Mich., Lansing, Mich., Grand River, Mich, Lordtown, Ohio, and Fairfax, Kansas City.

Increased sales of the Cobalt and G5 - both built in Lordtown - have raised demand for the company's Windsor-built transmissions. But the plant is still scheduled to close in two years, when GM will replace its compacts with a global platform that will be built in Lordstown and around the world.

The new compact, which will go into production in early 2010, when Windsor Transmission is scheduled to clsoe, will be equipped with a new transmission that won't be built in Windsor.

GM announced last month it will add a third shift to its Lordtown, Ohio, assembly plant so it can produce more Cobalts and G5 compact cars. The new shift raised some hope in Windsor that closure of Windsor Transmission might be postponed.

The Following List May Help You Identify Your Chevrolet, Buick, Pontiac, Oldsmobile, or Cadillac Transmission:

Automatic GM Transmissions

Early models: The GM Hydra-Matic automatic transmission was a startling success, installed in the majority of GM models by 1950 and taking GM's competitors by surprise. Through the 1950s, all makers were working on their own automatic transmission, with four more developed inside GM alone. All of GM's early automatic transmissions were replaced by variants of the Turbo-Hydramatic by the 1970s.

* 1940–1967 Hydra-Matic — Oldsmobile (now the trade name for all GM automatic transmissions)
* 1948–1964 Dynaflow — Buick
* 1958–1959 Flightpitch — Buick
* 1961–1963 Dual Path Turbine Drive — Buick
* 1950–1973 Powerglide — Chevrolet (also used by Pontiac)
* 1961–1964 Roto Hydramatic — Oldsmobile/Pontiac
* 1964–1969 Super Turbine 300 — Buick/Oldsmobile/Pontiac (Oldsmobile Jetaway)

GM Turbo-Hydramatic Automatic Transmissions: The Turbo-Hydramatic automatic transmission was used by all GM divisions and formed the basis for the company's modern Hydramatic line. The basic rear-wheel drive Turbo-Hydramatic spawned two front-wheel drive variants, the transverse Turbo-Hydramatic 125 and the longitudinal Turbo-Hydramatic 425. A third variant was the light-duty rear wheel drive Turbo-Hydramatic 180 used in many European models.

* Medium-duty rear wheel drive automatic transmissions:
o 1964–1992 Super Turbine 400/TH400/3L80
o 1968–1986 TH350/TH350C/TH375B/TH250/TH250C
o 1972–1976 TH375 — Light duty automatic transmission version of TH400
o 1976–1987 TH200/TH200C
o 1981–1990 TH200-4R
o 1982–1993 TH700R4/4L60
* Light-duty rear wheel drive automatic transmission
o 1969–1998 TH180/TH180C/3L30 — 3-speed European/Asian model
* Transverse front wheel drive automatic transmissions
o 1980–1996 TH125/TH125C/3T40 — 3-speed light-duty
o 1984–1994 TH440-T4/4T60 — 4-speed medium-duty
* Longitudinal front wheel drive
o 1966–1978 TH425 — 3-speed
o 1979–1981 TH325 — 3-speed
o 1982–1985 TH325-4L — 4-speed

GM Electronic Hydra-Matics Automatic Transmissions: The next-generation automatic transmissions, introduced in the early 1990s, were the electronic Hydra-Matics based on the Turbo-Hydramatic design. Most early electronic transmissions use the "-E" designator to differentiate them from their non-electronic cousins, but this has been dropped on transmissions with no mechanical version like the new GM 6L80 transmission.

Today, GM uses a simple naming scheme for their transmissions, with the "Hydra-Matic" name used on most automatics across all divisions.
3/4/5/6 L/T ## -E
Number of forward gears L=Longitudinal
T=Transverse GVWR rating "E" for Electronic
"HD" for Heavy Duty

* First-generation longitudinal (Rear Wheel drive)
o 1991–2001 4L30-E — 4-speed light-duty (used in BMW, Cadillac, Isuzu, and Opel cars)
o 1992– 4L60-E/4L65-E — 4-speed medium-duty (used in GM trucks and rear-wheel-drive cars)
o 1991– 4L80-E/4L85-E — 4-speed heavy-duty (used in GM trucks)
* First-generation transverse (Front Wheel drive)
o 1995– 4T40-E/4T45-E — 4-speed light-duty (used in smaller front wheel drive GM vehicles)
o 1991– 4T60-E/4T65-E/4T65E-HD — 4-speed medium-duty (used in larger front wheel drive GM vehicles)
o 1993– 4T80-E — 4-speed heavy-duty (used in large front wheel drive GM vehicles, especially Cadillac)
* Second-generation longitudinal (Rear Wheel drive)
o 2000– 5L40-E/5L50 — 5-speed medium-duty (used in Cadillac's Sigma vehicles)
o 2007– 6L50 — 6-speed medium-duty (used in GM Sigma platform cars)
o 2006– 6L80/6L90 — 6-speed heavy-duty (used in GM trucks and performance cars)
* Second-generation transverse (Front Wheel drive)
o 2008- 6T40 - 6-speed light-duty
o 2006– 6T70/6T75 — 6-speed medium-duty

Other General Motors Automatic Transmissions:

* Aisin AF33 — 5-speed transverse automatic made by Aisin
* Allison 1000 Series — 6-speed longitudinal automatic made by Allison Transmission
* VTi transmission — continuously variable transmission

Manual General Motors Transmissions:

* Aisin AR5/MA5 — 5-speed longitudinal manual made by Aisin
* Aisin AY6 — 6-speed longitudinal manual made by Aisin
* FDF Germany F35 — 5-speed transverse manual made by FDF Germany
* FGP Germany F40 — 6-speed transverse manual made by FGP Germany
* GETRAG 282 — 5-speed transverse manual designed by GETRAG and manufactured by Muncie GETRAG
* GETRAG 284 — 5-speed transverse manual designed by GETRAG and manufactured by Muncie GETRAG
* GETRAG F23 — 5-speed transverse manual made by GETRAG
* GETRAG 260 — 5-speed longitudinal manual made by GETRAG
* New Venture Gear 3500/4500 — 5-speed longitudinal manual made by New Venture Gear
* Tremec T-56 — 6-speed longitudinal manual overdrive made by Tremec
* Tremec TR-6060 — 6-speed longitudinal manual overdrive made by Tremec
* ZF S6-650 — 6-speed longitudinal manual transmission made by ZF

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