TURBO HYDRAMATIC TRANSMISSION. This OEM flywheel flexplate is in very good condition. The flywheel is in very good condition with minor average wear to a few teeth, but most teeth have no wear (see video). Turbo Hydramatic 400 '400LW' Liteweight '400XLT' Xtra-Lite; Turbo II Two Speed; Turbo III XST Three Speed; Turbo Hydramatic 350 '350XLT' Xtra-Lite; Torque-Flight 727; C-6; C-4; Turbo Hydramatic 700R4; Turbo Hydramatic 4L80E; Turbo Hydramatic 4L60E; Xtreme Marine Transmission. Chevy turbo 400 hydramatic Question? Yesterday I was lucky enough to score on a 77 chevy halfton with a 12 inch lift and 38.5's for a hundred and fifty bucks:):):). Any way Im not familier with a turbo 400 hydramatic I was just wondering how strong they are and if you run em?

Super Turbine 400 / THM400 / THM375 / 3L80 / 3L80HD

The THM400 can be visually identified by an oil pan number four shown at Transmission Pans. It was first introduced for the 1964 model year under the name 'Turbo Hydra-Matic' in Cadillacs. and 'Super Turbine' in Buicks. The following year, application expanded to Oldsmobile and Pontiac and to some full-sized Chevrolets. Many of the Buick, Cadillac, and Oldsmobile THM400s produced between 1964-67 were equipped with a Switch-Pitch torque converter variable-pitch stator, which is sought after by collectors and drag racers. These can be identified outside the vehicle (with the torque converter removed) by a narrow front pump spline. Externally the switch pitch version has two electrical connections, where the non-switch pitch THM400 has only one. GM used a Switch Pitch torque converter in the Buick twin turbine Dynaflow transmission between 1955–1963 and the Super Turbine 300 two speed transmissions used by Oldsmobile Pontiac, and Buick divisions between 1964-1967.

A variant of the THM400 known as a THM375 is a THM400 with a long output shaft that mates to the smaller THM350 drive shaft yoke. It can be identified by '375-THM' cast into the tailhousing. Internally the clutch packs originally had fewer friction plates. Some 'Heavy Duty' THM350s were also designated THM375-B. Another variant is the 3L80HD, often referred to as a Turbo 475. The 3L80HD has a straight-cut planetary gear set. There is no externally visible way to determine whether the transmission contains the straight-cut planetary gear set. The THM425 front wheel drive transmission shares almost all its internal parts with the THM400.

By 1980, the relatively heavy THM400 was being phased out of usage in passenger cars in response to demand for improved fuel economy. The Presidential Limousine used during the Reagan Administration, a modified 1984 Cadillac Fleetwood Brougham, was the last known GM passenger vehicle to use the THM400, alongside the C- and K-series (full size) Chevrolet/GMC pickups and G-series (full size) vans ending in 1986 thereafter it was renamed to the 3L80. Today, the United States Army HMMWV is the only vehicle using the THM400. The civilian Hummer H1 originally had the 3L80s, but the current model has had a 4L80E since the mid-1990s.

Through the end of the '70s substantially more CBOP (Cadillac/Buick/Oldsmobile/Pontiac) bellhousing THM400s were produced than any other THM400. Chevrolet bellhousing THM400s, while not rare, can be hard to find and are, as a result, usually more expensive to buy. Other bellhousing patterns are, accordingly, rarer. The THM400 was never produced with a multicase bell housing.

Other auto manufacturers have used the THM400 and its 4L80E successor, including Ferrari (in the 400/412); Jaguar/Daimler (in pre-1994 XJ12 and XJ-S coupes) and their Daimler stable mates; Rolls-Royce (in 1965–1980 Silver Shadow and 1980-1992 Silver Spirit series cars, along with their Bentley stable mates); the Nissan Prince Royal; AM General; and Jeep (usually found in the FSJ pickups and SUVs. Early Jeep THM400s used an adapter between the engine and transmission bell housing while later models had an AMC specific housing. Though identical except for the bell housing pattern used through the '60s and ending in 1979 the THM400 was mated to the Dana model 18,20 and was the only transmission used with the Borg-Warner 1305/1339 all-wheel-drive transfer case used only in Jeeps, It has been known to adapt a THM400 to other engines using adapters.

THM400 transmissions are very popular in automotive competition due to their great strength. Much of this strength comes from the use of a cast iron center support to suspend the transmission's concentric shafts that join the clutch assemblies to the gear train. The center support, which is splined to the interior of the transmission's case, also provides a robust reaction point for first gear (the gear train's reaction carrier is restrained from counter-rotating the engine in first gear by a roller clutch whose inner race is part of the center support). Since the first gear reactive force is evenly distributed around the periphery of the case, the types of mechanical (and some times violent) failures that have plagued other competition transmissions are rare.

The THM400 was the first three-speed, Simpson-geared automatic to use overrunning clutches for both first and second gear reaction, a feature that eliminated the need to coordinate the simultaneous release of a band and application of a clutch to make the 2-3 gear change. Owing to this feature, as well as the use of a large, multi-plate clutch to provide second gear reaction, the THM400 is able to withstand very high input torque and an enormous number of shifting cycles, as would be encountered in frequent stop-and-go driving. As a result, it has met with considerable success in commercial vehicle applications.

For 1987, GM changed the nomenclature of their Turbo Hydramatic transmissions — the THM400 was renamed to the '3L80' (three forward speeds, longitudinal positioning, and an arbitrary 'strength' of 80, the second highest such rating assigned). The 3L80HD was introduced in 1987 as the HD unit used in passenger trucks. In 1991, a four-speed overdrive version, the 4L80-E, replaced the THM400 in Chevrolet/GMC pickups, vans, SUVs, and commercial vehicles. The 4L80E (and its successor 4L85E) was the first Hydramatic to incorporate electronic controls — almost all of the THM400/3L80/3L80HD's components are interchangeable.

Transmission fluid cooler line connections are found on the right hand side of the THM400. The lower connection is the cooler feed, and the upper connection is the return. The case is tapped for either self-sealing 1/4'NPT fittings, or 1/2'UNF fittings with a washer seal. 5/16' or 3/8' rigid coolant lines are generally connected via appropriate double-flared adapters.

4-Wheel drive truck applications used a shorter output shaft that coupled with a female transfer case input shaft.Early transfer cases mated directly to the THM400 with an cast-iron adapter,usually a vertical oval shape.Later models used a circular style iron adapter which is generally considered the stronger of the two.

Gear Ratios are:

• First Gear - 2.48:1
• Second Gear - 1.48:1
• Third Gear - 1.00:1
• Reverse - 2.07:1

The TH400 is an aluminum cased three speed automatic transmission that was produced by GM. It was introduced for the 1965 model year and made its debut in Cadillacs, and is respected for its durability and adaptability. The TH400 came in two wheel drive and four wheel drive vehicles, passenger cars and heavy duty trucks, as well as GM vehicles and those made by other manufacturers.

More than almost any transmission ever made, it has found its way into a wide variety of vehicles outside of the GM family. The TH400 has appeared in Jaguars, Hummers, Ferrari’s, and many more.

TH400 Specs

3L80

In the early 90’s GM rebranded all of their transmissions, They created a standardized naming system across their product line, and changed the name of the TH400 to 3L80.. The 700R4 became the 4L60 and so on. There is no difference other than the name. 3L80 stands for three gears, longitudinal mount (rear wheel drive), and the 80 signifies that it can handle 8000 lbs. in gross vehicle weight(supposedly).

Note that unlike all the other GM transmissions of the time there was no E at the end of the nomenclature. This is because the TH400 was never designed to communicate with the CPU of the vehicle/The 3L80 was the last non overdrive transmission used by GM in regular production trucks and vans. It was eventually replaced by the 4L80E. It uses the B-O-P bellhousing bolt pattern which makes it compatible with nearly any GM engine. It also does not use a locking torque converter.

Th375 and Th475

There are were a few one of versions of the Turbo 400 as well. These are the TH375, and the TH475. The Th375 was manufactured for cars with low horespower engines in the 1970’s. It was modified to fit the TH350 driveshaft yolk. If you are looking to purchase a TH400 avoid it. It’ll have The TH475 was used in heavy duty trucks in the 1970’s, and can handle a lot of power.

Turbo Hydramatic Thm-200

TH400 Identification

If you were to line up every automatic transmission that GM ever produced, you’d be hard pressed to find one that is larger than the turbo 400. It is just huge. If it was lined up with a 200-4R, TH350, or 4L60E it would be easy to identify a TH400. It would be far and away the largest transmission there.

Since it’s not very likely that you are going to run into a lineup of automatic transmissions being the biggest isn’t going to be very helpful.

There are 13 bolts on the pan underneath the transmission. If you count 13 you are almost home free, but the Th350 also has 13. Since these are the two most common GM automatic transmissions of the latter half of the last century it’s very important that you figure out which is which.

The TH400 uses an electronic kick-down mechanism, which means that there will be an electric plug on it. The TH350 uses a mechanical linkage that attaches to the carburetor. Th350 has the vacuum modulator in the back, and the TH400 keeps it on the side.

Turbo Hydramatic 375

Using the pan bolt pattern is the easiest way to identify the TH400. Both the TH350 and TH400 have a similar look. They utilize a kick down cable, and they both use the same bellhousing bolt pattern. Identifying the Th400 is really as easy as knowing the differences between it and the TH350.

Also, take a look at the bolt pattern itself. The Th400 has a much more complex pan then the Th350. The Th350 is basically a square with a corner taken out of it. See for yourself. The TH400 on the other hand has 9 different angles on the the pan. It’s one of the more complex pans that GM made.

The Turbo 350 has a much simpler look. Here it is, Notice that it looks like a box with a slice taken out of the corner. That corner would be on the driver’s side of the vehicle.

Identifying Turbo 400 By the Tag

You’ll find the identification tag above the transmission pan on the drivers side. It is machined into the transmission in most cases. So, it’s really not really a tag, which can make it a bit more difficult to identify if the transmission is really greasy. Take some brake parts cleaner with you if you really want to get a good look at it.

Try using this guide to help you lock down what model number you may be looking at.

Common TH400 Problems

• Early Shift– One of the most common issues with the TH400 is that it’ll shift too early. This is almost always cause by the vacuum line that runs to the modulator from the intake manifold. While they came from the factory with hard lines, many people will swap them out for soft lines when doing a swap, since finding a hard line for the particular vehicle can be an issue.
• Late shift– The Th400 will often shift a little later than a person would like, espescially at the track. This is usually caused by its electric kick-down switch.
• General not shifting right– If you’ve checked that the kick down circuit is ok, and the vacuum line is too, than it may be time to look at the vacuum modulator itself. It’s more likely to have fluid in it than it is to have gone out itself.

Turbo Hydramatic 350

TH400 and Non-GM vechicles

Maybe the best compliment comes from your competition. And at least a dozen auto makers have paid GM to use the TH400 instead of creating a competitor for it. These include Toyota, Ferrari, Rolls-Royce, and Hummer. This is a true testament to its bulletproof reliability and ease of tuning.

The Turbo 400 has been used in Jeeps from the factory. Early model AMC Jeeps used an adapter plate to mate it with the GM bellhousing bolt pattern. Later, a specific TH400 was made just for Jeep. This version tilted the transmission about 4 degrees in order to better accommodate the transfer case. It has not been produced for quite a while and is considered pretty rare. The Turbo 400 is compatible with most Jeeps. However, the CJ5 has to narrow of a wheelbase to accommodate it. The specialty jeep TH400 case is 24 1/2 inches long.

When looking at a Jeep that came from the factory with the Turbo 400, it’ll be bolted to either the BW 13-39 or the Dana 20 transfer case. In the 1960’s some Jeeps came with Buick engines, so they used neither an adapter nor the Jeep specific transfer case. Some of the AMC specific adapters on these transmissions have been prone to failure.