It also mentions 3 different sizes for the tail shafts. Obviously, there was some application across all GM vehicles. ![]() This article talks specifically about Chevrolet vehicles. (All credit and footnotes to as the source) The tail shafts for the TH-350 are available in 6-, 9- or 12-inch lengths and the tail shafts for the TH-400 are available in 4-,9- or 13-inch lengths." The TH-400's body is 25 inches and the TH-350's body is 21 5/8 inches long. The overall length of the TH-400 is 38 inches, while the overall length of the TH-350 is 33 5/8 inches, if both use the longest tail shafts available. The TH-400 pan also has two circular indentations on the humped side of the pan. The TH-400 uses an oblong-shaped pan with one side having a "hump" in the pan and one side is curved while the other two sides are straight. The TH-350 uses a square pan, with one corner cut off. Both transmission pans have 13 bolts, but they have a different shape. Look at the transmission pans on both transmission. Both were designed to be used in Chevrolet V-8 cars and light trucks. Also, the TH-350 had a kick down cable, while the TH-400 did not. On the TH-400, it was located on the right rear of the transmission. On the TH-350, it is located on the right front of the transmission. The TH-400 was a high-torque transmission that was used in heavy cars - it was a much stronger transmission than the TH-350. With modification, the TH-350 could be used as a high-torque transmission in a light car. The TH-350 was a low-torque transmission that was used in heavy cars. "The turbo 350 and turbo 400 are GM transmissions that were used from 1969 through 1979 for the TH-3 through 1990 for the TH-400. But, most prefer a 3 or 4 speed for street-only driving. Another advantage is that strip times can be more consistent because of having only 1 shift. The main advantage of a 2-speed trans is less chance of traction loss, in low gear. ![]() Although many badmouth the ST300, my trans guy said he can build one that will work in my 455 bracket car. Both cars came with TH350.Īs mentioned, any of these trans can be built for HD street, street/strip, or strip only service. I'm about to put a short tail TH400 into an '80 Bird. Bought a '74 Ventura drag car which had a long tail TH400 in it. You can even use a Chevy PG, TH350, or TH400, by using an adapter plate.Ģ of my last 3 bracket cars show the use of non-original type trans. But, it had exclusive features which set it apart from all other cars.Īny of the trans mentioned here can be used in a Pontiac. I realize that some don't consider the the X-body version a real GTO. ".The TH-400 was first introduced in the 1967 GTO and was used in all GTO's from that point on." If you take the time to read through this thread, you may get a better idea about the TH-400. It has an electric kickdown switch that works off the gas pedal. They could be manually held in gear when shifting or placed in Drive to shift automatically. The TH-400 used in the standard and higher output GTO engines were modified to shift harder & faster. You can build a TH-350 to handle the power of a Pontiac engine with the advantage of less HP to turn it and it is lighter. The TH-400 is stronger than the TH-350 in stock form, but heavier, uses more HP to turn it, and has a different gear ratio than the TH-350. You can use the longer tailshaft in a GTO with a few changes. The Long tailshaft TH-400 was used in the full size cars. The TH-400 was first introduced in the 1967 GTO and was used in all GTO's from that point on. Turbo-Hydramatic 350 3-speed (Pontiac code M-38) from 1969-'74 Turbo-Hydramatic 400 3-speed (Pontiac code M-40) from 1967-'74 Powerglide 2-speed (Pontiac code M35) from 1970-1973 ST-300 which was a Buick 2-speed used from 1964-69 Unfortunately electronically driven speedometers have rendered speedometer repair shops obsolete.Click to expand.From the information I have, Pontiac used 4 different transmissions in the 1964-'74 Tempest/Lemans/GTO. Cop car tolerances here at that time were +-2mph. A 75 year old did three for me just before he closed his shop and got them to +1mph accuracy at 90mph reading on the cal machine and dead accurate at 75 on the dynamometer. Watching a speedometer guy calibrate one is fascinating. The needle drive magnets may have gotten weak which requires zapping them. Generally requires removing speedometer from the car and having it cleaned, oiled and calibrated. If it's more than 5mph off from GPS it needs attention. Keep in mind modern tire sizes are smaller diameter than what these cars came with and will throw it off. If it's accurate within half a tenth after all these years you're good on mileage. ![]() Hold speed at the normal limit and watch what odometer is doing over the stretch of a mile. Take the car out on a non-crowded Interstate or other limited access road that has mile markers.
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