Differences Between a TH350 & a 700R4 Transmissionby Michael Gunderson
The TH350, also known as THM350, Turbo Hydramatic 350, or Turbo 350, is a three-speed, automatic shift transmission developed by Chevy and Buick and introduced in 1969. It was typically coupled with Small Block V6 and V8 engines and was used in most of General Motors rear-wheel-drive cars and trucks until 1984. The 700R4, also known as TH700R4, THM700R4, 4L60, or 4L60E, is a four-speed overdrive, longitudinally positioned, automatic shift transmission introduced in 1982 as the TH350's replacement. It was widely used in Chevrolet and GMC rear-wheel-drive vehicles until 1992.
Length And Weight
The TH350's case length is 21 5/8 inches. Depending on the tail shaft housing, its overall length can either be 27 5/8 or 30 5/8 inches. The 700R4's case length is 23 3/8 inches and its overall length is 30 3/8 inches. The TH350 weighs 120 lbs., while the 700R4 weighs 155 lbs.
Oil Pan Shape
The shape of the oil pans is one way to differentiate between the TH350 and the 700R4. The TH350's oil pan is shaped like a square with one of its corners cut off, while the 700R4's oil pan is basically rectangular.
Gear ratios measure the number of revolutions the engine makes for every revolution of the transmission's output. The TH350's gear ratios are as follows: 2.52:1 for first gear, 1.52:1 for second gear, and 1:1 for third gear. The 700R4's gear ratios are 3.06:1 for first gear, 1.62:1 for second gear, 1:1 for third gear, and 0.70:1 for fourth gear.
The 700R4 has an overdrive while the TH350 does not. Overdrives allow for high-speed cruising, which saves fuel while lowering torque.
The need for a more fuel-efficient transmission was one of the main reasons the TH350 was phased out and replaced with the 700R4. Vehicle owners report fuel savings of up to 30 ercent after converting from the TH350 to the 700R4.
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