General Motors TH350

GM TH350 "Turbo 350" Transmission Ratios & Specs

The General Motors Turbo Hydra-Matic 350 is a three speed automatic transmission introduced for the 1969 model year. It was developed by GM's Chevrolet and Buick divisions to replace the two speed Powerglide transmission. The "Turbo 350", as it is commonly referred to, was used in GMC and Chevrolet pickups until 1986, when it was replaced by the TH700R4, which is a four speed overdrive transmission. At roughly 120 lbs, the TH350 is relatively light and has a earned a reputation of reliability and strength in applications ranging from drag racing to off-roading.

The TH350 is a minor downgrade from the TH400 - as a general rule of thumb, the TH350 was GM's small block transmission, while the TH400 was reserved for big block engines. Its Achilles heel is the excessive end play between the fluid pump and center support structure, which allows the direct clutch drum to wobble back and forth slightly. The problem is easily fixed during a rebuild thanks to improvements developed by the aftermarket. Despite this flaw, the TH350 is extremely popular and can be affordably built to handle tremendous abuse. Novak Conversions, who specializes in adapters for Jeep drivetrain conversions, claims the TH350 is the shortest and strongest automatic transmission than can be adapted into a Jeep. The clutch and band specs depend on the transmissions original application, but the consensus is that the bigger the original engine, the stronger the transmission is. A lockup converter was introduced around the 1980 model year, called the TH350-C, which was implemented into order to boost fuel economy.

 

TH350 Transmission Ratios

1st

2nd

3rd

Reverse

2.52 : 1

1.52 : 1

1.00 : 1

2.07 : 1

 

TH350 Transmission Specs

Type:

3 speed automatic transmission

Applications:

1969 - 1986 GMC, Chevrolet cars and trucks (as well as vehicles from other divisions of General Motors).

Case Material:

Aluminum, 1 piece case casting with integral bellhousing

Case Length:

21.75"

Weight:

~ 120 lbs

Fluid Type*:

DEXRON ATF

Identification:

1 piece aluminum case (bellhousing and case are a single casting).

 

GM TH350 transmission pan bolt pattern

*Required fluid type and fluid capacity may vary with application and model year - refer to vehicle's owner manual.