Looking at my pan, I'm pretty sure I have a th350 in the wagon, but it does have an OD or locks up in 3rd? I can't tell. Is it possible to have a th350 with a lockup converter that will make it feel like it has an OD?
TH350 Lockup?
- Thread starter Tony_SS
- Start date
Yes. Simply check for an electrical connector on the driver's side of the trans near the shift lever. GM made both a TH250C and a TH350C lockup transmission. They look almost identical on the outside. The TH250C is a bit weaker than the TH350C and therefore undesirable for performance applications. To identify the 250C, check to see if the trans has an external band adjuster, a stud and locknut sticking out of the case just behind the cooler lines. The 350 transmissions do not have an external band adjuster.
The TH350C transmission did feature a lock-up torque converter. The lock-up clutch will apply in third gear at cruising speeds typically around 40+ MPH. The lock-up clutch internally locks the turbine to the front cover of the converter, which provides a true 1:1 drive ratio to the input shaft and eliminates all converter slippage. The lock-up feature was designed to help improve fuel efficiency and reduce transmission operation temperature in steady-state cruising conditions. When the lock-up applies, it can feel like an additional forward driving range is being applied, giving it that sense or feel of "overdrive", although it's actually just a true 1:1 ratio through high gear in the TH350C.
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