GM Roto-Hydramatic 375 (Slim Jim) transmission

Roto-Hydramatic 375

Also known as Model 10 or Slim Jim.

Used 1961-64 in some Buick, Olds and Pontiac models.

There is some disagreement as to this being a 3 or 4 speed transmission. It only shifted twice, so many people consider it a 3 speed, but it had an internal torus torque multiplier (similar in principle AND operation to today's torque converters) that did give it an initial additional "ratio".

Do not confuse with 375 THM used later that was an adaptation of the 400 THM, but with a 350 THM size output shaft spline or the version of the 350 THM that GM called a 375 THM.

This was an hydraulically controlled transmission.

TV rod adjustment

Disconnect rod, push (and hold) the gas pedal to the floor, push the TV rod (and hold it) until it bottoms in the valve body, adjust the length of the rod until it will just assemble back together.

Gear Ratios:
starts out at 3.50:1 and becomes 2.93:1 when "torus becomes hydraulically coupled" 1st gear
1.56:1 2nd gear
1.00:1 3rd gear
2.42:1 reverse

Transmission

Pan and Gasket

(click on picture to enlarge)

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