GM Roto-Hydramatic 375 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.

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

(click on picture to enlarge)

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