This switch is grounded by the so-called "4th gear switch" that locks out OD in 1st through 3rd and in reverse. There is a momentary contact push-button switch in the center of the "H" pattern on the M46 shift knob. A "bad" cone clutch can cause slippage, but there are usually other symptoms as well.
Power is transmitted through the cone clutch at all times, even when the overdrive is disengaged. It has the planetary gear set typical of an automatic, including a cone clutch. The overdrive is a single-speed automatic transmission, if you will. The M46 is really a 4-speed transmission (M45) with an output shaft tailored to accept the Laycock overdrive that is bolted up to the back of it. last use of the bw od was about 68 in american cars.
Volvo and laycock overdrive manual#
the only american car i saw which had the manual trans laycock od (denorman) was the later model amc gremlins and hornets in 74. the m46 od must have had some kind of lockout which limited od to 4th gear. most 3 pedal cars then had 3 speed transs with column shifts. but you did have to get up to 28mph in 1st to use the od mode in all three gears. interestingly in these old american cars you could actually obtain 6 speeds forward if you skillfully worked the clutch, throttle and t handle to go into and out of 1st, 1st od, 2d, 2d od, 3d and 3d od. studes used this trans too which i think was the chevrolet bw model. this also employed a split second ignition interrupter wired to the coil as a sensor which allowed the upshift to od without torque load unless you locked od out with the pullout t handle under the dash. the old bw ods which many of the 50s/60s cars employed actually used a centrifugally actuated speed sensor so as to not to shift up to od if the engine speed was too low(lugging). didnt realize it employed a hydraulic pump too. wasnt sure if the m46 used an electric solenoid.