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For 1975 and 1976, AMC offered a Laycock deNormanville overdrive.

The 150T (or T-150) was used in many Jeeps and the overdrive was used by Volvo behind their 4-speed transmissions.

The service interval recommended by AMC is to check the fluid every 5,000 miles and fill with 80W-90 or 80W-140 G4 lubricant. Both the 150T and the overdrive are very resilient and reliable units. Based on reports of each unit separately, a thinner MTF oil or a 75W-90 synthetic GL4 compatible fulid should perform adequately and may provide smoother cold shifts. Never use a limited-slip additive or ATF.

The transmission and the overdrive share fluid and are filled together, although they must be drained separately. The capacity of the assembly is approximately 4 pints, and the overdrive should be turned during filling to prevent underfilling of the transmission case.

The transmission is drained by removing the bottom bolt holding the adapter to the case. The overdrive is drained by removing the pan. There is no drain interval, and no filter interval. I recommend that fluid is drained and refilled from the transmission itself every few years, depending on service.


A series of electrical switches triggers the solenoid to divert oil from the direct circut to the overdrive circuit. The solenoid itself takes only a little power to operate, approximately 2 amps to engage.

If it is not practical to use the original kickdown switch there are two alternatives. A GM electric kickdown switch mounted on the accelerator for a Turbo-Hydromatic 400 or SuperTurbine 200 will work. The other way is to replace the switch under the hood with an adjustable torque-converter unlock switch for a GM Turbo Hydramatic 700R4. An old vacuum delay valve inserted in the line to slow the disengagement of the overdrive will make it more pleasent.

Power flow is as shown.

Torque Specifications

The Speedometer Adapter Clamp Bolt is torqued to 100 in. lbs.


  Set To
In Use
Oil Pan Bolts 6 5-7
Clutch Apply Bar Lock Nuts 8 6-9
Main Case Pressure Plug 12 9-15
Main Case-Rear Case Nuts 11 9-12
Relief Valve Plug 16 14-18
Pump Body Plug 16 14-18
Pressure Filter Plug 16 14-18
Speedometer Drive Gear Locknut   50 40-60

You may also want to download the Overdrive section from the 1975 TSM.