1957 Mark I with “over drive” toggle

Hello I have a mark I and I has an over drive toggle left of the steering wheel. It does not do anything when I move it. I was wondering if anyone knew how it worked, what it does and what pats,I may need to check to repair it?

Thank you


First thing I would check is whether the gearbox fitted to the car is still an overdrive box.

All is original my wife’s grandparents bought it new and it came off the line in March after the fire, it has been in the family since day 1 …

I can’t speak for the Mk1. The Mk2 overdrive lever is mounted on the RHS of the steering wheel, with the turn signal lever on the left. It’s just a simple switch that operates a solenoid that brings the pump in the overdrive into operation. FWIW. Paul.

With a multimeter I would check fuse, switch and overdrive solenoid. I have had a solenoid fail in a Triumph before. All presumes you’re arrangement is electrically similar to a Mk2. Paul.

When Jag is an Automatic, this place in dash is used for same looking switch but with different function and bezel, a “speed hold” or alike.

Assuming this toggle switch is cleat plastic and should light up when overdrive is available. Turn the ignition on and place the car in 4th gear, the switch should light up. If it does not, you most likely have an electrical issue. As mentioned above, check the fuses (there are only two). JS

Mark is correct…
Turn battery power on…
Put into 4th gear then throw the switch, you should hear a click.
Switch on and off , there is a plunger switch .
Theres alot going on
bad switch
bad clutch
bad planetary unit
bad wiring
Good luck

The Mk1 probably has the same switch as the XK150, which is still available if yours is bad. This switch itself is not lighted, but there should be illumination if the steering cowl is like the mk2, highlighting “Overdrive”. This is how I set up my mk2 when I converted to manual od from automatic. As already stated by others, nothing will happen unless the car is in 4th gear.

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Thanks everyone for your responses. Sorry new to this and being north of the 49th cars pretty much put away for the winter. I have an automatic, and just went out and looked at toggle and it says intermediate speed hold, so thinking it either keeps the car in the gear it is in, or it tries to maintain the speed it is at (is one of these correct)? Thanks. Jim

The IHS switch keeps the box in the middle gear. Because there is no vacuum signal (just accelerator position) the box can tend to labour after dropping into top (direct), if going up a hill or similar loading. It’s a kind of override that allows the driver to manage engine revs and a tendency to “bog down”.
If left switched in the car won’t move to direct top. Can change it on the run if the car is labouring in top. Paul.