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Tach for '52 Merc?

I just got my '52 Mercury back from a tune up a few weeks ago and I just love driving it now. I have a concern though. My overdrive has been acting up (at least I think so). It seemed to work again today…

To see if it is actually engaging and slowing the motor I thought I could install a tach to help me out.

What kind of tach would you need for this car and how would you go about installing it?


What engine in the '52? Is it electronic ignition or the original-style points and condenser? Most tachs for cars tie into the signal for the coil. But, if you have a modern engine with HEI or coil-packs or coil over plugs, you may need additional accessories to properly attach an aftermarket tach to the system.

For tachs, I like SunPro, if only because I know they are accurate and reliable

When you purchase a tach it comes with installation instructions. But usually the wires to the tach go green=negative side of the coil, black=ground, white=tach illumination, and red=switched power to the tach.

Tachs come priced from inexpensive to very expensive. Depends on how much you want to spend.


This car had a 6 volt, positive ground system. A tach that straps around the steering column would be period correct.

oldtimer 11, this is true with an original engine, but I doubt overdrive was an option in '52. I suspect a drivetrain upgrade, possibly with a re-wire to 12V neg. ground, is involved.

UPDATE: Oops, I was wrong. OD was an option with the 3-speed in '52. But, this was on a manual shift. Engaging it means manually shifting it into OD. I still think this car has been modified.

The overdrive was electrically operated and would not engage until the vehicle reached 30 mph. If the car is original it is likely 6v positive ground so be sure the tach is compattable. Post your results. I will look for an old shop manual.

Somewhere, in some dusty corner, there will be a 6 volt positive ground Sun tach…You could use a 6 volt negative ground unit if you carefully mount the tach so it’s isolated from the car body. Then, just reverse the ground and coil wires…

Is the car still 6 volt points ignition?

As I recall, those overdrives were cable operated by a dash mounted control handle…

It has the original flathead V-8 255. It has points and condensor. It still has the 6v positive ground as well. I have not modified the overdrive other than installing a switch to send power to the solenoid once I am above 30mph - the overdrive relay does not work and that is why I did this.

An old Chilton manual indicates that the cable control engages the OD but the locking pawl will not engage unless the governor closes the speed switch at 27 mph and the shift lever is in forward gear. A solenoid engages the locking pawl. There is also a switch on the accelerator that drops out of overdrive at wide open throttle or idle.

If your overdrive is working, you should feel it engage. Accelerate the car in high gear to about 45 mph and release the accelerator. You should feel it go in. Overdrive can also be engaged in second gear. Run it up to 30 mph in second and release the accelerator. If it engages, you will defintely feel it and hear a difference in the engine.

I’ve read that it’s hard on the overdrive to use it in 2nd gear. But, yes I know you can do it.

I don’t understand why it would be hard on the overdrive to use it in second gear. The overdrive unit is mounted behind the transmission. The output shaft of the transmission is turning the same speed at 30 mph whether the car is in second gear or high gear. The engine, of course is revving up higher. If you continually accelerate up to 60 mph in second gear and then engage the overdrive, you may be putting extra wear on the engine, although I would bet that your Mercury could go at least 70 in second gear.
Overdrive second gives you a ratio someplace between second gear and direct drive (high gear). It gives your Mercury more flexibility with the additional gear ratios.

By the way, be sure to get the tachometer for your Mercury. Any Mercury with that great flathead V-8 should have one mounted on the steering column. Of course, you must have dual exhausts with glass pack mufflers. Show the other motorists on the road that you mean business.
I know that the 1949-51 Mercurys are cult cars, thanks to James Dean. However, I think that the 1952 Mercury is an impressive car. I like the airplane type lever controls for the heating and ventilating system. As I remember, the 1952 Mercury was on the Ford platform while the 1949-51 were on a shortened Lincoln chassis. The 1952 was a little lighter and had better performance than the earlier Mercurys.

Tlarson is correct about using the overdrive in first or second gear…Back in the days…Hot-rodders would put a switch on the shift lever so they could engage the overdrive in any forward gear. (The overdrive cars usually had 4:11 rear ends) This allowed the functionality of a six-speed transmission! However, the poor Borg-Warner overdrive unit could not withstand that kind of abuse and were often destroyed, making them very hard to find in salvage yards…

Many of those old Mercury’s wound up with Oldsmobile OHV V8 engines and the revolutionary 4-speed Hydramatic transmission…By 1956, with Fords new 272-292-312 cubic inch OHV V8’s becoming commonplace and Chevy’s amazing 283 V8 “Power-Pack” cars making themselves known, the age of the Flatheads was over…