Overdrive

[old guy rich]

Last April I bought a 49 Merc overdrive trans from Ehlien and started putting
it in Monday. John also gave me extra driveshaft, flywheel, P/P and relays. Had the flywheel surfaced and balanced, new clutch, pressure plate, throw-out bearing and pilot brg. New overdrive wiring harness. I finished up tonight and went for a test drive. Trans is excellent, quiet, smooth and runs like a new one. Overdrive works great, now a have a highway friendly car.
I want to say thank you very much John, always nice dealing with a Ford Barn member. Old guy Rich.

[apba12m]

I love my overdrive trans in my 52 merc so much that I am keeping it when I customize the car. Its like having a 5 speed, I am just moving the shifter to the floor to give me more steering column options ie tilt and power steering.

[rotorwrench]

Both My 51 Mercs are early November 1950 cars so they still have the same basic trans as the 1949 models. It was a poor mans automatic transmission and improved performance & mileage a lot.

[old guy rich]

I just took my wife out to eat and do a little shopping, really wanted her to see the overdrive in operation. She thinks it is great that we will get better mileage now and can drive on the highway. I love it. old guy rich

[Dick Webber]

My first car was a 49 Mercury with overdrive. It was wonderful. I bought a copy of it years ago and finally have all I need to add OD to it. I'm looking forward to it.

[Paul Bennett]

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Did you wire in the switch on the accelerator pedal? I heard the switch was discontinued on the 1951 Mercury. Aside-are you becoming aware of 28 mph?

[Mac VP]

The reverse lockout switch was discontinued after 1950 for both Ford and Mercury, not the throttle (kick down switch). The governor (assuming he still has this control in his unit) controls the relay/solenoid at the 28 mph threshold.

[Paul Bennett]

Since I have a '50 w/OD, I have an interest.
My diagrams say 'RAIL' switch & discontinued in '51. I misspoke on acc pedal sw aka 'kickdown' sw.

However, my '50 does NOT have this 'RAIL' switch, the governor is wired directly to the 'kickdown' switch.
1. Is the 'RAIL' switch the 'reverse lockout' switch?
2. What is the function of this switch?
3. As a 'reverse lockout' did it open or close when reverse was selected?

I've yet to drive my car but I can't imagine going 28 mph in reverse.
Perhaps the governor generates an opposite polarity voltage in reverse. Function info would answer that. ?Curious minds?

[Mac VP]

The RAIL reference is the reverse lockout switch. It received that description because it is operated by the internal overdrive shift rail.....sometimes directly and sometimes through a steel ball. It's a normally closed switch that opens when the transmission was shifted into reverse. So, it would OPEN the circuit to the governor when you shifted into reverse. The result was that the solenoid would loose power, and retract the OD pawl, taking the transmission out of the overdrive mode.

The switch was discontinued sometime in 1950/51. A Ford service bulletin in 1951 stated that the mechanic should bypass the switch if he found it to be defective, rather than replace it. He was to leave it in place but to join the two wires together.

The reason for discontinuing the device was that they realized it was a redundant control and was not necessary. There always was the mechanical system there for disengaging the overdrive when shifting into reverse. So, you could say that it was a cost saving measure.

If these transmissions were able to shift into reverse while staying in overdrive mode, the freewheel cam assembly would be damaged, which was the reason for preventing that from happening. In all Borg Warner overdrives the lockout rail always shoves the sun gear out of the balk ring gear when you shift into reverse. This physically takes it out of overdrive mode, preventing damage to that freewheel cam.

A side note of prevention.....get in the habit of shifting the overdrive out of OD (pull the control cable out) when you park. Also you should always use your hand brake after parking. If left in overdrive mode and hand brake NOT set, the car could roll. Another rare problem could be damage to the freewheel cam if a wrecker had to pull your car backwards while it was in overdrive mode.

Hope this helps....

[38coop]

That's some good information Mac.

[40cpe]

There is some confusion about the term "in overdrive". To some, the trans is in overdrive if the handle under the dash is "in". To me, the trans isn't in overdrive unless the solenoid is activated and the sun/planetary gear is in operation. There is a sprag clutch in the OD section that drives the car in forward gears while the handle is in (but the overdrive not activated) but also allows the car to free wheel when decelerating. The car would not back up if the rail switch didn't internally pull the OD cable to override the sprag clutch. This is why the car will roll forward when parked in a forward gear with the OD handle in. Mac can explain this more eloquently/technically than I can.

[nbrskn]

I put and OD from a 68 f 100 behind the Merc engine in my 46 Ford 2dr
Used bell housing from 49 ford. Shortened front shaft on trans 1/2 inch.
the bell housing hole for front bearing on trans had to be enlarged.

Put trans in reverse when parking. will hold car in place.
reverse locks OD out. Never ever PULL the OD handle out when car is in motion . Yes you can to those who know the OD ,but I live by the rule
DONT pull out.

[rotorwrench]

The electrical part of the overdrive system is "live" as long as the system isn't locked out if you have that lockout switch. It doesn't go into planetary operation until it reaches the governor on speed. My early 1951 Mercury cars were still equipped with the 1950 style transmission and pressed steel half bell. It still had the lock out switch behind the lockout rod on the overdrive tail housing. When they deleted the lockout switch, the system is live all the time. Lock out keeps it from engaging but it is still live.

The rail lock out switch was deleted on the late 1951 Mercury line somewhere in February of 1951. This was the first of the "new gears" type transmissions with the separate cast iron bell housing in the Mercury cars. All other system components were still in use to include the operation relay, kick down switch, function solenoid, and the governor switch. Ford cars used their own type bell housing and clutch so they only changed their gears in the 1951 model year. There were other subtle changes but it's harder to tell the transmissions apart when you set them side by side. On the Ford cars I think they deleted the lock out switch and changed the rear mount somewhat from the 1950 cars. The change on the Mercury cars was a lot different.

[Mike51Merc]

Technically, the OD should be inactive at speeds less than 23mph and most people don't shift into reverse when moving forward at speeds more than 23mph. Makes me wonder why such rail switches were thought to be necessary in the first place.

[old guy rich]

Hi guys, I like all the comments and very good info from all you more knowledgeable folks. My system is installed in a non O/D car and is wired exactly the way the factory diagram shows. Everything works correctly, I couldn't be happier. I used all the old parts John gave me, I didn't have to buy any new parts except the O/D wiring from Mac. I did buy new T/O brg and pilot brg. Thanks for all the info. old guy rich

[Dobie Gillis]

Originally Posted by Mike51Merc

Technically, the OD should be inactive at speeds less than 23mph and most people don't shift into reverse when moving forward at speeds more than 23mph. Makes me wonder why such rail switches were thought to be necessary in the first place.

Belt and suspenders engineering...

[rotorwrench]

It was there so the solenoid would not energize when the governor reached on speed while the overdrive was locked out. The coil in the overdrive solenoid draws a good bit of current when it can't engage fully. This was why they had the lock out switch was to save electrical energy. These old cars only had a 35 amp generator so they were trying to conserve electrical buss energy and keep the solenoid from getting hot when in lock out.

Most folks never locked the transmission out unless they were towing a trailer or driving in mountainous terrain.

[old guy rich]

Update. My wife and I just took the Merc on the highway for a test drive. The car is very comfortable at 70 mph in O/D. No tach, but the rpm is considerably lower and the car is much quieter. Small vibration in steering wheel at 70, I'll have the wheels balanced again and go from there. It is now officially and highway friendly car, loving it !! old guy rich.

[cb186]

I cannot sing the praises for the OD enough. I got my 52 from my dad about 4 years ago. He bought it in 1980 as a Ford-O-Matic car and swapped in the OD when he restored the car a few years later. He never finished getting the OD working, so it was just a 3speed. I set to work on getting it working once I got it home and what a difference it made! So much quieter and the flathead doesn't get hot on the highway anymore. Love this tranny.