Merc OD

I test the kick down switches with an Ohm meter to make sure the two circuits open and close as they should. If it has a rail switch then it has to function or it can be bypassed. Governor switches are pretty reliable but should be function tested. The operating solenoid has two internal breakers to function the ignition after drop out and to bypass the pull in coil to the holding coil. A person can pull the cover off and bench test the unit. They aren't too difficult to remove and reinstall. The dash relay can also be tested to insure function.

I usually pull the OD handle out if the system isn't working. If the transmission still functions with the handle pushed in then that's a good indication but a person won't know about the planetary till all the electrics are functional and it actually shifts into overdrive. Make sure the shift rail is working smoothly and that the unit has oil in it.
 
If you have continuity between the 2 terminals closest to the floor then you don't need to bypass the switch. The switch is normally closed and interrupts the ground to the relay when you go full throttle (and interrupts the ignition and solenoid).

If you don't have continuity then jump the white wire from the rail switch to the red with white tracer wire going to the relay. See picture attached.
 

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Dan in MI said:
If you have continuity between the 2 terminals closest to the floor then you don't need to bypass the switch. The switch is normally closed and interrupts the ground to the relay when you go full throttle (and interrupts the ignition and solenoid).

If you don't have continuity then jump the white wire from the rail switch to the red with white tracer wire going to the relay. See picture attached.
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532243
 
One thing you said in post 13 was you put power to the relay and it closed. That I hope was not what happened as you need to ground the relay to actuate it which turns on the OD system. A good bench test in the car is to ground the third terminal on the relay, it should click and you should hear the solenoid click at the same time. The third terminal is the one going to the speed switch/governor via the kick down switch. if you need a new kick down switch Napa has them or they did 3 years ago. If it free wheels the overdrive gears are in workable condition. Tim
 
In post 22/23 I have an additional "box" (lack of knowing what it actually is) between the rail switch and the governor. It's not a wire leading directly from the rail switch/actuator to the governor.

I've read something about an additional switch on the 49 and 50 mercury that they did away with half way through 50 and all together in 51. Most guys eliminate whatever this switch is because it gives problems. I can get a picture of it tomorrow in hopes someone can correctly identify what I'm looking at.

Napa by me is closed on Sundays and we're not answering the phone when I called earlier, they're the only place locally that I'm aware should have the kickdown switch.

My plan for tomorrow is run a direct wire with a switch. I have plenty of rust holes that make it easy to do this for the time being.
 
Pvmt-Pndr said:
Temperance MI, just north of toledo.

Duplicating the test I'm seeing as high as 12 ohms while spinning my drill max rpm. An open circuit when not spinning
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12 ohms is very high, you should get near zero. Take a look at the contacts and carefully clean them. You don't need to remove any metal, but you do want to clean off any baked on grunge or corrosion.


Pvmt-Pndr said:
In post 22/23 I have an additional "box" (lack of knowing what it actually is) between the rail switch and the governor. It's not a wire leading directly from the rail switch/actuator to the governor.

I've read something about an additional switch on the 49 and 50 mercury that they did away with half way through 50 and all together in 51. Most guys eliminate whatever this switch is because it gives problems. I can get a picture of it tomorrow in hopes someone can correctly identify what I'm looking at.
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That extra "box" is the rail switch in the diagram above. The purpose of that was to turn off the electrical part of the overdrive when you pull the cable out and lock the unit out of overdrive. If your new wiring harness includes connections for the rail switch you can bypass it by putting both wires on one lug.


Pvmt-Pndr said:
My plan for tomorrow is run a direct wire with a switch. I have plenty of rust holes that make it easy to do this for the time being.
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If you find like manually controlling the solenoid we can talk you through making this a safe and permanent method. I have swapped overdrive transmissions into several old Fords without adding all the controls. It becomes a preference thing whether you prefer the factory controls or manually controlling it.
 
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You never know what someone may have added to one of these systems, The rail switch was considered to be redundant when the Mercury cars went to the 259 series transmission in early 1951. I'm glad that my early 1951 cars still have the earlier transmission that has the rail switch. When the shift rail is moved out of overdrive by pulling the cable handle, it shuts down the capability for the system to function and blocks the pawl from being able to move. With no rail switch, the electrics still function and waist electrical energy.

I maintain my rail switches and keep good used ones in my inventory of spares for the two Mercury cars I own. I'm a believer in keeping the original system fully functional. It provides several operational safe guards that manual switch function of the operating solenoid would bypass.

I also want to add that the overrunning clutch function is not an indication that the planetary is functional. It has to be engaged into overdrive to tell if the planetary is functional. The freewheeling unit is just that and it sets behind the planetary gear train. Freewheeling capability is the only way that the system can function to shift and downshift. Engine braking is minimal when the shift rail is in the overdrive position. When it's locked out, engine braking is restored. While in OD it saves wear and tear on the timing gears but the service brake wear increases. There is always a trade off. The overdrive adds in a more fuel efficient function by addition of the taller ratio and by the ability to coast more efficiently when letting off the throttle pedal.
 
You're absolutely right about it being the rail switch, I'm not sure how I overlooked that.
Any idea what the rail switch should ohm?
I'm not seeing any smoking gun on why my system isn't working. I have no interest in not having the system functioning any way but factory long term.
Just to clarify. My easiest way to force the system to work is to install a toggle between the wires running in and out of the rail switch into the car. I have plenty of nice switches
 
The rail switch is either open or closed so ideally the OHM reading is 0.

Putting a toggle switch in place of the rail switch will only force the OD to work IF the rail switch is the only problem. Instead of using the switch just connect the 2 wires together like the late 1951 vehicles and try it. Remember, nothing will work until the governor at the tail end of that circuit completes the ground when it reaches 27 mph (or where ever it is set at). If it works then the rail switch is the problem. If it doesn't work then you need more testing. The next test would be to put your switch between the wire running to the rail switch from the kickdown switch directly to ground. If it works then the problem is in the rail switch, wire to governor, governor or the governor ground.

This doesn't mean that there is an issue on the power side of the circuit. Correct voltage, good relay and fuse, wire connections, solenoid and solenoid ground can all be issues. Having multiple issues is a real possibility. The best thing I can tell you is read the manual I sent earlier, understand the whole system and check everything.
 
The test to see if the overdrive mechanically functions is to simply add a switch and wire that activates the solenoid. This ignores all the other electrical controls and test the mechanical part of the overdrive. Putting power to one of the two connections on the solenoid will cause it to engage. Wire your test switch to that side of the solenoid and verify you can hear the solenoid engage when you turn on the switch. If that works take a test drive. Make sure the lock out cable is pushed in. Get up to around 30 mph in third gear, turn on the switch, then let off the gas pedal. The order of operations is important, engine must be able to drop rpm by 30% after the switch is turned on. If the solenoid and planetary set are ok the overdrive will engage. To drop out of overdrive turn off the switch and let off the gas, the transmission will free-wheel.

Let us know the outcome of this test. If this is successful then we can diagnose the control side.
 
38 coupe said:
The test to see if the overdrive mechanically functions is to simply add a switch and wire that activates the solenoid. This ignores all the other electrical controls and test the mechanical part of the overdrive. Putting power to one of the two connections on the solenoid will cause it to engage. Wire your test switch to that side of the solenoid and verify you can hear the solenoid engage when you turn on the switch. If that works take a test drive. Make sure the lock out cable is pushed in. Get up to around 30 mph in third gear, turn on the switch, then let off the gas pedal. The order of operations is important, engine must be able to drop rpm by 30% after the switch is turned on. If the solenoid and planetary set are ok the overdrive will engage. To drop out of overdrive turn off the switch and let off the gas, the transmission will free-wheel.

Let us know the outcome of this test. If this is successful then we can diagnose the control side.
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I hooked a wire from the battery, through a 30 amp fuse directly to the solenoid and no luck with the OD kicking in. I can clearly hear the solenoid moving but there is no engagement.
 
I would crawl under the car and check that the solenoid is installed properly. When it is installed properly but unbolted (the bolt holes lined up with the transmission holes) you can pull down on the solenoid and it will not slide out. If it does slide right out reinstall it properly. It must be rotated slightly for the flats in the shaft to line up and go into the slot in the pawl. If that isn't done carefully you don't get engagement. I learned that the hard way on the first overdrive transmission I installed.
 
rotorwrench said:
Freewheeling capability is the only way that the system can function to shift and downshift. Engine braking is minimal when the shift rail is in the overdrive position. When it's locked out, engine braking is restored. While in OD it saves wear and tear on the timing gears but the service brake wear increases. There is always a trade off. The overdrive adds in a more fuel efficient function by addition of the taller ratio and by the ability to coast more efficiently when letting off the throttle pedal.
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Was "timing gears" a typo? Did you mean transmission gears? Lots of good easy to understand info on overdrive in this thread and I've looked around a lot. I'm in my first o/d car and trying to learn as much practical stuff as I can.
 
When the engine is acting as a brake on a vehicle with a standard manual transmission, the compression in the cylinders is the braking force. This also causes more force to open the exhaust valves. This puts more pressure on the cam and gear train as well. The extra pressure is not necessarily detrimental in the short term but over the normal overhaul life, it will cause more wear on cam lobes, cam bearings, followers, and gears. It's more evident on engines with timing chains than gear drives. Push rods on ohv engines also wear more.

How much a person uses the engine to slow down versus using the service brakes is up to the individual. Manufacturers of large truck engines tend to make the affected components hell for stout so that the engine can take a lot of Jake braking from those that use a Jake brake to offset use of service brakes.
 
Run a wire from the switched side of the relay to the solenoid power terminal or wire and disconnect the wire to the coil. Tim
 
It's been a busy week for me. I haven't messed with the car at all. It's going to be decent weather this weekend, I'm going to take it out and see if maybe the problem was me before I dig into it even more. Everything there should work. I was treating it more as a 2 speed rear end and shifting it like that. After rereading I believe I was doing it wrong and possibly not allowing it enough time to engage. At least I hope that's what it was. I had a 1969 C60 basically a little semi by today's standards with a 427 and 2 speed rear. I drove it enough to become second nature to shift it properly. Plus I was just excited that it should have worked. I'll report back after another drive, hopefully with good news.
 
@rotorwrench. Thanks for the explanation. That's some eye opening automotive theory. Tradeoffs in everything. I certainly will factor that into my driving habits and keep the brakes in top shape.
 
The original idea on how to operate the Borg Warner overdrive was to use it as a semi-automatic transmission for around town driving. They generally had somewhere near a 3.9:1 rear axle ratio so that the car could start out in 2nd gear from a stop. As soon as the car got up over 25-MPH just let up on the throttle and it would shift into 2nd & OD like an automatic transmission. The only time the clutch was needed was to pull away from a stop and during a full stop.

When automatics came out in 1951, they were designed to start out in 2nd gear unless manually shifted to 1st or pushing down hard on the throttle pedal.

I grew up on a farm so I'm real familiar with 2-speed truck rear axles. Using the switch right on the shift lever makes it easy to shift but its set up for split shifting to make best use of ratios for hauling heavy loads. The shift mechanism in the rear axle is relatively simple compared to the Borg Warner OD transmission set up. The old Columbia OD rear axle worked in similar fashion to the trucks except they were vacuum operated. The real old trucks with 2-speed axles had manual linkages operated by foot or hand lever.
 
Update: IT WORKS! I was correct in me being the problem with the manual switch installed. At low speeds going off the sound of the exhaust it isn't very obvious. At 50+ mph it's undeniable.

It's wet outside and I wasn't very happy taking her out in it but it was worth it. She's now back in my garage drying out.

For those reading in the future like me who don't know anything about a merc OD... when the OD kicks in it feels like a modern automatic trans converter locking up, quiet, hardly noticeable but there if you're paying attention. She no longer feels like I'm close to over reving it at 60. Now aside from a little exhaust and motor noise at 60 I can hear all the other flaws of the car....

I'm going to replace the kickdown switch because it's ugly and splitting apart. I have a box full of parts for it I'm going to move on to now and I'll get the OD working like it should later for now I'm happy to know it works.

Thank you everyone for all of your help! I'll be on soon asking about all kinds of other things.
 
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