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Borg Warner R-10 and R-11 Overdrives Part Two


In part one of this series I covered the top ten things you need to know if you have a B-W overdrive transmission in your antique vehicle. If you missed part one it is still available you can look for it in the Garage Tech index. Meanwhile with the basics covered this article is a little more in depth and covers some of the operation, troubleshooting and maintenance of the B-W overdrive transmission. So pay attention here and you are guaranteed to learn something.

Driving a B-W overdrive vehicle starts off with the cable pushed in and the vehicle pulling away in first gear as normal. As the vehicle accelerates the driver shifts into second gear.

At approximately 28 mph (BTW - nobody knows why 28 mph and not 25 or 30 mph) a click will be heard from under the hood (which is the activation of the relay on the firewall by the governor) the driver then backs off on the gas briefly, and the transmission automatically shifts into overdrive. The shift is smooth and feels exactly like a shift from an automatic transmission.

The driver must release the accelerator completely so the overdrive transmission does not have to engage under engine load. In an automatic transmission a shift will occur (eventually) even if the throttle is held open. For mechanical design reasons in a B-W overdrive set up, the driver MUST let off the throttle completely to allow the shift to happen.

With the vehicle in second gear overdrive, the overall ratio is not quite as high as third, but higher than second. This is a perfect ratio for in town use. Between stoplights you don’t need to shift into third. However, if you continue accelerating and shift into third (from 2nd overdrive) and you will then be in third gear overdrive, the perfect ratio for the highway.

A common question is… “Can I use overdrive first gear?” The answer is maybe, but you would have to exceed and maintain 28 mph or higher for the overdrive to engage and stay engaged. 28 mph is pretty fast for first gear so 1st gear overdrive is rarely achieved. This means that while a B-W overdrive transmission has sometimes been called a six-speed, it technically provides only five usable forward ratios.

While you are in overdrive if you back off the gas you will feel engine braking in both second and third gear. Because the transmission is still in overdrive, the engine braking is not as strong as if the transmission were in 2nd or 3rd direct drive but the transmission does not coast. If the transmission does coast, the overdrive transmission is not operating properly.

Third gear overdrive is great for gliding along at highway speeds but it can lack power for passing or hill climbing. To get the transmission out of overdrive, push the gas pedal to the floor. The engine will rev up and the pedal will engage the kick down switch, the ignition will be grounded out for about two engine revolutions, (so the overdrive transmission does not have to shift under engine load) and the overdrive will disengage and the transmission will be back into direct drive. This shift feels exactly like the kick down of an automatic transmission. Complete your pass or top the hill in direct drive...then let off the gas completely for a moment, and the transmission will shift back into overdrive.

If you begin slowing down and shift from third overdrive to second overdrive, then slow down further as if approaching a stop light, as soon as the speed falls below 28 mph the power to the overdrive will be cut and the transmission will shift back into direct drive.

This automatic loss of overdrive is a designed in safety feature because you must start out from a complete stop only in direct drive. To try to start out from a standing start in overdrive, you will crush all of the needle bearings inside of the sun gear. That would cost you dearly!

Some owners have rewired their overdrive to by-pass the governor by adding a manual switch to turn the system on & off. If you do this remember…it is very easy to forget and attempt to take off from a stop in first gear overdrive. I have had customers remember for two or three years only to forget… and hear the crunching sound followed by a loud pop! They of course know immediately what that sound is… but by then it’s too late!

Meanwhile… as you slow down below 28 mph, you are automatically put back into second gear direct drive. However, because the sun gear is no longer being held (transmission no longer in overdrive) the transmission will freewheel. This event can be very surprising to someone who is not familiar with the operation of an overdrive transmission as suddenly there is NO engine braking! Since this occurs only below 28 mph there should not be much need for engine braking and using the normal brake pedal to stop the vehicle should work just fine.

But this is also where another novel aspect driving with a B-W overdrive transmission becomes apparent. All B-W overdrive transmissions (in all years of manufacture) used a non-synchronized first gear. They never built a B-W overdrive transmission with a synchronized first gear.

By the 1960s full syncro transmissions were fully available, so why didn’t they make a fully synchronized overdrive transmission? Turns out a B-W overdrive transmission doesn’t need to be synchronized! Drive in second gear overdrive, slow down below 28 mph, and the trans falls out of overdrive and into freewheel mode. Step on the clutch and pull the shift lever into first and you will find it slips into first gear as easily as if it were synchronized, even if you are rolling.

This ‘synchro effect’ happens because the free- wheeling clutch prevents power from being transmitted from the driveshaft into the transmission. Push in the clutch, and there are no forces on the gears. When you pull the shift lever into first gear it slips in easily. The most clashing you get when shifting into first gear at a rolling speed, is a slight “ratcheting” of the gear teeth that you would expect if you were shifting from neutral into the low granny gear of a truck 4 speed or the reverse gear in any transmission.

The freewheeling feature also makes clutchless shifting possible. Start in first, pull away and then WITHOUT depressing the clutch pedal, back off the gas and shift into second as easily as if you had pushed the clutch!

If you shift into third gear before 28 mph (and engaging the overdrive) again there is no need to depress the clutch pedal to make the shift.

If you have allowed the transmission to engage the overdrive in second (backing off the gas) then depressing the clutch is necessary to shift from 2nd to 3rd. These operational features are what made the B-W overdrive transmission very desirable in the days before fully automatic transmissions. No clashing shifts into first; No clutch necessary to shift into second; Automatic shift into second OD around town.

Parking and Pushing

Pulling out the overdrive cable on the dash operates a lever on the side of the transmission that mechanically locks the sun gear to the planetary gears. The cable should only be pulled out while the vehicle is stopped.

When the overdrive cable is pushed in then the transmission freewheels. This happens as long as the vehicle is below 28 MPH (or the system has no electrical power) the overdrive will not engage.

This means that to push start an overdrive equipped vehicle, the cable needs to be pulled out (to lock the transmission out of overdrive) so the transmission will send power to the engine when the clutch is released.

Parking is the other situation that pulling out the OD cable is necessary. If you park pointing downhill and put the shifter into first, second or third without pulling out the cable, the vehicle will freewheel and roll away. To overcome this you can either pull the overdrive cable out or place the shifter into reverse.


In order for the B-W overdrive transmission to back up, the freewheeling clutch MUST be locked out.

There is a shaft/rod built into the overdrive transmission that automatically accomplishes this whenever the transmission is put into reverse. So to park safely (set the brake) and then either pull out the OD cable OR place the shifter into reverse. This locks up the driveline and prevents all rolling.

How The Overdrive Transmission Affects Rear-end Ratios…

All B-W overdrive transmissions function at a 0.7 overdrive ratio. Since all standard transmissions use a 1:1 ratio in high gear, to find out your final drive ratio in overdrive, simply multiply the rear end ratio by 0.7. For example…a 4.11 gear set becomes 2.87. A 3.70 gear set becomes 2.59. A 4.56 gear set becomes a 3.19 ratio.

An overdrive transmission can also compensate for small diameter wheels & tires. Smaller wheels & tires spin an engine faster. 16” wheels turn the driveline slower than 15”, which spin the driveline slower than 14” (as the wheels/tires get bigger they carry more weight and lower the engine speed but they also reduce the available power.

All things are a compromise) All these factors need to be considered when outfitting a vehicle with a B-W overdrive transmission. If you use a rear axle ratio that is too high (numerically low) and/or couple it with wheels/tires that are too big in diameter a vehicle can actually slow down or use more fuel when it is operating in overdrive


The Borg-Warner overdrive transmission (R-10 and R-11) combines both mechanical and electrical components. The mechanical components are very well built and proven reliable and as long as the transmission and the overdrive unit are kept filled with gear oil (see maintenance below) with most of the problems being electrical, which are very easy to trouble shoot.

Take an overdrive vehicle out for a test drive with the overdrive cable pushed in, if the overdrive transmission freewheels above 28 mph (and you don’t feel the automatic shift) the trans is OK but there is an electrical problem.

The overdrive transmission electrical system is protected by just one fuse clipped to the relay on the firewall. This fuse gets power whenever the key is turned on (four post relay). Begin your diagnosis by checking for power at both sides of this fuse. 

Because the relay is under the hood, the fuse and it’s mounting clips easily become corroded due to the environment that they live in. Remove the fuse, and clean all the contacts thoroughly and check for voltage. If there is no battery voltage present, trace the wire back to the key switch to find the break in the wire.

If you have good power on both sides of the fuse at the overdrive relay, the next check is made under the vehicle. At the back of the transmission is the governor. This is a cylinder shaped device that is driven by the speedometer gear with ONE wire coming out of it. Inside the governor are weights that spin with the driveshaft. When they reach the magic speed of 28 mph, the wire going into the governor is grounded which engages the overdrive.

For some reason the governor wire coming off the governor was always made using the old cotton cloth insulated wire from the 1930s. This wire always seems to have a frayed spot along the insulated coating. It is also a good idea to remove the lid on top of the governor and check the points inside to make sure they are not stuck together or coated with oil caused by transmission oil leaking into the governor from the transmission (bad seal)

With the ignition key turned on, jump the governor wire to ground. You should then hear a click from the relay on the firewall. That means the signal from the governor is reaching the relay on the firewall.

Power comes from the fuse through the relay, which is then activated whenever it is grounded. Power from the relay to the governor does pass through the kick down switch. If there is no relay click when grounding the governor, check for battery voltage at the battery wire and trace it back to the kick down switch and then back to the relay to find the open circuit.

If you have battery voltage at the governor and you hear a relay click when you ground the governor, then the relay should be sending power down to the solenoid. As soon as the solenoid gets power, it too should click. If the solenoid does not click, check to see that it is receiving full battery voltage from the relay. A faulty relay can sometimes reduce the amount of battery current delivered to the solenoid so check to make sure the solenoid has full battery voltage at the number (4) terminal.

Which Solenoid Terminal Is Which…?

There are two wiring terminals on the overdrive solenoid. The number (4) terminal on the solenoid gets its power from the relay, and activates the solenoid plunger shaft. With the solenoid shaft pointing away from you (just like it is in the car) and the two solenoid terminals on top of the solenoid at the 11:00 and 1:00 positions…the RH terminal is always the number (4) terminal.

You can apply battery voltage directly to the number (4) terminal using a car battery or a 10 amp battery charger) and then by grounding the negative jumper wire (or lead from the charger) to the case of the solenoid, the solenoid should engage. If it does your solenoid is good.

90% of the time all the electrical problems are nothing more than loose and dirty connections. Remove the wire connections at the relay and the kick down switch and ensure that they are clean.

I have had to carefully spray the terminals with electrical contact cleaner and polish the contacts using steel wool or a scuff pad to restore the connection.

On a rare occasion you might have to bend the tabs on the bottom of the relay cover so you can remove the cover and gain access inside the relay to file the contact points, but that is rare. We have new solenoids, relays and kick down switches available if yours are defective.


Maintenance of a Borg-Warner overdrive is pretty easy. The most important thing to remember is that there are two places to add GL-1 gear oil into the transmission. There is the normal plug/hole in the side of the transmission but another plug/hole is in the tail shaft area. Fill both to the bottom of the hole with GL-1 gear oil (which was factory fill) as you would for any standard transmission. 

It will take about a gallon to fill both the 3-speed transmission and the overdrive transmission. You will have about a pint left of your gallon when you are done, depending on how much you dribble on the floor during installation.

Lubing The Dash Cable

In a functional system you will find that you rarely need to to lock out the system. If you are restoring an overdrive equipped vehicle you will most likely find that the overdrive cable has not been used and is stuck.

The cable must be removed completely to free it up. A big nut behind the cable secures it to the bracket under the dash. A 1/2” nut & bolt secures the functional cable end to the lock out lever on the transmission.

The upper bolt on the solenoid (in some applications) secures the bracket that holds the outer cable. (Once unbolted, this sheet metal bracket is spread apart to remove it from the cable) Unbolt everything and pull the cable out through the firewall into the interior.

By twisting the outer cable you should be able to break loose the inner cable enough to remove it. Use sandpaper to clean all the corrosion from the inner cable. Then use a wire wheel/brush to remove all the crud from the outer cable. Next insert the inner cable back into the outer sheave and spray the entire assembly with WD-40 or similar lubricant. The outer cable is composed of wire tightly twisted around the inner cable.

This design allows the lubricant to easily seep inside. Reinstall and work the cable back and forth and it should begin to move easily. If it is too far-gone we have new cables available in the parts section of our website.

Checking the Governor

When the transmission gets “stuck in overdrive” you already know what to do first, if you read the tech tips and related information discussed earlier. Besides the careful rocking motion and solenoid service discussed earlier, you need to check one more thing if you are still having trouble… the governor.

First remove the cover of the governor and then hold the governor contact points apart. Next ground the cover of the governor by touching it against the transmission case. If that causes a  “click” to be heard, the “click” indicates a short circuit in the governor cover assembly and the cover assembly wiring connections or the wiring itself  is “shorted out” and needs to be repaired. If there is NO click, the governor is ok and you need to look to the solenoid for your defect.

Removing and Replacing The Governor

To remove the governor from the transmission, first disconnect the wire at the cover (or wire end connector) and loosen the governor housing using an (1-3/8”) open, end wrench to turn the nut at the base of the governor. To replace the governor insert the governor into the transmission housing and engage the teeth of the governor drive gear into the teeth of the speedometer drive gear. Next, tighten the nut located at the base of the governor housing using an (1-3/8”) open, end wrench. Reconnect governor wire and check for proper transmission operation.

Reverse Lockout Switches

If your reverse lockout switch fails there are not any new ones available so your best bet is to remove the defective switch and connect the two wires together that were connected to either end of the switch. Reverse lockout switches were discontinued on B-W overdrive transmissions beginning in the early 1950s. Your B-W overdrive transmission will work fine without one.

Don’t forget to read the other Garage Tech entry on overdrives…that covers the top ten things you need to know if you have a B-W overdrive transmission in your antique vehicle. Between this entry and the other one you should have a pretty good idea how an overdrive transmission works and how to troubleshoot it. 

And last but not least don’t forget to order a copy of Randy’s book “The Official Guide to the Borg-Warner R-10 and R-11 Overdrive. The book includes history interchange information, tech tips and a complete illustrated service guide. The book is available in the overdrive section of the parts pages.

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About Me

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Since 1987, Fifth Avenue owner, Randy Rundle, has been making antique, classic and special interest vehicles more reliable and fun to drive.