Installing an R10 Overdrive Transmission

[Loren]

I've been wanting to do this from the moment I heard there was such a thing as a Plymouth Overdrive.

 

I was able to buy one from a fellow who had a 1952 Suburban like mine. I got the drive shaft, a 12 volt relay and a throttle switch.

The Solenoid was used but it was also 12 volt. I had planned to put this one in my Suburban which will be 12 volt, so all was good.

However, my plans changed when I scored the 49 Business Coupe. This car will stay 6 volt.

So that meant changing the Solenoid and the relay. When I went treasure hunting in my storage I didn't not find the throttle switch so I bought a new one. (more on that later)

If you have to buy new, you will find they are reproductions and unlike the originals the terminals are not labeled.

Confusion reigns!

I decided to follow the Mopar shop manual as closely as I could using wires in the colors they used in the schematics.

More confusion.

As always you will need the trouble shooting section of the manual to diagnose why it does work the first time.

Then you find that they didn't always hook things up the same. One drawing has the wires going to the Horn Relay and the other has the Ignition Coil (two wires) and the Voltage regulator as connections. Either set up will work but I like consistency.

The reproduction Solenoid has terminals which should be labeled #4 and #6 and are not.

Look for the drain opening and install that towards the bottom, The #4 terminal this the one closest to the bottom when installed.

The Relay has no markings either. The Trouble shooting section of the manual is helpful here with much better drawings.

Note: if you don't see it right away, IGN means the power source from the key switch not the Ignition Coil. The Ignition Coil is grounded via the #6 terminal on the Solenoid thru the momentary contact side of the Throttle Switch. The BAT terminal is hot all the time. It's the one with the fuse (but not all relays have the fuse)

Before you go to all the trouble of installing the Kick Down Switch, check the continuity between terminals #8 & #9.

Those are the ones nearest the threads.

The reproductions are assembled with what looks like wheel bearing grease inside and that blocks the contacts.

I had to pry mine apart and clean out the grease. I tried replacing it with Vaseline but that didn't work either so I put it back to gather dry.

One thing you will need to do on the short wheel base cars is make an extension to the hand brake cable. The thread is 5/16 x 24 and you will need a coupler. Most hardware stores have 5/16 x 18 couplers in the bin next to the all thread rod. I found mine in the drawers with the hardware. There was no all thread rod in 5/16 x 24 so I had to buy  a  rod and thread it myself. Looks better anyway.

Next is the Overdrive Cable. I used the full length of the reproduction cable I got. The fewer the bends the better. Route the cable in the same path as the hand brake cable except near where the HBC attaches to the transmission. Just let it go under the Solenoid with the bracket attached on the bottom bolt.

Finally you have the speedometer gear.

When I test drove my car I was passing everybody and then it dawned on me the speedo gear was wrong.

Overdrives from the factory had 4.1 to 1 rear axle gears. My 49 has 3.73 gears (currently).

I pulled the speedo gear from the Overdrive and something did not look right, it had big burrs on a plastic gear. There is nothing on a 49 that's plastic I was thinking.

Then I got the gear from my old transmission and it was completely different and metal.

So very carefully I inserted the gear first to see if it felt right. Then I screwed in the collar.

A 1 1/16 inch 12 point short socket fits.

A road test proved all was well.

 

The Overdrive is absolutely transformative!

There is a certain charm about the 1949-54 Plymouths and the Overdrive does nothing to diminish it, in fact it enhances their charm and makes them even more useful.

Some may find it takes getting used to the Freewheeling feature but as an old-time SAAB owner (dating back to 1969) I am right at home with it.

Not having to use the clutch to shift every time is most welcome. In off road racing we always used the Freewheeling to save the ring & pinion gears. I liked it because when you're screaming around a corner things get busy and Freewheeling allowed you to "Pre-Select" your gear shift for the next straightaway.

 

I know some folks are using the T5 transmission. I do not like them. The T5 has an overdriven 5th gear which is good. However, it is a 5 speed which means you have 4 other gears when you really only need 3. When it comes to a three passenger Business Coupe, the T5 turns it into a 2 passenger coupe. Most are sourced from S10 pickups and they have the worst selection of gear ratios I've ever seen (even the automatics!). So with the T5 you have to clutch in every gear, while the Overdrive you don't. In traffic you "row" the car!

 

If anyone needs more information, I am happy to help. 

[kencombs]

And the R10 can be driven as a 5 spd if desired.  2nd and 2nd OD are really useful in traffic.