Overdrive

[Jim Shepard]

I've got a 50 PU and have been wrestling with how to get a little more top speed. With my 4:11 rearend I'm only doing about 50 mph and the motor is really screaming. I've thought about changing the pumpkin or swapping out the whole third member. Someone suggested an overdrive unit. I've looked in my Motor Manual covering the fifties cars and there are many cars of that era that had overdrive, usually with a three speed, which is what my truck has. I'm guessing one of these might bolt up, but can someone tell me how they work? The manual mentions a soleniod, which I know is electrical. How do these things shift?

[blueskies]

can someone tell me how they work? The manual mentions a soleniod, which I know is electrical. How do these things shift?

Jim-

I have the R-10 Borg Warner OD in my '50 Plymouth.

The OD and the transmission are one unit, the OD section cannot be bolted to the back of the standard three speed transmission.

They way the OD works is very simple.

There is a lockout cable to prevent the OD from enguaging, handy when you want to decend a long grade, because the system freewheels if it is not locked out with the cable.

The rest is automatically controlled with a series of electrical circuits.

There is a governor that energizes the system when you reach a cut-in speed of about 26 mph. Once the cut in speed has been reached, the system will automatically shift into OD when you release the torque on the transmission by letting up on the throttle. The system will then stay in OD until you either drop below the cut-in speed, or use the kickdown switch.

If you drop below the cut-in speed, the system will automatically shift out of OD. If the system is wired per the factory setup, when you mash the pedal to the floor, the kickdown switch is pressed and it will shift out of OD, much like a modern automatic under full throttle.

I have the kickdown switch mounted to my shift lever, so I have it working a bit differently than the factory intended. You can read about this on my site under the Transmission Page.

There is also a relay and solenoid that are part of the system, and a reverse lockout switch (that works with the lock out cable, mounted to the tranny). I bought these parts in 12v, but they are available in 6v too.

I think the OD is a great thing, it is what makes my car a daily driver instead of a parade car. I can cruise all day long at 75mph and get 19 mpg with my hopped-up flatty. The system is reliable and simple, I have nearly 12,000 miles on my OD with out a single issue to date.

I would do it the same way again if I were to build another flatty power car.

Pete

[Jim Shepard]

You didn't say - is yours an original setup? Alos, my manual does show a separate OD unti that looks like it bolts up to the back of the transmission. Of course, it also doesn't say what make it is. Did MOPAR ever make a separate unit that might work with my three speed tranny?

[blueskies]

You didn't say - is yours an original setup? Alos, my manual does show a separate OD unti that looks like it bolts up to the back of the transmission. Of course, it also doesn't say what make it is. Did MOPAR ever make a separate unit that might work with my three speed tranny?

My OD/transmission is a 1955 Dodge unit.

The transmissions look the same from the outside, and the tail shaft of the regular three speed is the same length as the OD section of the OD/transmission. However, there are a few internal differences in the transmission half of the OD/transmission. The reverse shift rail is much longer, and extends into the OD case so that when you put the transmission into reverse, the shift rail presses the reverse lockout switch which is mounted on the OD case.

Here's a pic of my transmission going back together with the OD. You can see the reverse shift rail sticking out of the transmission case toward the OD case:

To my knowledge, all of the R-10 transmissions with OD are the same. You might call George Asche, he is the undisputed guru of the mopar OD, I'm sure he will know...

Pete

[Jim Shepard]

Thanks for the information. My interest in keeping my tranny has to do with additional cost, but also I didn't want to mess with the linkage. Did you have any issues with the column shift or linkage? Did you have to shorten the drive shaft?

[Young Ed]

Jim I don't think you can put that car OD behind a pickup tranny. That 3spd is totally different. I have tall 16in radials and a 3.90 rearend in my truck and it cruises nicely.

[Normspeed]

I'd say it would be easier and cheaper to change rear gears, either with a different gear set or a swap to a newer rear end assembly.

Guys, not trying to pirate the thread but while there are some transmission folks on this thread, can you tell me what the short Mopar transmissions in this photo might fit? Trucks maybe?

[Jim Shepard]

Your 3.90... what did it come out of? Did you just swap the pumpkin or the whole third member?

[Young Ed]

both possibly truck trannys. The one wiht the longer input might be the fluid drive version. They would have to be post 47 because of the column shift. Another possibility is the short wheel base tranny from 49-52.

[Young Ed]

Came out of a early 50s plymouth car. Just swapped center section.

[55 Fargo]

Jim, I have a 1955 Fargo truck frame, but the engine trans and drive train remain on it, the rear end is from a late 70s Cordoba, I think, I bought this for the engine, so possibly you could switch the diff to a more modern one with taller gears. If you can get a 3.90, great, go with taller tires to help lower the RPM. I am in a similar boat, I currently have a 4.30 in my 47 Chrysler coupe, not sure who the brain was behind putting that in this car. To make things worse I have p205 70 15 temporarey tires on it, first thing I am going to switch to P225 75 15 tires, they are over 2 inches taller and will help bring down the rpm. At 45 mph, this setup is already busy at 50 to 55 its screamin, with the new tires, I should be able to drive at 50 to 55 mph, a lot better, until I can either get an OD trans or swap the diffs...........Fred

[blueskies]

Thanks for the information. My interest in keeping my tranny has to do with additional cost, but also I didn't want to mess with the linkage. Did you have any issues with the column shift or linkage? Did you have to shorten the drive shaft?

Jim-

don't know anything about the trucks, but on the regular wheel base cars, the OD transmission is a direct swap for the stock three speed. The only difference is the additional cable and electrics.

I think the trucks have a different bell housing, so I don't know how that affects the rest of the linkages, etc.

Pete

[Reg Evans]

Jim,

How tall are your tires? I have 750 x 16's on one here and they are 31" in diameter. Quite a difference in rpm compared to a 650 or 700.

Maybe one of my junkers down the hill would have a better ratio. Come and have a look sometime.

[Jim Shepard]

I know we talked about that when I was up there in July. I will change my rear wheels if you have two 16's. I still think I need to do something further. I'm really leaning toward a three speed with OD. Maybe I just need to start scouring the wrecking yards. I think with an OD and taller tires in the rear, plus some slight engine mods (dual carbs and exhaust), I'll be satisfied. I'd just like to cruise a little closer to 65mph without the motor breaking. Maybe I can get up your way sometime in October...

[Reg Evans]

I do have a couple of 16" rims with the hub cap clips on them. Let me know when ya wanna come up.

[Jim Shepard]

Will do. Probably the latter part of the month.

[wilmot andy]

I have a 49 dodge, with the fluiddrive. I was looking at an adaptor and T5 tranny, but what years dodge would I have to look for to get a transmission with OD? Would these be a three speed with OD, and use the existing shift linkage? I know of a few junkyards nearby, but would like to know what years or mkes I would look for. Thanks, Andy

[bkahler]

Jim,

My 51 B3B has 3.73 and came from the factory that way. You might also consider looking for a B3 series rear that has that ratio. I believe 51 was the first year 3.73 was offered.

I don't know how it drives as I've not yet had it on the road. Someday I might be able to report on that!

Brad

[Young Ed]

That ratio was available in the job rated series too. The option manual shows my 46 could have had a 3.73 but not the 3.90 I put in it. Weird.