Identifying Od Transmission R7 Or R10

[40desoto]

How would I identify my OD transmission?  Its off of my 1940 Desoto coupe.  I found this interesting article that mentions that Chrystlers and Desotos where using these overdrives since 1937.. 

http://www.dacoglu.com/desotocd/11A_ThreeSpeed%20With%20Overdrive/Plymouth%20Bulletin%20-%20Overdrive%20Transmission.htm

 

Did they have R10's in 1937?

 

I have attached a picture

[P15-D24]

Usually their is a casting mark on the side with a R7 or R10. 

[Dodgeb4ya]

1940 DeSoto's had as an option a Warner R7B OD transmission.

Bob

[Alshere59]

As was mentioned earlier the R7 will be cast into the side and also there will only be one solenoid where an R10 will have two.

Here are a couple of pictures of my R7. You can see the R7 in my second pic to the right of the solenoid.

[40desoto]

Thank You I have just found the cast on it.  It is an R7B.  what exactly is the difference between an R7 and R10  R10's seem to be pretty expensive nowadays.   Anyone know what i could expect to get for this R7B?

[greg g]

The R10 is a more modern box with on demand cut out through a kick down shift.  I believe the R7 Can only be engaged through a lift of the throttle pedal when engaged, but must be disengaged manually through the actuating cable control.  Internally they are basically the same as far as gears and ratio is concerned.  Not sure if the R7 wil operate in secod gear like the r10 does.  Both are a good choice if you are looking for a more relaxed cruising gear for you car.

[suntennis]

The R10 OD has a speed sensor which is part of the second solenoid which wil prevent going into the OD gear until a speed of around 28 mph. I think with the R7, the car could go  into OD gear at any speed.

[Alshere59]

The R7 engages at 28 and can be kicked down with a switch same as the R10. It also operates in any gear as long as the 28 mph +- is reached. The differences as far as I can tell without owning the R10 is that it lacks the second solenoid and uses a centrifugal unit to engage. You do have to let  off the gas after you hit 28 mph for it to engage. Not sure if the R 10 has that method or not to get it to engage.. George Asche would have better info.

The wiring diagram is here. http://p15-d24.com/files/file/37-r7-od-wiring-diagram/

 

 

As far as cost George Asche normally prices them at about 200 less. That was a few years ago. Do you know if it works?

[wayfarerstranger]

Is there any benefit to be in od 1st & 2ng gear ?  and couldn`t you rig it where you could just drop it in OD when you reached a higher cruisin speed then have it disingage when you drop down to a low speed  manually or automaticly ?

[Alshere59]

The way you describe is pretty much how I use it. I have used it around town just going from 2nd to 2nd Od for roads at 35 to 40 that are stop and go but mainly I use it for roads posted 50 mph and higher. 1st gear would have to be at 28 mph so not likely to engage.