Has anyone converted to an overdrive transmission? I have a 55 Plymouth 6 cyl. I want to convert to an overdrive transmission. The gear ratio's in this car are low and at 50 the motor sounds like it is screeming.
Someone advertises in Hemmings Motor news that he has overdrive transmissions for Plymouth and the car will be able to reach speeds up to 70mph. ( The speed limit in Florida. ) The problem is he only has a cell phone number, no address or business name. I am wondering if he is on the up and up or is he a scam artist. He is based in Oregon. Any information would be helpful.
Thanks in advance,
Chuck
Ive never done it but I know many people have. The name I hear often when it comes to these types of modifications is:
George Asche
1693 Fertigs Road
Venus, PA 16364
814-354-2621
I installed a George A. overdrive in my 40 Ply. P-9 about 2 years ago now. It was the BEST thing I've done on my otherwise original. The bonus is the "fast 2nd gear" feature it adds. Ask George about the neat feature.
Don
Chuck,
Just remember -- if you want to drive 70 mph, you will need brakes good
enough to stop your car from those speeds.
I have overdrive in both my 50 and 51 Plymouths. These units were available as an option starting in 1952 They were manufactured by Borg Warner and use the same internal parts as those used in most other cars which offered overdrive during that era.
No difference in brake specs was offered in a car which was overdrive equipped and I have not encountered any problems in stopping my cars from legal speeds however if you are stopping from greater speeds you may encounter brake fade. One solution is to use the eleven inch brakes found on Desoto and smaller Chryslers.
A highly recommended option, in my opinion.
When converting a vehicle to overdrive the gear ratio of the rear end must be taken into consideration. As a general rule a factory supplied OD will have a lower gear ratio than a non OD vehicle... If a vehicle has a gear ratio in the 4's or mid to high 3's, e.g. 3.52, 3.72. 3.89, the OD will work great providing low ratio's for hilly country and lower cruising RPM's
An OD trans will kill any vehicle that has gear ratios higher than 3.52... The first step towards considering an OD is to find out just how fast the engine is turning at any given speed.
Put a tack on the engine to find out the RPM's, many times the noise you thought was a high rev'ing engine is actually fan noise... Bill
Bill, I think I'm confused but after a second reading I guess any ratio getting closer to 1 to 1 is higher and the ratios getting further away such as 4:11 would be betting lower right. So the 3.9 in my '41 coupe would be OK with an overdrive. I purchased one last year and I plan to install it this winter in the car. I was concerned about authenticity but then i drive the car a lot and it would be really nice to have that OD in the vehicle.
thanks, Brian
Cars originally equipped with OD usually had a 4.1 to 1 rear axle ratio as did most Plymouths of the 40s which used 16 inch tires. After the switch to 15 inchers the most common ratio was 3.9 to 1. My 50 and 51 both have 3.9 ratios and overdrive added later and everything works well.
It might be a good idea to use a vacuum gauge after installing the overdrive just to see if the engine is straining to keep up. I have a 40 with 16 inch tires and 3.9 ratio.(optional) I fear that the 201 may not do well with overdrive so I have not yet installed one. If I do and the engine seems overtaxed then I will change the ratio to either 4-1 or 4.3 to 1.
Thank you to all that took the time to answer my question. You gave me alot of good answers and alot to think about.
The numbers used for rear end ratios can be very confusing... The thing to keep in mind is the higher the number, the lower the ratio. Most modern vehicles have ratios in the 2.0's, however, they have smaller tires than the average 28" 600x16. As it has been pointed out in the previous comment, a vacuum gauge can be very helpful to make sure the engine is running within it's optimum power range.
If you install an OD in your car you should always disengage the OD when traveling in hilly country. The OD will minimize the down hill holding power of the engine and put more strain on the brakes. This is especially true on the modern AOD transmissions. I always shift my trans out of OD/AOD in the mountains.
An additional feature of the older style manual OD's is the free wheeling feature. Once the vehicle is moving there is no need for the clutch when the vehicle is under about 38 mph....Bill
This is the information I got out of a 55 Plymouth Service Manual. My car is a 55 Plymouth 6 cylinder currently has a 3 speed transmission.
Gear Ratio's 3.73 to 1. Optional-Mountains and hilly country 4.1 to 1.
With overdrive 4.1 to1.
After reading the comments, and I Thank You for them. It sounds like I will have to change the rear gears to a 4.1 to 1 if I add an overdrive set up to the car.
Am I on the right track?