Overdrive Question

Vic Piano

Vic Piano

Well-known member
I’ve been thinking about installing a Mitchell Overdrive unit in our ’39 CS as I’ve just about given up on finding a Columbia for a reasonable price…:( I have a few questions that I hope some of you can help with. First; the car has a 3.78 rear so, of the two ratios offered (26% & 36%) which would you recommend for extended highway driving, and why? Second question; have any of you installed one of these units in a ’39, if so, did you have to modify the rear floorboard just in front of the rear seat riser to clear the gearbox? As always, any help is appreciated. Thanks, Vic
 
Vic there are plenty of the later Columbia's around at reasonable prices. Years ago I bought 13 for $3,000 which made 8 or so complete rears. Most all of these were from 40 Fords. I also made a jig to modify the 48 to the 39 width so if you find one bring it over and I'll fix it for you. For me it's either a Columbia or the next choice would be a 3:54 rear. These engines have plenty of power for a 3:54. G.M.
 
Vic,
I have never owned a Columbia but the 3.54 gears made my `35 a different car and I live in hilly country. One of the best changes I have made.

Shadetree
 
George & Shadetree, thanks for the information, the swap to 3.54 gears would be less expensive and, from what you both say, an excellent alternative. George, I've got the Columbia for our '39 LZ and, if you don't mind, I'd like to have you take a look at it before we install it. Vic
 
Not to hijack the thread, but does anybody know why manufacturers decided to add overdrive units instead of just adding another gear in the ******? It seems that a 4 spd (or 5 spd) overdrive transmission like we have today would have been a less expensive (and less complex) option.
 
Vic, reproduction 3.54 gears with a 6 spline pinion will drop right in that '39. Those gears are available from Speedway Motors for ~ $350.00. In the meantime maybe a Columbia will show up at a reasonable price and you could do a switch if not totally happy with the 3.54 gears.
 
Im really happy with the mitchell. I have a 35 and had to modifly the floor. You could just make it like a bigger trans tunnel. Even though i ordered the 36% reduction It maths out to be a .74. I got the stick shifter for it and its really awesome. You can split any gear or just leave it in overdrive. I have a 4.11 and 650 tires and spin about 2500 rpms at 70mph.
 
Vic, I have a Mitchell in my 41 pickup, 3:54 gears and 26% unit.
2100 rpms at 70 mph. It's a pickup, so no problem with the floor.
I love it and recommend it. Two guys and 4 hrs, easy install.
Talk to Sue Mitchell, she can answer any question you might have.
 
Vic, on my two Model A's, the coupe has a Mitchell 26% with 3:78 rear and the roadster has a 3:54 rear with std. three speed trans. The Mitchell is far superior to the 3:54 rear for performance in my judgement. The Mitchell is more versitile especially when climbing hills. The gears are synchromesh so shifting from high to low range is very easy and it gives you a long second gear on accelleration in high range. It's a sturdy unit and has been in my A for 5 years with no problems.
 
I sure wish they made them to where they would fit later models like my 55 F100. Speeds above 60 with the stock 3:92 ratio really winds the RPMs on the 223 six banger.
 
Mike51Merc said:
Not to hijack the thread, but does anybody know why manufacturers decided to add overdrive units instead of just adding another gear in the ******? It seems that a 4 spd (or 5 spd) overdrive transmission like we have today would have been a less expensive (and less complex) option.
Click to expand...

Direct drive is determined by the speed the car will operate most of the time. You want to runt the motor in the rpm range where maximum torque is delivered. These cars spent a lot of time at 35-45 mph. Nothing like today. You wanted to be able to speed up or slow down a bit without having to shift. Direct drive in the transmission also does not load any gears. The cluster spins free while the main shaft is locked up. This make for quieter operation and less stress on the gears. An overdrive gear will mean gears are meshing. I am going to guess they are able to do that today because of better engineering with closer tolerances and better machining methods.

In a torque tube setup a ttwo speed rearend made the most sense for different driving conditions. I am making some guesses here so feel freee to make any corrections or add anything I may have missed.
 
I put 3:54 in my 34, but in the 34 you have to use an adapter & shorten the drive shaft, not so in 35 up. I am very pleased that I did so.
Gary.
 
Thanks to everyone that responded, I appreciate all your input only now I'm “impaled on the horns of a dilemma”... I've got to decide if I want to go with the Mitchell OD or a 3:54 ratio...??? Based on the information I’ve been given, there are pros and cons to each option. Cost is a major factor however; the overall performance is as well. I don’t think I’ll do anything until after I get back from the Moonshine Festival. I’ve driven the ‘39CS on a lot of highway speed driving over the 20+ years I’ve owned it, but I think it’s time to kick it up a notch. Thanks again to all. Vic
 
Another alternative is to install a B-W overdrive. The overdrive is modified to fit the torque tube much like the Mitchell. Originally the B-W was attached to the rear of the transmission.

These conversions are done by a fellow in Ohio ... Lloyd Young, I believe. And also a couple of guys in California. The price is considerably less than the Mitchell or Columbia.

The strongest, rock-solid, simplest, most versatile overdrive is the Mitchell.
 
Hoop said:
Another alternative is to install a B-W overdrive. The overdrive is modified to fit the torque tube much like the Mitchell. Originally the B-W was attached to the rear of the transmission.

These conversions are done by a fellow in Ohio ... Lloyd Young, I believe. And also a couple of guys in California. The price is considerably less than the Mitchell or Columbia.

The strongest, rock-solid, simplest, most versatile overdrive is the Mitchell.
Click to expand...


Thanks Hoop, now you've added another dimension for me to think about... Looking forward to seeing you at Amelia. Vic
 
Vic, found this phone number for Lloyd, 614-837-7832

(Amelia, one feature will be the 50th anniversary of the Ferrari 250 GTO. See you there.)
 
Heres what the Mitchell looks like, ready to install. The unit can be set up to use in a later car with open driveshaft. Call and talk to Sue Mitchell, she can answer any questions you might have as to it's adaptability.
 

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Vic, I have been watching this thread with interest as I want to do something with my '40 Ford Conv. I would love to have a Columbia set-up, but locating all the parts along with the cost compared to other options puts it on the "back burner!" I was thinking Mitchell for a while (and still am), then I purchased a 3:54 gear set from Speedway for $350. It is still sitting on the bench as I type.

I have a 3:54 gear in my '32 5-W. It works great! I generally cruise around 55-60. That's fast enough...especially with the mechanical brakes etc. of the '32.

Let us know what you decide....can't wait! :)

Good luck, Pat
 
Vic, you might also look for an overdrive transmission out of a 40's Zephyr. It would work great for you also.
Butch
 
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