History BW Overdrive: Five Gears for the Price of Three!

This is the way I have been running two different overdrives for over 20 years on a dd/only vehicle now at 114 k miles in this form. I have a push/pull switch mounted conveniently on the dash using the 'T' throttle knob and position, to those of you that are familiar with Advance Design Chevrolet trucks. I am three on the tree and I have modified my home-bent shifting rods to accept heim joints for smooth shifting. Further modification was done to the shifters in the engine compartment, I shortened them and I used the shortest transmission shifter arms to achieve smaller radii. By doing this my shifting is precise, short and crisp.

The first OD I had was a Muncie 319 with the non-synchro 1st gear. The OD I am using presently is the Saginaw version, 1969 vintage with all synchro gears.

I drive a '49 Chevrolet half ton with a '56 235, Edelbrock intake with two X two Carter-Webers, Fentons, X-pipe, 2- 22" cherry bombs (that I doubt have any damping materiel remaining after 20 years).

I recently achieved 17.8 mpg on a random tankful of fuel on a 1200 mile round trip. I find that I enjoy driving at 72 mph as the vibration/harmonics seem to be in a great 'sweet spot'.

Squirrel said something that was spot on so I'll have to walk back to see it. Yes, he mentioned how the Overdrive ON Lamp functions... the way I have it wired above, the light comes on when the governor reaches the cut-in speed, for me ~30 mph. An interesting side note to this '69 OD governor is that it has two adjustments where a guy could actually adjust the cut-in point to achieve a 6 speed! I actually had her set up this way for a couple years... 1st, 1st overdrive, 2nd, 2nd overdrive, 3rd, 3rd overdrive! A true 6 speed. You should have seen friends faces when I 'rowed through the gears'! Hahahahaha.

They are super transmissions, but alas I am a driver not a hot-rodder, but 114 k is a testimony to their durability I would think, of course your results may vary.

My truck no longer has the limiting 4.11 gears of the torque tube. I retained the '49 axle housing, burned off the articulating closed driveshaft axle mounts and also re used the '49 axles. With welded on saddles and a '57 truck 3.90 rear, a driveshaft was fitted to the overdrive. For you math majors that is .70 Overdrive X 3.90 Differential = 2.73, 3rd gear in overdrive. I sport 1936-1937 17" Chevrolet artillery wheels and with Michelin 235 75R 17 tires, which, at 30.88" are a street legal 'poor man's overdrive'. This combination is excellent gearing for the rolling piedmont foothills of central Virginia.

 

Ditto on the Mercury! My first car was a 53 Merc three speed that a previous owner had removed the OD. Very nice car you have!

 

Two really good sources for parts are, DriveTrain.Com, and GarageMotorSports.Com; the later refurbishes solenoids and governors, and does complete transmission overhauls. DriveTrain.Com offers rebuild kits for just about any manual transmission you may have, small and hard parts, and gasket sets. I have personally used both of them without complaint. GarageMotorSports.Com is also on that auction site we all know and love. I am Butch/56sedandelivery.

 

I made my 3 spd OD into a 6 speed using the following diagram The switches are on a control panel bolted to
the bottom of the dash. It probably isn't practical (my truck has a 348 with 3:38 gearing in the differentials). but it is fun. I can't find the article online anymore, but a pdf attached.
don

 

Fun idea but seems not very user friendly. Even using the BW unit as a five speed is overly complicated with marginal if any gains to be had.

 

This is just something I wanted, so I constructed it. I don't think it is complicated, but I have
been accused of making the simple overly complicated, so you may be right. However, I don't
believe everything needs to be entirely rational, otherwise the world would be very boring.
don

 

Actually 6 gears....mine works in first gear 2 .