Overdrive

[Guest sndtubes]

Hey everyone, I have a 1930 Buick Model 46. I have installed 3.5 rear end gears, but I think the car still could benefit from having an overdrive installed. Does anyone know if this can be done on torque tube car such as this, or anyone who could do it?

thanks

Mike

[NTX5467]

A 3.5 rear axle ratio x .70 = not enough rear axle ratio for adequate performance in overdrive, typically. Not enough fuel savings to justify the expense either. Less engine rpm at cruise doesn't always equate to significant fuel savings. Even in the 1950s, OD equipped vehicles had rear axle ratios on the order of 3.90s, 4.11s, or deeper so they could have better performance (and less shifting once in direct or high gear) and still have good cruise economy (one reason that ODs used to be the "hot tip" for better performance in those times too). Modern vehicles with more power, more torque, and electronic engine controls work much better with a 3.42 gear and OD than the earlier engines with much less sophisticated carburetion, manifolding, and such. Don't forget that a larger tire with that 3.50 rear axle ratio makes it a lesser numeric axle ratio compared to a smaller diameter tire so that 3.50 could actually be "acting" like a 3.00 compared to the same gear with a smaller tire.

Just some thoughts,

NTX5467

[Guest sndtubes]

Hey thanks for the tips. In theory I would agree with you. However, in practice, I think the car could handle an overdrive still. It seems that when I get to 50MPH or so, I'm ready to shift gears again. The engine is racing pretty good at that point. I'm sure, of course, I'll be shifting out of overdrive to go up hills, but on relatively flat surface and down hills I think an overdrive would be great. I did find that Gear Vendors can do the job, but it's about 4 grand and I'm not sure it will be worth that much to do it.

[NTX5467]

Sometimes, engine sounds can be deceiving and not fully accurate for the rpms being turned. Putting a tach on it might be a better gauge of things.

Enjoy!

NTX5467

[Matt Harwood]

I'll second the overdrive not always meaning better economy. A real-world test recently became available to me in my wife's new Audi TT roadster. It has a trip computer that will give instant fuel economy, and I have noticed that for anything below about 70 MPH, fifth gear (direct) actually gets significantly better mileage than sixth (overdrive). I presume this is because it requires more throttle to keep the car moving at slower speeds in overdrive.

I do understand what you mean about needing another gear based on engine sound. I've found that the sounds are deceiving. I work at a dynamometer company, and frequently we have cars being tested that sound like they're screaming along at 9000 RPM, but are actually just cresting maybe 4000 RPM. I've often thought, "He'd better shift pretty soon," during a test, only to find that the car can continue to accelerate for another 50 MPH in that gear. So don't base your assumptions on engine sound. You should easily be able to calculate engine RPM at a given road speed using the tire diameter, differential gears and high gear in the transmission (probably 1:1 in these old cars).

Hope this helps.

[Guest]

I have been following this thread since i am trying to get the overdrive in my Packard to work correctly. One thing I think about when travelling at highway speeds in old cars is that cruising above 50MPH may be a nice thought but the brakes, steering and suspension on these old cars were not designed for higher speeds. I have talked to several owners of Model A Fords for instance who have upgraded the engines and added overdrives to be able to maintain modern highway speeds but are still running with skinny tires and mechanical brakes. This is simply not safe. The answer of course is modify your Buick totally with modern engine, suspension, and juice brakes but that is an option that I do not like to see on any antique car let alone a fine auto like a Buick. My advice is to use the vehicle within its design limits and enjoy the world at the slower pace. Just my 2 cents.

[Guest]

I don't think you need an overdrive. I think you will find too much shifting if you get one. You probably are not used to the noise that these engines and cars make at speed.

According to the owners manual on my 1930 Pontiac the carb is designed to give optimum mileage at 55 mph. I have driven this car as my daily driver since 1959 (approx 1000 miles per month). About half the mileage on the highway and have no trouble cruising at 55mph 3225rpm.

As for the brakes there seems to be a lot of misinformation about mechanical brakes. How well or fast your car stops depends on the amount of rubber on the road, the square inches of braking surface in the drums and the coefficent of friction of the braking material. It has nothing I repeat nothing to do with how the shoes are expanded. Mechanical of hydraulic as long as the shoes are pressed against the drum with sufficient force the wheel will stop turning. I can lock all four of my wheels with less than half of the available pedal travel. Once the wheels lock what else is there? As far as steering and suspension go I can take my hands off my steering wheel at 55 mph and still travel straight down the road.

Of course my wife disagrees with me but I am as comfortable in my Pontiac at 55 mph as I am with her new Malibu at the same speed. Mind you she has air conditioning so maybe she has a point.

[Guest]

Tinindian, How can I argue with a testamonial like this! Driving a 1930 Pontiac more than 500,000 miles ( 1959-2004 = 540 months X 1000 miles = 540,000) must be some kind of record! Driving it at 55 mph for 250,000 is as equally truly amazing! I am truly and profoundly impressed!! Obviously I should have bought a Pontiac and not a Packard. Has the engine ever been rebuilt?

[Guest sndtubes]

Hey thanks everyone for your input.

Yes I have considered that the car is not really safe over 55 mph on anything but straight, smooth roads. The brakes are now quite good after a complete overhaul of them, and the steering is up to 1930 standards which isn't saying much!

The car does seem pretty comfortable at 50 to 55 mph which I would guess is probably just fine, so I'm giving up on the overdrive for this car for now. I am now thinking that since I've changed the rear end ratio, that in order to not lug the engine, I'd have to drive 60 or more in overdrive which just wouldn't be safe. I would never consider making any major modifications like modern engine, transmission, etc. A faster rear end is about the extent of the major mods. I wouldn't even consider 12V.

I did install an overdrive on my 48 Plymouth (which is sadly in my garage needing restoration). The overdrive was from a 1951 Plymouth and fit right up to the transmission and drive shaft. It made a huge difference in performance and highway comfort.

For all of you who still wish to install an overdrive on your torque tube car, it can be done with an outfit called "Gear Vendors 1-800-999-9555" They make a custom torque tube adaptor to fit their overdrive to your antique car. It is a .78 overdrive,so it isn't a real deep reduction. They are quite spendy: about 4 grand.

I'm really impressed with the guy driving his 1930 Pontiac daily. I think that's just great. I drive my Buick at least 4 times per week depending upon weather and I just love driving old cars. I'm 43, so I didn't grow up with these types of cars, so it is a real blast for me. Kudos to you, my friend, for driving that old car. Cars were made for driving!!