Aftermarket overdrive transmission for pre-war GM cars?

[TimFX]

Id love to drive my 1935 Oldsmobile on the hiway but, it struggles beyond 65mph. 

 

Is there an overdrive transmission, like the Mitchell for the Ford?

 

 

Thanks

Tim

[Matt Harwood]

Gear Vendors.

[Joe in Canada]

https://www.gearvendors.com/index.html

[Bloo]

Mitchell does make a kit for open driveline cars, which the Oldsmobile is.

 

[edinmass]

The Olds chassis isn’t safe in stock configuration at 65 mph …….. an overdrive may help if the engine can pull it. The brakes, steering, and suspension on the car are best operating at 45 mph or less. Trying to make the car do something it isn’t designed for can cause a multitude of problems. I certainly understand wanting a car that is a better performing car on todays roads……..but you need to keep perspective on safety. I have no clue as to displacement or horsepower, but spinning that engine that fast and hard is looking for trouble.  Very few pre war cars operate safely on todays interstates.

[Dandy Dave]

Yep, What Ed said. 😬

[Bloo]

I believe those have independent front suspension and Bendix floating anchor hydraulic brakes, so better than a lot of 1935 cars. 65 sounds too fast, but I can still see wanting overdrive.

[dictator27]

Overdrive was not intended to increase a vehicles top speed.  It was meant to reduce engine rpms at the vehicles designed cruising speed and reduce engine wear.

[60FlatTop]

18 minutes ago, dictator27 said:

Overdrive was not intended to increase a vehicles top speed. 

That's about it. When the cars were built the roads weren't ever built to go that fast on. Find one of those old bypass routes and try it in a modern car.

[edinmass]

45 minutes ago, dictator27 said:

Overdrive was not intended to increase a vehicles top speed.  It was meant to reduce engine rpms at the vehicles designed cruising speed and reduce engine wear.

Absolutely…….but in this particular case, he was looking to go faster………

[Marty Roth]

My older cars go fast enough as designed.

Seeing America Slowly makes sense to me.

We use overdrive to reduce engine revs.

For example, the 5.08:1 differential ratio of our 733 Packard Touring is effectively revised to 3.55:1 via the Borg Warner unit. Despite that, the car is still surprisingly comfortable and capable at modest backroad touring speeds, and I don't need to keep up with the "Soccer Mom" in the Mini-van/Crossover/CrewCab F-350 who is speeding, texting, and swatting at the unbuckled curtain-climbers and rug-rats in her charge, all at the same time.

[Pfeil]

19 minutes ago, Marty Roth said:

My older cars go fast enough as designed.

Seeing America Slowly makes sense to me.

We use overdrive to reduce engine revs.

For example, the 5.08:1 differential ratio of our 733 Packard Touring is effectively revised to 3.55:1 via the Borg Warner unit. Despite that, the car is still surprisingly comfortable and capable at modest backroad touring speeds, and I don't need to keep up with the "Soccer Mom" in the Mini-van/Crossover/CrewCab F-350 who is speeding, texting, and swatting at the unbuckled curtain-climbers and rug-rats in her charge, all at the same time.

 

"My older cars go fast enough as designed."

Seeing America Slowly makes sense to me.

 

Make perfect sense to me. How about I follow you to a nice place for lunch, perhaps a small mint julep and then some club sandwiches and a coffee? As long as I can keep up with your train of thought and not the rest of the idiots on the road I'm doing just fine.

Thanks for framing it Marty! 

[Marty Roth]

12 minutes ago, Pfeil said:

 

"My older cars go fast enough as designed."

Seeing America Slowly makes sense to me.

 

Make perfect sense to me. How about I follow you to a nice place for lunch, perhaps a small mint julep and then some club sandwiches and a coffee? As long as I can keep up with your train of thought and not the rest of the idiots on the road I'm doing just fine.

Thanks for framing it Marty! 

Any time you find yourself near "The City That Care Forgot".

Local club is headed to Baton Rouge Saturday, and the Corvair Group is driving to Manchac for thin-fried catfish following our meeting there at Middendorf's .

 

PM me anytime-

There are usually local activities, and especially when the rest of the country is dealing with winter

[TimFX]

Ed certainly makes the best argument for not going over 65 in a pre-war vehicle. 

 

I think ill just stay off the hiways  

[Pfeil]

Automotive perspective.

I have a stock deluxe 1964 VW beetle, 1200cc 40hp with a 4th gear of 0.89 and a final drive of 4.375 to one.

I have a stock 1965 Euro Standard model beetle 1200cc 36hp with a 4th gear of 0.80 and a final drive of 4.43 to one.

If I use a newer transaxle, say a 1967 beetle with a 53hp 1500cc with a 4th gear of 0.89 and a final drive of 4.125, neither of my two cars would be able to cope on hills, the key to their problem is they don't have enough torque to get the job done.

 

When I look back at my dad's 1940 Pontiacs rear axle ratio it was 4.30 to one, there was an economy axle option, but it still was a very deep 3.90 to one. That was Pontiac's optimal mileage axle!

Then looking at my dad's 1950 Pontiac with a straight eight with a very deep rear axle at 3.90 to one.

 

When I look at a stock 1962 Pontiac Catalina with a 389 2bbl automatic we are looking at an engine that produces 405 ft lbs. of torque so it's easy to see why Pontiac equipped this car with a 2.69 rear axle ratio.

Try to get this perspective around your head. These guys that built these cars already did the calculations. 

[kfle]

Mitchell does make an overdrive for non Ford Model A's.  It is the Mitchell 1000 and I used to have one in my 1922 Maxwell.  Ed brings up a lot of good points and things to consider.  In my Maxwell, I maybe got a top end of 5 mph more, but the true benefit was having a cruising speed that had lower strain on the engine and it made for a more comfortable experience while touring.  I wouldnt expect highway cruising for any old car as not only do you have the higher speeds, but typically you have people weaving in and out of traffic and old cars dont work well with that kind of driving.

 

Here is the Mitchell overdrive.  Mitchell Model 1000 | Mitchell Overdrive Manufacturing (mitchelloverdrives.com)

 

 

[Grimy]

I added a Mitchell OD to my 1925 Pierce-Arrow Series 80 which was cursed with the deepest diff ratio, 4.88 (other ratios were 4.45 and 4.64, assigned by where delivered with no customer option).  That car was comfortable at 36-37 mph but the engine was screaming at 40-41 mph.  Several of us made a group buy of 26% OD ratio units (the available 36% would be 'way too much).  It was a relatively easy installation:  a driveline shop made up two short driveshafts, u-joints and flanges for about $250, and the original driveshaft now stands in a corner.  Comfortable cruising is now 48-49 mph, and to save you the math the effective final drive ratio is 3.61.  Occasionally I need to get on an interstate or other high-speed highway for a limited time, and this does the job.  I do not wish to exceed 45-50 in one of these cars.  For those of you who have driven the Fandango Pass road in Modoc County (rutted corkscrew upgrade at its east end), I can tell you that the gear of choice is 1st OD.

[TimFX]

It really is about lowering the rpm’s at the end of the day. 

 

Ill look into the companies suggested to see if they have something for my Olds

 

 

[Pfeil]

6 hours ago, TimFX said:

It really is about lowering the rpm’s at the end of the day. 

 

Ill look into the companies suggested to see if they have something for my Olds

 

 

No, it depends on where the sweet spot your engine likes it best for any given circumstance(speed/load) and for every different type of engine that sweet spot is different.

 

 In driving a car with a CVT you can really see this formula at work. In one of my newer cars when I'm at 3000 ft. and the terrain is flat, I set the cruise control to 71mph and the engine rpm is 2100, my mpg is 42mpg. A slight incline may produce 2300 rpm to maintain 71mph and milage might go down to 39mpg, however now this is the new sweet spot given that extra load from that hill. CVT is the only trans that instantly adjust optimal engine speed and engine power to any given situation or load. If I floor it to pass another vehicle, the engine will go to the point where the maximum engine horsepower intersects the engines max torque and holds it at that RPM/Torque, at a steady state until the job is completed, which in my cars particular case is 6200rpm, all the while the trans is constantly adjusting the ratio so that that max engine hp and torque are in that sweet spot, something a car with a gearset can never really accomplish, even a 10 speed automatic. Thats why a CVT is a true constant variable transmission.

Edited August 17, 2023 by Pfeil (see edit history)

[Stude Light]

I’ve taken my 1939 LaSalle on the local interstate a couple of times as it will easily drive up to 75 mph with the 3.92 axle and really tall tires. Rebuilt engine, clutch, trans, axle, entire brake system, suspension, steering, shocks, new Diamondback tires. I went through the entire car to make it a reliable driver.
 

It drives just fine on the highway but just doesn’t feel safe driving at that slightly higher speed. The amount of kinetic energy goes up with the square of speed so going from 60 to 75 mph could be a 60% increase in energy that your brakes or lateral tire patch probably couldn’t handle. An avoidance maneuver could easily turn catastrophic. Additional background: I was a test engineer for chassis systems at GM for 30 years and have plenty of advanced driving experience and if my gut says don’t do it, I don’t.

I’ll stick to the secondary roads at 60-65 mph.

 

BTW: My biggest fear in Michigan are deer which involves straight line braking…far safer than avoidance maneuvers.

 

”In front of the grill, go for the kill”

[hook]

It's true that speeds above 65 are a bit nerve wracking for an old car, but some cars were designed for it and even advertised it. Take this add for a 1931 Franklin for instance. Read the text about 80 feeling like 50! And no, I'm not in the habit of cruising at 70 or 80.

[Bloo]

Nobody could actually do it for any distance because of the condition of the roads. Of course the manufacturers knew that. My guess is there was a high speed gearset available that most of the cars did not have. After all, the way most drivers judged a car in those days was by it's ability to pull hills without downshifting. Lower gears make a big difference, and an awful lot of antique cars have them no matter how powerful or how expensive.

[wayne sheldon]

If I recall correctly what I read years ago? California's statewide speed limit during the 1930s was 35 mph. California, especially in those days, had great distances between major cities. Many people in those days still remembered the time when the fastest they ever traveled was on the back of a horse! In those prewar years, the majority of drivers never ever went over 30 mph. It is just how it was in those days.

Bragging about a car being capable of sustained sixty plus may have made for some compelling advertising? However it meant little in the real world of most people.

There was nothing new about that either? Ford, in 1908, practically guaranteed their model K 6-40 roadster capable of 70 mph! Again, not that most people would ever find a road they would be willing to try it on.

[EmTee]

 

Riding may be like gliding, but I'll bet stopping was like sliding...

[hook]

40 minutes ago, EmTee said:

 

Riding may be like gliding, but I'll bet stopping was like sliding...

The Franklin in that article had 4-wheel Wagner Lockheed hydraulic brakes with 14" diameter by 2" brake drums. A system similar to what cars had up to the 1960's until the industry went to dual master cylinders and disc brakes.

[EmTee]

Still a pretty small tire contact patch for a large car though...

[hook]

2 hours ago, EmTee said:

Still a pretty small tire contact patch for a large car though...

Yes, that's true. However, when you compare pounds per square inch of road contact for a 4000 pound car, my Franklin with 650 or 700 X 19 tires has a heavier footprint (per square inch) than a lot of new cars of the same weight. The biggest problem as I see it is the tire construction. The present day radials stop better than the old bias type. Of course, I could put radials on her. Or maybe a drag shute! But they're such a pain to restuff in traffic!!!!!!!!!!!!!!!

Edited August 21, 2023 by hook (see edit history)

[hook]

1 hour ago, JBP said:

Was it a blanket corporate decision at GM not to offer overdrive (or at least, not consistently) across all platforms and lines? I seem to remember an OD was available at Chevy for awhile, but it was never something I saw strongly marketed or pushed by GM. 

I'm no authority on the subject, but I think the automatic transmission help kill overdrive.

[Frank DuVal]

I know the 66 Chevy had overdrive available, according to the owner's manual, but this is not the time frame being discussed...

[Berdu]

Hi all - I went in the other direction with my 1921 Maxwell. I needed lower gears for the back 40, trailer loading and in particular very slows parades. So I added an additional transmission like the old tandems used to have - now I've got 13 spds. (4X3 plus double reverse is my lowest)- love it!!

Bernie

 

Edited September 9, 2023 by Berdu (see edit history)

[EmTee]

On 9/8/2023 at 9:13 PM, Berdu said:

now I've got 13 spds.

Wow - 3 more than my old bicycle!