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After logging many miles with an R9 overdrive, I am quite pleased. However, there is one aspect of its function I have concluded I would like to change and that is the engagement speed. The governor switch engages at about 22 mph per Packard's plan.

I know Packard chose this speed range so that the driver could negotiate city traffic without having to upshift and downshift, just let the OD go from 2nd standard to 2nd OD and back again as speed necessitates. For that matter, you can start in 2nd and leave it ther. There is a great explanation of this in the 41 110 Brochure on this site. This period in automotive history show great focus on ways to make the driver's job easier and the technical offerings show it: transmission freewheeling, overdrive, electromatic clutch, brake hill holder, variable coupling fluid drive, etc. all leading up to automatic transmissions.

As I said, I would prefer it engage at a higher speed such that I can shift to third and let the OD take care of cruising speed needs. Also, when decending hills it is occasionally awkward to accelerate while freewheeling to then have OD engage without freewheeling,

Packard offered several different speeds for the governor switch (but I don't know if they are available from our vendors) and makes clear cautions to mechanics in the service literature about not attempting to change the speed by bending or changing the switch springs. I can see why...a small tweak to that system may have a large result...hard if not impossible to correctly adjust. So, still not giving up, I put my engineering background into action and began evaluating the physics of the governor. I determined that a reduction in the mass of the two brass counterweights would increase the engagement speed. I further determined the amount of mass to remove in order to have an engagement speeed of 30mph.

Having the guts of a used governor found in the bottom of a swap meet box, I asked a friend whose machining skills far exceed my own for some help. After removing the confirmed amount of material and making sure the weights were still balanced, I reassembled the governor, installed it and took the car out for a nice drive. I am pleased to report that the OD engages exactly as the math predicted with engagement at 30mph. Now the OD no longer "gets in the way" for those specific situations and I can shift up into 3rd and let the OD take over.

If anyone wants to know more about the details, I am happy to ramble on a bit more.

Pat
Packard Engineering Department

Mr. Overdrive Guru:
Is it possible that you needed that change because you have added the system, as opposed to it being factory installed? Or possibly, because the rear end gear in your car is still the same as what you had without overdrive?
I ask, because I have never thought that anything about my overdrive or the way it works needs changing.

I have a '47 with the 356 engine and overdrive also. I find that by 22 mph I am in 3rd gear anyway except when I am drag racing I love that long windup in 2nd overdrive! I guess perhaps the difference lies in the fact that the engine is more powerful and perhaps difference in differential ratio (mine has a 4.10:1). I am interested in how you determined what weight to remove from the governor so please enlighten us.

I too have felt that the speed for the overdrive to engage is too low. I would prefer an engagement speed of 30 mph as it would better suit my driving style. And, like clipper47 I have a '47 Custom Clipper.

(o{I}o)

Regarding the fact that my car didn't originally have OD: good point. My car has a 4.54 rear end, which was the middle choice for the non OD car (4.7, 4.53, 4.3?). For OD cars, 4.7 was standard ratio and 4.54 was optional. So, if I had the 4.7, my sitiation would be worse: OD would engage at an even lower speed and at cruising speed mean the engine is running faster than with a 4.54 rear end. There were different speedometer/governor gears to correct for the axle differences too. Of course, rear end ratio may be more critical to my six cylinder car as since the horsepower to weight ratio is greater for the larger cars. I am happy with the 4.54 rear end.

So, now for the fun physics. The governor used on the R9 and R11 (and I think all of Borg Warners full electric ODs) uses the simple but proven design of two centrifugal weights that swing outward, lifting a pushrod that develops a force on the switch inside the governor switch cap. The force is proportional to mass of the rotating weights multiplied by the square of the rpm of the governor. The rpm can be equated to the car's speed. So, since the force of the governor top switch is constant, the tradeoff between mass and speed (velocity) can be calculated per the math below as long as any material removed from the brass results in the weight still having the same center of mass (if not, then the force on the switch changes and the math below is not accurate):

m1= original weight mass = 28grams
v1= original engagement velocity = 22mph
m2= new mass value to be determined
v2= new target engagement speed = 30 mph

So,
a) m1 x v1 x v1 = m2 x v2 x v2
b) m2 = (28x22x22)/(30x30) = 15 grams

So you are left with 15/28ths or 53% of the original mass. Here are values for other speeds:
25 mph: 21.68 g
30 mph: 15.06 g
35 mph: 11.06 g
40 mph: 8.47 g

Notice that to get really high engagement speeds, a large amount of mass must be removed. This is because of the speed squared relationship. I chose 30 mph because it seemed to give a good tradeoff.

I considered two different ways to remove material. The first involved machining material off the outer surface of the weight. This approach would make the determination of how much material to remove easy, would maintain the center of mass, and would be simple to machine, but would remove a bevel on the lower part of the mass that cleverly limits the weight's travel at high speed and therefore prevents large forces acting on the switch (smart engineers back then).

The second approach was to drill a hole along the center of mass. This would maintain the center of mass, would be even easier to machine, but more difficult to accurately predict mass reduction without more math. However, instead of predicting exactly what drill size would result in mass reduction, I could sneek up on the target with progressive drilling and weighing. This sounded good and worked better. The final drill size was 3/8" drilled radially at the centerline of the center of mass.

My photos of the weights did not turn out well (I knew I should have had you there, West), but if there is enough interest I will either take the unit off the car and take some new photos, or create some drawings. The dissassembly of the governor was a delicate operation, and the counterweight shafts have a knurled end that must be restaked. It was also a good opportunity to get some oil in the small bushing bearings in the device.

As I mentioned in the earlier post, I am very pleased with my result and happy to help anyone else through it.

Pat

This is one of the best technical modifications I have ever read. And a vitally important topic too. I hereby offer to submit a governor for modification/photographs rather than put you to the task of removing yours (again). My motive for this is to share the modification information "show and tell" with other non-packardinfo people at the next Salado meet, where I have for the last 5 years been responsible for the technical training sessions. Back me on this JW...thanks

Quote:

David, I got your back.

(o{I}o)

Pat, my congratulations on a very nice piece of work, very well though-out and presented. Isn't science wonderful! I suppose an alternative approach would have been to fabricate weights of a less-dense metal like aluminum?

Pat, My congratulations on a fine piece of work. This is truly one of the finest technical postings that I have ever read regarding Packard overdrive systems. I would gladly contribute a spare R-9 governor for you to modify if you need another one to include with pictures although your words alone need no further enhancement for me.

Do I see the emergence of a small new business to service and modify overdrive governors?

(o{I}o)