Ruckstell axle...underdrive or overdrive?

[stickshift]

I've always thought the Ruckstell axle was an under drive. Most of my driving is with the shifter pulled back, or in low. Last weekend I drove my Model T into town delivering gifts to relatives so they could also see my "T" that they heard about, and on the way home I decided to get on the highway and see what she's got. I was topped out at 45 and put the shifter forward. The engine actually lugged until I gained more speed. I was going over 50, which I didn't really want to do, but like I said the engine needed more RPM. I think I could have easily gone 55 but I slowed down and pulled the Ruckstell shifter back again to stay at 45. This tells me that it's an overdrive, right?

[redmodelt]

The Ruckstell is an under drive.

[G Baese]

The Ruxtell axle is a two speed rear axle. The standard Model T ring gear has 40 teeth with an 11 tooth pinion. This would give a lower low, a standard low, a lower high and a standard high. Great for hilly runs, especially in a heavy sedan.
While the ring gear remained 40 teeth, a 9, 10, 12 and 13 tooth pinon was available, giving both under and overdrive capabilities to the standard ratio.
The nine tooth pinon gave a 4.44 to 1 rear-end ratio; the 10 tooth pinon a 4 to 1, the standard 11 tooth gave a 3.63 to 1, the 12 at 3.33 to 1 and the 13 tooth pinion gave 3 to 1, the most commonly used ratio for roadsters and flat-land touring, which in effect is an overdrive.
Hope this adds a more complete look at how a Ruxtell 2-speed rear-end could be used.
Best regards and Happy New Year,
geary

[stickshift]

There is a metal plate riveted to the rear axle.
Could this tell me what ratio I have?
Thanks

[stevests]

No - you need to do some math or split the housings.

[stickshift]

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I jacked up the rear of the T and cranked the engine with the hand crank while my son counted one revolution of the rear wheel. I was in ford high and the Ruckstell lever forward (high). I turned the crank about 1.75 revolutions for one turn of the rear tire. This may not be the correct way to check the gear ratio. I know most manual transmissions are 1:1 in high gear (non overdrive). Can I use this info to figure the Ruckstell ratio? I'm including the Ruckstell serial number just in case that says anything.

[G Baese]

If the rear is jacked up with both wheels in the air, the action of the differential can throw the test off, sometimes one wheel will spin in the opposite direction, depending on the drag within the differential. Only jack one wheel up, repeat the test and compare the result. The pinion is the determinant, the ring gear is 40.

[stevests]

Not necessarily - the gears could be 13-39 for a 3-1 gear set. A 40 could use either 11 or a 12 tooth pinion.

The numbers on the patent plate is the serial number.

[stickshift]

I gave it another whirl with only one rear wheel up and the results were pretty much the same. Closer to 1.8 revolution of the crank to 1.0 revolution of the rear wheel. I came across this archive from another forum that was interesting. They do use the word "over drive" when they talk about the special gearing. Since I live in the hills, this doesn't do me much good. But then again, I bought the car in Sacramento where there are no hills.

[G Baese]

stevests,

Thank you for the correction. Never saw a 39 before.

[stevests]

No worries - 13-39 gears mostly used in the flatlands & higher h.p. engines.

[redmodelt]

"ford high and the Ruckstell lever forward (high)"
You are either in Ruckstell or you are not.
With the shift lever forward, the Ruckstell is disengaged so you are in Ford direct if the low/"C" pedal is up or Ford low if pressed down.

[Dan McEachern]

Ford never made a 13/39 gear set. These were made and sold by Mark Auto for many years. The Ruckstell company made a special 13/40 gear set for use in their rear ends. The 13/40 tooth Ruckstell ring gear is recessed on the mounting surface. This ring gear and the Ford 40 tooth ring gear are not interchangeable.