Model T Transmission


#1

I was reading an article about restoring a Model T, and they said it was important the parking brake worked, b/c if it didn’t, when the engine started – b/c you were standing in front of the car to hand crank it – the car would run you over.

But why would that happen? Wouldn’t you put the transmission in neutral before hand cranking the engine?

It also said Model T transmission used a 2-speed “epicyclical” gear method , something like that. Does that have something to do with it?


#2

The Model T did not have a.clutch. As I remember from my dad’s description, there were three pedals. The left most pedal was the low-high pedal. All the way down was low. Letting the pedal all the way out put the car in high, while half way down was neutral. The center pedal was the reverse pedal. To go backward, the low-high pedal was held halfway down and the reverse pedal was depressed. The right pedal was the brake. I think the parking brake, when set, held the low-high pedal in neutral. The throttle and spark advance controls were on the steering column. Some states had two different driver’s licenses. One was to drive a Model T and the other license allowed you to drive other vehicles.


#3

Boy that’s something to think about. I like the current arrangement better. A local old car enthusiast (dead now) had an outdoor equipment business. In the back he had a garage full of restored old cars. I was up there one time and he took me back to the garage and cranked over one of the cars. It started right away and It didn’t go anywhere. Maybe the brake was on or maybe a different manufacturer, I really don’t remember.


#4

I recall that there was a hand operated clutch and brake plus the foot brake and the clutch bands on the transmission. Years ago a good customer had a “Brass” model T that he put in parades and that’s how I understood they were set up. I’m sure that the hand brake operated like parking brakes on many cars and trucks made even into the 1960s in that it was on the transmission output. The foot brake operated rods to the rear wheels. All the brakes were band type I believe.


#5

Many of our class 4 - 6 trucks at work use a hand-operated parking brake, which acts on the transmission output

Meaning the parking brake backing plate, shoes, drums, etc. are attached directly to the back of the transmission


#6

http://www.fordmodelt.net/images/model_t_pedals.jpg

http://www.modelt.ca/drive-fs.html


#7

Nope, the opposite. All foot pedals operate bands in the transmission.


#8

The car that I saw must have had some after market brakes installed.


#9

My father used to tell the story of my great grandfather, who refused to put his Model T in reverse because he thought cars weren’t meant to go backwards. Looking at the configuration of those controls, my great grandfather doesn’t seem quite as nutty as he seemed before.


#10

I used to hear the story of the guy that had two garage doors. One at the front and one at the back. He would have both open so that went he drove his Model T in and couldn’t stop, he could just go around again for a second try. Now I understand. Who woulda thought you needed three feet.


#11

A misadjusted or or dragging low gear band could deliver enough torque to make the car roll even when it wasn’t totally engaged. The car didn’t really have a neutral as we know it. When the pedal was pushed down, it tightened a band that stopped the low speed drum forcing the output shaft to turn through the planetary gear set. When it was released, it engaged the high gear clutch which was a disk clutch that locked the transmission into direct drive. In between, both the band and the clutch were disengaged, hopefully, unless things weren’t adjusted right.

The two “gears” was a choice between planetary reduction and direct drive.


#12

Here’s a diagram of the Model T transmission.
On this diagram, gears B,D, and E are planet gears. They freewheel on pin b but they are a single unit and must spin together as they are a single unit. These are called the “triple gears” and there are three triple gears on three pins on the flywheel spaced 120 degrees apart.

Gears A, F, and G are three independent sun gears. Gear A is the output gear and it is driven by gear B. Gear F is the low speed sun gear, and brake band J locks it stationary when the transmission is in low.
Gear G is the reverse sun gear and it is locked stationary by brake band H when the transmission is in reverse.
Brake band K brakes the brake drum to stop the car and inside the brake drum is a multi disk clutch which locks the output shaft to the flywheel shaft for direct drive when the transmission is in high.

The output gear A has 27 teeth and so does the planet gear B that drives it. a 1:1 ratio.
The low sun gear F has 21 teeth and it mates to a triple gear D with 33 teeth.
The reverse sun gear G has 30 teeth and it mates with the triple gear E with 24 teeth.
If the engine is not running and you turned the low speed sun gear F one complete revolution, it would result in the output gear A to turn 21/33 or .6363 turns in the same direction that the sun gear was turned. When the sun gear is locked stationary and the planet gear F walks around it for one revolution, in effect the planet gear’s orbit tries to turn the output gear one revolution but the rotation of the planet gear from gear D walking around stationary gear F causes gear B to rotate it backwards 21/33 of a revolution. One revolution - 21/33 of a revolution leaves you 12/33 of a revolution being delivered to the output gear or a gear reduction ratio of 2.75:1

In reverse, brake band H locks gear G with 30 teeth stationary. It mates with gear E which has 24 teeth for a ratio of 30/24 or 1.25:1.
When it is locked, rotation of gear B tries to turn the output gear backwards 1.25 turns for each orbit of the gear resulting in the output gear being driven backwards 1/4 turn for each engine revolution. The reverse gear has a 4:1 reduction ratio, which is why a lot of people used reverse to climb really steep hills in these cars.

One more thing you will notice is that all the gear teeth are integer multiples of 3. This allows all three triple gears spaced 120 degrees apart to be identical and interchangeable and still line up with the teeth on the other gears.


#13

Back to your original question. It’s obvious when studying how this car’s transmission worked that this transmission has no real neutral in the sense of a manual transmissions neutral. The “neutral” of the model T is the clutch pedal half ways down so that neither the high clutch is engaged nor the low band is tightened. This pedal engages the high clutch when released and tightens the low band when pushed down. Both of these run in engine oil, the transmission did not have its own separate oil supply.
I have experienced many motorcycle multiplate oil bath clutches and they do have a little drag when disengaged due to oil viscous drag. When the oil is cold, the drag would be so much that my old Bridgestone 175 would often die when I put it in gear with the clutch pulled in, I would have to break the clutch loose by putting it in gear and then pushing it a little or by giving the engine a little gas while putting it in gear.
It’s not hard to imagine that in the days before multi-grade oils, the model T transmission’s clutches and bands could have enough viscous drag to make the car roll forward even though both the band and clutch are released, especially if someone misadjusted that low speed brake band so it barely released when the clutch pedal was up or on a cold morning when the oil was like molasses.
I have heard stories of people starting the car and then having to hold the car back once the engine started.


#14

https://www.youtube.com/watch?v=Fo72r-jcnnY


#15

@B.L.E and others … Thanks for the explanation. I’m remain a little confused though how the brakes work on a Model T. Both the driving brakes (the one you control w/the foot pedal on the right labled “B”), and the parking brake. Do they both work only on the drive shaft?

Edit: @idiot666 … in the vdo, that method she used to crank seems problematic should the engine ever kick. Seems like you’d want to hold the crank with only one hand, and in a way that if the engine kicked your hand would just slip off the handle.


#16

Here’s lots of info on how the Model T works:
http://www.barefootsworld.net/ford-t-4-beginners.html
There are two brakes, the driveline brake activated by the right pedal, and the rear drum brakes (mechanical) activated by the brake lever.


#17

I believe the driving brake works on the transmission output shaft and the hand or parking brake works the brake drums on the rear wheels. The front wheels had no brakes. I guess Henry figured brakes good enough for horse drawn carriages were good enough for horseless carriages.

Here’s a paper that goes into the Model T transmission design.
https://www.asee.org/public/conferences/1/papers/838/view


#18

What she did was perfectly safe, as long as the timing was properly adjusted for starting the engine. The risk of the crank kicking back and hurting her is only a danger if the timing lever is improperly set.


#19

The Model T had a rather unique ignition system. Each spark plug had its own ignition coil and each coil was designed to shoot a continuous stream of sparks as long as it was energized. The distributor contacts distributed the 6 volt DC to what ever coil needed to be firing. The coil had a set of points that vibrated continuously by the coil’s magnetic field much like an electric bell. When the coil was energized, you could hear a buzzing tone coming from that coil.
It was the original multispark ignition system.
Some people would prime the engine and crank the engine to where the piston was just after top dead center and then turn on the ignition and the engine would just kick off on its own.
A lot of old Model T coils were re-purposed as electric fence shockers by farmers.


#20

I know that th Model T had a coil box, but I don’t remember how the coils were powered. Was some sort of battery used? One couldn’t prime the cylinders and then turn on the coils to self-start the engine unless something powered the coils.