Planetary Gear Calc

3 speed automatics like TH 350/400 use 2 planetaries.
Internal Ring Gear A is the first planetary having the power applied to it.
(ring gear is also called annulus gear)
The Sun Gear A of the forward planetary

Internal Ring Gear B of the rearward planetary
The Sun Gear B of the rearward planetary

(What is described as "gearset B" is the gearset whose annulus is connected to the output shaft, regardless of actual physical position.
Depending on the specific layout, gearset A may be located behind gearset B or vice versa;
this description and all the calculations below are based on each gearset's function, not its position.)

Here's some info:

The early TH 400 had I think
sun gear with 39 teeth
planet pinions with 21 teeth
ring gears with 81 teeth each.

Later Turbo 400 Ratios:
Sun Gear = 26 Tooth
Ring Gears = 54 Tooth
Planet Pinions = 14 Tooth

This is what some aftermarket gear set is (was?)

the sun gear has 36 teeth
annulus A has 90 teeth
annulus B has 66 teeth

This comes out to 2.13 1st gear and 1.40 2nd gear.

the sun gear A has 42 Teeth
sun gear B has 30 Teeth
Ring Gear has 74 Teeth

This comes out to 2.12 1st gear and 1.41 2nd gear.

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We can get lots of different gear ratios out of any single planetary set.

Planetary A data

	Input	Output	Stationary	Gear Ratio
A	Sun (S)   0	Planet Carrier (C)   0	Ring (R)   0	0
A1	Planet Carrier (C)   0	Sun (S)   0	Ring (R)   0	0
B	Planet Carrier (C)   0	Ring (R)   0	Sun (S)   0	0
B1	Ring (R)   0	Planet Carrier (C)   0	Sun (S)   0	0
C	Sun (S)   0	Ring (R)   0	Planet Carrier (C)   0	0
C1	Ring (R)   0	Sun (S)   0	Planet Carrier (C)   0	0

Planetary B data

	Input	Output	Stationary	Gear Ratio
A	Sun (S)   0	Planet Carrier (C)   0	Ring (R)   0	0
A1	Planet Carrier (C)   0	Sun (S)   0	Ring (R)   0	0
B	Planet Carrier (C)   0	Ring (R)   0	Sun (S)   0	0
B1	Ring (R)   0	Planet Carrier (C)   0	Sun (S)   0	0
C	Sun (S)   0	Ring (R)   0	Planet Carrier (C)   0	0
C1	Ring (R)   0	Sun (S)   0	Planet Carrier (C)   0	0

Then some of the gear ratios are influenced by one/some of the 2nd planetary ratios. (Sun gear A may be influenced by Ring gear of B)

Also, locking any two of the three components together will lock up the whole device at a 1:1 gear reduction.

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Another chart to view:

Gear Combinations/Ratios
Ratio	Ring	Sun	Carrier
Slow Forward Reduction	Held	Input	Output
Fast Forward Reduction	Input	Held	Output
Slow Reverse	Output	Input	Held
Fast Reverse	Input	Output	Held
Slow Overdrive	Output	Held	Input
Fast Overdrive	Held	Output	Input
Direct Drive	Input	Input	Output
Neutral	Free	Input	Output

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