SRAM 3 speed ratio

Doug Goncz said:

I have brother Jeff's 3x7 hub ready to disassemble for an overhaul and to count
the teeth on the sun, planet, and ring gears. I need an accurate ratio for the
hub and Jeff needs a spare hub.

Jeff said all I have to do is unscrew the left cone.

Is that really all I have to do or will I need various "keepers" to hold the
works together after I unscrew the cone and pull the insides out?

The whole "guts" will come out once you've removed the left cone.

Quoted message said:

Will I need to unscrew the right cone as well?

Not to get the "guts" out, but you will need to disassemble that module
to count the teeth. Nothing will go "sproing!" and shoot across the room.

Quoted message said:

IIRC the "cone" on this hub is a race about an inch in diameter with loose
balls requiring grease to hold them in place when reassembled. They're going to
fall out when I loosen the "cone", aren't they?

No, the balls are in a retainer.

Quoted message said:

Disassemble over a level table with a towel on it, right?

Not necessary. These are actually very easy hubs to work on.

Sheldon "Planetary" Brown
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I have unscrewed the left 17 mm lock nut while holding the left 15 mm cone,
unscrewed the cone, and pulled the works out from the right.

Oh. That's gonna need a snap ring tool.

I have one.

I put it back together and will go deeper later.

Yours,
Doug Goncz ( ftp://users.aol.com/DGoncz/incoming )
Student member SAE for one year.
I love: Dona, Jeff, Kim, Mom, Neelix, Tasha, and Teri, alphabetically.
I drive: A double-step Thunderbolt with 657% range.

Quoted message said:

From: [email hidden] ( Doug Goncz ) ( Me )

Quoted message said:

Oh. That's gonna need a snap ring tool.

The ring gear is 47 teeth, the sun is 17.

Yours,
Doug Goncz ( ftp://users.aol.com/DGoncz/incoming )
Student member SAE for one year.
I love: Dona, Jeff, Kim, Mom, Neelix, Tasha, and Teri, alphabetically.
I drive: A double-step Thunderbolt with 657% range.

Quoted message said:

From: [email hidden] ( Doug Goncz ) ( Me )

Quoted message said:

The ring gear is 47 teeth, the sun is 17.

So the planet gears must be 15 teeth. 15 + 15 + 17 = 47. Pitch circles are
additive without knowledge of module.

Now, what are the ratios of a 17-15-47 epicyclic gear train?

I note that when I took the hub apart, I soaked the assembly in dispersant to
remove the old grease, and removed only a single E-ring to pull the planet
carrier. I used the snap ring tool on the E-ring, but didn't use it on the snap
ring holding the planet carrier together.

I counted the ring and sun gear teeth by marking with a pencil, twice each,
getting the expected prime numbers.

I greased the insides with Siloo Spray White Lube, and greased the inside of
the hub body. I greased the bearing. I reassembled the hub and adjusted the
cone. It spins very freely and yet it constrained.

I removed the right cone, too, wiped out a bit of dirt, greased that bearing,
and noted that the hub spins more freely forward than in reverse. This would
happen rarely in operation. The reason is that the moment arm to the forward
bearing is larger, much larger, than the moment arm to the cone bearing, which
is the one in operation in reverse.

So the hub now will coast very freely.

I have a rim and will see if Jeff wants me to lace it up. Otherwise, I have got
my counts and will soon have my ratios.

Did I estimate the planet teeth correctly?

Can anyone here show me the ratio formula?

(P-A) / A or something like that?

Yours,
Doug Goncz ( ftp://users.aol.com/DGoncz/incoming )
Student member SAE for one year.
I love: Dona, Jeff, Kim, Mom, Neelix, Tasha, and Teri, alphabetically.
I drive: A double-step Thunderbolt with 657% range.