Tuesday, July 24, 2007

Pulley TLC II

After reading Pulley TLC, some readers requested more information, so here are some pictures and instructions. Of course, these pointers assume that the reader possesses a modicum of mechanical aptitude — well, at least enough not to have his/her extremities hacked off by the derailleur mechanism while removing the pulleys, or getting his sexy goatie sucked into the chain and being asphyxiated. If in doubt, please bring your bicycle down to your friendly local bicycle shop (LBS) and have the mechanics do it for you (in which case, I suggest that it is cheaper to purchase a new pair of pulleys instead).

Whilst Ivy employs a 1997 Shimano RD-M950-GS rear derailleur, Cloe uses a newer 2006 Shimano RD-952-SGS. The pulleys between the two models are not interchangeable: the older RD-M950 pulleys have 10 teeth, while the RD-M952 pulleys possess 11 teeth.

The G-Pulley (or Guide Pulley) sits closest to the cassette / cogs; when mounted, it has some axial float. The T-Pulley (or Tension Pulley) sits at the end of the derailleur cage; when mounted, it has no axial float.

Bent-nose tweezers is a very useful tool to have here.

Squirt some plastic-safe degreaser (Finish Line makes a good product. The child-resistant locking tabs are a PITA though.) on an old toothbrush and scrub off the crud and grime from the pulleys. Rinse off with warm water. Don't worry about getting degreaser or water in the bearings — YOU WILL — but you are about to service them anyway.

G-Pulley. The metal shields should be loose enough to drop off when the pulley is flipped over; if not, use a magnet.

Using the bent-nose tweezers, gently press the axle (NOT THE SEAL) of the G-Pulley until it comes to the end of its travel. A 2 mm gap between the seal's inner lip and the end of the pulley axle will be exposed. Do not push any further.

Now flip the bent-nose tweezers over, slip BOTH prongs under the inner lip of the seal, and gently but smoothly pry the seal off by rocking the tweezers back. The seal should pop off. You want to be gentle here and not deform or tear the seal.

Place seal #1 in a safe place.

Carefully turn the pulley over and use the bent-nose tweezers to push the axle and bearing assembly out.

Place axle and bearing assembly in a safe place.

Now repeat the earlier process to remove seal #2.

Clockwise, from the top. Seals #1 and #2 removed. Bearing assembly. Pulley axle. G-Pulley.

Be careful with the bearing assembly. The bearings are about 1.6 mm (under 63-thousands of an inch) in diameter and would be near impossible to find if dropped. I use a transparent plastic vial with some degreaser (or denatured alcohol) to remove the grease and contaminants.

The G-Pulley axle is bisected lengthwise by a C-clip. This is what limits the axle float of the pulley. Nothing is to be gained by removing it.

Dust shields, axle, seals, bearing assembly, 16 ball bearings (8 already re-inserted into the bearing cage), and pulley, all cleaned, degreased and dried. The Delrin™ bearing cage splits into 2 identical, locking halves. The AA-sized battery is there for a sense of scale.

Re-insert bearings into bearing cage. Put a dab of grease on the reverse side of the bearing cages and gently press the opposing halves of the bearing cages together to form a single unit.

Place bearing assembly in a safe place.

Dab some grease on the outside of the axle.

Gently slide the entire bearing assembly over the axle.

Place seal #1 over one side of the pulley and gently press the seal in place. A little grease might help. The seal should pop into place.

Using a Q-tip, smear the outer race of the pulley with grease, placing extra grease at the bottom, at seal #1. Check for lint after you are done. A foam-tipped applicator (e.g. commonly used in cosmetics) is a better tool as it doesn't leave lint behind.

Using the bent-nose tweezers, lift the entire bearing and axle assembly and drop it in place. Ensuring that your tweezer tips are pressing on the bearing cage and NOT on the bearings, gently press bearing assembly half-way down. Some grease may ooze out, this is normal.

Using a grease gun, fill the gap between the top of the bearing cage and where the seal goes with grease.

Now grasp the pulley, take seal #2 and gently press it into the place. Some grease will ooze out, this is normal. Clean up the excess grease.

Replace dust shield #1.

Turn G-Pulley over and replace dust shield #2.

You are done with the more difficult pulley. Place it in a safe place.

Try to resist the unbearable urge to call everyone in your phone book to brag about what you've just done, they'll hang up on you.

Time to work on the T-Pulley.

Use a thin, sharp tool, such as a utility blade to pry the dust shield off. Very little force is needed. I simply use a fingernail.

Flip the pulley over and repeat for the other side.

T-Pulley with dust shields removed.

Using just ONE prong of the bent-nose tweezers, insert the tip from the inner (axle) side of the pulley and lift. Do not use a blade here as you will cut the seal. Be careful not to tear the seal. The seal should pop off with very little force.

Place seal #1 in a safe place. Flip pulley over and repeat for the other side.

Bring the dust shields, seals, and the pulley to your parts washing basin / sink, use some degreaser and clean them with an old toothbrush. Rinse with warm water and dry.

After everything is DRY, repack the bearings with new grease. Again, a grease gun manages the job with a minimum of fuss and waste.

Grasping the pulley, take seal #1 and gently, but firmly, press it in. Again, some grease will ooze out, it is normal.

Flip the pulley over and do the same for the other side with seal #2.

Using a Q-tip or cosmetics applicator, remove the excess grease. Ensure that no lint is left behind.

Firmly press in the dust shield onto the axle.

Do the same for the other side.

Place T-Pulley in a safe place.

Clean the derailleur cage, pulley bolts, and reassemble everything (remember to include the chain  :-P ). Place a tiny dab of Loctite™ 242 (or better yet, if you can find it, 243) on the pulley bolts before installing.

You are done.


Anonymous said...

Awesome instructions. Question: Why doesn't the tension pulley completely come apart (unlike the guide pulley) ?

-ben said...

Thank you :-D

It appears that the bearing cage (retainer) for the tension pulley is non-removable. In any case, removal is unnecessary as the cage and ball-bearings are large enough to be easily scrubbed clean with an old toothbrush and degreaser — once the seals are off. As you brush, the cage and ball-bearings would rotate somewhat, exposing dirt and grime in hidden areas.

Remember to use dishwashing liquid on the seals. They don't like degreaser.