Rear derailleur update
 

Hi,

I would like to know what do you have to check when you want to update your RD. I have a 2004 Giant Yukon. Do i have to change the hanger?

Thanks

No, unless it's damaged. The bike end of the hanger is specific to each frame, but the RD end is standardized.

When you've mounted the new RD, and before dialing in the shifting, you might want to double check that the hanger is straight. A rough check is easy if you shift the RD to a gear combination where the cage is nearly vertical. Then check to see if it's parallel to a yardstick or boom handle set vertical against the wheel, touching top and bottom.

I agree with FB. Also I'd add that if it is bent, a good bike-shop shoud have a tool for straightening the hanger. If it's badly bent, I wouldn't suggest manually straightening it with a wrench, as many people do, as this could fatigue the metal. A small bend can be done this way - but leave a big bend to the shop with a DAG-1 or DAG-2 (Park Tool name for tools).

Have fun.

So each frame has got only one type of hanger compatible? So I could mount any derailleur to it? Do all b-screw fit are standardized to fit on any hanger?

Yes all B screws are standard
.

I thought I was pretty clear. Every frame uses a specific hanger (there are about a hendred or so out there), but the derailleur mount end is the same for all of them, and all (modern) derailleurs are designed around the one standard.

Are you planning to replace the rear derailleur? If so what RD do you have now. A new one (if needed) needs to have a compatible actuation ratio. Many Shimano RD's are cross-compatible.

I disagree to a degree with some of the replies. I see that some Shimano rear ders parallelogram springs get soft over time. Whether it's the actual spring or the pivots getting 'tight' i don't know. I do know that sometimes the der won't pull the cable (even after new casing/inners) hard enough to have a shift into the smallest rear cog consistently. Disconnecting the cable from the der solves this. A sensitive hand can feel this lack of returnability. Install a new der and the returnability is stronger and the problem is solved. Andy.

How does the specific tool used affect the issue of bending stress in the hanger? A bend is a bend is a bend.

True. But the DAG's work by re-bending the hanger from the center of threaded hole the RD is screwed into. This exerts an even pressure that moves the whole hanger evenly. This results in less fatigue/stress to the area of the original bend. It's a "kinder & gentler" approach.

Because the guy doing the repair is confused. We both know that the tool is only an easier way to see if the hanger is straight, after bending, without distorting the mounting hole. I use a screw driver and allen wrench to do quick hanger straightening, with the der in place, all the time.

It's like budding wrenches that think a truing stand makes for a better wheel... :) Andy.

A 6mm key in the RD mounting hole bends the hanger in the identical way. The value of the tool is the gauge capability, not that it has any kind of magic in how it bends.

Not magic per say. But it does a good job and it's fun to use. Besides - if the hanger (which is made out of weaker metal by design so it will bend and break before the frame does) does break you can yell at the tool. If you do it manually with a hex wrench, then what can you yell at? :p

Hmmm, a 6 mm key in a 10 mm hole sounds like a good way to damage the threads, particularly if the hanger is aluminum.

A 5mm (the size most current and recent rear der's use for the hanger mounting bolt) placed in the der's mounting bolt while the der is mounted provides enough leverage for minor hanger corrections when the hanger is AL. A long and thick flat blade screwdriver placed behind the hanger, wedged between the small cog and drop out, adds leverage for more force. Since most hanger bends are mostly all inward this is a fast and easy method to fix most bends. Andy.

That was an editing error. The key goes in the RD mounting bolt, not the hanger.