Jim’s Tech Talk
By Jim Langley
When my friend texted for help with the balky shifting on his beautiful Pinarello Dogma, I had a pretty good idea what the problem was. He babys his road rockets, so I was sure it wouldn’t be worn or abused components.
I told him to bring his rig over to my home bike shop and with a little luck, I’d be able to fix it in about 10 minutes and get him back on the road. Boy, was I wrong. My supposed quick fix turned into a tricky repair that tested my skills and patience.
Replaceable Derailleur Hangers Are The Norm Now
I’m sharing how this job went down because it had to do with the Pinarello’s replaceable derailleur hanger. If you own an aluminum or carbon bicycle, it probably has one of these. It’s the little piece that hangs below the drive-side rear dropout. It’s the piece of the frame that the rear derailleur is threaded into.
You might not be able to see that it’s a separate piece without removing the rear wheel. Or, you might see the bolts holding it on simply by looking closely.
The reason most non-ferrous bicycles have replaceable derailleur hangers is because hangers can get bent or even broken simply from the bike falling over. If the hanger was built into the frame and it was badly bent or broken, it could mean having to replace the entire frame. So replaceable hangers are a very good thing.
On my buddy’s Pinarello I first put it in the repair stand, ran it through the gears and checked the cable tension, since when loose, they can cause shifting issues. If that had been the case, I would have simply turned the cable adjustment barrel to tighten the cable and he’d have been good to go.
That wasn’t the issue so I moved on to my second guess, which was a bent derailleur hanger. I know he carries his bike in the back of his station wagon and I’ve seen plenty of hangers bent this way. They’re only made of soft aluminum and the derailleur acts as a long lever that can bend hangers without excessive force. This is why cyclists should only lay down bikes on their non-drive side.
Seeing a Bent Hanger
Sure enough, by standing behind the bike and looking, I could see that the hanger was bent. To do this, you look at the chain. Be sure the chain is on the small chainring and one of the cogs toward the middle of the cassette first. Looking from behind the bike, you’ll see that the chain forms a vertical line from the cassette down to the bottom derailleur pulley.
If the hanger is bent, the line that the chain forms will no longer be a straight vertical line. Instead it will start straight at the cassette but then bend inward toward the wheel. If you see this and also have shifting problems, your hanger is likely bent. (The photo is NOT the Pinarello, it’s of a straight hanger.)
Most replaceable derailleur hangers are made of aluminum. Sometimes, it’s possible to straighten them easily. So, still confident I’d have my friend out the door in a jiffy, I picked up a long 5mm allen wrench and commenced an easy straightening procedure that can work nicely.
All I needed to do is put the allen in the derailleur attaching bolt. Once in place, the allen wrench can be used as a lever. You do want to make certain the allen is fully and firmly attached inside the derailleur bolt. Also, leave the rear wheel in the frame as it ensures that all bending force is applied to the hanger and none to the dropout itself.
You can then gently apply upward pressure and try to straighten the derailleur hanger. Easy does it, though. Bends are usually slight, so you probably won’t need to pull very far to get the hanger back where it was before – or close enough to it to restore the shifting.
No Such Luck
Or, if you’re unlucky like I was, instead of the hanger straightening, it might break. You can’t see it in my photo, but it was clear to my eyes that the Pinarello’s hanger broke because the aluminum it was made of was full of air pockets – some flaw in the forming process probably.
When it got bent, it withstood the impact and did not break. But, when I tried to force it back, it had become brittle from the first bend and failed right where the aluminum was weakened.
Getting the Right Replacement
My go-to for replacement derailleur hangers is Wheels Manufacturing. Here’s their hanger page. Note that their hangers are sold on Amazon, too.
Their tools and search functions make it easy to find the right hanger. Be sure to read any and all fine print. I would have bought the wrong hanger save for Wheels’ fine print telling me that many people confuse two hangers for Pinarellos.
The only way to tell the difference is to measure the bolt hole spacing. Which I did and realized I needed the “other” Pinarello hanger. Thank you Wheels Manufacturing!
Removing and Replacing Hangers
Replaceable hangers are held on in many different ways but it should be obvious once the rear wheel is removed. All my non-ferrous road bikes have hangers bolted on with 2 tiny countersunk hex-drive flat-head metric screws. The Pinarello was the same with two 4mm screws.
Wheels Manufacturing hangers come with the screws that should work for the bike. The photo shows one of these small screws on the end of one of my favorite tools, Prestacycle’s Ratchet.
Notice I said “the screws should work.” That’s because until this Pinarello, Wheels’ screws have worked fine. But, I found on this Italian stallion, that one end of the hanger needed a longer screw. Which was strange because on the hanger that broke the screws were the same length.
Had I used the same length screws, though, one would have only been holding the hanger by 3 threads! When the wheel is in the dropout, that does the lion’s share of holding the hanger in place. But, there shouldn’t be any chance of the hanger loosening when taking the wheels on and off.
So, to fix the issue, I placed another order with Wheels Manufacturing for longer screws, which they also sell. I first looked for them on my favorite online hardware store McMaster-Carr but would have had to buy way more than I would ever use. Still, that’s an awesome resource for hardware should you need it for your bike projects.
With one short and one long screw in hand I was finally able to install the new hanger. I put a trace of grease on the frame dropout where the hanger fits to prevent any possible noises. I also put a drop of temporary Loctite on the bolt threads so they’ll stay tight.
The final check was to sight from behind the bike to make sure the derailleur was now straight and to check the shifting. Everything looked and worked fine, so only a week later, my friend’s 10-minute repair was finished. While it took way too long, at least I can say with confidence that the hanger is now better than new!
Ride total: 9,583
Jim Langley is RBR’s Technical Editor. He has been a pro mechanic and cycling writer for more than 40 years. He’s the author of Your Home Bicycle Workshop in the RBR eBookstore. Check out his “cycling aficionado” website at http://www.jimlangley.net, his Q&A blog and updates at Twitter. Jim’s streak of consecutive cycling days has reached more than 8,000. Click to read Jim’s full bio.