-
Posts
-
-
Last week I got a stick in my derailleur while walking my bike up a set of stairs on a local trail. I noticed the stick before pedaling but just pushing the bike with the stick in there was enough to tweak my drivetrain. The bike was still rideable but shifting became completely unreliable.
I took everything apart – chain, derailleur, pulleys, hanger – to figure out what the problem was. It wasn’t clear whether the derailleur cage was bent or if it was the hanger – everything looked pretty normal. After swapping out the derailleur hanger for a spare I found shifting improved so I got out my carpenter’s square and sure enough, the old hanger was bent ever so slightly.
So here’s my question: does anyone have a good method for testing the true-ness of a derailleur hanger? And for minor bends, is it possible to get the thing back into shape? (I’m guessing no).
-
Its pretty much impossible to chech the trueness of the hanger without taking it off. The quickest check is to take it off and lay it on a piece of glass (table top). Flip it over and check both sides at eyelevel, if you see light coming from underneath its bent. And yes if its SLIGHTLY bent you can flatten it back out in a clean vice very slowly and patiently. But beware if you do bend it back it is weaker now and will most likely crack or break next time it gets whacked.
-
if it isnt shifting properly, its bent.
-
"trek7k" wrote
Last week I got a stick in my derailleur while walking my bike up a set of stairs on a local trail. I noticed the stick before pedaling but just pushing the bike with the stick in there was enough to tweak my drivetrain. The bike was still rideable but shifting became completely unreliable.
I took everything apart – chain, derailleur, pulleys, hanger – to figure out what the problem was. It wasn’t clear whether the derailleur cage was bent or if it was the hanger – everything looked pretty normal. After swapping out the derailleur hanger for a spare I found shifting improved so I got out my carpenter’s square and sure enough, the old hanger was bent ever so slightly.
So here’s my question: does anyone have a good method for testing the true-ness of a derailleur hanger? And for minor bends, is it possible to get the thing back into shape? (I’m guessing no).
I have retrued many a derailleur hanger by hand while it is still on the bike.
That said, I know Park Tool makes an actual tool for retrueing a hanger. With the hanger still on the bike, the tool threads into the hole where the derailleur attaches. The tool features a long handle that is extendable, with another piece that extends straight out from the handle. The idea is to line it up with your rim, and then move it around the wheel. If the hanger is not true, you’ll have some space between the marker and the wheel in spots and it might hit the rim in others. Using the leverage of the long handle and the piece to measure against the wheel, you can accurately straighten a hanger by hand.
Of course, I’ve always assumed that if your rim is bent too, then you’re just SOL.
Found the link: http://www.parktool.com/product/deraill … auge-dag-2
-
"tjc58" wrote
But beware if you do bend it back it is weaker now and will most likely crack or break next time it gets whacked.
Technically it’s stronger, but more brittle. But you’re right, a trued hanger is more likely to crack and break off, which could be a good or bad thing I guess depending on where the derailleur ended up…
Everyone carries a spare hanger and a tool to install it, right?
-
Everyone carries a spare hanger and a tool to install it, right?
I carry a extra hanger and tool(s),have never had to use it though,although I’ll be counting the days to see how long it takes to bend one since I opened my mouth about it,hahaahhaah.
-
I always carry one too.
-
What kind of material is the hanger usually made from? Clearly it’s designed to yield before the derailleur parts to protect the expensive bits.
Placing the hanger on a table it looks like it’s bent 1-2mm max but of course that gets magnified along the length of the derailleur. Not sure if I’ll try to bend it back – I’m just glad I only need to replace a $15 part instead of a $100 part.
-
"trek7k" wrote
What kind of material is the hanger usually made from? Clearly it’s designed to yield before the derailleur parts to protect the expensive bits.
Aluminum.
-
Yeah, I figured aluminum but what type of alloy? Clearly it has different properties from the aluminum used in derailleur parts.
-
"trek7k" wrote
Yeah, I figured aluminum but what type of alloy? Clearly it has different properties from the aluminum used in derailleur parts.
No idea 😃 Something cheap and easy to cast and machine. No heat treatment I’d imagine. Like you said, it is, by design, the weak link in the system.
-
My old bike (91 Trek 830) the derailleur hung right on the frame. It hung up once and bent the "hanger" for say and I had to send it away the straighten that part of the frame. The derailleur was complete trash also.
-
You must be logged in to reply to this topic.