How many of you make it habit to check the rear derailleur hanger for proper alignment after a new purchase? Obviously, if you see damage, it is worth checking but is this one of the standard must-do steps you mark off in your checklist?

I ask because I am curious if the Park DAG-2 is a gauge worth having around or if the occasion rarely presents itself to justify the purchase.

Or perhaps there is a crafty homemade solution that has already been presented in the past?

Its really not too high on my list of priorities for choosing a bike or not. Most of the time their out of alignment anyways, and if its just a bare frame its very hard to tell if its out by eye.

The tool is also rather expensive here (circa. €75) and for the amount of times I would be using it, not really worth it. My LBS does it for a few euro.

For vintage bikes I just use a large cresent wrench and my eyeball to get things aligned. For 9 spd and above, that tool would probably be nice to have but having to adjust a hanger on such a bike is a rare event for me so I don't need to have the tool in my basement. My co-op has one as does any decent LBS.

Checking the hanger is a must on any aluminum frame,as even with replaceable hangers they can be hard to source and/or expensive. On steel frames, as long as there are no cracks there shouldn't be a problem although a really bashed up hanger often indicates a poorly treated bike.

Some have made their own. I've been lusting after one for a long time but haven't been able to justify buying one yet. I'm the only home mechanic I know who owns the dropout straightening tools, which might indicate I've gone a bit too far.

Straightening the derailleur hanger is cheap enough if you bring in the bike with no rear derailleur attached and hand it to the mechanic. He can do it right quickly and cheaply that way. It may be $5 to $15 each time.

In the meantime, I've been eyeballing it and bending it when needed at home.

I agree that eyeball methods can be entirely sufficient.

As long as a known-straight derailer is on there, and a not-to-encrusted stack of cogs, one can sight down the cage pulleys from above and behind the bike by manually rotating the cage 90 degrees.

After such an evaluation, one can use a long adjustable wrench to correct both the twist and bend-in that may need to be corrected.
Positioning the wrench at the right angle will correct both simultaneously, usually by pulling outward.

It is very important to use a wrench that clamps fully over the threaded hole, so as not to distort it.
It is also importnt that the wheel be installed backwards in the frame (for wrench clearance) and that the QR lever be tightened (to prevent bending the axle dropouts out of alignment).

The job of bending the hanger back can take a few tries, flipping the wheel in the frame several times, when dealing with different hanger materials and with lack of wrench experience, but when the derailer finally sights straight, it is in fact straight enough for any indexing system at that point.

A bent hanger on an Al frame that does not have a replaceable hanger is a big deal as the hanger could crack if one tries to bend it back to alignment, at the very least it will weaken the hanger and make it susceptable to cracking later.

Chombi

I own those and only work on 4 bikes of my own and seldom anyone else's. The cost to have a shop do an alignment on two bikes pretty much offset the purchase.

Pretty much what I do as well on all of my bikes. Works great if you do it properly, and yes, I have aligned quite a few bikes with a 13" crescent wrench and then checked them later with an old DAG-1, and they have seldom required any additional tweaking.


I just recently made up two homemade sets of the square-headed allen bolt versions like those that were recently posted here (one 130mm and one 135mm), and I think I will eventually use an old derailleur mount bolt to fabricate a homemade derailleur hanger alignment tool as well. And no, you have not really gone too far, you just meticulous....

Good info, guys. Thanks for all the opinions.
Being a home mechanic, but repairing/restoring different steel frames from time to time, I may pick a DAG-2 in the future (when we are all swimming in money, right?!), otherwise, I suppose the crescent wrench method will work.

If I had that tool I would likely use it on a new/rebuild. I do prefer the Dura Ace tool but I am not sure if it is still produced and the few I have seen on ebay are pricy.

I don't have the tool but help with a bike charity that does and when fixing or rehabbing old bikes it has been really valuable. the tool helped me get several bikes working that the big old crescent wrench didn't. I want one.


the org if any one is local to san jose

https://www.goodkarmabikes.org/

I have the park tool and use it on every build. Most if not all have been out. The Dura Ace tool is very nice but hard to come by, and lot more $$$

I have the Park DAG tool (and the dropout alignment tools). I use them on every bike that passes through my hands. I would say more than 50% of the derailleur hangers have been bent and a fairly large number have also had dropout issues. And these are bikes that more or less looked fine by eyeball. So I think the tools are worth it but I'm a tool geek too so I may not be the best one to ask