The argument against using tools: There are a few different companies out there who manufacture tools made specifically to straighten rotors, simply pinching the rotor and acting as a lever to allow you to bend it easier. Some are designed to be used two or three at a time, with one or two holding a section of the rotor in place while the remaining tool acts as the lever. There is even a feeler gauge that allows you to see exactly how far the rotor is out, but nothing works as good as using your bare hands.
There are a few issues with using metal levers (
this includes crescent wrenches as well) to straighten rotors, but the first is how easy it is to actually bend the rotor while using these tools. That isn't a good thing? Nope, especially for the home mechanic who might not be doing this repair that often. The extra leverage allows you to very easily bend the rotor too far, making the problem worse than it was when you started the repair. While it would be easy to blame the mechanic and not the tool, some bent rotors only require the slightest amount of force to straighten and some require much more, but a rotor tool can make it difficult to feel the amount of force that you are applying. Using your hands will give you a much better feel for what you are doing, allowing you to make smaller adjustments at each go.
Rotor straightening tools are often quite skinny as well, and applying pressuring to a very focused point on the rotor may do more harm than good. It is often much more effective to use your thumbs to spread the force out as you work the rotor back to straight. The worst case scenario is when so much force is applied by using a rotor straightening tool that it actually kinks the rotor where the tool makes contact, instantly turning it into scrap metal.
But aren't your hands dirty? When was the last time that you cleaned your rotor straightening tools? Your hands have oil on them right now, even if you've just woken up and haven't touched anything yet, which is why you'll want to clean them before doing this job. Getting that oil or grime from your hands onto the rotor will only be detrimental to the performance, so if you are going to try and straighten your bent brake rotor by using your hands you'll want to make sure that they are clean. Very clean. Wash them thoroughly, being sure to rinse off any and all soap that you've used, and then dry them with a towel that you know is clean. Alternately, you can just throw on a new pair of nitrile gloves and be done with it.
Some helpful pointers: • Much like truing a wheel, this is one of those repair jobs that will only get worse if you try and rush it. Take your time, find the
exact place where it needs to be straightened and make very small adjustments at each go. You want to avoid bending the rotor too far or doing it in the wrong place, both of which can cause the rotor to have a wave bend where it is out of true to both the left and right. That's when things can start to get tricky...
• While a small to medium gentle bend in a rotor can usually be trued out with great results, sharper kinks are likely going to be a death blow. Having said that, it certainly doesn't hurt to try and straighten anything.
• The rotor may be out of true in multiple spots, but only work on one at a time to keep things simple.
• The edges of a rotor are usually quite sharp. Be careful not to cut yourself!
What's needed: • Your clean hands (
nitrile gloves help)
• A clean rag
• A sharpie
• Brake clean
Step 1. You first need to identify the exact spot where the rotor is out of true. It is easiest to let the rotor tell you where it's rubbing the brake pads - instead of trying to peer down at the gap between the pads and rotor, listen to the sound it makes when it rubs. You may have to listen carefully, but slowly rotating the rotor through the caliper will tell you exactly where contact is being made.
Step 2. Use a black marker to indicate the exact position and how long the bend is. Only mark the very top edge of the rotor, not the braking surface. This will make keeping track of your progress much easier, especially if there are multiple locations on the rotor that are out of true. If there are multiple places that need attention, concentrate on one at a time.
Step 3. If you need to true the rotor by pushing it in towards the bike, wrap your fingers around the spokes and gently push with your thumbs. Go easy, you'll find that not much force is needed to make substantial changes. If the affected area is long, spread your thumbs far enough apart to straighten it. Apply pressure and then turn the rotor through the caliper to see how effective you've been. Repeat as needed.
Step 4. If the rotor needs to be pulled out away from the bike place one hand at the top of the tire to hold the bike in place and use two or three fingers to gently pull at the rotor. Again, start with only a small amount of force, working your way up to applying only as much pressure as needed.
Step 5. Even though you washed your hands prior to touching the rotor you should still give it a good spray with a brake cleaner to rinse off any oils. Let it air dry.
Have you tried to straighten a rotor this way? Maybe you have a technique you want to share? Tell us about it below.
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Parktool.com to see their entire lineup of tools and lubes
This only applies for when it is the rotor on the REAR wheel
But it is a quite good idea to mark the rotor!
-1 remove bent rotor
-2 set aside
-3 install new, unbent rotor
-4 hang old rotor on garage wall for decoration
Also, oldfaith, I would not douse the whole caliper like that, especially with brake clean. You risk the cleaner getting into the piston/caliper interface (bore) .......I just dont think its a good idea. Also, it will soak into the pads and the stuff you are using could have ingredients that wont evaporate out.
the brake cleaner is not so good for your brakes.. it DOES leave a residu..(some brands more than others..i found one good brand we have @ work.. it is normally the cheap house brand) i believe in alcohol too which is said above aswell..
since i do not get to high speeds i really feel the deteriorating braking power of using brake cleaner,. (note alcohol does make the brake fade too, but it lasts only a very short time ! ) if you do use brake cleaner.. i found out paper towels work great.. and they are disposable,,.
NOW CHECK THIS >>>
what i have seen some time ago ..baffled me !
my mate took 2 hammers,,. found the bend in the rotor and using the WOODEN end of one hammer against the disc and hitting the hammer part with the other.. on the lower part of the arms of the disc.. IF i am correct ! if the bend is inwards (to the wheel) hit the out side and vice versa,, he tapped his disc straight in no time,. i practiced it at home with a soon to be replaced hope trial disc.. which i ended up using for 4 months longer or something..cause i got it straight !
it works great.. start with small taps.. dont try to bend the disc arm ! just frighten it and it will return to its original form !
with bend rotor surfaces this does not work.. than use the method as noted somehwere here to.. take rotor off the wheel.. lay it on a flat (glas table !) surface to check the bends..and mark them,, take it OFF the glas table, and whack it straight on a flat piece of wood with a rubber or metal hammer.. note the hammer surface must be clean and smooth !
use a wooden surface so the impact of the hammer can go somewhere,.
1 - A clean paper towel obviates the need for cleaning the rotor afterwards
2 - Rotors can have some really strange complex bends. Circular items exhibit more stiffness in the direction of the bend, so learn to feel for that resistance with your fingertips.
3 - Know when to give up. Especially in the shop, I hate to see mechanics spending two hours trying to save a fairly cheap part.
4 - Rotors aren't necessarily straight even right out of the box, so you might end up straightening it even if you buy a new one.
Shimano mechanic at last weekends Tara Llanes Classic said same thing - "use your hands first". Shoulda woulda coulda. Got it close enough, but from here i'll be taking Mt-Bike-E's advice - Vice and 2 pcs of Oak. .....And perhaps fewer beers.
Just tried straightening the botched rotor again. This time by hand as shown here. Sweetness, success. Thanks Mike Levy @PB!
Thanks
I found Hope floating rotors especially hard to bend back, which is annoying as they're twice the price.
See here for a cheaper alternative: superstar.tibolts.co.uk/product_info.php?products_id=455
go ride a round for a few minutes without using your brake,
MAKE SURE YOU DONT USE YOUR BRAKE!!!
then you put the bike on the stand. where ever there is no line is where you bend it.
if the line is still there ride more.
works for me, makes it easy to find the spot
So, assuming everyone is straight up, tools work, and no tools work - moving on......