On my Mountain bike. I have hydraulic disc brakes
front brake
one part of the disc is metal rubbing on metal, like one part is out of alignment abit
so you here the scraping noise.
How do i properly align the disc. i been pushing and pulling the part by hand but still not able to get it perfect
or is it with my wheel itself? do i have to align/tighten the spokes?
Align wheel itself?
thanks

As you are saying part of the disc, it sounds like your disc is slightly warped, this can be corrected, see here https://www.parktool.com/blog/repair-...d-installation.

For aligning the calipers, see the instructions for you brand of brakes.

You shouldn't need to touch the spokes, if you do, there something major wrong with the wheel.

Take a look at the space between the pads mounted in the caliper and the rotor and you will find that you are dealing with a very narrow gap. It is important to reallize this as you can push/pull/bend your rotor all day long and not fix the rubbing problem until you reallize the resolution you need to be pursuing.

When truing the rotor start by flexing the arms of the spider holding the outer diameter of the rotor to the center of the rotor. Finer tuning of the rotor may require flexing single small segments of the outer portion that runs through the brake pads. Use an adjustable wrench or tool specific to this task (Park makes one). There is a company that sells the tool in a pack of 3 where two tools are used to stabalize the rotor and a third placed in the middle of the other two is used to bend the disk...This system works well in theory but in reality I have found using this system to be a pain and more trouble than its worth compared to using a single tool on the rotor. I use a park ts-2 with their rotor truing guage and a dial caliper at my home shop.

Once you know that your rotor is straight do the following:
1. Mount your wheel properly in your frame.
2. Loosen the bolts holding your caliper to the frame adapter or to the frame if there is no adapter. You want the caliper to be able to float around on the bolts.
3. Spin your wheel.
4. Grab your brake lever and hold it firmly while you tighten the caliper bolts.
5. Keep an eye on the caliper while tightening the bolts to ensure it does not creep when tightening the bolts.
6. Your caliper should now be centered on your rotor. If not, sight down between the pads and the rotor to see which pad is rubbing and whether it is the top or bottom portion of the pad that is rubbing the rorot. Loosen the caliper bolt closest to the portion of the pad that is rubbing and apply a little pressure against the side of the caliper to creat the gap needed and then tighten the caliper bolt. Now your caliper should be centered without rubbing.

Hydraulic disk brakes generally work reallly well but can be frustrating to dial in. I normally only ride with a tube, pump, and tire levers, but since obtaining a mt bike with hydraulic brakes I keep 5mm allen wrench in my saddle pouch to facilitate centering my calipers if I have to pull a wheel for any reason.

-j

I don't have a lot of experience with discs, but I still take issue with this...

IMO it's better to ensure the wheel doesn't move when you grab the brake and tighten the bolts.

Either way it should work. In my head spinning the wheel is to move the caliper to center over the rotor but in reality it should not matter as long as the rotor is true. When grabing the brake lever one should squeeze tightly in an effort to keep the caliper from rotating out of alignment when tightening the bolts. Spinning the wheel can be eliminated unless like me you do it because it makes you feel better .

-j

I was thinking the caliper could be holding the disc in a way that wouldn't clamp down properly when the bolts were tightened, if it the wheel was spinning first, or if it even got bumped before the bolts are tightened.

The bolts should probably only be loosened just enough to free the caliper and no more.

Would it be ok if i took the Disc part off my wheel and used a tool or something to make sure its 100% straight. its more of the actual disc that has a slight bend, hard to see, but when spinning wheel its only one part of disc that i hear metal on metal
otherwise wheel does spin quite freely

Might have more adjustment using the angle adjustable washers from V brake, pads
under the ISO Adapter to the caliper mounting Bolts .

Watch some videos.

https://www.youtube.com/watch?v=0fosSuyiCDE
https://www.youtube.com/watch?v=nHdQkm14JVw
https://www.youtube.com/watch?v=oOpXGZqpjQg

Yes it would be ok...but you may find it easier to apply leverage, especially once any major bending is out of the way, with the rotor installed on the hub. The goal is to have a rotor as close to flat/straight as possible so apply whatever method works best for you and the tools you have.

-j