Truing this Disc rotor is trying my patience

ClintBX

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Mar 6, 2014
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Hi ESFMs,

I'm at my wit's end getting my rear disc rotor to stop clipping at that one spot.

I have a 203mm rotor on my DD hub motor and am using a TRP Spyre mechanical caliper. The rotor is an alligator wind cutter.

The rubbing part is exactly where the valve stem of my tire is.

I've spent the past 2 weeks trying to true the area with my parktool truing tool and it doesn't seem to matter how gradual I'm being, I always over correct. And when I go to back out of that, I'm right back to square one.

The warp isn't very visual either. I can only see where it's out by spinning it fast enough.

I've tried recentering the caliper several times, sanded and cleaned the pads and cleaned the rotor.

I'll upload a video. Tell me what you think.

Clinton
 
Are you sure it's not rubbing on the outer edge of the disc? It sort of looks like some shiny spots where it's rubbing. If so. adding a washer to move the caliper out may provide enough clearance.
 
junk speed hole filled rotor is probally not drilled on center.


Get a better quality rotor.
 
E-HP said:
Are you sure it's not rubbing on the outer edge of the disc? It sort of looks like some shiny spots where it's rubbing. If so. adding a washer to move the caliper out may provide enough clearance.

I had issues when installing the caliper in the beginning. My 203mm adapter was making the caliper overhang and I was only making contact with 3/4 on the pads. I had to get a 180mm adapter and use cone washers to get complete contact. In my trial and error, I had it too low at one point. I've since confirmed that it's not hitting the top of my caliper
 
Is it possible to have issues with the hub causing lateral fluctuations? I'm not sure if my eyes are playing tricks on me but it looks like the hub itself is fluttering from side to side
 
Hydraulic brakes are self adjusting and more tolerant of slightly out of whack rotors than mechanical brakes. My first set of disc brakes were mechanical. They were very fussy to adjust every time I took a wheel off of the bike. I almost gave up completely on disc brakes until I got a set of hydraulics and all those problems went away.
 
ebuilder said:
ClintBX said:
Is it possible to have issues with the hub causing lateral fluctuations? I'm not sure if my eyes are playing tricks on me but it looks like the hub itself is fluttering from side to side
Would be rare and generally this would occur due more to an accident versus a manufacturing defect because the manufacturing process of hubs aka datams pretty much dictates a true hub for any name brand hub and perhaps yours isn't but I have a tip for you if you want to drill down on this possibility.

Remove the rotor from the wheel. Generally there are a couple of types of rotors...some are bolted and others are screwed on which requires a special tool to remove.

In an event, remove the rotor.

Install the wheel on the bike with no rotor....best to remove the caliper too which is two bolts as you know.

Take a zip tie and curl it around your front fork stanchion and use the tip of the zip tie cut at an angle as a dial indictor and position it on the land where the rotor mounts and spin the wheel. If it skips as you believe may be the case, then you have a defective hub.

Please know the conical washer orientation is a pretty big deal and if the washers for example are upside down, the caliper will not locate flush when tightening the caliper bolts. Let me know if this is clear because a common mistake for those that haven't worked on disc brakes and we each learn by experience and hopefully never stop learning.

It's a rear hub actually. What is the correct orientation for cone washers? I have 2 sets per bolt. Between adapter and caliper, I have concave on the bottom and convex on the top. And between the caliper and the head of the bolt, it's convex at the bottom with concave at the top.
 
ebuilder said:
They are referred to as a convex washer and a concave washer. One pair of these is between the caliper body and where it connects to the frame bracket or post 'per bolt'. Think of it as a sandwich.
You can see the "sandwich" in this picture from my Giant Revive build thread:
file.php


https://endless-sphere.com/forums/viewtopic.php?f=6&t=117124&p=1732379&hilit=disk+adapter#p1732379
 
ClintBX said:
I've spent the past 2 weeks trying to true the area with my parktool truing tool and it doesn't seem to matter how gradual I'm being, I always over correct. And when I go to back out of that, I'm right back to square one.

Can you post a pic or link to this tool? Is it for straightening a warped rotor?
 
ebuilder said:
E-HP said:
ClintBX said:
I've spent the past 2 weeks trying to true the area with my parktool truing tool and it doesn't seem to matter how gradual I'm being, I always over correct. And when I go to back out of that, I'm right back to square one.

Can you post a pic or link to this tool? Is it for straightening a warped rotor?

If you have a money tree in the backyard you use this method:
https://www.youtube.com/watch?v=O0c2Ez2v0PU

If you don't and most don't:
Bigger is better:
Big Crescent wrench.jpg


Connect this to either front fork stanchion or rear seatstay:
Zip Tie.jpg

The parktool just seems pretty crappy if it took two weeks and still no success. Or, not the right tool for the job, so wondering what this disc truing tool looks like so I avoid getting one.
 
Recently had a cargo trike build where one of the disc brake rotors had a wobble.
Turned out the rotor was fine and the disc mounting surface on the hub was not machined properly.
It was a very small amount but enough to cause the kind of noise as seen in your video.
Measuring the run out of mounting flange with a machinist dial indicator confirmed the problem.
My DIY fix was to touch up the disc mounting surface on the hub with a Dremel.
A simple holder was fabricated to firmly clamp the Dremel and then slowly rotated the wheel by hand taking very small cuts.
Slips of paper were used between the DIY mount and the Dremel adjusting the depth of cut.
In my case this method saved a bunch of time.
Making a mount for a file instead of a Dremel could work as well.

Moral of the story ... check the hub.
 
ebuilder said:
Just don't need one E-HP. A large crescent wrench turned all the way down to the rotor thickness works even better than the Park tool because of the adjustability of a crescent wrench which can keep some fractional preload on the sides of the rotor.

OK, I saw a picture of one on Amazon. I can't believe they charge money to that.
 
ebuilder said:
Clever Steve. In effect you created a lathe or milling machine. Rare for the hubs to be out of true at the rotor interface by virtue of how they are created.

Rare for sure.
When other new discs where tried the results were the same.
That's when the dial indicator came out.
Some of the hard lessons over the years is not all new things are actually made correctly.
When something doesn't function, double check everything.
My lathe and mill are too small for this task.
 
E-HP said:
ClintBX said:
I've spent the past 2 weeks trying to true the area with my parktool truing tool and it doesn't seem to matter how gradual I'm being, I always over correct. And when I go to back out of that, I'm right back to square one.

Can you post a pic or link to this tool? Is it for straightening a warped rotor?

Yeah, it's the DT2. I don't think it's the tool causing my problem. I got this because I hear a crescent wrench can do more damage to the rotor. And it has one nook that allows you more room. Using a wrench with your hand parallel to the wheel when you have to bend the rotor inward can be limiting. On a regular bicycle wheel, you might be fine because you've got the spaces between the spokes but not so when working with a gearless hub motor.
 
ebuilder said:
E-HP said:
ebuilder said:
Just don't need one E-HP. A large crescent wrench turned all the way down to the rotor thickness works even better than the Park tool because of the adjustability of a crescent wrench which can keep some fractional preload on the sides of the rotor.

OK, I saw a picture of one on Amazon. I can't believe they charge money to that.
Only for those willing to buy it. :) I never have nor wanted to.
Also, since rotors aren't all the same thickness, they design that slot for widest rotor width...aka worse case to fit in the tool which leaves a gap for thinner rotors. With a crescent wrench you can turn the wrench jaws down to line-to-line with the rotor sides. A crescent wrench is much better. Of course Park doesn't want to sell a crescent wrench. ;)

They also sell crescent wrenches🙃
https://www.parktool.com/en-int/product/adjustable-wrench-paw-12
 
I've done one final adjustment. Not the be all and end so of it but just to have so it's good enough to ride it again (I've been on my rim bike in the meantime)

A quick test ride gave a cautious optimism. It made no sound at all... Well nearly no doing at all. But I want getting a clipping sound every rotation.

I decided to throw out the rule book and try something new.

When recentering the caliper, I didn't touch the brake lever or even squeeze the caliper itself by hand. Instead, I decided to hold the caliper so that the inner pad sat flush against the rotor, and then, I tightened the outer piston all the way into the rotor so that it centered the caliper still on the adapter. After tightening the 2 mounting bolts, I loosened the outer piston until both pistons had relatively identical travel to the rotor, adjusted the barrel adjuster and I was done.

I came to the conclusion that since I can only adjust the outer piston because there's no space to put an Allen key between the caliper and the hub, I may as well leave it all the way loose as a default and work with the outer piston mostly. Up until now, I've had to remove it at the adapter to adjust that inner piston. PITA.
 
ClintBX said:
I hear a crescent wrench can do more damage to the rotor.
How so? If used carefully the only possible damage I can see is if the wrench jaws were greasy from previous use on greasy or oily items. But even then, any grease transferred to the rotor can be cleaned with alcohol.

ClintBX said:
... leave it all the way loose as a default and work with the outer piston mostly.
You'll find it doesn't work like that. Upon applying brakes, the moving piston side will contact the rotor, continuing its inward motion bending the rotor until it contacts the inner pad.

Sometimes a rotor can be trued, lasting for a short time, only to again spring back to its previous warp. Probably the metallic grain gets rearranged from overheating or defect. Frustrating for sure. Happened to me (203mm Shimano rotor, leading me to think good quality). Trued it several times before finally giving up on it and replacing it with a beefier slightly thicker Avid with less holes and empty space, wider "spokes."
 
99t4 said:
ClintBX said:
I hear a crescent wrench can do more damage to the rotor.
How so? If used carefully the only possible damage I can see is if the wrench jaws were greasy from previous use on greasy or oily items. But even then, any grease transferred to the rotor can be cleaned with alcohol.

ClintBX said:
... leave it all the way loose as a default and work with the outer piston mostly.
You'll find it doesn't work like that. Upon applying brakes, the moving piston side will contact the rotor, continuing its inward motion bending the rotor until it contacts the inner pad.

Sometimes a rotor can be trued, lasting for a short time, only to again spring back to its previous warp. Probably the metallic grain gets rearranged from overheating or defect. Frustrating for sure. Happened to me (203mm Shimano rotor, leading me to think good quality). Trued it several times before finally giving up on it and replacing it with a beefier slightly thicker Avid with less holes and empty space, wider "spokes."

It's a dual piston caliper. They engage equally regardless of the piston adjustment. I've got it pretty centered this way.
 
ebuilder said:
Btw, OP, you don't have to replace the rotor. Just file down the high spot with a flat file...file a little and test where you hear the high spot and when sound disappears, you are good.

Or you can put a pair of M6 washers under the caliper to raise it up a mm or so.
 
ebuilder said:
Chalo said:
Or you can put a pair of M6 washers under the caliper to raise it up a mm or so.
Quite right. Believe the OP has a stack of washers for spacing.

Eww. That's proof that he's using the wrong IS or post mount adapter, or else using an adapter than needs spherical adjusting washers but doesn't have them.
 
Chalo said:
ebuilder said:
Btw, OP, you don't have to replace the rotor. Just file down the high spot with a flat file...file a little and test where you hear the high spot and when sound disappears, you are good.

Or you can put a pair of M6 washers under the caliper to raise it up a mm or so.

This would be less ideal because it's could cause an overhang situation from engaging the rest of the rotor. That's a good way to replace pads prematurely.

Besides, I've ruled out radial deviations. It's all lateral
 
ClintBX said:
It's a dual piston caliper. They engage equally regardless of the piston adjustment. I've got it pretty centered this way.

I've been using the cheap floating discs: https://www.amazon.com/gp/product/B07DRCVCZH/ref=ppx_yo_dt_b_search_asin_title?ie=UTF8&psc=1

They've held up well.

I swapped out my old bb7 calipers with some cheap knock off 4 piston hydraulics yesterday afternoon. Literally 15 minutes each to swap and set up. No adjustment, just squeezed the lever and tightened the bolts. My bb7's made a little noise but now these are totally silent. I didn't expect that. If it bothers you, then swap out your discs.
 
E-HP said:
ClintBX said:
It's a dual piston caliper. They engage equally regardless of the piston adjustment. I've got it pretty centered this way.

I've been using the cheap floating discs: https://www.amazon.com/gp/product/B07DRCVCZH/ref=ppx_yo_dt_b_search_asin_title?ie=UTF8&psc=1

They've held up well.

I swapped out my old bb7 calipers with some cheap knock off 4 piston hydraulics yesterday afternoon. Literally 15 minutes each to swap and set up. No adjustment, just squeezed the lever and tightened the bolts. My bb7's made a little noise but now these are totally silent. I didn't expect that. If it bothers you, then swap out your discs.

I'm glad you're having an easier time than me. I'm out riding mine right now and my approach seems to be working. I even tightened up the barrel adjuster for a firmer lever.

I will eventually change the rear rotor, but mainly because the braking sucks. I can't even lock into a skid if I need to.
 
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