Bad Experience Changing Out Rotor

James Kohls

Active Member
So I dinged up one of my rotors causing it to rub. I tried to true it, but figured this is a good time to upgrade from the Formula rotor. So, I bought a replacement. All I checked was 180mm and 6-bolt design. Big mistake #1 (oh yes, there's more)!

For starters, the bolts holding my old rotor on the rear wheel were torqued on really tight. They are extremely shallow Torx bolts and of course with 6 to loosen, I stripped one. I was able to take a hammer and force a hex bit into the hole and remove it, but the screw is ruined. Thankfully, my new rotor came with screws (wait for it).

Hooray, the old rotor was off. All I have to do is put it on the wheel, put the screws back + 1 of the new ones and I'm all set, right? WRONG!

So, the motor wire comes out on the brake side...*sigh* and it is protected by this odd sorta half moon shaped looking thing. The hole in the new rotor wouldn't and couldn't fit around it.

This is what I bought:


This is a Formula One rotor:


Anything that looks like the first picture will never fit on your rear hub motor Turbo, sadly. It needs the clearance of the larger opening to clear the half-moon-motor-protector-thingy.

So, I put the old rotor back on. Did my best to straighten it and for testing, borrowed one of the screws that came with the new rotor. Big mistake #2! The screw was longer than the original. No biggie? Well, after putting the wheel back on, I realized it would no longer turn. It was that pesky long screw. So off the wheel came again (boy I'm getting good at that) and now I have a rotor with 5 screws until I can find a replacement.

When I get another replacement, I'll post some photos and maybe a video, if I have time. Time to go to sleep.
 

Berry78

Active Member
You poor thing. Definitely feel your pain. Once had a $600 flat tire because of wrong-sized nuts. (car, not bike).

Thanks for sharing, it really will help others!
 

Douglas Ruby

Well-Known Member
The "half moon looking thing" is the torque arm of the powered rear hub that transmits the power into the frame. The rotor you purchased appears to be a Shimano 2-piece SM-RT76. It would probably work on your front hub, but definitely not on the rear. I believe that the following is the one-piece Shimano SM-RT56 disc used on the 2016 Turbo S (by looking at pictures on the web):



Note the picture below.


Note, the following is the Formula FD781802SB 2-piece rotor. It also looks like it has a bit more cutout so may not have issues going over the torque arm on the rear hub:

 

B.M.

New Member
For starters, the bolts holding my old rotor on the rear wheel were torqued on really tight. They are extremely shallow Torx bolts and of course with 6 to loosen, I stripped one.
The same thing happened to me. We had to drill the head of the screw away to get the rotor of. After that I wanted to drill the rest of the screw out but messed it up. At the moment I also have just 5 screws holding the rotor.
Drilling the screw out is really tricky because the motor housing is aluminum and compared to the steel bolt it's so much softer. I hope I will succeed with a second try. Rest of the screw is still in there:mad:

The length of the screws is 6 mm. This is not a normed length. Most new rotors will be delivered with screws 10 mm long. You definitely need to shorten to 6 mm length.
 

James Kohls

Active Member
Well I picked up some new rotors today. Back to loud squeaks, but no rubbing. @Douglas Ruby is correct and the Shimano RT-56 should work. The Local REI only has RT-66, but the center shape is the same. It is a tight fit, but it works. You need at least a 44mm opening. Here is a photo of the half moon shaped thingy your replacement rotors must fit around:





New Rotor:





We'll see if they quiet up after a breakin period.
 

reoutput

Member
So that weird shaped nut comes off. I didn't realize what nut the thread was talking about till the one of the pictures showed it up close. It has a 2.5 or 2 MM locking screw somewhere on there. I only know this because it fell off when I was changing one of my flats on a ride and later inspected the weird nut thing.
 

James Kohls

Active Member
So that weird shaped nut comes off. I didn't realize what nut the thread was talking about till the one of the pictures showed it up close. It has a 2.5 or 2 MM locking screw somewhere on there. I only know this because it fell off when I was changing one of my flats on a ride and later inspected the weird nut thing.

Huh. I'll have to take a closer look at it. I guess, I didn't look hard enough at options to remove it. Thanks @reoutput!

I did go for a ride last night and it is already getting quieter—much faster than the old Formula rotor. Did some heavy braking with it for break-in. Will keep updating as I see how it performs and report on braking and noise.
 

Nutella

Active Member
You can also just replace the torx bolts with button hex heads from your local hardware store, get stainless to avoid corrosion. The torx thing is a recent addition to disc rotors and while the manufacturers will often tout that they did it because it's a stronger interface for your wrench, the other reason is that it speeds assembly with auto loading tools.
 

James Kohls

Active Member
100 miles on the new rotors and they have broken in nicely. The rear brake still has some low level squeaks. The front brake, which would squeak occasionally, but was mostly quiet, never squeaks anymore. These Shimano RT-66 feel like they have better stopping power, but that was never really a huge weakness with the Formulas. Holding both in my hand, the Shimanos certainly feel more substantial and stiffer. Probably due to fewer hole cutouts—makes for a more rigid rotor. Wet braking performance is just as good.
 

bazzapage

Active Member
I replaced pads to Koolstop (with red fins!) as recommended by @Douglas Ruby and I have to say I have no complaints now. I'd still prefer something with contact adjustment but they are quiet and powerful. When I have 30,000km on the bike and my rotors are worn I'll think about a change :)
 

Allan47.7339

Active Member
So that weird shaped nut comes off. I didn't realize what nut the thread was talking about till the one of the pictures showed it up close. It has a 2.5 or 2 MM locking screw somewhere on there. I only know this because it fell off when I was changing one of my flats on a ride and later inspected the weird nut thing.

The locking screw probably did not fall out. It's just loose and I've had that happen a couple of times. I think it is 2mm. I would hate to lose the anti-rotation nut.


Also wanted to say the Formula R1 rotors are on ebay. I think they are not so common and inventory is being reduced.
 

reoutput

Member
On a side note, you might want to mark or memorize which way the nut goes when it falls off. I spent an embarrassing 15 minutes trying to get the axle in until I thought about what was going on. I had installed that retaining nut backwards...ugh. Stupid nut....lol
 

James Kohls

Active Member
Good news is the new brake rotors work (not that the old ones didn't).

Looking at the car on the left...should have been looking to the right.

I have noticed under heavy braking the front will start to scrape. Not sure if this is because the caliper isn't retreating properly or if the rotor is deforming temporarily. I'm guessing it is the caliper.
 

Ling

New Member
The information here is invaluable, I really appreciate the hard earned pearls of wisdom!

What are you using to record the video? I'm interested in recording my ride in case something does happen one day.
 

James Kohls

Active Member
The information here is invaluable, I really appreciate the hard earned pearls of wisdom!

What are you using to record the video? I'm interested in recording my ride in case something does happen one day.

Thanks. I use a Garmin Virb Elite. I actually have two...one pointing forward and one pointing backward. Got mine refurbished on amazon. Works great.
 

Allan47.7339

Active Member
I use a Cycliq Fly12 on the front and a Fly6 on the rear for my commutes. Once in a while I need to review or save the video but usually I just delete them. The Fly12 runs about 10 hours recording and the Fly6 about 6.
 

reoutput

Member
Update to this thread, do not over torque the 2MM because it will not allow the through axle to to be inserted. Changing a broken spoke I decided to really tighten that screw and 30 mins later finally figured out why the axle wouldn’t go back in. Just an FYI