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Mossyrocks wrote: ↑Mon Jun 28, 2021 6:57 pm What are the thickness limits?

Front disc: Limit 4.0 mm (0.16 in)

Rear disc: Limit 4.5 mm (0.18 in)

ionbeam wrote: ↑Mon Jun 28, 2021 6:52 pm When the pistons pop out of the caliper you will know it's time to replace the rotors

Once you decide what kind of rotors to buy, it will be time to replace them. What brake pads have you been running that have thinned your rotors at such a young age?

The front pads were replaced once with OEM. The rear has had one OEM replacement and one EBC.

Rear Brake disc thickness limit 4.5 mm (0.18 in)
<front> Brake disc thickness limit 4.0 mm (0.16 in)

2006 FJR...

ionbeam wrote: ↑Mon Jun 28, 2021 7:03 pm

Mossyrocks wrote: ↑Mon Jun 28, 2021 6:57 pm What are the thickness limits?

Front disc: Limit 4.0 mm (0.16 in)

Rear disc: Limit 4.5 mm (0.18 in)

Just looked them up in the FSM. The total wear allowance is just 0.5mm (Original thickness spec is 4.5mm F and 5.0mm R)
Any likelihood of the rotor failing if you are even as low as 3mm F and 3.5mm R? Or is there some other reason for that spec?

I checked mine with a digital caliper but you really need a micrometer (or caliper with shims) to get past the edge ridge.

dcarver wrote: ↑Mon Jun 28, 2021 7:43 pm Rear Brake disc thickness limit 4.5 mm (0.18 in)
<front> Brake disc thickness limit 4.0 mm (0.16 in)

2006 FJR...

Might I ask what your rotors are at.

Mossyrocks wrote: ↑Mon Jun 28, 2021 6:57 pm What are the thickness limits?

Isn't it in your FJR Service Manual?

Doesn't anyone read the previous posts before replying?

FYI, the Chinese wave rotors are a full 5 mm thick for FJR front rotors, stamped minimum 4mm. I have a rear on another bike, it was also 5mm.

Found fronts, <barely> used, eBay $49.60

No idea Galfers and EBC are so pricey

Now to find a used rear...

Thanks for replies guys

edit
found rear too

I’m going to restore mine to original thickness by troweling some JB weld on to them

I have cheepo wave rotors on both my spare rims.
Ran them on the Alaska trip

Currently running the front now.


Canadian FJR

I'll let you know how they work out

Well, my suspicions were correct. The 1st front brake tap of the day always made 2 distinct clunks. I could tell one was from the left and one from the right. Backing up, same thing. I figured the stock rotors were wearing on the rivets and clunking back and forth. Turns out I was right. you could look at the stock rotors and see that the outer was about 2mm ahead (or behind) of the inner. 1st ride with the wave rotors. NO MORE Clunking, and not only that, but all of the noise coming from the front end that I thought was just old plastic getting loose is gone.

Fresh rubber, fresh rotors, fresh pads, feels like a new bike. 82,500 miles on the stock rotors, they were down to 3.5 - 3.8, but the rivets were the clunking sound and all the noise from the front end. I'll keep you posted on how they wear. My last set of front pads were installed 14K ago, I wore them out pretty quick.

I have around 50,000 km on a set of Chinese aftermarket front wave rotors that I put on my spare rim.

Just cleaning the bike (surprise) and the left one has significant movement/ play. Almost like a full race floating
rotor. Right side is tight. I suspect the bobbins are wearing. Not sure what my plan is yet.not sure how long it’s been like this.

Canadian FJR

I found this interesting because I clean my bobbins every winter.

https://m.youtube.com/watch?v=hOA5cOrvwRw

Canadian FJR

CollingsBob wrote: ↑Wed Jun 30, 2021 6:24 pm I’m going to restore mine to original thickness by troweling some JB weld on to them

Missed this earlier. Don't forget to surface grind it when done. The money you save over the life of about a bazillion replacements might pay for your surface grinder.

Canadian FJR wrote: ↑Sun Oct 17, 2021 2:45 pm I found this interesting because I clean my bobbins every winter.

https://m.youtube.com/watch?v=hOA5cOrvwRw

Canadian FJR

Loved the video. Good explanation of the hows and whys of floating rotors.
Never felt the need to clean the bobbins. I suppose cleaning the dirt and grit out of them using something like brake cleaner (without rotating them) wouldn't hurt but it doesn't seem to be necessary.

FJRoss wrote: ↑Mon Oct 18, 2021 11:09 amNever felt the need to clean the bobbins. I suppose cleaning the dirt and grit out of them using something like brake cleaner (without rotating them) wouldn't hurt but it doesn't seem to be necessary.

FJRoss,

Clean rotor bobbins will let the rotors "float" and run cool. Jammed rotor bobbins can cause the rotors/brakes to overheat, even when the brakes are not used. Rotors should not be too hot to touch, when you have not been on the brakes. Slow down with compression braking, use the other brake to stop, and check your rotors for excess heat now and then.

One night, I saw a bike with a rear rotor glowing red-hot on the freeway. I blew the horn and waved the guy down, but he took an exit and then stopped to check. That rear brake was ready to burn, or maybe explode. I did not get to talk with him, due to heavy traffic.

This can be a serious problem.

Red wrote: ↑Mon Oct 18, 2021 11:31 am

FJRoss wrote: ↑Mon Oct 18, 2021 11:09 amNever felt the need to clean the bobbins. I suppose cleaning the dirt and grit out of them using something like brake cleaner (without rotating them) wouldn't hurt but it doesn't seem to be necessary.

FJRoss,

Clean rotor bobbins will let the rotors "float" and run cool. Jammed rotor bobbins can cause the rotors/brakes to overheat, even when the brakes are not used. Rotors should not be too hot to touch, when you have not been on the brakes. Slow down with compression braking, use the other brake to stop, and check your rotors for excess heat now and then.

One night, I saw a bike with a rear rotor glowing red-hot on the freeway. I blew the horn and waved the guy down, but he took an exit and then stopped to check. That rear brake was ready to burn, or maybe explode. I did not get to talk with him, due to heavy traffic.

This can be a serious problem.

I suspect the glowing rear rotor was a stuck brake - possibly a pivot issue. Unlikely to have anything to do with bobbins or a floating rotor issue.

As explained in the video, the floating rotors enable the rotor to expand and contract without either shearing the attachment bolts or causing the rotor to warp. This will still work as long as the bobbins aren't so compacted with crud as to make them effectively solid. Why would the floating aspect cause the brakes to run cooler (or hotter if the bobbins are dirty)? In fact, having a thermal "break" between the rotor and the hub means that conduction of heat away from the rotor is blocked - just don't see any reason why dirty would run hotter.

An argument could be made that dirty bobbins may not allow for full contraction of the rotor (after thermal expansion). Theoretically, this might cause the rotor to warp. Dirty bobbin would not prevent the initial expansion.

Can't really say if my view on this is the right one or not. Can only say that I haven't had any issues with overheated brakes or warped rotors.

FJRoss wrote: ↑Mon Oct 18, 2021 12:15 pm

Red wrote: ↑Mon Oct 18, 2021 11:31 amOne night, I saw a bike with a rear rotor glowing red-hot on the freeway. I blew the horn and waved the guy down, but he took an exit and then stopped to check. That rear brake was ready to burn, or maybe explode. I did not get to talk with him, due to heavy traffic. This can be a serious problem.

I suspect the glowing rear rotor was a stuck brake - possibly a pivot issue. Unlikely to have anything to do with bobbins or a floating rotor issue.
Why would the floating aspect cause the brakes to run cooler (or hotter if the bobbins are dirty)? In fact, having a thermal "break" between the rotor and the hub means that conduction of heat away from the rotor is blocked - just don't see any reason why dirty would run hotter.
Can't really say if my view on this is the right one or not. Can only say that I haven't had any issues with overheated brakes or warped rotors.

FJRoss,

Definitely the glowing rotor was a "stuck" brake. "Why" is a serious question.

If the rotor bobbins are clean, the rotor can "float" between the pads as a rotor should. Any light contact between the rotor and pads then will not have enough force to cause heating. The rotor runs cooler, but not because of heat conducting (or not) to or from the hub. The bobbins are too small to do that, really.

Dirty rotor bobbins can cause the rotor to contact one brake pad, with some force. The rotor heats up, and the brake pad heats. Brake fluid has a boiling point. That temperature is usually posted openly on the container label. Once you get to the boiling point, the brake fluid "steam" causes pressure as if the brake lever has pressure applied. That pressure pushes the brake pads harder against the rotor, making more heat, and the process continues until the brake fails, or a wheel locks up. You can only release that braking pressure by opening a bleed screw. If you touched the brake lever (either hand or foot), the brake lever would have seem to be locked rigidly, with no free play at all. You may or may not notice a "drop" in engine power, due to the braking force being applied.

In the case of the red-hot rotor that I saw, the engine was able to "power through" the braking force temporarily, but the increasing heat would have caused a brake disaster very soon. On the front brakes, you may not know there is a problem until the front wheel breaks traction and skids, meaning a total loss of steering control. If you ever find any loss of free play in the front brake lever, stop under control while you can; a hot brake will NOT fix itself until it cools off by standing still. Until the problem has been fixed, by servicing the caliper mounts or rotor bobbins, or both, the heat problem will happen again and again.

Water in the brake fluid can cause the runaway heat issue also, just by riding hard. Water boils (making steam pressure) at a lower temperature than brake fluid. That is why we replace the brake fluids on a regular basis.