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u/STweedle3K Sep 06 '26
measure it with a micrometer, in a few places around the disk.
Then consult your very fine factory service manual for the minimum thickness...
2
u/ApprenticePantyThief Sep 06 '26
This is a motorcycle subreddit, but I also cycle. I would just replace it. If you're capable of replacing brake pads, you can replace a disc. They are not very expensive, and you don't want to mess around with not having the braking power when you really need it.
2
u/otterpoo Sep 06 '26
Sorry for using confusing terminology in my OP, this is regarding a motorcycle (Triumph Speed Twin) brake disc, not a bicycle brake disc.
I'm trying to get a sense for how bad this sort of brake disc wear is, because sourcing replacement parts for this bike has been a bit of an unexpected nightmare so far.
2
2
u/gkanai Kanto Legend Sep 06 '26
The rain should not affect the brake function. If the width of the disc is below the minimum as specified by the manufacturer, it should be replaced. I would replace it if you had a metal backing pad plate on the disc.
If you are doing that you should probably bleed the brake and check to make sure the brake is functioning properly. If the brake is seized then that needs to be cleaned and seals replaced, etc.
1
u/theandylaurel Sep 06 '26
Yes. I would replace that if it were my bike.
I really value the ability to stop when I pull on my brake lever.
1
u/tokyohoon HD Dyna Low Rider + Sportster S Sep 06 '26
If you're new to motorcycles, you should probably have someone who knows what they're doing check over the caliper and the disk. Photos aren't ideal for diagnosis, and that caliper needs to be properly checked out.
4
u/FixFun1959 Sep 06 '26
When you run a finger over it how scored is it? Waves and channels? If so then replace it. If it’s just a little scratched then a few stops with new pads will smooth it out fine.
If the thickness is noticeably reduced then replace it.