Bent brake discs

[steved]

Hi all

On my 1996 CBR600 I have a severe shuddering under heavy front-braking and an on-off sort of thing when I front-brake whilst pushing the bike. This is not apparent when the rear brake is applied.

Am I looking at a warped front brake-disc or two?

[Postie]

Hi all

On my 1996 CBR600 I have a severe shuddering under heavy front-braking and an on-off sort of thing when I front-brake whilst pushing the bike. This is not apparent when the rear brake is applied.

Am I looking at a warped front brake-disc or two?

probably, but it could also be a problem with your calipers. When was the brake fluid changed last? I have experienced a similar problem on a CBR250, changed the fluid and it was fine, it just needed a flush.
If you can get the front wheel hoisted in the garage, just free wheel spin it, you will soon see if it has a warped disk.

[Matt Bleck]

does the lever feel like it's pushing back?

[SuperDave]

Steering head bearings maybe?

[NinjaBoy]

had something similar on my CBR600F4.... try tightening the steeringhead nut... 1/8 turn. It will make it slightly harder to turn but got rid of my juddering

[steved]

Thanks for all the suggestions. I had a play last night and got the front wheel up by rocking it back on the centre-stand. Discs seem straight which is nice as they expensive yo!

Time for the next simplest option, fluid-change.

[MSTRS]

Other thing that can happen is a high spot on one or both discs. Caused by uneven cooling Eg holding in the brake lever after heavy braking (to a stop). Fix by having the affected disc ground.

[steved]

Other thing that can happen is a high spot on one or both discs. Caused by uneven cooling Eg holding in the brake lever after heavy braking (to a stop). Fix by having the affected disc ground.
Looks like you were right. Upon measurement of the discs, they have uneven thicknesses around the disc which seems to be causing the on-off thing. They aren't thick enough for grinding unfortunately (about 5 mm thick, WOF = 4 mm?) so it looks like I will need to replace the discs.

[Postie]

Looks like you were right. Upon measurement of the discs, they have uneven thicknesses around the disc which seems to be causing the on-off thing. They aren't thick enough for grinding unfortunately (about 5 mm thick, WOF = 4 mm?) so it looks like I will need to replace the discs.

http://www.kiwibiker.co.nz/forums/showthread.php?t=30080&highlight=waihi
post 15
a guy in Waihi will do you a good trade on your old disks.

[steved]

http://www.kiwibiker.co.nz/forums/showthread.php?t=30080&highlight=waihi
post 15
a guy in Waihi will do you a good trade on your old disks.
Cheers Postie. I have been having some trouble sourcing second hand discs and OEM are just insane so I may be forced to go the fabrication route.

Trade on old discs? What does he use them for? Buggy's discs look a little exotic and I was hoping to spend a lot less than him. Are vanilla discs quite a bit cheaper?

[Postie]

Cheers Postie. I have been having some trouble sourcing second hand discs and OEM are just insane so I may be forced to go the fabrication route.

Trade on old discs? What does he use them for? Buggy's discs look a little exotic and I was hoping to spend a lot less than him. Are vanilla discs quite a bit cheaper?

the ones Bugjuice got were about $300 each I think, not 100% sure, but the guy in Waihi takes the old ones off you, not sure what he does with them, but he does do standard ones also. Just normal round ones. Give him and email for a quote and he will tell you what designs he has.

[Warr]

Dont want to burst your bubble re the Waihi produce. But sitting in my garage is my second set from him. Build quality is not amazing. Disc's are rather high tech. I finally spotted a set on eBay. Cost me $US50 for a mint set of OEM's. Got them shipped to my sis in California who got them to me in a friends luggage for nothing.
Some people will ship to NZ but most have no idea where NZ is so dont hold your breath! Do a search on eBay and ask if they will ship to NZ at what cost.

[slob]

I had a similar problem when I first bought my GSX-R. It turned out that the problem was caused by worn pins (the one the pads slide on) - I changed those and the shuddering went away!