warped disc's

[TonyW650]

Hi guys quick question, er what's the signs of a warped disc?
I've got a undulating sensation on the lever and left hand disc is a lot hotter that the right disc.
I've sat there and worked each piston in and out, cleaned them etc.... made it a bit better but still there. Anything else I can try? Bobbins on discs are rather dirty would that make any difference, as in disc not floating correctly?

[Ckennedy]

Good way to check if it's the disc is to get the front wheel off the floor and spin the wheel. If it suddenly decreases speed after spinning freely then it is warped. And if you do replace always replace in pairs, even if you get your hands on one with similar mileage.

[Kev L]

Stick bolts through the bobbins and turn them with a spanner to make sure they are allowing the discs to run true.

[Miztaziggy]

When I suspected mine were warped, I took the front wheel to a tyre place and they checked it for me on their machine.

[darkember]

A good straight edge should give you an indication. You may also want to check that your front wheel is correctly installed. There is a particular sequence you need to follow when tightening to get this correct. It is on here somewhere but cannot lay my hands on it. No doubt somebody will add the link to this post:)

[TonyW650]

Some of the bobbins were as tight as hell so I've just tried them first.
Only noticed it after I lent it to a mate and he said he cleaned it for me and used brake cleaner on the discs etc....

[mattycoops43]

I am agreeing with the bobbins comment, most likely suspect.

I have just changed both of mine though because i had a warp somewhere.

I have to challenge the 'always change both' comment though. Why?

I had a damaged disc on my fazer, and changed one for a similar age/mileage disc from a bike breaker. Was totally fine, and solved the prob. As long as they are similar thickness and you put a set of pads on so it can all bed in nicely, what's the issue?

[VTRDark]

I just done by bobbins today. What a pain in the butt job. Watch you back when doing them Tony. I had an aching back afterwards from sitting on a garden chair leaning forward spinning the wheel round doing each one.

As for the tightening sequence when putting a wheel back on, leave the pinch bolts to last and always push the forks up and down a couple of times before tightening them up. This lines them up square.

(:-})

[TonyW650]

Well, done the bobbins and its made it better, still have a pulsing at lever, so suspect left hand disc is warped as its getting alot hotter than the right hand one, stripped the calipers and worked all the pistons in and out so know its not them
I ended up sitting on a pillow with legs either side of front wheel, and I can hardly move this morning lol

[tony.mon]

Well, done the bobbins and its made it better, still have a pulsing at lever, so suspect left hand disc is warped as its getting alot hotter than the right hand one,

Might be the other way round, as the pads will bite better on the true one, therefore creating a lot of friction, whereas the out of true one, whereas the out of true one will only allow the pads to contact on one side at a time.

[TonyW650]

Never thought of that tony hmmm
Cleaned every thing up again, pistons, bobbins etc will try it in next few days, got loads on as prepping for bike party which is helping keep me occupied

[TonyW650]

Either which the discs are warped. Been checked on a run out gauge and they is bit warped duh lol

[8541Hawk]

Either which the discs are warped. Been checked on a run out gauge and they is bit warped duh lol

I personally never trust a run out gauge on a floating rotor.

Yes semi-floating is in that group also and maybe even more doubtful to trust the run out reading as all you need is a bobbin to stick a little and you get a false reading.

The first thing I would do is take the bike out and go through the "beading in new brakes" procedure I posted last week as it is usually old pad material that causes the issues.

You could also pull the rotors and use a hone: http://www.braketech.com/index.php?opti ... Itemid=100 if they are really bad.

Before you go out and buy new rotors that you more than likely don't need.