Front discs - 1 warped, 1 not. Looking for advice opinions, help, sarcasm etc.

[darrsi]

What would show that?

You can get hotspots by holding the brakes on at traffic lights.
If the disc is very hot, part of the pad can be deposited on to the disc (you would see the shape of the pad embedded onto the surface).
Then what happens is when you brake normally the pad will grip on the deposit first, then the cleaner parts of the disc, causing uneven braking. This would be more likely to occur with cheap pads though.

It's another 'possible' cause of juddering to add to the list.

If you can see any uneven deposits then there are 2 ways of removing them.
You can either try wet 'n' dry paper in even circular motions, or take the bike out and do some heavy braking and try and burn them off.
Problem is, if your judder is being caused by something else then none of this will help anyway.

If you have sticking pistons on one side of the caliper, so the disc is only being pushed from one side, then that can obviously cause issues as they will be trying to bend the disc which will be flexing. Another 'possible' cause of judder.

[darrsi]

What about head bearings?
Are you getting any knocking sound/feeling at all when braking?

[darrsi]

Yeah, you can't be doing with that kind of issue, it's very off putting whilst riding and you find yourself concentrating on the problem.
I was scared to brake hard as the brakes would grab, and i found myself over using the rear brake to compensate until i eventually got things sorted.

[Fazerider]

(Second attempt to post... aim was a bit off first time!)



There needn't be a caliper fault, though an overhaul is a good idea anyway. A bent disc can be caused by incompetent drivers giving the bike a nudge when parking… if they get the angle right they can easily apply enough force to bend the right disc without knocking the bike over if it's on the sidestand.
Whatever, it certainly sounds like you need a replacement. I get about 40k from them and have bought second-hand ones on ebay several times without a problem, though bought new EBC discs about 18 months ago.
If your bike is still on the originals then the bolts will be a bit stiff. I prop the wheel up over a low flame on the stove for twenty minutes until the alloy is getting uncomfortable to touch, then they can be undone without any drama because the heat softens the thread lock and expands the screw holes due to the different coefficients of expansion of steel and aluminium.

[darrsi]

(Second attempt to post... aim was a bit off first time!)



There needn't be a caliper fault, though an overhaul is a good idea anyway. A bent disc can be caused by incompetent drivers giving the bike a nudge when parking… if they get the angle right they can easily apply enough force to bend the right disc without knocking the bike over if it's on the sidestand.
Whatever, it certainly sounds like you need a replacement. I get about 40k from them and have bought second-hand ones on ebay several times without a problem, though bought new EBC discs about 18 months ago.
If your bike is still on the originals then the bolts will be a bit stiff. I prop the wheel up over a low flame on the stove for twenty minutes until the alloy is getting uncomfortable to touch, then they can be undone without any drama because the heat softens the thread lock and expands the screw holes due to the different coefficients of expansion of steel and aluminium.

"....incompetent drivers giving the bike a nudge when parking...."

[size=1em]Bit random, and as likely as being bent by a pram or shopping trolley!!![/size]

[size=1em]And at the moment there is no real evidence to suggest a new disc is needed at all yet, not until he's done a few tests anyway?[/size]

[size=1em]This is what i was saying earlier about people immediately jumping to the conclusion of a warped disc, even though it may not be the case! [/size]
[size=1em]If they were a cheap replacement, then fair enough, but they're not, so it's worth finding out for sure before splashing cash about for fun.[/size]

[darrsi]

I'm not understanding if its running so far out, how could it not be warped? perhaps the caliper got stuck causing 1 pad to stick on making the disc warm enough to warp?

Can you spin the front wheel freely?


I would suggest at least give your calipers some sort of clean up or service first because if they're not functioning correctly then even a new brake disc will be put to the test, and the caliper may have been the cause if the disc is dodgy.


Cheapest 2nd hand pair of discs on Ebay are just over £90, or a new single disc is a minimum £120+ each, but then that won't be the same disc as you have so that's not a good option. I dread to think of the cost of an original disc? (just checked, £196.52 each :rolleyes )
If you get 2nd hand then you could use your old pads if they're in good nick, but a new disc means new pads.

[Fazerider]

"....incompetent drivers giving the bike a nudge when parking...."

[size=1em]Bit random, and as likely as being bent by a pram or shopping trolley!!![/size]

[size=1em]And at the moment there is no real evidence to suggest a new disc is needed at all yet, not until he's done a few tests anyway?[/size]

Well, not really. Cars are heavier than a pram. :rolleyes
The OP has measured the disc runout and it's out of spec. Which is evidence.


Generally a sticking piston causes the disc to warp i.e. become dish-shaped, because the force is applied evenly around the disc. When that happens the brakes become very spongy, yet there will probably be no runout. Fizzy's disc is bent, which is more likely to have been caused by external force.

[solorider]

A few years a go I had a FJ1200 and I was told the bike had warped discs,the judder was quite bad, when I did more checks I found it wasn't the discs at fault but a knackered wheel bearing, there was no noise or issues while riding only while braking.

[darrsi]

[quote author=darrsi link=topic=8895.msg88693#msg88693 date=1374185128]
"....incompetent drivers giving the bike a nudge when parking...."

[size=1em]Bit random, and as likely as being bent by a pram or shopping trolley!!![/size]

[size=1em]And at the moment there is no real evidence to suggest a new disc is needed at all yet, not until he's done a few tests anyway?[/size]

Well, not really. Cars are heavier than a pram. :rolleyes
The OP has measured the disc runout and it's out of spec. Which is evidence.


Generally a sticking piston causes the disc to warp i.e. become dish-shaped, because the force is applied evenly around the disc. When that happens the brakes become very spongy, yet there will probably be no runout. Fizzy's disc is bent, which is more likely to have been caused by external force.
[/quote]

As i explained earlier, the best test is to swap discs and try it out on the other side on it's own, but even that's not foolproof, as i found out when mine turned out to be my braided brake line! But he may find that the disc works fine on the left side, only one way to find out though!

Just for the record i browsed through my previous posts with the problem i had and i was very specific in detail in all the things i had tried and tested (several times), and out of 3 mechanics and this whole forum not one person suggested that the brake lines could be my problem (including myself).
That's why i'm suggesting keeping an open mind at the moment, because i spent a lot of time and money finding out the hard way before fixing it!
And that was only because it was the last thing possible to try  :'(

Yet when i first had the juddering on braking, me and the rest of the world said warped disc straight away, and it made perfect sense, because it gave off all the right signs.
Certainly wasn't the case though.

[darrsi]

One thing i just remembered, my neighbour, who's a mechanic, gave me a hand with a stubborn disc bolt when i first had my problem, and as i had already bought a shiny new set of discs because warped discs looked like the definite cause at the time he volunteered to bin my old discs for me with his other scrap in his garage.

I won't be doing that again in a hurry as now i know there was nothing wrong with them at all, but you live and learn!  :'(

So if you do get another one do not throw anything away, in case it all starts happening again after fitting the replacement. 

[AdieR]

LH disc 3.85 / 3.87mm; don't know the minimum limit on the FZS bikes, but on the later FZ6 the disc limit is 4.5mm  - possibly time for new disc/s anyway?

[darrsi]

Very nice 

[Chris]

very nice indeed, has it solved the problem?

Chris

[Chris]

Thanks mate, What pads have you got? Was thinking to go for the sbs ceramic ones everyone says are good.

Glad it's sorted for you.

Chris