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

[Fizzy Pies]

The run out tolerance on the front discs is 0.2mm.

The RH disc runs out 0.6mm.

The LH disc runs out 0.075mm.

First why would they be different?

Second is it worth replacing only the bad disc? If so would a used one be better?

Thanks

[alexanderfitu]

Would be thinking the caliper seals on one caliper are either past it, or the pistons are getting stuck due to corrosion etc.

Would be a good idea to remove the pistons on both calipers and clean them up well and replace the seals whilst you are it

[Chris]

my guess would be a sticking piston or something similar in the caliper that has held the pad on the disc and that's why only one disc has warped.

I'm not sure about the replacing one or two discs, i'd say it probably doesn't matter if you do one side as long as you replace the pads too although can you buy just one disc at a time for the front?

Chris

[alexanderfitu]

normally not that bad, cleaning them is not so bad, getting them out using a air compressor is the easiest way.

[Dead Eye]

Its easy enough to find a single disk on eBay instead of having to buy a pair

I agree with everything that's been said above as well, sounds like sticking pistons

[darrsi]

Do not think of the discs as a pair, the discs and calipers are totally independent and will behave differently.

"Warped" is an over used word where discs are concerned, as it is not always the disc that is the problem, as i have found out myself over time.

[Dead Eye]

I think it was just a general statement as darrsi had issues whereby everything pointed to the discs but ended up being fault braided brake lines

[AdieR]

Don't know what discs you have on there (Yamaha / aftermarket), or when / who fitted them - if the disc seat surfaces have been dirty or poorly cleaned when the discs have been fitted, that can cause disc run-out (look up "disc thickness variation" - DTV is not the same as warped brakes).

[darrsi]

Another simple task to do which can appear to cause issues is dirt build up in the rivets of the disc.
Easiest way i found to clean them up is get a nut and bolt and gently tighten them up through the rivet hole and then turn the nut, it should move reasonably easy.
If not, use brake cleaner on the rivet as you're turning them to get any built up crap out of them.

Changing discs is not a good habit to get into unless you are certain it's the problem, they can be bloody expensive for starters.
They can be bought separately if needs be, but if you buy new you will need to get pads for that disc.

As AdieR says, when a disc is put on the wheel, the hub surface needs to be spotless, just the slightest bit of old baked on dirt in the middle can magnify the run out, but if this was the case you should've noticed that straight away anyway.

Are you feeling pulsing through the lever, juddering on braking, what exactly brought your attention to this in the first place?

[darrsi]

One way to know for sure, and i'm sorry but it's a total pain in the arse, is to swap the discs over then take off the right caliper, put a block or whatever between the pads to stop the pistons coming out and tape it up to make it secure, then cable tie the caliper out of the way.
So all you are left with is the original right disc working with the left caliper ONLY.

As i said a total pain in the bum but if it doesn't judder then you know you have a good disc and the problem is elsewhere.
It's time consuming, but definitely money saving if it turns out to be okay.

I have been through all of this several times which ultimately ended up with me replacing the front end of the bike, until the last thing to look at was the braided lines, and if i didn't know better now i would've still not thought they were the culprit as they weren't leaking or anything!

If you do choose to do what i suggested, be prepared for siezed disc bolts, and on removal make sure it is absolutely spotless on the hub under the disc before reassembly.

And don't even think about skimming the disc either, they're not thick enough at all to do that.

[darrsi]

Do you have braided lines, or originals out of curiosity?

[darrsi]

Original

I never expected braided lines to fail at all, but originals are a different story.
Just bear that in mind if things don't work out as planned.

My bike felt like i was breaking on cobbles.

A warped disc for instance would push the pads apart further than normal which would mean you'd have to pump the lever a couple of times for it to work, bad news in an emergency stop.
Saying that, if the left side was okay it would compensate for the right misbehaving i s'pose?

[Soapy]

More tips. If you do remove the disc, the bolts normally have threadlock on them. Tywrap the brake lever and crack the disc bolts. Use a breaker bar to give you leverage. If they don't look like they want to move don't force it. Try tightening them first that will sometimes break the lock. I had to replace the front disc on my Triumph Scrambler. When I pressed the lever I could feel it pulsing. Triumph discs are made of chocolate.

[darrsi]

Front disc bolts are a lot more forgiving because they are semi floating discs, as in they're in 2 parts.
The heat from the outer part of the disc takes the main heat of braking.

The rear disc takes all the heat as it's one piece and transfers the heat to the bolts which then fuse to the wheel.
In short those bolts can be a complete bastard to remove in comparison.
If you haven't attempted the rear before, prepare yourself for a world of pain.
I ended up having to buy a 2nd hand wheel after all attempts at removing the bolts failed miserably  :'(

[darrsi]

It's a good move to buy a few spare bolts before attempting any of this to save time.

Brakes are very complex, but once a few tricks are learnt and undertaken, and then you keep them maintained, life becomes a lot rosier! 

[simonm]

Insane and stupid idea which would waste time but if you swapped the front disc's over would it not move the judder to the left if it was the disc ?


Just if you wanted to waste some time checking the disc before you consigned it to the bin.  I guess if you took the disc off you'd be able to tell if it was out of true anyway.


Just spit balling since I'm no mechanic.

[alexanderfitu]

http://www.wemoto.com/bikes/yamaha/fzs_6...r_-_front/

?

They should be ok, I always go for oem when possible, done want to be doing the job every year!

[darrsi]

Insane and stupid idea which would waste time but if you swapped the front disc's over would it not move the judder to the left if it was the disc ?


Just if you wanted to waste some time checking the disc before you consigned it to the bin.  I guess if you took the disc off you'd be able to tell if it was out of true anyway.


Just spit balling since I'm no mechanic.

That is indeed the general idea, you move the disc to try and confirm that it the disc at fault, rather than the caliper for instance.
But to do this you cable tie the other caliper out of the way so you are just using the left one, so that there's no confusion.

If it doesn't judder, then you know the disc is okay, so now you are looking at the caliper, brake line, etc.

For a new brake disc you're looking at a minimum £120 each for a half decent one, or you can buy 2nd hand but there's always that small chance you could be buying another problem.
So unfortunately you just have to be patient and start the slow process of testing things through a process of elimination, otherwise it can become an expensive nightmare, as i found out.

This all brings back bad memories.....  :'( 

[darrsi]

Could the front wheel not be turned around instead of swapping discs?

No, the speedo sensor is fitted inside the left side of the wheel hub.

[darrsi]

My first thought now is to remove the right disc, and lay it on a flat surface, if I can see the error recorded roughly half a mil Ill know the disc is fooked. But still need to check the caliper too.

That would only show a badly warped disc, it wouldn't show disc variation or hotspots.