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Brake pulsing/biting after disc machine/new pads

Discussion in 'Technical and Troubleshooting Torque' started by RGVroomDaddy, Feb 1, 2006.

  1. Hi All,

    Took my front discs off the zxr250 today and got them machined and also put new EBC pads in and on the first run it is a complete disgrace. Really bad “pedal” (lever) pulse and looking at the discs and judging by the frequency of the pulse it appears that the pad is biting either on or off the cross drilled sections … looking at the discs it appears to be worse on one side since there is a different wear (or deposit of pad material) around the cross drill holes. Anyway, I couldn’t really do a proper bed in since it was wet and it would have chucked the bike with all the vibration if I had tried to stop hard.

    I guess one possibility is that the dudes f%cked one or both the rotors when they machined them (also one of them is now slightly under spec … 3.4 when min is 3.5mm even though I asked him not to go passed min thickness). Personally, I wouldn’t have thought this would be a prob myself unless braking really hard thus leading to quicker fade.

    Basically wondering if anyone has any suggestions … here are some of the courses of action I am considering tomorrow:

    1. Try to bed them in a bit more and hope it gets better.
    2. Get a dial gauge and check the runout of the rotors.
    3. Pull off one of the calipers and secure it to see if it is just one of the rotors
    4. Take it to the brake shop who did the machine (it is a car shop not sure they can do much with the rotors on the bike)
    5. Take it to a bike mechanic and get them to check it out

    Also wondering if anyone has had similar experience? Wishful thinking is it will just go away ;)



  2. For a start here is my urgent suggestions

    1 / As your discs are the full floating type (zxr) get a 0-25 mic and check if the discs have been machined parrellel with each other. if not there scrap 0.01-0.02 max

    2/ Get a Dial gage and check for run out of the disc (Note) also check that when they machined it the have not seized / damaged the buttons that secure the disc to the carrier make sure it can move slightly on the carrier. if so its a trip to the mechanics for new buttons etc and rebuild the disc / carrier.

    3/ have the cross holes been deburred ???

    4/ Do Not and I mean Do not ride the thing until you resolve this

    5/ Warning to others watching here front brakes are critical do not trust them to the local brakes plus etc for maching they bare absolutley no comparrison with car discs and are easy to stuff up as there machinery is not geared for floating discs

    6/ Try Planet Disc in wantirna south (03) 9801 7067 to sort this mess out

    Sorry if i sound preachey about this mate its an easy thing to stuff up but your life has been put on the line with this one and thats not on
    good luck
  3. Good stuff Brucey.
  4. If the rotors are floaters (as Brucey suggested)then they need to float, it's easy when refitting to get them bound up and mounted solid. They should rattle a little when mounted.
    A little under size shouldn't be a problem, more important that the faces are parallel.
  5. Puzzled it out for you mate you have semi floaters on youre bike they should be tight in the carrier ie limited amount of movement this is where the brake guy made the mistake of thinking they are solid mounted

    Youre brake guy has chucked it in the lathe and skimmed it but as the tool point has passed over the vent holes in the disc (the cut is now known as intermittent in machining ) it has sent a harmonic through the disc causing the surface to move initally high then as pressure decreases it comes back in till the next hole.

    They should have been demounted from the carrier and then ground.

    Thats why you now have polished and then smeared sections on youre rotor

    I think they are both scrap now from what you have described

    Sorry mate
  6. I didn't think ZX2R were floating discs, I thought they were floating look? Run a dial indicator on them while they are fitted to the wheel, maybe they were straight but are being pulled out of shape when they are bolted down?

    I'd also say that if the discs check out ok, look at the wheel bearings.
  7. Thanks for the info Brucey.

    I called Max at Planet Disc and he thinks he might be able to salvage them and said no major problem even if they go down to 3.2mm so I am going to keep my fingers crossed and take the discs plus the pads down to him tomorrow morning.

    Otherwise it is $240 per disc if they are cactus :roll:

    P.S Johnny O, they are indeed semi floating discs.


  8. Don't you just HATE it when in the process of allegedly fixing something, people make it worse? Hope this works out ok for you, NBH......

    {I sent my notebook PC back to Perth for a warranty fix, with no sound and the USB ports not working. After a week they sent it back, 'fixed' and it didn't even power up!!!!!!!!!!!}
  9. Actually, none of my repairs either bike or car have gone especially smoothly lately ... I think a combination of having been a bit unlucky plus out of practice!

    If it turns out to be a problem with the initial machining I might suggest that it go in the FAQ or as a sticky ... I am surprised I haven't heard of this before. I guess people either:

    a) Just run with scored rotors
    b) Buy new ones
    c) Can't find anyone except pros who know what they are doing that will machine them!

    The thing that is annoying is that I rang my usual brake place darbys brake and clutch and they said they couldn't do motorcycle discs but put me on to Highway Brake and Clutch who supposedly could :roll:

    On the upside, I put a seal kit in both calipers because the outer dust seals were stuffed (half popped out) and that seemed to go ok.


  10. well both these places i know of really well. very good when it comes to car and truck.. and neither of them would be able to bike discs. at least darby was smart enough to know better..
  11. My bike had pulsating front brakes when I got it. Last owner assured me that it didn't have warped discs when questioned, so had to figure it out on my own.

    Firstly, eliminate whether or not the discs are warped (either through machining or heat). Jack the front of the bike up, hold a pencil against the fork leg just near to the disc and spin the wheel. If it's out, your eye should be able to detect it. I could tell whichg side was the problem side by going for a ride, using only/mostly back brake, pulling in and feeling the temperature of each front disc. If these are fine next suspect will be the brake lines.

    When some mechanics take the calipers off bikes, they let them 'hang', not a good idea. If there's any air in the caliper part of the line, it will then travel up tro the lever, where the pulsating will become more pronounced. A good bleed will get rid of the air. That's where my pulsating was coming from, it turned out that the dealer that I bought it off had just replaced the steel lines for standard items without bleeding it properly.

    If bleeding doesn't fix it, last hope would be the pads. Not something that's easily checked, easier to try another set. Hope this helps
  12. The pencil trick sounds like a good one in the absence of a dial gauge, I will give it a try when I get the discs back but I have already taken them off to take to Planet Disc tomorrow.

    Definitely not air in the lines since I bled them when I did the calliper seals. The pads are going to get checked with the discs tomorrow so hopefully will get it sorted out.


  13. sounds like you've got it sorted but I'll mention I've had similar problems with my fzr250 in the past. I ended up taking the front disc (its only got one!) into awesome discs in ringwood, where they machined it up nicely for $90. Worked great for a few months, but the pulsing eventually came back - leading me to suspect the caliper needs a bit of an overhaul. What causes disc warping anyway (I've done a couple of track days and plenty of twisty riding)?
  14. Fark, $90 is pretty harsh for a disc machining ... hope he doesn't charge me $90 per disc :shock:

    Max from Planet Disc told me Awesome Discs is his son and uses the same machine. It's a bummer that yours warped again but mine was ok before the initial machine so hopefully won't be an ongoing problem. If the machining fixed it and it is back I suspect the single disc is cooking on the track. Not a whole lot you can do but get a thicker, heavier disc that will dissipate heat better but this will increase unsprung mass and could effect handling but not sure by how much.

  15. funny how you get rolled as a newbie, i initially brought the problem to my mechanic who suggested it would cost around $250 to get the disc machined (including labour).
    even i got scared off by that, so i thought the $90 was reasonable. Live and learn...
  16. I have paid from $20-$40 per disc in the past (paid $44 for the pair at Highway, would have been good value if they did it properly :roll:)

    $250 is pretty outrageous even assuming they had to remove the discs themselves.

  17. Ok, got it mostly sorted ... took the discs to Max at Planet Discs (he is a good bloke BTW) and he machined them up plus the pads for $120 pair so pulsing is completely gone.

    Down side was highway had made a complete mess of them, they were .6mm out so I ended up with 3mm discs which is .5 under spec.

    Oh well they seem to be ok but might crap themselves on a track day when I work up the confidence to give it a go, so will have to see how they stand up and decide if I need to replace them at great cost.

    One small remaining problem is despite two bleeds, the brake lever is still pretty spongy. Doesn’t quite reach the throttle but not far off on a decent application. Any body got any tips?

    I followed the bleed procedure from the manual (same as I would do a car) and no air is coming out even despite shit loads of pumps and about 20 open/closes each side!

    I will have a play with the cable adjustment tomorrow to see if there is just too much slack but thought I would check if anybody else had any ideas. I did replace the seals on the callipers but can't see any leaks or anything.

    P.S Not overly impressed with the EBC Kevlar pads even on smooth discs ... think I will bite the bullet and go sintered next time and accept the cost of disc wear. Maybe I am just spoilt by the custom discs (off a VR4 gallant turbo) and bendix ultimate pads on my turbo Mazda 323.


  18. Sounds like as good a result as you could expect given that it was a fix of someone else's mistakes....

    I presume you have also changed the brake fluid as part of this process?? If you have then maybe the lines themselves are spongy....
  19. Yep, have put about 1/2 a litre through it with all the bleeding I did :LOL:

    Brake lines is a good suggestion. I guess I have the "It's only a 250 I don't want to spend too much money on it" mindset). If it wasn't I wouldn't hesitate to put braided lines on it but I will probably end up doing it anyway since being happy with brake feel on a bike is pretty important!

    Hopefully I can improve it with some adjustment this arvo.


  20. Maybe not braided lines, why not just replace with genuine new lines and see if that makes a difference, you've got to be losing the 'feel' somewhere.......