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Sudden loss of brake performance.

Discussion in 'Technical and Troubleshooting Torque' at netrider.net.au started by GreyBM, Dec 13, 2008.

  1. Yesterday coming home in the rain I felt they had no stopping power. Had to squeeze really hard and although I could feel them slowing me, they weren't slowing me much. They weren't like that when I went to work in the morning.

    Wondered if it was contaminant making the disks or pads greazy or maybe glazed pads. So last night I pulled out the pads and cleaned everything and roughed up the pad surfaces. Effectively still no change.

    I can't see any sign of leak and still have pressure so don't think that is the issue. The fluid looks clean and was changed about a year ago, so it should be fine still.

    I guess air in the line could explain the feel I get but can't see how that could happen during the day.

    Anyone got any ideas.

    I always felt my brakes could use more stopping power and was already thinking about getting some braided lines so my solution is to just take it off to the mechanic and getting them checked out as part of a general brake overhaul. But just curious what the hell will cause brake performance to deteriorate so fast.

  2. Glazed pads or glazed disc. Just add water for a sphincter puckering experience.

    How long since you cleaned the calipers?
  3. Thanks for the reply Rog.

    Must admit I was suspicious of glazed pads. But after cleaning them I gave them a good sand which I understood would remove glazing. And I've ridden in rain before but never had the same effect.

    As for cleaning callipers, they looked pretty grotty. I didn't need to take them off to remove pads so I had limited access. That, along with annual fluid flush would have been the next project if I hadn't decided to get it all done by the mechanic.

    I am just amazed by how fast the performance (or lack thereof) changed. Glad I didn't need to do any e-braking.

    I can understand that glazing affects performance but how does the water add to the problem? I would have thought that once the pads hit the disk they would wipe off the water within a revolution or two.

    And for the future, when you use brake cleaner, is it designed to be sprayed around the piston to clean them up or does it affect the seals?
  4. GBM,

    I gather you still have stock brembo's on your machine, so here is a checklist.

    1. check front wheel bearings for collapse or looseness (dont ask)

    2. look for signs of fluid leak at the master cylinder.

    3. pull calipers and check for seal integrity and free movement.

    4check all hoses pipes and joints for leaks

    your brakes should pull you up very well in the wet, cast discs do not have the same issues as SS ones, the only thing with the brembos is that you need to trust them and give the brake lever a firm squeeze to activate, you cant stroke them gently like the newer stuff.

    get the brake calipers disassembled and seals removed before hitting with brake cleaner, the rubber does not like it much.

    good luck
  5. Doesn't hurt seals. gets rid of crud, but do it carefully.
  6. Thanks guys.

    Also noticed my manual says when replacing the pads to break/brake them in gently for the first 80-100 kms or else they will glaze if you hit them hard.

    So what goes on in the pads that changes so that after that time that they won't glaze (or is it just won't glaze as much) if you hit them hard?

    Face it, sooner or later you are going to hit them hard.
  7. Ah, the wonderful world of motorcycles.

    What it says in your manual is the direct opposite of what I was
    told when Noah was a boy, the early '70's.

    I've done the following for every set of pads since:

    Find a quiet straight road, usually industrial on a sunday.

    up to 30kms brake hard to 10kms...do not stop

    up to 50kms brake hard to 10kms...do not stop

    keep going up to 110kms or more if you go quicker often.

    after this it's very important to ride for about 10 k to let 'em cool...try not to come to a stop, there is a chance that the pads will stick to the disc.

    I just do the fronts and use the rear brake till the fronts are cool.

    The theory is that heating the up that much burns out the residual
    chemicals used in the bonding .

    Don't know but I've never had brake fade in 36 years on the road.
    (I do the car one's the same way)

    (Insert usual disclaimer here)
    It's just what I do.
  8. Yep for every piece of advice there is an equal and opposite advice.

    I noticed in Robsalv's sticky on brake pad ratings he mentions that different manafcturers have different breaking in techniques.

    Not that anyone has ever mentioned that to me over the years when I have had pads replaced in various vehicles.
  9. Does your bike have servo assist with the brakes? Another possible problem area.
  10. If it went suddenly and it wasn't fluid on the pads, then I'd guess a seal is leaking. If it's not leaking at the calipers (clean them and you will know), then it will be the master cylinder.
  11. Pump the lever a few times and hold firm and consistent pressure on the lever, if the lever 'creeps' in to the bar and there is no external leak it's likely leaking past the master cylinder piston seal. Try that to start. Also if you're roughing up you pads, best method i've found is find a bit of concrete/paving and rub your pads into that, works very well.

    As for 'bedding in' your pads, best to start easy and work up to firmer braking... Trick is to get heat into them slowly. Seen many new pads glazed/fried within minutes of being installed, friend of mine used to love to see how quickly he could kill new brake pads in his companys fleet cars after he'd serviced them lol.
  12. Once again thanks guys.

    TP: No, no servo assist, ABS, linked brakes or any other fancy doohickies. Just a lever and master cylender at one end, callipers and pads at the other and a few bits of tubing in between.

    Kranzy: Nope. no reduction of pressure in the system if I hold the brakes on. To me this seems to means the system is intact. Also consistent with not finding any leaks.

    When I took the pads out, after spraying them liberaaly with cleaner, I both gave them a sand and then since that looked a little coarse, gave them a scrub over the concrete.

    I guess maybe glazed pads would explain bad performance. I also thought about bleeding them again but decided not to bother as I decided to get the lines replaced this week.

    So I can think of a couple of things which could contribute to less than sparkling performance but nothing that would cause such a sudden loss of performance, aside from a leak, which I don't think is happening.

    The bike is with the mechanic getting the new lines made up. I have asked him to give it a thorough check so if he discovers anything I will report back.

    Guess I will bed the new pads in slowly like the manual says . Besides if after the new pads and lines, I get improved braking I need to get used to it slowly or the first sudden brake I try will likely leave me sliding down the road again.
  13. Could be things like seized pistons or something too, be surprised if you'd glazed the pads anyway BM.

    Be great if you did let us know what he finds, I'd be interested to find out.
  14. The bike is back and the brakes work. Mechanic thought old pads looked ok but I said chuck 'em to be sure.

    The callipers were inspected and serviced and I now have braided lines. The bad news is that there was nothing obviously wrong.

    All I can think of is that maybe the combination of old lines, and possibly contaminated/glazed pads and rain all worked there magic to make brake performance drop off.

    It's a mystery. But as long as the current set up keeps working I'm happy. Poorer but happy.

    Oh well saves me flushing the brake fluid this weekend.
  15. I love a happy ending.
  16. better to have it sorted than wonder when it's going to do it again, cool to hear there was nothing major wrong.

    When the brakes on Caths R65 started going funny, it was because the wheel bearings were collapsing and the little bit of movement was pushing the pads out, converted to caged roller bearings and new spacers so it wont happen again.
  17. It could have been your fluid as well. When it gets older it absorbs moisture which can "boil" when it gets hot and cause brake fade. They would have put new fluid in with your mods.
  18. as long as they've checked them over properly that's great.

    mmm... sexy sexy braded lines... just put a set on myself, I love 'em. :cool:

    :woot: Enjoy mate, good luck