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Brake pad drag, how much is too much?

Discussion in 'Technical and Troubleshooting Torque' at netrider.net.au started by robsalvv, Nov 25, 2007.

  1. Ok, so here's the story.

    I recently replaced the front brake pads. The previous ones were looooow.

    I changed the fluid too. Fluid level is just below the maximum fill line.

    So anyway, the front wheel would basically free wheel with the old brake pads in the resting position - there was only a small amount of drag. Then I put the new pads in and now the front wheel has a strong amount of drag - it wont free wheel - a good hoike gets a third to half a turn.

    Is this explained as simply as saying that the pads are slightly over tolerance in thickness?

    The consequence of this drag is that it heats up the disc and the pads are glazing. This means the front squeaks and squeals noticeably at slow speeds and if it's been a while between braking, the first use is as wooden as Pamela Anderson's acting.

    The brakes are otherwise functioning normally.

    Sooo, thoughts please. What's with the extra drag?

    FTR, the brake pads are the "metal gear" http://www.metalgear.com.au organic pad, which are an inexpensive OEM replacement... I'm not sure I'd recommend them though - they certainly feel like a step down from the OEM pads - but that could be the glazing issue????

  2. yeah, i personally wouldnt ride if it was dragging as much as u say. I remember a post here where someone did a front flip from brake drag.

    Just a though. Did u change the fluid with the new brake pads in or the old ones. U should always change fluid with the old brake pads, Then push the pistons in and put the new pads in. This could have caused your problem.

    I would check that the pistons in the caliper are not gummed up. running pads very low exposes the piston to all the brake dust, goo, dirt etc.

    Are the pads seated correctly??
  3. Thanks for that post Natta.

    :-k hmmmmm, better pull the pads and re-check the pistons.

    The pistons did push back easily though...

    I must admit, I put the pads in, then changed the fluid. Didn't think the order mattered. How would the reverse order cause the dragging symptoms?

    I don't think the dragging will cause a stoppie... I wouldn't ride it if I thought it would!

    Yes I've checked, the pads are seated properly.

  4. did you bleed the system or just change the pads and top up the fluid?

    Try bleeding it.
  5. Edit: next tie ol' fella, read all the posts first.

    I'd suggest trying to bleed a bit of fluid out.
  6. I'll bleed the level down to mid point in the reservoir to see whether that helps (the rubber boot under the cap ***could*** be pressurising the system). I'll pull the pads out for a look and have a good sticky while I'm at it.

    I've replaced pads a few times before... this is the first time this dragging issue has ever happened.

    Thx for your responses.
  7. Definitely run some brake cleaner over the pistons, that'll help clean them and sort any stiction issues. I had that problem with the Fireblade. I didn't realise how much they dragged until it was on the race stand one day... :oops:

    Cleaned the pistons and right as rain.
  8. I always clean the pistons with a toothbrush before pushing them back in the caliper, on a bike older than a couple of years I'd be taking out the caliper pistons and cleaning the seals, you'll be surprised by the difference.

    Sometimes between races I push the pistons back in the caliper to get the boiled fliud and air back up the line and some fresh fluid into the caliper.
  9. Thanks guys. Sound advice. :)
  10. Its an old trick that a friend taught me. It helps to bleed the system properly. Because the pistons are out a fair bit from brake wear. If u bleed with the pistons with the old pads, less of the piston is in the caliper to block air. With new pads the pistons are all the way in, so there is alot of bends/curves for air bubbles to get trapped. Air could get trapped behind a single piston( normally the further from the bleed bolt) causing uneven piston pressure that could cause the drag.

    Caliper overhaul works a treat. Its quite easy too.
  11. I would check that the pistons in the caliper are not gummed up. running pads very low exposes the piston to all the brake dust, goo, dirt etc.

    re the pads seated correctly??[/quote]

    I agree with Natta, In the majority of cases, dirt, gum, road grime etc attaches to the brake piston over time. When u push the pistons back in, two things happen, A) the grime can/has damaged the seals and 8) the piston can no longer move freely and becomes stiff in the caliper bore.
    I am familiar with 90% of different manufactured brake pads, some with anti-squeel plates etc but, providing they are the listed pads for that caliper, I have never came across pads that are to thick and cause the problem u are having. There is a small amount of tolerance in the caliper/piston to offset a bees dick difference. If u are lucky, u will get away with just cleaning the pistons in situ, however, it certainly would make a difference if u disassembled the calipers and kitted them, not a difficult job and pretty well self explanatory. Use rubber grease when assembling (just a smear) or fresh brake fluid. One thing to alway's check when calipers are dragging and especially if they are as bad as yours is to check the freeplay available at the brake lever, all brakes, hydraulic or mechanical should have freeplay at the lever/pedal, a bees dick to a couple of mm is fine. If there is no freeplay, as the brakes get hot and the fluid expands they will in the worst case, lock on with disasterous results. Most common cause is fitment of the wrong brake lever, close enough is not good enough and many a bike has come to my shop for smash repair over the years caused by incorrect lever fitment. Also never fill the MC above the maximum mark, it needs room to go when expansion occurs.
    Hope I haven't bored u, but don't take chances where brakes are concerned, especially the front ones.

    Tex & Bundy
  12. +1 if the brake is draging that much when cold it will be heaps worse when everything heats up and expands. Is there free play in the caliper end i.e. can you push the pistons in more with the bleeder cracked or not?

    Sorry just looked at the date when you started this thread what did you find by the way?
  13. The free play is fine. I also bled out some fluid and extended the pistons - to check for dirty pistons - but they look good. Bleeding the fluid and I guess bedding the brake pads in good and proper has helped a bit, but the dragging issue is still there.

    I'm thinking I'll put a caliper removal on the todo list and give the calipers some bench love. Even though the bike's only done mid 30km's, it's coming up to 6 years old and my bet is the brake calipers have never been done.

    There were also signs of uneven brake pad wear on the old set, so this task is probably worth doing.

    It just funny how the dragging issue didn't show up before.
  14. Well, I finally pulled the calipers off and had a good look at those 4 pot Nissins and those pistons weren't as clean as I thought.

    I couldn't believe how stuck a few of the pistons were. If I was more organised I would have done a seal change as well... but cleaning the pistons improved the brake performance a heap and the drag issue has cleared up.

    Thanks for those piston cleaning tips gents. I'll make it a standard activity whenever I replace brake pads.

    I managed to accidentally pop two pistons right out on the first caliper... :facepalm: ...what a mess!! LOL... Avoided it on the next one though...
  15. Good to hear that everything is sorted. A good caliper clean makes a work of difference, and its fairly simple.

    Did u have fun bleeding the system? i hate bleeding a dry system, such a pain in the butt
  16. I ended up with a flamin cramp in my hand pumping the lever to get the air out. It took aaaaaggeeeesss. I can see why car brake bleeding is automated.

    I went riding today and the metal gear pads seem to have bedded down better after some hard brakes. I still don't think they have the bight of the OEM's, so I'll probably up spec when I get sick of them or they're worn.

    Thanks for the help :)
  17. Yesterday I bled my brakes and there was a bit of a grinding noise at some points. The result was excellent, my bike dips and rises harder when walking the bike (haven't road tested yet), but do my calipers etc need taking apart and cleaning?
  18. A big horse syringe (get one from your vet) is brilliant for this.
  19. :? Grinding noise? While you bled it?
  20. Grinding noise??

    Anyhoo, the bikes off getting a major service, which is including a caliper service and seal replacement - so I'll be able to see what a fully cleaned up refreshed caliper means for pad dragging.

    Oh and braided brake lines are being fitted to the front too... looks like those metal gear pads will get upspecced soon...