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Violant vibration when hard braking.

Cave_DwellerCave_Dweller Posts: 114
edited December 2013 in MTB workshop & tech
Hey, this is my first post and first time on the forum. I own a Scott Ransom 40 (here comes all the hate comments lol), it was a gift from my brother to get me back into biking after many years of not being able to ride. I find it a great bike to be honest but having a bit of trouble with my brakes. The bike is a 2006 model and it has Shimano Deore brakes from the factory, 203mm rotor front and 180mm rear. The same ones as these, not my picture. deore535_zps77a597d2.jpg

When I brake hard enough with the back brake to lock up the wheel it sends a really bad vibration through the whole bike. It's more of a shake than a vibration it's that bad and it causes the back wheel to come off the road as if it's bouncing. It's like something is tensioning up and releasing, like the back wheel twisting and springing back but I highly doubt that is the problem, the wheels are good and solid. Whatever it is it makes the whole bike bounce. I'm finding it hard to explain it. It has only just developed this mystery problem, it has been fine before and I haven't done anything different or knocked anything.

-) I've tried cleaning all discs and pads and it's not solved it.

-)Tightening/checking all suspension linkages and they are fine apart from the bushes on the shock, there is a bit of movement there and need replacing.

-)Tightening all bolts/linkages to do with the brake calipers.

-)No movement on the disc bolts and pads are aligned perfect on the disc.

-)The brakes seem to be working fine. During this weird vibration the pads are still maintaining pressure.

One other thing I tried it actually made it worse, I swapped the front pads for the back ones. The front pads were not as worn down so I put them on the back, but having the thicker pads on the back seem to have made it a lot worse. I don't know if this is because they are working better because they are bedded in more but it's still a mystery.

None of the above have solved the problem and I don't really want to take it to my local bike shop. It's been a long time since I have worked on bikes and I want to become independent again, I used to be great with bikes. Also with christmas coming up it's hard enough as it is without spending extra money lol. If I need to replace anything it will have to wait till after.

If anyone has any ideas or tips on what to try next then it would be much appreciated. Cheers :D

Posts

  • russyhrussyh Posts: 1,375
    Is the rotor warped? Take it off and lay it on a flat surface.
  • Nah the rotor is not warped. When I had it off for cleaning the other day it was completely flat on the table. I wish it was something simple like that though lol.
  • cooldadcooldad Posts: 32,599
    Use the front brake.
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  • cooldad wrote:
    Use the front brake.

    I do more than the back, it's just the fact it never used to do this so something must be wrong somewhere :)
  • jimothy78jimothy78 Posts: 1,407
    Have you checked the spoke tension in the rear wheel? If it's not consistent, then the braking could be setting up some sort of resonance within the wheel itself?
  • As you have said, the bushes on the rear shock have play. I would replace them first and I am pretty sure that will fix your problem. I wouldn't have thought it was anything to do with the rotor (unless the rotor bolts were all loose) as the OP has said it only happens when the rear wheel is fully locked up.
  • I've sorted it a bit now but not 100%. Completely took apart the back end of the bike, re-greased all the bearings (I found a dodgy bearing that I missed before), adjusted the air pressures in the shock and tightened up the spokes in the back wheel a bit. I ordered some new bushes for it yesterday so I should have them next week. Whilst adjusting the back wheel quite a few nipples broke and there wasn't even a lot of tension on those spokes, I think the whole back wheel is in need for some new spokes/nipples. After I sort the new bushes and find some new bearings without paying Scott's prices the wheel will be next on my list to repair.
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