Join Date: Dec 2008
Location: Under the Downunder
Bikes: MTBs, BMX, Pocket MTB
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Originally Posted by scrappy1620
I searched the forum and couldn't find an answer. Since I put mechanical disc brakes on my bike I've noticed when I apply my rear brake the rear wheel hops. It stops me and locks up but hops. It does this no matter how hard I squeeze the brake. When I had my rim brakes the rear wheel did not hop and would lock up.
F.Y.I. I'm using Nashbar brand disc brakes. Has anyone else experienced this problem?
Thanks in advance for any information.
What you may be experiencing is what some call "brake jack." This occurs on certain rear suspension designs (particularly single pivot systems, including faux-horst link configurations). True Horst-link designs (or four bar linkage, or Specialized FSR) don't do this. Other swingarm designs that employ a "floating" caliper mount (rare these days) also eliminates this, but has a weight penalty.
You didn't mention what your bike is, but there are two easy ways to test if your rear suspension is susceptible to brake-jack:
1) Sit on FS mtb and squeeze the front brake lever fully, and bob up and down on your saddle to make your rear suspension move as much as you can. It should feel lively and unrestricted. Then, with the front brakes still fully locked, engage your rear brake fully and bob up and down again. If your suspension becomes stiff and unyielding then you have "brake jack."
2) Get a friend to sit on your bike and do the saddle thing (with front brake only) and closely watch the disc brake caliper in relation to your rotor. As the rear suspension move up and down, watch if the caliper is moving forwards and backwards in relation to the rotor circumference. If it does, this is what causes brake-jack. If you did this test on a true Horst linkage, or rear suspension designs with floating rear brakes, the caliper remains in the same spot in relation the rotor throughout the full range of suspension movement.
this is the case for your bike, I don't believe that bolt-on remedial attachments are worth pursuing. I think it would be better to learn and adapt a new rear braking technique and be "easy." You possibly didn't notice it with your rim brakes because of slippage, but it would've been there all along.