steam Posted January 2, 2011 Report Share Posted January 2, 2011 The front brake on my Rev 3 is grabbing. Any ideas how to stop it? Quote Link to comment Share on other sites More sharing options...
liviob Posted January 2, 2011 Report Share Posted January 2, 2011 Tell it to keep its hands to itself. Is the disc bent? Quote Link to comment Share on other sites More sharing options...
dan williams Posted January 2, 2011 Report Share Posted January 2, 2011 Can you be more specific? Are they grabby when you use them in a section or are they grabbing just by themselves? I don't know your level of experiance or ability so please excuse me if this comes off as me being a jerk. The top guys actually like their brakes to be really strong so there may not actually be a problem with your brakes they may be quite good. I've found some top expert bikes to be unridable for me as every control is light switch fast. Likely issues that can affect the brakes is if the bike has sat for a long time with the pads in contact with the rotor the surface of the rotor can be uneven and the braking will seem grabby because the area where the pads were will work better then the rest of the rotor. The same happens if the rotor is contaminated with oil or brake fluid. micro-fractures in the metal will retain a small amount of oil causing the rotor to not provide the proper friction. There are some contaminants that can cause a rotor to be stickier. Again if this occurs in an uneven pattern across the rotor the result can seem like intermittently grabbing brakes. The other possibility is the pads being contaminated but that usually results in brakes that are weak. One of the common "cures" for contaminated brakes, other then changing them out, is to do some high speed runs dragging the brakes to heat up the rotor and pads and then when they are nice and hot throw cold water on them. I know it sounds ridiculous but it actually works. The other is brake cleaner which can work or it can just spread a contaminant. In theory brakes are very simple mechanisms so usually there's a simple fix for just about any problem. It's just figuring out the problem that's a pain. One thing to make sure you don't do is the rookie mistake of fixing the rotor in place. Trials bikes use "floating" rotors so there is play in the rotor mounting to allow it to self center on the pads. If you torque down the rotor bolts and don't break the hub (a common result) then all bets are off. Grab the rotor and make sure it has some play in it. Please lt us know what you find. Quote Link to comment Share on other sites More sharing options...
steam Posted January 2, 2011 Author Report Share Posted January 2, 2011 If I touch them, i repeat,touch, in a muddy secyion the front brake locks with disastrous consequences. on the tarmac they compress the forks very quickly. I have the preload adjuster screwed half way in. Quote Link to comment Share on other sites More sharing options...
liviob Posted January 2, 2011 Report Share Posted January 2, 2011 (edited) Is this a new bike to you or is this a recent condition. Have you recently installed new brake pads. The pads may not be the same as oem pads. Some metallic pads are very quick to bite especialy when wet. Try a new set of oem pads. This condition might go away. Also do they drag. If so maybe your brake lever is not returning all the way out not allowing the master cylinder piston to return to its resting position. Edited January 2, 2011 by Liviob Quote Link to comment Share on other sites More sharing options...
dan williams Posted January 4, 2011 Report Share Posted January 4, 2011 Yeah that's just the way experts like them. Trials brakes don't "chase themselves" into engagement so they're unlikely to be malfunctioning just that you haven't got the feel for them. You can try letting the lever adjustment out further so they engage nearer to the bar or moving the perch closer to the end of the bar to reduce your finger's leverage. You could try filing grooves in the pads to reduce the surface area of the pad. My guess is you're just not used to them. Remember more then one finger on the brake is too many. If you're throwing two or a handful at the front brake like it's an old drum brake Bultaco any modern bike will put you on your head. Quote Link to comment Share on other sites More sharing options...
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