seized calipers or warped disc?

Hey there guys, get this:

Tuesday, got the bike out rode all day brakes fine, no problems.

Sunday, got bike out rode to Ace cafe, front brakes bumpy, juddery, almost like one of the calipers is not working? admittidley bike is parked outside with cover over, but rain has managed to get onto the discs and start some surface rust, would this cause warping?

would be grateful for any tips or reponses.

Only thing that causes warping is too rapid cooling of the discs from being excessively hot. I have blued my discs many times on track days with no probs.

Sounds like you need to clean out the calipers and re-lube under the seals.

If you got paddock stands then get the front wheel in the air and gently prise back the pads away from the discs. spin the wheel slowly and eye up the discs against the caliper, if they’re warped then you should see this quite easily.

Am sure there are many ppl on here local to you that can help you if your unsure how to proceed.

Also sounds like callipers to me as well. Take the calipers off and clean out as much as you can. Gentle pressure should push the pistons back into their housings, if not, its a full strip and some new piston seals, that should do the job.

I’d agree it’s unlikely to be a warped disc (but possible, high mileage and thinning discs ncan cause it), but the fazer has sliding calipers, and only pushing pistons from one side (of each caliper), the back pad is drawn on to the disc by the front pistons pushing that pad onto the disc and dragging the caliper body with the back pad on it into contact.

The body of the caliper rides on two rubber shrouded pins, these sometime dry out and need re-greasing, I’d look there first as it’s only a 10 minute job.

If however you find this isn’t the problem and you are unable to “pump” out the pistons with the lever (as can be the case if the brakes haven’t been looked at and the bike was used over winter) then a good trick is to remove the whole assembly (lever/ mastercylinder/ hoses and calipers) still together, dump the calipers (still attached to the hoses) into a bucket of hot soapy water, leave them for 10 minutes or so and they may just move.

The two pistons in the caliper are fitted with two seals, an outer dust seal (thin square section) and an inner fluid seal (wider), it’s not uncommon for brake dust to get behind the dust seal and force it to come either fully or partway out, if this is the case you’ll need to get the calipers services and new seals put in or buy a set of seals from Mr. Yamaha ( about £20 I’d guess) and do it yourself, the buildup around the pistons is brake dust, but it sets very hard, it can be removed with a wire brush or carefully with a small screwdriver, take extra care around the pistons themselves as they will also have a line of buildup around the tops, try not to scratch them as this may lead to leads and replacement being needed.

If you’re not sure and local (I’m SE25) drop me a PM and I’ll take a look.

Hope that helps.

Cheers Mark.