Noticed a bent front rotor on my 'new' f4i during the tire job. There's a large black streak on the rotor surface, and the pads were very abnormally worn compared to the other side front rotor/pads. The pistons were froze in the caliper on the bent rotor side as well. We managed to get the pistons to pop back out. I guess this was the reason I had to pump the front brakes a few times on cold starts to get any brake power. Sound about right? Do I need a new caliper? I already got a straight rotor on the way, and new pads for left and right.

The other front side brake mechanism looked good, pads still had a lot of meat. The bike is an '01 f4i with 9k miles. Thought I was getting a bargain as it was dropped on both sides. The scratches and scuffs look worse on the side with the bent rotor. I'm guessing it got dropped on a curb or something.

Anyone else had the same issue? Hoping I can put a straight rotor and it will be fine. The froze caliper seemed to work normally again when we tested it... What kind of long-term wear does this put on it? I didn't even notice it was froze when I test rode the bike. How come there's still no pulsation after unsticking the caliper and temporary reassembly with the bent rotor?

Thanks.

 

The rotor might not be bent? Unless you can obviously see it is. The brake pad might have been incorrectly installed, or the piston sticking could have cocked the brake pad sideways a bit and allowed it to constantly rub giving you the black streak.

 

hold off on the caliper. have you bled the system yet?


if not, grab an old toothbrush and some soapy water, get the pistons a little bit out of the caliper and start cleaning until they come clean. i'm sure there's a very distinct dirty line, get that gone and they should all start to move pretty evenly.


as far as the rotor, if it's really bent, time to buy a new one. just make sure you have the directional right, lightly sand the rotor, new pads and bed them in. (it's going to take 100 mi or so to properly bed in - so no hard riding)



there are videos on youtube showing you how to clean your caliper and pistons.

 

I'd vote for a rebuild, they just need mainteance not replacement.
If the caliper was frozen, it could over-heat and warp the rotor.
Although if it's not "pulsing", the rotor might not be warped.
Did you check the run-out?

If it's really been frozen, I'd replace the seals to the pistons.
Not just free them up. Why do this job again, if they turn out to be sub-par.

As Conrice mentioned, do a google on you-tube, there are a lot of videos on
this procedure. It's one of those things you need to do, to a 'new' used bike,
anyway. That's the only way to be sure of optimal service, on a very important
sub-system of the bike.

Good thinking to go ahead and do all of the pads (r/l). I like to start with
a level field, where I know complimentary parts are on the same future
maintenance schedule.

Ern

 

The pads on it were stock, I'm sure. Wish I had pics, but the pads were almost completely gone on the bent rotor side and unevenly worn across the surface. The pads on the good side still had about 50% material with nice consistent wear. I don't think the wheels had even been taken off this bike...

The pistons were frozen into the caliper, not against the rotor. We got the pistons to pop out with a screw driver and pumping the brake with a chunk of wood in the other caliper.

As for the rotor, it's definitely bent. You spin the wheel on the stand and you see it's lop-sided. I'll get some measurements with run-out gauge from harbor freight before I install the new rotor.

As for no pulsation with a bent rotor... A guy on the kawi forums said this:
Is the either/or? I did notice some braking resistance problems with having to put a lot of pressure on the lever in order to stop. Thanks for the input, guys, definitely want to do this right the first time.