Front brake pulse

[Guest]

Hello-
I have a 79 gs850g. When the front brake are applied I have a pulsing effect. If this were a car, I would guess warped rotor. Looks like new rotors are hard to come by for this old machine. Can they be surfaced? Or is there somewhere else I should look on the brakes for the problem? New pads last year. Wheel off over winter to have it painted, the rotors were removed at that time and marked L &R.
Thanks
Chuck

[cowboyup3371]

It is possible you have bad rotors but there could be other things too. When was the last time your wheel bearings were replaced? Also how about the brake lines - are they still the original rubber or have they been replaced with stainless steel lines yet? Have you flushed the old brake fluid out and replaced it yet?

[Chuck Fryer]

New SS lines and fluid last year. I've never replaced the wheel bearings.

[cowboyup3371]

I would definitely replace them (can get AllBalls at a decent price) while you confirm whether the rotor is in good shape

[rphillips]

It may just be me, but, I've had much better luck with motorcycle brakes, at a local machine shop than I ever had at an automotive brake shop or parts house.

[Cipher]

I warped a rear once pulsed horribly though the warpage was quite small. a sheet of glass make a good ad hoc measuring surface.

def check mount points of wheel for dirt or a smidge of paint.

[Brendan W]

My guess is the rotors are not back flat in the wheel.
I would take them off and make sure that the mating surfaces are absolutely spotless.

[bwringer]

The other thing that can happen is that overheated pads ruin the heat treatment in one spot, leading to a spot on the rotor with more or less friction. Sometimes you can even see these as a blue or dark spot on the rotor.

If you're feeling the pulsing through the brake lever, the rotor is physically warped. If you're feeling it mostly in the suspension, then you have a hot spot. Or some combination of these.

In any case, replacement is usually the best option; GS rotors are not really thick enough to turn.

[Chuck Fryer]

Checked rotor run out, lh.002 rh.004
But, I greased the slide pins and all is fine now.
Thanks for all the replys.