Front 'juddering' problem

[viper61]

Hey all,

Recently bought some good used discs to replace mine with as I suspected slightly warped front discs. Changed them yesterday with some brand new pads and same problem is there with same intensity. I don't think the discs were to fault in the first place. Either that or these were the same, although they were from a reputable seller and guaranteed straight.

Anyway noticed that the discs were slightly tight with the new pads upon replacement so i'm suspecting a stuck piston in the caliper, so looking at changing the seals if I can get some in time and perhaps do them on friday.

Could a stuck piston give a slight vibration at the front under heavy-ish braking? It could be down to wheel balance I guess but it's not all the time, which wheel balance would indicate. Any other suggestions guys? It can't hurt to strip and clean the calipers and replace the seals to i'll do this anyway as a matter of course I think.

Cheers

[Le_Blur]

Have you checked your headstock bearings are correctly adjusted?

[amorti]

Have you checked your headstock bearings are correctly adjusted?

Headstock bearings, fork bushes, wheel bearings, in that order. But I would still suspect the discs.

What are you doing changing pads without cleaning up all the pistons? That is the fastest and surest way to seized brakes, with the fun it brings of warped discs and boiled brake fluid.

[arsey30]

Bolt a dial gauge to the fork and check the disc runout.

Honda spec 0.03mm or 12thou
Old discs I have checked that work OK were within 8thou.

If warping is bad you may even see it if you spin the wheel quickly, but if pad is binding that may not be possible.

Tight disc bobbins will not help.

[Neosophist]

+1 +1

Tough one to call... most likely a bearing faliure if discs are good, in the same order as amorti has pointed out, commonly headstock but don't be surprised if it's a fork bush either.

get a cheap dial-gauge off ebay for a couple of quid and check the run-out.. if it's too expensive

You can 'crudely' check for any significant runout on the discs by using a flat screwdriver.

Jack front up, bars on full lock to stop left / right movement.

Tape the scrwedriver to the forks or a block or something that you can put by the brake disc...

move the screwdriver so the tip of the screwdriver is touching the brake disc (i use the corner part of the flat screwdriver as it's smaller) back the screwdriver off the smallest fraction you can, now when you spin the front wheel any high spots in the disc will make a 'scrapey' noise as they hit the screwdriver.

[viper61]

Hey guys, cheers for the feedback. I cleaned all the calipers, tried to get most of the crud out of there as best I could. To be honest a caliper strip and re-seal was coming within the next couple of months but haven't had time / money recently so this was just going to be a quick replacement until the full overhaul.

With regards to headrace brearings. No. I haven't checked these. Good call. I will have a search on how to check. Pretty much done everything on the bike and tinkered with most things except the front end. I think i'll check the headstock bearings next then and possibly overhaul the forks with new fluid and bushes too. I put in some RO springs a few years back so could do with a fluid refresh. How straight forward to change the fork seals while i'm at it? I'll have a search...

Cheers neo for the disc checking tip too, might give that one a go when back in the garage with it just to be sure.

Thanks all.

Rob