Interesting problem with brakes (intermittent shuddering)

[riffer]

Throwing this out to others with more nous than me.

Following the replacement of the brake pads on the RF after the EBC's cracked on me, I've had an intermittent shuddering under braking.

Basically, if I jump on the brakes they shudder, but if I pull on them gradually they don't.

My first thought was that the pistons aren't evenly going out when I pull the brake lever. So I pulled the calipers apart in the weekend, and yes, I was right - hold up the caliper with the pads out while my wife gently pulled the brake lever and the pistons were coming out unevenly.

So clean out all the brake dust and crap off the outsides of the pistons with brake fluid and a toothbrush and now they are coming out much more evenly - not perfectly, but heaps better.

And yes, I've improved braking performance under 100km/hr. Brakes that were quite wooden now have a much greater degree of initial bite. But this problem with the shuddering when I grab a handful of brakes persists.

Now, I've checked the brake discs for out-of-true-ness; a bit crudely by taping a screwdriver to the fork and spinning the wheel - but hey - it works and I don't have anything better. Anyway, they are perfectly straight so that's not the problem.

I've noticed that one of my discs has interesting wear on it - it's like in cross-section its convex - the total amount of convexity wouldn't be more than say a quarter of a mm. Just enough to notice if you run your finger across it but hard to see.

So I guess my question here is - what's my next step - should I rebuild the pistons seals completely, or look at getting the convex brake rotor skimmed?

Do any other KBers have any relevant experience in resolving these issues?

Life on one income with 4 kids, a mortgage and child support payments pretty much precludes my preferred option - just buying a new rotor.

I'd appreciate some mechanically experienced ideas thanks.

[TLDV8]

The convex thing is a bit odd but working off what you have already done and starting with the simple stuff (Taking for granted the problem only just started).........What did you do to the braking surface on the disc before changing the pads ?..Some folk go as far as bead blasting but i normally find scuffing the surface with medium grit wet/dry sand paper is good enough to remove any old contamination.

[Motu]

Machine or replace the rotors - or park the bike up.Farting around with pads and calipers won't fix this.

[imdying]

Now, I've checked the brake discs for out-of-true-ness; a bit crudely by taping a screwdriver to the fork and spinning the wheel - but hey - it works and I don't have anything better. Anyway, they are perfectly straight so that's not the problem.

Sorry mate, that doesn't work, and they're just as likely to be bent somewhere. Only takes a couple of thou of thickness variation or run out to make them shudder, and mr screwdriver isn't going to tell you anything near that level of accuracy

Time to buy some new discs mate, try cycletreads. Ask about, I'm pretty sure other GSXR ones might fit? Have a look on ebay too

[TLDV8]

Does the brake lever pulse when you get the shuddering ?

[Paul in NZ]

Wot Motu says

I've never detected a problem like that and a skim has fixed it.

Check your wheel bearings, steering head bearings and make sure and floating mounts do float.

Often 'warped' disks are not warped, it's just a variation in thickness.

ABC brakes in the city can machine em off the bike. They can be a bit agressive so a smack upside the head when dropping them off helps.

Paul N

[riffer]

Often 'warped' disks are not warped, it's just a variation in thickness.

ABC brakes in the city can machine em off the bike. They can be a bit agressive so a smack upside the head when dropping them off helps.

Yeah, that's exactly what I was thinking. The previous pads were crap, and they've left the rotor convex. I'm sure they are not warped because its an intermittent shudder. I'll ring ABC and see what they can offer. The rotors are only 10,000 kms old.

Cheers Paul.

[riffer]

Well, I spoke with Peter from ABC, who advised me they won't work with Full Floaters. but who recommended me to Gunther at PG2000 (Precision Grinders) in Lorne Street, who's a motorcyclist as well.

Gunther's given the bike a look, measured with micrometer and reckons they're not warped. However, they do have variations in thickness, caused by the nasty sintered metal pads I'm running, which have picked up some small stones, and created a "dished" effect, which is the exact opposite to what I reckoned. Go figure. Still, he's the expert, not me.

So, firstly he's proposed I go with an immediate replacement of pads with kevlar ones, and if this doesn't fix the problem, he'll machine the disks for $60 each.

They have no minimum stamped on them (aftermarket ones) and the minmimum thickness he measured was 4.85mm.

[FROSTY:Me]

Mate before doing that try this sequence of work.
1) remove the pads --Get a sheet of Glass and lay a sheet of 600 grit wet and dry sandpaper and put it on the glass--add water and hold the pad flat on it--sand the pad surface flat.Hose off the residue.--Do it for all 4 pads.

2) Buy a tube of rubberlube No need for a tub just the toothpaste tube sized tube will be fine. --Pump the pistons back out and get rubberlube on them and onto the seals Be generous but once youve pumped the piston in and out a few times wipe off the excess.
3) remove all the pad mounting pins and sliders. sand them smooth and use a little bit of rubberlube to let the pads etc slide freely.
3) Put a big easy out into each of the full floater "rivets' And spin it up not enough to make it rattle but enough to get it spinning.
4) clean out all the holes and slots in the disks.
5) Check the wheel and steering head bearings are correctly tensioned and are in good nick.

hey Not being smart mate but sometimes its the small things that catch us out

[F5 Dave]

Only other fitting for RF900 is the Bandit 12, erm maybe the 600 dunno, but not GSXR.

Do check steering head bearings with no weight on the front, any slight knotchyness is bad.

But yeah the discs. I may have an old set of pads with reasonable meat around when I replaced my discs I fitted new ones. Heck I still have the old discs, but at least one is warped but lasted a while after ground by Gunter.

Will be away till after weekend but if you want either remind me Monday.

[SuperDave]

Don't be so quick to just replace discs, as Frosty says sort the simple things first and replace the discs as a last resort. I had a similar problem with my old FXR on the front and replaced the disc, only to find that the disc was fine and my steering head bearings were the true cause of the problems.

[riffer]

All good points.

I'd pretty much ruled out the steering head bearings. As the ones on my old FZR were so dodgy (ovalisation of the race sockets - common on these bikes) I got pretty good at checking this problem out.

I've lifted the front end and pulled the wheel as hard as I could (like they do when you get a warrant) and there's no play at all.

I did intend to regrease them at some stage before next warrant so it might be a good idea to look into this.

As for the wheel bearings, when I do the stuff that Frosty's suggests on the weekend I'll check out them as well. I know when I had the sockets and chain replaced last month they did the rear bearing as well as it had rusted completely (naughty naughty Simon - should have checked this ages ago).

It's the bikes fault really for being so damned reliable. I've done 22,000 miles on the sucker since the weekend before Easter last year and, expect for the spluttering in the wet which I sorted, has never, ever had a problem. All I've done is change tyres and spray oil on the chain.

Oh well, at least I get to work on the bike in the weekend...

Thanks for all the ideas guys.

to be continued ...