Front end braking issues

[Renton]

Bike: GSXR 1000 K6

The front end judders under heavy braking. It's done it since I got the bike, so initially I replaced the wheel bearings which seemed to cure it for a while.

However the problem has reared it's ugly head again when I was out in heavy rain yesterday, and anything more than gentle pressure on the lever and the front end would be shaking its head like Stevie Wonder.

There's plenty meat left on the pads. Though I'm not sure that makes any difference.

Any recommendations for things to check?
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This is my motorcycle. There are many others like it, but this one is mine.
Without me, my motorcycle is useless. Without my motorcycle, I am useless.

[andym]

Could be the discs are warped, have you checked them?

[Renton]

Yes visually, and with a micrometer for general thickness. But how would I check and be able to tell if they are warped?
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This is my motorcycle. There are many others like it, but this one is mine.
Without me, my motorcycle is useless. Without my motorcycle, I am useless.

[RhynoCZ]

Have you checked the steering bearings?
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'87 Honda XBR 500, '96 Kawasaki ZX7R P1, '90 Honda CB-1, '88 Kawasaki GPz550, MZ 150 ETZ
'95 Mercedes-Benz w202 C200 CGI, '98 Mercedes-Benz w210 E200 Kompressor

[Renton]

[Tankie]

You should be looking for any play in the headstock ,they might not need replacement , just adjusting , also have a look for any play in the fork legs
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[RhynoCZ]

By what you've described, I would definitely check the bearings there as well. You're going to have to lift the bike though, the front wheel off the ground and you can not lift it by the forks. The whole front end must be lose.

When the bike sits on the ground or you lift it by the forks, you can't tell the bearings are going bad, untill they are in a really horrible condition.

Also do as Tankie says, check everything is tight.
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'87 Honda XBR 500, '96 Kawasaki ZX7R P1, '90 Honda CB-1, '88 Kawasaki GPz550, MZ 150 ETZ
'95 Mercedes-Benz w202 C200 CGI, '98 Mercedes-Benz w210 E200 Kompressor

[stinkwheel]

I've also had this happen on bikes with badly feathered front tyres.

Also on bikes with a sticky brake piston causing the pad to wobble back and forth. Particularly the leading one (the one the disc passes under first in normal rotation). It's one of the reasons most 2-pot callipers have a larger piston on the leading edge of the pad.
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I did the 2010 Round Britain Rally on my 350 Bullet. 89 landmarks, 3 months, 9,500 miles.

[MCN]

Take the pads out and rub them on a sheet of wet and dry.

Then take a bit of wet and dry to the discs too.

There may be brake pad deposit bonded to the disc or/and pads.

But steering head bearings are a good place to look too.

Be careful when you raise the bike to check steering as it all gets top heavy and embarrassingly un-steady.

Easy if you have a centre stand.

You can maybe make do with a couple of axle stands under the front peg fulcrums. Maybe the arse end is heavy enough to sit down and let the front wheel lift clear.
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Disclaimer: The comments above may be predicted text and not necessarily the opinion of MCN.

[RhynoCZ]

Stinkwheel got me thinking and it could be your front tyre. I remember my mate had terrible front tyre on his 919RR, the bike would go alright, but during braking the front end felt like you were riding on the cobble stones.

Anyway, if you decide to lift the front end, use the paddock stand to support the back first, that'll give the motorcycle more lateral stability. I learned this the hard way when I was lifing a motorcycle with a car jack placed under the engine. Everything went alright, but then a slight lateral movement and the bike went down. I was working around the front end, so I grabed it before it fell down (extra human power activated, I felt like the mama bear when someone threatens her baby bears) and it didn't touch the ground, uff. My mate then jump to me and helped me to lift the bike again.

So use the paddock stand at the back, then either lift the bike by the engine with a car jack (a piece wood between the jack and the engine would be nice)OR you may as well lift it by the frame to the ceiling of your garage. I did both and I perfer the jack under the engine method.
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'87 Honda XBR 500, '96 Kawasaki ZX7R P1, '90 Honda CB-1, '88 Kawasaki GPz550, MZ 150 ETZ
'95 Mercedes-Benz w202 C200 CGI, '98 Mercedes-Benz w210 E200 Kompressor

[MarJay]

This sounds exactly like my CBR600. Juddering under braking over about 60mph. A minor pulse on the lever under that.

I replaced the brake discs for good secondhand items and the problem went away. It wasn't the wheel bearings, it wasn't the head bearings (which I don't think can cause this sort of thing).

The old discs were completely full of corrosion around the mounting buttons, and although I cleaned them thorougly I suspect the damage was done once the discs were overheated with this corrosion in place.

You can test disc runout with a runout gauge, or you can use a cable tie around the fork with the free end touching the disc. You then spin the wheel and see if the disc moves in relation to the tip of the cable tie.
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Remember kids, bikes aren't like lego. You can't easily take a part from one bike and then fit it to another.

[Renton]

Thanks for all the replies

I'm guessing it's not tyres, as I got the bike with BT016's and have since been running two sets of M7RR's and the problem has persisted throughout.

Thanks MarJay for the alternative way to check disk run out (I didn't really want to pay out for a dial gauge that I may only use once or twice.

I have an Abba stand with front lift arm, so I can check for movement with the head stock bearings etc.

But any ideas why the problem may be so prominent only in wet weather? It is noticeable during normal weather conditions, but only under heavy breaking. During the rain yesterday, it felt so bad even stopping at traffic lights that I thought my front was about to give way.
____________________
This is my motorcycle. There are many others like it, but this one is mine.
Without me, my motorcycle is useless. Without my motorcycle, I am useless.

[Luckyfish13]

It could be radial play on the brake discs...floating discs should only have play side to side, if they move up/down/radial at the rivet mounts then the brakes bind
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