Front-end shake under braking?

[rogson]

When I took a mates bike for a warrant today I noticed the front end vibrate/shake when braking. The shake is up-and-down rather than side-to-side and I don't feel any pulsing in the brake lever. It is more pronounced when braking hard and from higher speeds. The bike got the warrant and I jacked-up the front end and checked for play in the steering head bearings when I got home but didn't notice any. I also checked for run-out in the front wheel (its cast not spoked) and for obvious warping of the brake discs but everything looks good. I haven't been able to check/tighten the steering head nut because I need to get hold of a 31mm socked/spanner to undo the lock nut first. The front tyre has 12,000km on it and while it got a warrant the tester said it was only just legal.

Is definitely the steering head bearing or could it be a soft spot in the tyre - or something else?

[bugjuice]

when were the shocks last serviced?

[rogson]

when were the shocks last serviced?

Don't know - but I would (confidently) guess never. Bike is 2001 model and has had 3 owners. According to the odometer it has only done 12,000km. Front tyre is Battlax BT54 (same on rear) which is probably original factory fitted jobbie. So 12,000km total mileage is probably right.

I doubt whether its a suspension problem.

Interestingly, my mate says he hasn't noticed the problem, to which I can only surmise he doesn't really use the front brake - like many others I fear!

[idb]

It would surely have to be the wheel or tyre out of round.

[FlyingDutchMan]

Mine used to do it. The only things I changed on the front before it vanished was new tyre and fresh fork oil. Fork oil goes pretty rank after 12 months.

[WINJA]

its sometimes hard to determine if its the head bearings , have you stood beside the bike , squazed on the brakes and pump the bike back wards and forwards hard as you can , it may yet be a fork leg , get your mate down there when you do it to isolate and identify sounds and movement , i once saw an r1 where the lower aluminium casting was loose on the chrome slider

[k14]

Have you checked the tyre pressures? Could be something as easy as that.

[WINJA]

have you checked the tyre pressures? could be something as easy as that.
i spose racing youd have seen that overinflated tyre skipping thingy

[k14]

i spose racing youd have seen that overinflated tyre skipping thingy

yeah thats why i say, had problems like that before.

[Big Chim]

when were the shocks last serviced?

How often should you service them?? is that just changing over the fork oil??

[beyond]

Ok, this is something a lot of people miss.
If you rule out the head bearing and wheel and disk runout then its more than likely dirty brake disk bobbins.

Modern bikes have floating front disks that work on the round bobbins connected to the hub. These fellas get dirty and lock up a bit and can result in exactly the symptoms you speak of. Get some soap and hot water and a real stiff brush and give these fellas a good working over. Sometimes WD40 is good too but make sure you dont get it all over your pads. In real bad cases you gotta knock them around a little bit with a hammer to loosen them up again.

12,000kms is too soon for head bearings unless you or a previous owner spent a lot of time with the front wheel in the air and chickened out every time coming down hard.

[R1madness]

There is nothing definite in this world. If the front tyre is as bad as the WOF guy said replace it and try again. If the problem is still there then do the steering head bearings. I may get flamed for this but it is not often that THIS problem is from anything else other that bearings or bent disks. 12000k is pleanty of time for ham fisted wheelstands to poke a set of bearings. The lack of play is NOT a sign that the bearings are ok. You may have checked them on a high point of the dents in the races.
Front forks SHOULD have the oil changed every 10000k but noone ever does.
Disk runout is the next most obvious thing. How did you check for runout? 0.5mm is too much but cant be seen by eye. try colouring in the entire disk surface with a black marker pen. Let it dry. Spin the wheel without the brakes applied. if there is runout the disk will drag on the pad and wipe off the marker in the spot that is bent. Do both sides of the disk. Repeat with other disk.
Good luck

[raster]

On my impulse it's the right front disk, feeling no pulse through the lever either.
With new pads and scuff of the disks the warp became visibly noticable as discoleration of the disk in areas.

Hit the picks at high speed, vision blurs.

[ajturbo]

Mine used to do it. The only things I changed on the front before it vanished was new tyre and fresh fork oil. Fork oil goes pretty rank after 12 months.

12 months??? 12 months???

shit... soooo 1983---- 2005... is that 12 months?? :spudwhat:

[vifferman]

I didn't know that about the disk gubbins/bobbins/goblins/nubbins - must clean mine. Perhaps I'll give em a squirt of chain lube or summat too..

My front end did wobbie stuff too - I thought it was just the suss right-hand disk, but after changing the tyre, head bearings, checking for oil and whatnot, the thing that made the biggest difference was the disk pads. the right-hand inner one was fookd. Also, all that monkeying around meant that the front end ended up properly straight, and the suspension became more compliant too. As well. Also.
So now it's all good.