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??:brick: :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..:whistle:

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. :first:

[Stevo]

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..:whistle:


Are you takin the Pess. Cos I'm not sure???? I wouldn't advise anyone to put chain lube there. As soon as the wheel rotates the centrifugal force would lube the disc and pads for you, even if care was taken not to put too much on. Could stop the shudder though:dodge:

[F5 Dave]

Urine was being extracted 4sur.

I’d bet on disc run-out too. But it doesn’t take long for knackered discs to take out the steering head bearings making some tiny notches in the bearing shells. You can’t usually tell until you take the forks off & turn from side to side the notchy feeling destroys feel.

My RF had a brand new WOF & knackered discs/shot head bearings - it was super scary to brake hard on, but the bike was cheap enough so I rode it carefully home (5 min) & took it apart to fix before I was tempted to ride it again.

[NinjaBoy]

had a similar prob with the CBR but only really appeared on trackdays when braking hard at the end of straights etc...

The CBR had new steering head bearings and new fork oil.... I solved (or rather Frosty did ... and a few other things) by tightening the steering head nut. (1/8 of turn)

Steering became a little slower but soon got use to that.

[Brian d marge]

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!

Thinking about this , Is it when u use the front brake or when you roll off the throttle without using the front brake,???

If its when u roll off the throttle and start deaccelarating , my guess is the rear shock is either stuffed, or the spring rate , preload setting is wrong for you wieght.

so the rake /trail change when you get on the bike , but you mate doesnt notice. try altering the ride height bias( raising the rear by preload , dropping the front in yokes ,,I would jack up preload a bit ...) when you ride it and see if the problem gets worse or better

Sorry, this took a while but I was thinking about this in the morning and reminded me of this thread ..

If its ONLY when u use the brakes then its a brake /bearing problem loose steering head bearing etc

out of round wheels tyres will show up on a contant throttle ( accelarating and deaccelarating also but is harder to pin point )

Worn brake top hats will go clunk ONCE when you apply the brakes but stay in that position as long as the brake pressure is constant .

Just a thought

Stephen

Stephen

[Stevo]

So what have you found so far Rogson?

[rogson]

So what have you found so far Rogson?

Well, its been an odyssey.

Firstly, remember the bike is only 4 years old, has done 8,000km and had just got a warrant.

As I said originally I started-out suspecting the steering head bearings so tightened them about 1/8th turn. This reduced the shudder but didn't eliminate it.

So I told my mate (the owner) it must be the front tyre. He fitted a new one ($200) - but the shudder was still present.

So, I told him it must be the front suspension. We removed and disassembled the forks, cleaned everything and reassembled them with new fork oil ($15) - but the shudder was still present.

So, I told him it must be a warped brake disc (even though I didn't detect any pulsing in the lever). So, I spun the wheel while applying just enough brake to drag a little and found the pressure/drag was even through the whole revolution, and concluded it wasn't the brakes.

So, today I jacked-up the front wheel, strapped the rear end (including the rear suspension) down so there was no chance of movement other than at the front end and checked for play.

First thing I noticed was some (very small) play in the wheel bearings. So, I replaced them with new ones ($38) - play gone!

Then I checked for play in the steering head bearings (by pulling and pushing on the front end) yet again, and found a small amount (just perceptible) when the wheel was pointing straight ahead but none when at any other angle. I traced the movement to the top steering head bearing, so tightened it yet again until there was definite drag when I moved the bars from side-to-side.

However, when I checked again for play with the wheel straight-ahead there was just as much as before.

So, after all this I have concluded it is damaged steering head bearings!

I informed my mate of this, and told him we need to disassemble the front end and replace the steering bearings. Not surprsingly he seemed reluctant - I guess I don't have much credibility anymore. After-all, so-far the odyssey has taken over 6 weeks and has cost him around $250 - and we're still not home!

[TwoSeven]

Stearing head bearings are a bugger. Its so easy to overtighten them and easy to not do it enough. I recently cured a similar problem on my 600 - when I put pressure on the brake lever the bars bounced up and down. When the bike was still and I jumped on the bars - it felt fine. Went away when I pulled the steering head apart and did it up again (torque).

[rogson]

Sorry for resurrecting this thread, but the final outcome may be of use to someone.

I finally got around to removing the steering stem and checking the bearings - and everything was OK, apart from being dry.
So, I regreased it and put it back together making sure I torqued the stem nut "just right". I also took the forks apart and checked the bushings - again OK.

So, back together and - would you believe it - the front end still shook!

So, I was pretty sure I had eliminated the steering stem and forks - what could be the cause?

The bike has an aftermarket Givi windscreen on it, that is raked back (toward the rider) with quite a long unsupported screen portion. I noticed it shook up and down quite a lot, especially when braking or on rough roads - could this be it?

So, I went for a ride and held on to the screen when the road was rough and while braking and cornering, which seemed to improve things. So, I took it off, went for a ride and the front is now as smooth as...........

Come to think of it, some other bikes I have ridden with big windscreens have seemed loose in the front end to me - could it be the screen?

[Steam]

Nah, it's great when people resurrect old threads to tell what happened in the end. More people should do that, we want to see how things turn out.

As to loseness in the front end, front wheel discs (solid front wheels) also lead to that loose feeling, so that sounds right. It must be the wind resistance or something.

[Edbear]

[QUOTE=Steam;896990]Nah, it's great when people resurrect old threads to tell what happened in the end. More people should do that, we want to see how things turn out.[QUOTE]


Yup! I agree! Coincidence is a funny thing. I've just been on a 4-day jaunt and for the first time noticed mild headshake at about 70km/h. Especially if taken one hand off the bars. Thought it couldn't be tyre pressure, as I always check them before each ride. Had a WOF recently and no probs since then until setting off on the ride. Was thinking steering head bearings and plan to check them. Front tyre has done about 12,000km, (Metzler ME33), now and showing wear though plenty of tread on the edges...:shutup:

Fork seals were done by the prevoius owner just before I bought it and he said he put heavier oil in them, I think 10w. and they're not leaking. Rear spring could probably do with a bit more preload, though, as I'm 93kg plus riding gear.

I always try to think about what recent changes were made in these situations and it could also be possible that my Brother-in-Law is to blame. :innocent: You see, my first stop was to visit them and he gave me a full 4lt pack of oil that he'd bought just before selling his bike to help finance their new home. Adding it to the top box no doubt considerably increased the weight up high at the very rear of the bike. Mebbe I should go for another ride now it's all unloaded and see if the wobble's still present. :yes: