Front-end shake under braking?

[wkingham]

I have a RF900 that has an issue in the front end. When I brake it feels like the front forks flex forward and back causing the front end to shake.

I have replaced the steering head bearing (which was stuffed), front wheel bearing and fork seals and fork oil. The problem is better but still not perfect.

When replacing the fork seals the bushings slid out and I had to put these back in place. I have not had this happen previously while replacing fork seals and was wondering if this meant the bushes were stuffed and possibly causing my problems?

Any help much appreciated.

[jrandom]

You sure your brake discs aren't warped, dude?

[wkingham]

It could be, but I think there is more there than just brake shudder.

Before replacing the head bearing the shake was so violent it was very dangerous to ride, I think due to this other parts may have worn out?

[Nasty]

Would still check out the discs I was told they shake and shudder when warped.

[riffer]

Welcome to Kiwibiker Wkingham.

Okay, steering shake problems on RF's can be due to:

- insufficient tension on steering head bearings
- warped discs
- bent brake pad holder pin causing brake pads to not slide properly together
- brake caliper pistons not going in and out smoothly due to wear or shit in the calipers.
- tyre wear (do you have triangulation of the front tyre?)
- out of balance tyre
- wheel bearing worn

Tell us more about your bike. What's the state of the front tyre? Remember any of these type problems are REALLY exacerbated on the RF as it has a disproportionate amount of weight on the front tyre as opposed to a gixxer so they push that tyre hard.

I got brake shudder on mine (only between 80 - 100km/hr) which was traced to insufficient steering head tension. Tightening the steering, cleaning the brakes, replacing the front and balancing it have made a huge difference.

Who replaced the steering head bearings? One good test of steering head bearings is to let go at about 80km/hr. If you get tank slap its too loose. On my bike now its set up right you can go into a corner and let go of the bars and it keeps going around the corner. Until I got it sorted it stood straight upright. What does yours do? Don't underestimate the effect of a badly worn tyre on the steering too.

[canarlee]

Would still check out the discs I was told they shake and shudder when warped.

they do shake and shudder while braking if the discs are warped! i rode my fireblade from auckland to napier like that, had the disc replaced and no trouble since:yes:

[riffer]

they do shake and shudder while braking if the discs are warped! i rode my fireblade from auckland to napier like that, had the disc replaced and no trouble since:yes:

Usually you can tell if its the brakes because the brake lever will pulse.

If you pull in the lever and it shudders, it's brakes. If it doesn't its probably something else.

[canarlee]

Usually you can tell if its the brakes because the brake lever will pulse.

If you pull in the lever and it shudders, it's brakes. If it doesn't its probably something else.

mate trust me, the whole front end was shuddering not just the brake lever and it was defo the disc!

[Disco Dan]

my old GSX600f used to wobble like that if I accelerated hard then let go of the throttle with only one hand on the bars. The frame was slightly bent and the head bearing was stuffed.

[wkingham]

Thanks for the comments so far.

The Front tyre is brand new and I did the whell bearings on Saturday. I did the steering head bearing myself with a few mates and we readjusted it this weekend as it was definitely too loose to start with. After adjusting it the problem has improved slightly.

When I sit on the bike with brakes on an pump the suspension there is a knocking noise that I can hear. When I hold the lower fork leg it feels as though the knock is in there. With the bush falling out when i Inverted the forks to do the seals etc I sort of think maybe that is the cause of the knocking.

When braking the level has a little pulse in it but the front wheel seems to go back and forth.

The pads have not been wearing evenly so maybe I might start by pulling the calipers apart and clean them out including pistons etc.

[xwhatsit]

mate trust me, the whole front end was shuddering not just the brake lever and it was defo the disc!

<hints id="hah_hints"></hints>He's saying that if the brake lever is shuddering, then it's going to be brakes; if the brake lever isn't shuddering but other things are, then it's not likely to be a warped disc. He wasn't trying to contradict you.

[riffer]

Which bush has fallen out of the forks?

I've pulled early RF forks (preload adjustment only) apart four times now.

At the top is the preload adjuster, which the damper rod cartridge screws on to, then the spring retainer washer, spacer, then the spring which goes over the cartridge.

The bottom of the stanchion has a bush on it - is this what you are talking about? If this has come off the stanchion and you've lost it - DON'T RIDE IT. You need to fix this problem.

Did you ensure that you used loctite on the damper rod bolt at the bottom of the fork when you did it back up? Also, loctite on the bolt where the cartridge connects to the preload adjuster? If the bottom damper rod bolt has falled out the cartridge is just banging up and down inside the fork. Also if the preload adjuster isn't loctited on to the cartridge this can come undone too - it has on mine and when I went over a bump testing it the whole fork went 'clunk' as it extended to the end of its travel and hit the stop. These may be giving you grief under braking, particularly if one fork is working and the other is not.

However if the brake pads are wearing unevenly it sounds more like the brakes need attention. Those Nissin calipers are a piece of cake to clean up.

[FROSTY]

Hey you aren't the dude who had problems with his cdi a few weeks back are ya?
If you are I have a STRONG suspission that yours is a bitza bike. The forks i saw looked more like RF400 forks than RF900 ones
Listen to riffer though --He has been working his way SLOWLY through the same issue.

[wkingham]

No not me with the CDI problem.

[Coldrider]

My ZX9 had a warped disc, I replaced steering head bearings, tyre, wheel bearings first. It was not pulsing at the brake lever but I think the six pots were smoothing it out abit.
A warped disc will show up at slow speeds, from 50kph pull the clutch in to elimate as much noise a vibration from elsewhere and brake mildly to feel the pulse. By braking mildly you should eliminate fork flexs and concentrate on the rotors, will give an ABS type feel. Realistically if the disc(s) are warped you should be able to see it, jack the front wheel up and rotate it, holding a screwdriver firmly by the forks, push it till the tip of the screwdriver touched the disc, looking end on you should see the disc moving to and from the screwdiver.
Otherwise have the disc measured for warp by a machine shop or enginneer to confirm or eliminate. the rotors are too expensive to replace without being sure.

[ManDownUnder]

I have a spare pair of RF900 forks at home, most parts are good, and all bushes etc are there. One pitted Staunchion, apart from that they're ok (have 75,000km on them though)

Available for general consumption by RF owners... replacement costs only (I bought the whole things for NZ$200 out of the US so a bush should be around... $10?)

If you need 'em come and get 'em.

[riffer]

Nigel - plotting here. If you are feeling inclined, and mechanically minded enough, a morning between the two of you could sort this out.

I'd start with swapping wheel between your bike and wkingham's and test riding it. No shudder under braking - the problem is in his rotors.

Once that possibility is removed it should be easier (and cheaper) to fix.

Can you two sort that out between you?

[wkingham]

Thanks for the comment.

Riffer the questions you mentioned about the forks I only took the top of and did the seals and oil change so I did not have the damper bolt out. When I inverted the shock to drain the oil, the bush that sits uner the oil seal slid straight out. The last forks I did was on a ZXR750 and this did not happen. This is what makes me think that the fork bushes need replacing. I haven't lost anything out of them.

I lifted the front wheel of the ground and use a screw driver to measure if the discs were out. By my naked eye they look straight and not bent.

I am going to take the brakes apart and clean out the pistons etc this week to see if this helps. Will keep you updated.

[Pussy]

Give Robert Taylor a call, 06 278 4160, he will more than likely have some good advice for you

[BMW]

I have a RF900 that has an issue in the front end. When I brake it feels like the front forks flex forward and back causing the front end to shake.

I have replaced the steering head bearing (which was stuffed), front wheel bearing and fork seals and fork oil. The problem is better but still not perfect.

When replacing the fork seals the bushings slid out and I had to put these back in place. I have not had this happen previously while replacing fork seals and was wondering if this meant the bushes were stuffed and possibly causing my problems?

Any help much appreciated.

try the brakes. Warped disks.

[Robert Taylor]

Welcome to Kiwibiker Wkingham.

Okay, steering shake problems on RF's can be due to:

- insufficient tension on steering head bearings
- warped discs
- bent brake pad holder pin causing brake pads to not slide properly together
- brake caliper pistons not going in and out smoothly due to wear or shit in the calipers.
- tyre wear (do you have triangulation of the front tyre?)
- out of balance tyre
- wheel bearing worn

Tell us more about your bike. What's the state of the front tyre? Remember any of these type problems are REALLY exacerbated on the RF as it has a disproportionate amount of weight on the front tyre as opposed to a gixxer so they push that tyre hard.

I got brake shudder on mine (only between 80 - 100km/hr) which was traced to insufficient steering head tension. Tightening the steering, cleaning the brakes, replacing the front and balancing it have made a huge difference.

Who replaced the steering head bearings? One good test of steering head bearings is to let go at about 80km/hr. If you get tank slap its too loose. On my bike now its set up right you can go into a corner and let go of the bars and it keeps going around the corner. Until I got it sorted it stood straight upright. What does yours do? Don't underestimate the effect of a badly worn tyre on the steering too.

This man talks perfect sense. Warped discs are the most likely problem, even if when it is in early stages and not yet apparent with lever pulsation. You should have them checked proffessionally by a qualified motorcycle engineer with all the adaptors to rig up a dial test indicator. It takes surprisingly little disc runout / wear to ''tip the balance'' on a sensitive bike like this.

You didnt state how many kilometres this bike has done, which I suspect are now ''getting up there'' so you will have ''complimentary'' wear issues raising their head. When people successively fit replacement brake pads they are usually aftermarket. That is not neccessarily a bad thing but very often the shims that clip onto the back of the oem pads are discarded. These are fashioned in such a way that it attempts to equalise pressure over the full face of the pad. I am not saying that refitting these alone will fix the problem.

But, a little bit of disc runout, worn fork bushings, sticky brake piston action all adds up to a sum total and can tip the balance. Calipers over time will corrode inside their hydraulic and dust seal recesses, this build up squeezes the seals harder onto the pistons causing less than smooth action. In the UK where they grit the roads during winter this is a real problem.

Bear in mind that when you are feeling for steering head bearing play your bare hands cannot simulate road braking and deflection loads. My own personal technique for adjusting headrace bearings is to first slightly overtighten them and back off until they have just a faint hint of drag. You have to be real pedantic becaause every time you tighten the crown nut above the top triple clamp that can also influence total torque applied to the headrace set.

The bushings in the forks that reside immediately underneath the fork seals are a slight interference fit in the fork tube, they should not just fall in. If so you may need new alloy legs or a very good machinist. Aside from that you could also have sacked out fork springs, assuming they are the originals and k's are high. There is also the possibility that there is wear debris inside the cartridges trapping open the compression shims a little. This means the forks will blow through their stroke a little too readily, youll arrive at the more compressed part of the stroke a little earlier and that wont be a happy combination with the undesirable brake disc runout frequency.

Tyre wear will also affect it, some brands will have a much stiffer sidewall construction. That may excerbate or reduce the annoyance you are experiencing.

[riffer]

Robert raises an interesting point here regarding the shims on the brakes.

My RF does not possess these at all and I'm wondering how much of an effect this would have on braking performance. Please refer to the brakes fiche pic I've attached to see where they should go.

Also - wkingham - I'm still concerned about this "bush" that fell out of your forks because it just SHOULDN'T.

Can you look at the forks fiche picture I've attached to this thread and tell us EXACTLY which part it is?

[Robert Taylor]

Robert raises an interesting point here regarding the shims on the brakes.

My RF does not possess these at all and I'm wondering how much of an effect this would have on braking performance. Please refer to the brakes fiche pic I've attached to see where they should go.

Also - wkingham - I'm still concerned about this "bush" that fell out of your forks because it just SHOULDN'T.

Can you look at the forks fiche picture I've attached to this thread and tell us EXACTLY which part it is?

It would indeed be interesting to very objectively answer that question on brake shims, if anyone has some proven, credible answers I would be interested.

Ditto re that bush, no way it should fall out.

[ManDownUnder]

Also - wkingham - I'm still concerned about this "bush" that fell out of your forks because it just SHOULDN'T.

Can you look at the forks fiche picture I've attached to this thread and tell us EXACTLY which part it is?

If it is what I think is it... it's part #5 which (for me) slid out quite easily once the retaining clip and fork seal was removed. It's the golden coloured one (Phospher bronze I suspect?). If that's gone there will only be one point of support (at the bottom) for the stanchion as it slides up and down, so under braking the fork seal itself will be crushed, esp under heavy braking.

As mentioned - I have one at home. I'm happy to have a go at helping but don't have the necessary gear to exactly measure oil back into the fork etc.

[riffer]

How critical is this measurement of oil anyway? I've always used a plastic jug and measured to the nearest 5mm or so.

What sort of tolerance is there in this quality of fork for variability of oil level anyway?

[ManDownUnder]

How critical is this measurement of oil anyway? I've always used a plastic jug and measured to the nearest 5mm or so.

What sort of tolerance is there in this quality of fork for variability of oil level anyway?

Don't know but it we catch it all, and put it all back in, +5 mls to allow for stuff that stays on the inside of the jug...?

[vifferman]

It'll be interesting to see Eggs Zachary what this turns out to be. When I first bought my VFR it had a similar problem, which I thought was a warped disk, but it turned out to be badly (and unevenly) worn pads. I think the problem was exacerbated by steering head bearings that were on their way out. Replacing the pads fixed the problem, but shortly after that the head bearings needed to be replaced - they weren't loose, but notched in the 'straight ahead position', which manifested itself as a slight reluctance to tip into corners.
Like the RF, the VFR is front heavy, so anything that's "out of whack" in the front - even low tyre pressure - is shown up by vibration or steering problems. Get a couple of things that aren't enough on their own to register as needing fixing, and you get misbehaviour.

[wkingham]

Yes its the bush # 5 that slid out very easily when I inverted the forks. I still have it and have put it back in but was surprised that it fell out.

Last night I started to take the brake callipers apart. When I took the pads out and pumped the brake to push the pistons out one is not moving. Once I have managed to get the pistons out and cleaned out the callipers I will see how it is and if this has made any effect on the problem. May put new pads in at the same time.

[ManDownUnder]

Yes its the bush # 5 that slid out very easily when I inverted the forks. I still have it and have put it back in but was surprised that it fell out.

Last night I started to take the brake callipers apart. When I took the pads out and pumped the brake to push the pistons out one is not moving. Once I have managed to get the pistons out and cleaned out the callipers I will see how it is and if this has made any effect on the problem. May put new pads in at the same time.

So to confirm - you had a shaking issue while the bush was out of the fork leg?

or

The bush was always in the fork leg while you were riding (i.e. you had the shaking issue even with the bushing in the fork).


I'm in Kumeu. Come over on Sunday and we can swap front wheels if you want.

[Robert Taylor]

How critical is this measurement of oil anyway? I've always used a plastic jug and measured to the nearest 5mm or so.

What sort of tolerance is there in this quality of fork for variability of oil level anyway?

Refilling by quantity is very inaccurate. Overfilling and then syringing back to specified oil level / tolerance range is the only way you should do this. It will be detailed in the workshop manual. Setting the oil level sets the secondary air spring volume, and that very volume determines the latter reaches of stroke progressivity. Simple way equals mediocrity, the correct way equals a better result.

That bush should NOT fall into the fork housing.There is a problem with the bushing and / or fork leg that needs to be rectified.

[ManDownUnder]

Refilling by quantity is very inaccurate. Overfilling and then syringing back to specified oil level / tolerance range is the only way you should do this. It will be detailed in the workshop manual. Setting the oil level sets the secondary air spring volume, and that very volume determines the latter reaches of stroke progressivity. Simple way equals mediocrity, the correct way equals a better result.

Noted.


That bush should NOT fall into the fork housing.There is a problem with the bushing and / or fork leg that needs to be rectified.

it was common to mine from memory so could be a design thing. It wasn't rattling around in there, but there was sod all holding it in... (actually the fork seal and retaining clip were holding it in...!)

[Robert Taylor]

Noted.



it was common to mine from memory so could be a design thing. It wasn't rattling around in there, but there was sod all holding it in... (actually the fork seal and retaining clip were holding it in...!)

There should at least be a small degree of interference requiring a heat gun to preheat the alloy leg and then allow it to drop in. The passage of time ( high kilometres ) has either worn the recess or stretched it. That and the other problems have a cumulative effect.

[Ocean1]

There should at least be a small degree of interference requiring a heat gun to preheat the alloy leg and then allow it to drop in. The passage of time ( high kilometres ) has either worn the recess or stretched it. That and the other problems have a cumulative effect.

Good application for loctite?

I've done it before, where the bush internal clearance was still good. The outside diameter would still need to be no more than a few thou clearance in the leg though, and well degreased...

I've also bored legs once and made oversized bushes (Ossa from memory), but in that case the bush OD was slightly smaller than the seal OD so there was room to play with.

[Robert Taylor]

Good application for loctite?

I've done it before, where the bush internal clearance was still good. The outside diameter would still need to be no more than a few thou clearance in the leg though, and well degreased...

I've also bored legs once and made oversized bushes (Ossa from memory), but in that case the bush OD was slightly smaller than the seal OD so there was room to play with.

No, because the interference fit is also designed to firmly abut the free gapped ends of the DU bushing together to give the appropriate clearance to the chrome leg. Loctite is a wonderful product, but not here. This is a job for a very fussy machinist.

[HDTboy]

Give me a yell if you need a hand on Sunday MDU, I've had a few forks apart.

[Ocean1]

No, because the interference fit is also designed to firmly abut the free gapped ends of the DU bushing together to give the appropriate clearance to the chrome leg. Loctite is a wonderful product, but not here. This is a job for a very fussy machinist.

Makes sense. Are most of them split bushes nowadays?

[riffer]

There should at least be a small degree of interference requiring a heat gun to preheat the alloy leg and then allow it to drop in. The passage of time ( high kilometres ) has either worn the recess or stretched it. That and the other problems have a cumulative effect.

Well bugger me. It's a tight fit but I definitely never had to use a heat gun. Sounds like a fair bit of wear there wkingham. Hopefully Nigel's got spare parts that can help. If you get stuck give me a yell. I've got a spare set down here too we may be able to cannibalise to help you out too.

Thanks for your comments Robert. They're much appreciated. I understand that precise measurement is always a good thing to achieve precise results but I'm not sure if you totally answered my question. I guess I really wanted to know if, given that the quality of the Showas in the Suzuki is pretty ordinary, being a few mls out in each fork is really going to make that much of a difference. Either way, next time I change the fork oil I'll pay more attention to it.

[FROSTY]

Robert--Can you explain why you Wouldn't use the old tried n true method ?

[Robert Taylor]

Robert--Can you explain why you Wouldn't use the old tried n true method ?

Well tried but seldom true! Refilling with a specified oil volume very rarely achieves the same oil level ( and therefore trapped air volume ) from side to side. If you are careful it can get close but there are those of us who are not content with ''thats near enough''.

Reference to setting the oil level and a minimum and maximum range has appeared in the workshop manuals of at least the more sophisticated models for several decades now. The text is certainly not there to use a little more ink and to hasten the demise of The Amazon forest!

Adjusting oil level is a wonderful way of tuning end of stroke air spring effect, just as useful for road going motorcycles as it is for road race and MX. If you go to www.ohlins.com there are downloadable front fork manuals that describe fork tuning inclusive of the effect of changing oil level.

If for example you fill the forks by specified volume and you decide to change to heavier rate springs that are otherwise exactly the same, you have also changed the effective oil level and end of stroke air spring pressure rise. Why? Because the firmer springs will have ( usually ) thicker wire that will displace more oil when installed.

For reasons such as that manufacturers high spec racing forks specify that oil level is checked with the springs installed, it removes a variable.

When I travel to racing meetings I include in my toolkit a large oil levelling syringe and a handful of small 5 and 10ml syringes, plus hyperdermic needles for bleeding and charging nitogen. That does not mean I am taking illegal mind and mood altering drugs! Rather, optimising air spring effect, end of stroke bottoming resistance and attaining maximum available fork travel ( without abrupt bottoming ) is one of the most frequent tuning variaibles employed by top riders and their techs.

In my workshop , be it forks for road race, mx or just a road going commuter I NEVER ever fill by volume, only by specified level and an adjustment made for the application.

Different race tracks require different oil levels, the street circuits such as Paeroa and Wanganui require a higher oil level.

Life can be as simple as you want it to be, but if you want to be ''closer to the front'' you have to accept embracing hard work, lots of thinking and complexity. Why accept mediocrity? Theres too much of that in everyday life.

[Robert Taylor]

Makes sense. Are most of them split bushes nowadays?

Indeed, that is so.

[FROSTY]

No doubt your method should be more accurate.What about situations where the forks give a false reading? Im thinking forks with them newfangled innner thingees

[Robert Taylor]

No doubt your method should be more accurate.What about situations where the forks give a false reading? Im thinking forks with them newfangled innner thingees

There are no false readings that I am aware of, I think you need to describe more accurately what you actually mean?

[FROSTY]

Where some components require filling with oil before assembily

[Robert Taylor]

Where some components require filling with oil before assembily

It is but a matter of ensuring that everything is fully bled and stabilised before setting the oil level, again, workshop manuals detail the procedure and those of us in the trade have streamlined ways of being able to do so quickly. But Im not crossing that line and divulging that too readily!

[imdying]

Sounds like we're back to 'If you don't know what you're doing, leave it the hell alone' :lol:

[Pussy]

From my personal experience, I reckon Robert is getting the hang of it!!
Sorry, RT

[Robert Taylor]

Sounds like we're back to 'If you don't know what you're doing, leave it the hell alone' :lol:

Thats usually good advice in all walks of life! And having come from an aircraft background that is extra prudent advice. As I have been at pains to point out previously almost everyday I see the often disastrous results of the ''kiwi can do attitude''. That mentality might be okay for pouring concrete but not when you are dealing with parts of machinery that if not serviced and set correctly have the ability to injure, maim or take life.
How many have incurred injury or lost life because of same?

[wkingham]

Can't make it Sunday. The callipers are still off as I have not had time to clean them out yet. Will hopefully get this done Saturday and let you know how things go.

Thanks for you comments

[wkingham]

Hi Guys,

Have put the brakes all back together after giving them all a good clean out. I also replaced the pads even though they still had quite a bit of meat on them but just wanted to cover all bases.

The problem is still there sad to say so it now leaves me with either the discs or the shocks.

Cheers

[Coldrider]

Measuring the disc for warp, and concave wear (pads chewing out the disc) will eliminate or criminate the discs.

[mogiman]

i had a rf400 which did the same i went through all the same processes as you only to find that the frame had a crack by the stearing head which let the forks twist under pressure normally under hard braking not sure if you solved your prob but i got mine wielded up bingo all was fine ,scared the s*** out me a few times till i found this

[wkingham]

Hi guys,

Have have finally got around to fixing the problem yesterday. The problem was the RH Front Disc. When I checked them they all looked sweet and probably due to the fact that they are floating etc.

Very pleased its all fixed especially since summer is so close.

Thanks for all you comments and advise. The front end is basically all reconditioned now and wont have to do anything with it for sometime now.

Cheers,

Wayne :2thumbsup

[riffer]

Glad to hear it worked out well. A bike as front heavy as an RF is always going to exacerbate any disk warp, no matter how minor.

Enjoy your bike!