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

[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

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!

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:Me]

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.