GSXR brakes pulsating

As some of you know just put a GSXR750 front end on the curvy, everything was fine until the whole bike started pulsating when braking at about 60mph. I can brake from slower speeds as hard as I like and everything is fine but as soon as I touch the brake lever at 50-60 the whole bike starts to pulsate, the mirrors start shaking etc, any ideas? I thought warped discs but wouldn't it be affected at any speeds?

Any help appreciated...once again!

Oh yeah I have the same trouble as svrash in which my brake pads wobble around a bit in the caliper so could this be the problem? (I havent noticed it before though just last night)

[Spanner Man]

Morning.
You're right, warped discs would be apparent at all speeds, though more noticeable at higher speed. Still check them mind you....
I would suggest close inspection of wheel bearings, headrace bearings, and fork bushes.
I would start with the headraces, I would hope that you put a complete new set in when swapping the front end, as any mismatch of bearings will have an effect on their performance.

Cheers.

Yep put a complete set of bearings in (could I have tightened too much or not enough?), how can I test the discs to find out if theyre warped? I wish i lived closer to Spanner Man then I'd book the bike in there!

Is the wheel weighted properly?

Matt

Yep weighted OK, I would notice if it wasnt when riding wouldnt I?

[21QUEST]

A bit of a weird behavior that. Even for a bike with seriously warpped discs or incorrectly adjusted head race bearings(unless very very loose maybe).

One thing you could do is to try get up to say 30 40mph, pull the clutch in and apply the brakes(lightly/feathering). This should show if the discs are likely at fault here.

If I were you I'll attack it like so.

I'll do the above warpped discs test. With the front off the ground check again for disc warpped etc. Also check the wheel carefully to make sure not buckled etc. All you need is a pencil, pen, head of a screw driver held as close to disc or wheel rim lip without touching. Hold it steady and spin the wheel. Infact do a good visual check without the improvised dial guage check above. If bad enough, you should notice.

Check your brake caliper Pad Pin and make sure one or both are still there(don't ask how I know).
Depends probably on the caliper you are using but some the the K series caliper don't have a circlip. Maybe it's just the SV1000 caliper but seeing they are simiar, I'll check it.

I'll definitely make sure the head race bearing as spannerman says are adjusted correctly.
Head race bearings adjustement are one of those jobs that only really comes to you after a few times of doing it. Even now I don't like it much because of the fraffing around that one has to do if not right once checked(after adjustment). Doing mine this weekend. A bit notchy just off centre.

Shame you don't live close to Surrey.


Ben


ps: I'll sort the other stuff later on today.

Tried doing about 40 then applying the brakes both lightly and then more sharply, nothing (smooth as a baby bottom!). Only occurs when I brake at about 60, dont even think it does it at 50!

Will take calipers off tonight and have a good look, will also have a look if the wheel is buggered.

Thanks for all the advice, keep it coming

Originally Posted by andyb

how can I test the discs to find out if theyre warped?

Put a striahgt edge like a metal ruler across the disc rotors and compair the gap between ruler and fricton surfaces of the disc

Warped discs may not be apparent at all speeds but will become more aparent the harder you brake, if your doing 20 and braking softly, you might not feel anything but if your doing 60 and braking harder then you would

I found that with the head bearings they needed tightening a couple of times, every couple of trips like, to get to a almost bedded in stage and i would think if the whole bike is shaking then this could be it

[jambo]

I found a similar issue with my ZX6R when I got that it was fine on the road but at my first track day about 3 weeks into ownership I found the front end shuddered horribly under hard braking. I suspected a warped disc, but I think probably the change of fork-oil was what got it in the end as I think it was a very poor rebound-damping thing. The bike had 3,500 miles on it but was 4 years old.

Suspension settings should be your last port of call as the above advice is where I'd start but if the oil in the forks is old / unknown it may be worth checking there's enough rebound & compression damping & preload on the forks.

On the off chance,
Jambo.

Originally Posted by jambo

..a fair point

I did put all my settings back to standard, as per the manual, when i got my forks, might be an idea to do that just to cross out a possible problem

I got the K2 and SRAD 750 manuals on PDF if you need the settings