Front Brake judder

[Chris]

Hi all,

This might be a bit of a read so stay with me! I've done the usual searches but not come up with much to help me. The bike is a 2002 fzs600 with 30k milesish.

The problem is a pulse through the front brake lever while applying the brakes, it happens at all speeds and appears to be once every rotation of the wheel. It is enough of a judder to make the mirrors vibrate and generally be very annoying while riding. I don't use the brakes that often but even with light pressure the lever pulses.

The problem began a while ago. I had taken apart the front end of the bike for various reasons, cleaning, upgrading etc. There was no pulse before I took it apart. While the bike was in bits I: had the front wheel powder coated, lightly sanded and painted the forks myself, fitted new bearings in the wheel and new sbs ceramic pads in the calipers. I reused the standard discs. Not long after I had it back on the road I noticed the pulse through the lever and it has been driving me a bit mad...

So things I have already done to try and solve it are:

1) made sure the mating surface for the disc carriers to the hub of the wheel were sanded/filed smooth to remove any uneven paint from the powder coating process

2) fitted brand new front discs, pads, braided brake lines to replace the original rubber ones, new fluid, new seals in the calipers and all pistons cleaned up/polished/red rubber greased and moving freely.

The pads in the left hand caliper have very small movement backwards and forwards in the caliper and by this I mean very small amount of movement but with the front of the bike jacked up off the floor if you turn the wheel back and forth then you can just hear the pads move slightly. You can also see on the inside on the caliper where the pads have worn a very slight channel into it. I have found a link to an old thread on the old site about how to modify the spring retainer for the pads to make them sit hard against the front edge of the caliper to eliminate this movement and will probably try that tomorrow.

When the front wheel is off the ground then there is a little bit of resistance from the pads as expected but there does seem to be a slightly tighter spot... Warped discs I hear you say... but how when they are brand new and when the problem was the same before with the original discs..

So the next things to try are:

1) pad retaining spring mod
2) Tomorrow I am going to tie one caliper out of the way at a time and take it for a small run to see which side the problem is on or if it is both sides that cause it to pulse.
3) Remove forks and use a file to make sure caliper mounting points are completely level and that when I painting the forks I haven't put it to thick on one mount making the caliper sit slightly squint (they look fine to the eye but guess a tiny fraction could cause a problem)
4) possibly new bearings but there is no noticeable wear on them and they've done less than 5k miles, they feel smooth to turn by hand and no vibration apart from when braking

I just don't really know what else to try and can't afford to just throw money at it. Anyone got any ideas?

Thanks,

Chris

[darrsi]

Oh my word, it's my nightmare all over again 

[Chris]

Yeah, was thinking that but can't be brake lines as the old rubber ones did it and still the same with new braided hel lines.

You modified your pad retaining spring didn't you? Got any pictures?

Chris

[darrsi]

I presume you've read my woes that I had for a long time?

I did all of what you have done......several times......and THE last thing possible to change was the brake lines, which worked.

The ones I had on were braided and looked fine, but obviously weren't.
I know you said you've got new ones but do not rule it out.
I don't s'pose you still have your old ones that you could try out perchance?

[Chris]

no, not got the old lines but like I said the problem was happening with them too.

Chris

[slappy]

Check the runout on the discs with a dial test indicator.

[darrsi]

Sorry Chris I was writing when you posted.
I did do the mod, but it obviously didn't help at all, and just becomes a real pain getting the pad pin back in, it's really tough to do.
It would help if your pads were chattering because they are ill fitting in the caliper, but otherwise the mod is unnecessary and won't help you.
If I can find them I will gladly send you them to try though if you want, rather than butcher yours for fun?

[Chris]

Thanks for that Darrsi. I'll see how I get on with other options but might take you up on that.

I will also try and check the runout. By eye it looks fine and it happening with two sets of discs (one set which is brand new) I can't believe it's the discs.

Chris

[darrsi]

Thanks for that Darrsi. I'll see how I get on with other options but might take you up on that.

I will also try and check the runout. By eye it looks fine and it happening with two sets of discs (one set which is brand new) I can't believe it's the discs.

Chris

I get home at 6pm, I'll look for them then.

[Chris]

Thanks Darrsi, much appreciated, don't go out of your way though.

Chris

[darrsi]

Thanks Darrsi, much appreciated, don't go out of your way though.

Chris

It's okay, I live there! 

[Chris]

Thanks Darrsi, much appreciated, don't go out of your way though.

Chris

It's okay, I live there! 

 

[darrsi]

Found them, PM me an address if you want them, I can have them in the post at work tomorrow mate.

[darrsi]

There's always the chance of a hotspot on a disc, normally caused by holding the front brake on when stationary, pad residue gets deposited on the disc through heat which will create a raised area for the pad to grab on.

[fazersharp]

There's always the chance of a hotspot on a disc, normally caused by holding the front brake on when stationary, pad residue gets deposited on the disc through heat which will create a raised area for the pad to grab on.

No actual help but I have always thought sitting with the brakes on would do some sort of harm but didnt know what. So long as the incline is not to much I sit with my right foot on the floor and my boots shin section behind the foot rest so I dont roll back

[darrsi]

There's always the chance of a hotspot on a disc, normally caused by holding the front brake on when stationary, pad residue gets deposited on the disc through heat which will create a raised area for the pad to grab on.

No actual help but I have always thought sitting with the brakes on would do some sort of harm but didnt know what. So long as the incline is not to much I sit with my right foot on the floor and my boots shin section behind the foot rest so I dont roll back

You're meant to use the rear brake when stationary, it's just not advisable to hold the front brake on for long for this very reason.
Saying that, if it's a windy day both feet are down and the front will get used.
There's different circumstances so no set in stone rules.

[fazersharp]

You're meant to use the rear brake when stationary, it's just not advisable to hold the front brake on for long for this very reason.

The thing then is that its foot off brake-- front brake on, then right brake foot down and left foot up to go into 1st.
Whereas me - into 1st - right foot up at biting point and - gone and I havent worn out my bulb 

[Sidewinder]

Hello bud, you sound like you know what you're doing so I hope I don't offend you by teaching granny to suck eggs!
I can only tell you of something that happened to me when I changed the discs on my car, when I was putting them on and doing them back up unknowingly I had a piece of rubbish on the back of the disc that although was a small tiny thing it was enough to cause that pulse you mentioned through the brake pedal, so after thinking the worst and how much is this going to cost I rang my mate who said he knew what it could be, he came round undid everything I done and took them off he cleaned both the hub and the back of the discs and showed me the dirt that came off of them he put them together and told me they had to be done up opposites just like a wheel (I didn't know that) and hey presto no more pulse and it never returned. It's just an idea and you may have already tried it, good luck in getting it sorted bud. 

[Chris]

I'll make sure and clean up the discs to make sure there's no deposits on there.

Thanks sidewinder, yeah, I made sure the surface on the hub of the wheel where the disc carrier sits was super clean and level after the wheel was powder coated so hopefully not that but that was the first thing I checked so good thinking  Amazing how something so insignificant can have such a dramatic effect on the brakes.

Chris

[darrsi]

Shit, penny has just dropped, i have read before about issues with powder coating wheels!


Here's an example, albeit for a car:


http://forums.mg-rover.org/showthread.php?t=358899

[Chris]

Yeah, that's why after they were powder coated I lightly sanded/filed them back to the bare metal on the hubs to make sure the surface was flat.

Chris

[darrsi]

Yeah, that's why after they were powder coated I lightly sanded/filed them back to the bare metal on the hubs to make sure the surface was flat.

Chris

I had my discs off so many times my hub surfaces were also spotlessly clean as well, i also bought new discs and managed to buy some very cheap used discs as well and kept rotating them on the bike in desperation to try and sort things out, as well as scrubbing the disc surfaces, and different types and makes of pads.
I have 98/99 forks on my 2000 bike, without the adjusters, which i personally thought were useless anyway, and i believe my wheel bearings were replaced too.
Oh, and the steering head bearings were changed too (not a fun job). You've not mentioned head bearings, i presume you've checked for any play?


When buying new discs it's very important to remove the protective film that's on the discs with brake cleaner until they are spotless, bit late now but thought i'd mention it anyway! You can try and burn it off by hard braking but can presumably contaminate the pads with it.
My calipers were serviced by me 2 or 3 times a year, that's why i got a bit good at doing it because it was so often. 
So, as you can see, a very similar, very frustrating scenerio. 

I still think the brake lines could be the culprit, in one way or another, but that's me probably being a little biased.  


Whilst i did all this myself, i also had 3 or 4 mechanics evaluate it too, and they couldn't figure out the problem either, it was 2 of my mates chatting who suggested changing the braided brake lines, but in fairness there was really nothing else left to suggest as it had already been done!   

[Chris]

so had a chance to try the bike with one caliper tied up out of the way and went for a little run and then tied the other side up out the way and went fro another little run.

Results are a little odd.. No pulse through the lever on either run but definitely a bit of rumbling from the front end enough to still shake the mirrors a bit. Wondering if this points more to front wheel bearings. I'm guessing that with both calipers on it's trying to pull the wheel either way causing the pulse through the lever as the brakes favour one side then the other. And with just one caliper on it isn't constantly trying to fight that force... It makes sense in my head anyway.

 Now, I do remember when I had the wheels powder coated that the front bearings were, what I considered to be very tight going in. Because of this when it came to fitting the rear wheel I sanded out the bearing seat to remove any primer from the powder coating process. So, it could be that the front bearings have been too tight... There doesn't appear to be any play in them on rotation while up on the jack or side to side (checked by holding top and bottom of wheel and then rotating wheel 90 degrees and pushing again etc all the way around). Head stock bearing also appears fine, no notches and doesn't settle in any position when front wheel is off the ground.

Have ordered new bearings for the princely sum of £8 so worth a try. Will remove old bearings and clean out bearing seats to make sure they are to bare metal.

Chris

[darrsi]

I find the simplest way to check if head bearings are maybe loose is by having the bike on the ground, push it forward a bit then pull hard on the front brake lever.
If they are not tightened up enough then you will hear and feel a knock.
Obviously if they were not torqued as they should be then braking force would cause a juddering sensation because of the play.

A bit like when you get a loose wheel on a shopping trolley!

[Chris]

Ok, will try that too. Thanks

Chris