Problems with a Wavey disk.

Akiraprise · Nitrous Nuisance Joined: 31 Jan 2005 Karma :

Hey, I've been having so much problems with my rear wavey disk on my rs125, here's the problems:

I fitted the wavey disk, and every time I brake theres a REALLY powerful wobbly feel through the pedal, I think that's due to the waveyness- of the disk, however it's so powerful I can barely use it to brake.

Next thing, my retaining clip snapped and the pads were free, got caught in the caliper in a stupid position and completely wrecked the disk, burnt pads and metal score marks everywhere.

The garage then grinded the disk down so it's smooth, and tightened the bolts (they came out) but it's still really dodgy.

I've taken the caliper off, cleaned everything, new pads, re-bled the system, also new pin, circlip and retaining pin.

The pedals still got SO much travel though, and barely any brakes. It's realyl frustrating, please help - what could it be?

16,000km RS125 Racing - if it's any interest

TA!

G · The Voice of Reason Joined: 02 Feb 2002 Karma :

You say 'RS125' Racing, I presume this isn't a GP bike as you give the 'mileage' in distance.
I'm also presuming it's not actually a race bike, so is just a road Aprilia RS125?

If there's loads of travel in the pedal, then it probably needs to be bled 'better'.

Wavey discs shouldn't give an odd feeling - they should be just as smooth as normal discs.
If you're still getting this, there's probably a problem somewhere else.

RI_HA · Spanner Monkey Joined: 11 Mar 2006 Karma :

im no expert but wavey disks?

do you mean the disc feels wavey instead of smooth?

if this is the case i suggest you bin them and have them tottaly replaced as they will be warped, this is quite dangerous and probably why you are getting so much shudder when you break.

Black Knight · World Chat Champion Joined: 22 Feb 2005 Karma :

Wavey discs are simply a straight swap. TBH is unlikely you would notice any difference in a road application.

Sound like something hasn't been fitted correctly to me.
____________________
Where does a turn end? 'Where you can do anything with the gas you want to, where you are brave again, where your attention is free from the turn, where you are sure you can do it better next time; that's the end' - Keith Code.

veeeffarr · Super Spammer Joined: 22 Jul 2004 Karma :

RI_HA · Spanner Monkey Joined: 11 Mar 2006 Karma :

cheers toby, didnt know they were an actual name of a disk Embarassed

I thought he meant that they were actually wavey as to no be flat like brakes should be

i stand corrected Thumbs Up

veeeffarr · Super Spammer Joined: 22 Jul 2004 Karma :

Akiraprise · Nitrous Nuisance Joined: 31 Jan 2005 Karma :

Not meaning the disk itself is pitted, I meant the disk is of a wavey kind, like Toby posted.

And the name 'RS125 Racing' name is the model, ie Extrema, Racing, and that new one. It's a road bike, not a GP bike lol.

The garage is re-bleeding it tomorrow.

Are the pads supposed to be a little wobbly when not pressed into the disk

Wavey disks: They look cool - the main reason I got it Razz

, heat dispersal and less rotating mass.

finpos · World Chat Champion Joined: 13 Sep 2005 Karma :

Suggested solution:

1. Take tarty wavey disk.
2. Throw in bin
3. Replace with properly manufactured/tested oem item (or pattern part)
4. braking harmony restored.

kids these days etc.

finpos.

Kickstart · The Oracle Joined: 04 Feb 2002 Karma :

Hi

Suspect that there is air stuck by the brake light switch banjo bolt, which is the highest point in the system on the RS125.

Does sound like the disk is warped. Possibly related to using the disk when it was not bolted in place correctly.

Main advantage of a wavey disk is mean to be that they slice off the top layer of the pad. Doubt they are any better for heat dissapation.

Pads should have a tiny amount of play in the caliper when the brakes are not applied.

All the best

Keith
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Traxpics, track day and racing photographs - Bimota Forum - Bike performance / thrust graphs for choosing gearing

Guest · Brolly Dolly Joined: 22 Apr 2004 Karma :

Check that the mounting faces of the disc and the wheel are scrupulously (sp?) clean - any bit of crap trapped between the two will throw the business area of the disc out of true and provede the symptoms you describe.

They might look good but any improvement over standard discs is imagined I reckon - fashion statement only Wink

Akiraprise · Nitrous Nuisance Joined: 31 Jan 2005 Karma :

I'm going to give Kickstarts and Guests advice a go, both seem very plausible.

I presume to get that air out I can't just bleed the brakes more, but have to take that part off, and put it lower than the caliper? Would that work or's that just a plain stupid idea - I haven't looked to see if that's possible yet though.

About the disk being warped - I asked the garage this, they had a quick look at it and said they doubt it's warped, but will do some test to make sure, it's i think around a centimetre thick steel, so would be very hard to warp from just the rear brake? Although the loose screws wouldn't help.

Guest - That's quite a good point actually, I cleaned the wheels whilst they were off but didn't really check that region, I think they were clean, but could've got loads of crap in with the loose bolts.

I shall see tomorrow - it's going back to the same garage and they'll hopefully sort it FOC, I'll keep you all updated.

element · World Chat Champion Joined: 23 Jan 2006 Karma :

if the disc is warped youd feel pulsing in the pedal... You'd feel the the wheel binding when using the brake too... Dead easy to check... Bike on center stand and spin the back wheel while looking at the disc spin in the caliper Smile

(might want someone to hold the front on the bike mind)

I wouldnt dismiss the possibility of a warped/bent disc because it sure does sound like it..

Smile

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BFG · Brolly Dolly Joined: 14 Feb 2005 Karma :

Warp test -
Duct tape a pencil firmly to the swing arm so the point is close to the outside edge of the disk and the pencil won't move.

Get the back wheel off the floor, and spin the wheel by hand. Look at the distance between the pencil point and the edge of the disk. If the disk looks like it going in and out, it's knackered. Smile

Kickstart · The Oracle Joined: 04 Feb 2002 Karma :

element · World Chat Champion Joined: 23 Jan 2006 Karma :

Guest · Brolly Dolly Joined: 22 Apr 2004 Karma :

element · World Chat Champion Joined: 23 Jan 2006 Karma :

Kickstart · The Oracle Joined: 04 Feb 2002 Karma :

Hi

Brake fluid is bad for getting lots of tiny bubbles if you shake the bottle before use (DOT 5 is even worse for this). Suspect that given time these bubbles join up to become visable ones, possibly helped by the system being under pressure. I cannot see how when it is just under pressure the light air will sink to the bottom of the system (and if it did you would never get it out of the system and the bleed nipple is on the top of the caliper normally).

All the best

Keith
____________________
Traxpics, track day and racing photographs - Bimota Forum - Bike performance / thrust graphs for choosing gearing

finpos · World Chat Champion Joined: 13 Sep 2005 Karma :

The theory behind the tie-back-the-brake-lever thing is that overnight all the little air bubbles gather and rise to the top i.e. into the master cylinder itself. Then when you release the lever in the morning, the collected air gets flushed into the reservoir.

Not sure how well it works - especially if you have dirty great air pockets in your pipes as opposed to little bubbles dispersed throughout the fluid.

finpos.