Bouncing Brakes??

[brainbug007]

I'm hoping someone can shed some light on this one.. The haynes manual for my motorbike said I should replace most of the braking elements after 2 years which I've done. So I put new pads, discs, lines & fluid in. Now when I brake it's a bit weird and hard to describe. At speed it seems ok but as I slow down (like when approaching a red light) and my speed gets down below say 10/15 mph, the front brake doesn't seem to work properly and the front of the brake bounces up & down on the forks so to speak as it finishes slowing down and the rate of deceleration doesn't seem very good. I'm wondering is this just something like the disc & pads wearing in? Or perhaps is this what people refer to as spongy brakes and there's air in the brake line?

[flyerncle]

Check the disc for runout as this will cause problems and it sounds like the fault you have.

[brainbug007]

Can't say I know much about what that is and the description on wikipedia isn't very good... any points for what I'm looking for?

[ayjay]

I agree -- take the disc off again and make sure its seated properly at all points.

[Talonmotorsport]

In plain English and not in text book terms it means that the disk could be mounted on the p#ss or it is not completely flat causing the feed back that you are talking about.

[flyerncle]

Should have been more specific,40 years in the trade is begining to tell.

Basically if the the disc does not run true with the hub (wheel ) it is bolted to,when you apply the brakes the pads will bounce on and off and the fluid will move back and forth up the pipe to the master cylinder giving the on off motion you describe as the clamping force is not constant.

[brainbug007]

Thanks for all the replys guys. I've taken the disc off & put it back on carefully 4 times now and it still hasn't resolved it. I was looking at the disc closely and it does seem to be warped slightly as there's a ring worn into the disc from the pads and on one section the ring hasn't worn in Suppose that's what i get for buying a cheap replacement off the bay. Not only that when I went to put it back on the last time, one of the bolts has snapped off when I was torqueing it up Proper cheap bolts they use on these bikes. Even though it had an 8.8 stamp on the top of the bolt, seems unlikely it's actually a 8.8 bolt if it snapped before torqueing up to 10nm (which seemed awfuly low for m6 bolt?)

[flyerncle]

Torqueing a bolt will increase its length causing it to stretch and this is the root cause of failure of a reused bolt in some cases.

Jap bolts tend to fail if used more than once,how acurate is the torque wrench.

[brainbug007]

Good to know I guess that they won't hold more than once. I would hope my torque wrench is reasonably good as it's one of the professional ones from halfords. Is it right though that an m6 should only be tightened up to 10nm as that seemed awfully low for holding a brake disc on?

[flyerncle]

Quite possible and I would replace them with something of a known and better quality.

the screws that hold the injectors on some Audi diesel engines are unbelievably small for the job and so is the torque,about 4 nm or so but they work.

As for Halfords "Profesional " I would not get too excited,known makes are possibly better.