Warped disc.

[j.newton1]

I noticed the rear disc had slightly gone out of true, because I could feel a pulsing from the brake lever. The options were, new disc, have the disc skimmed, or possibly try it in a press. None of these appealed to me, so I had a look on the web. A biker it the USA had in the past had the same problem, which he resolved in the following way. (NB. If you have more than your fair share of mechanical sympathy please do not read on ) You find the high spot of the distortion in the disk and mark it. You then find which way the high spot faces.(my high spot was towards the wheel).Take a fibre mallet and a short piece of wood. Place the wood though the spokes( or gaps if you have a cast wheel), place the wood on the high point and hit it with the mallet. Only hit hard enough to move the metal, without breaking it. I followed these instructions and with one hit of the mallet my disc is now running true. I have since ridden my scooter and pulsing of the brake lever has gone.

[poldark]

Well I guess it's one step on from the "just hit it with a hammer" approach!

Good result & cheap too.

[gn2]

The trick is knowing what weight of hammer to use

[SpikeOne]

You might find that it comes back again as the stresses release themselves. But hey ho, give it a go...

[michaelphillips]

Well I guess it's one step on from the "just hit it with a hammer" approach!

Good result & cheap too.

they say that if you keep the brake on, after a stop when you are then stationary, can cause warping of disk, its because heat is trapped in this position.
what do you mean by the words ... You find the high spot of the distortion in the disk and mark it

sorry not with it today

[michaelphillips]

general info:

If your disc is warped or bent you should be able to feel a pulsing back through the brake lever as the brake is applied. If you can, you will need a dial gauge and mounting stand to measure it and find out by how much.

To measure it, leave the wheel in the bike and raise it off the ground with a suitable stand and follow all relevant safety procedures to ensure both the bike and you are safe!

Now set up the dial gauge and zero it whilst just touching the disc. Then move the wheel round slowly while watching the gauge and note how far the disc is out of true. On a fixed disc if it is more than about 10 thousands of an inch or 0.25mm out then it is either warped or bent. With a floating disc you need to allow up to twice this to allow for the disc float. Less than this isn’t enough and is sometimes just production tolerance.

Whenever they are measured out of tolerance most people assume the disc is warped. This is because the term ‘warped’ is known to relate to discs so is used to mean ‘not flat’ rather than truly warped. Warping is, and can only be, caused by heat! To find out if your disc is warped first of all you need to look for discolouration. When a disc gets hot enough to warp it will change colour from its normal silvery colour to a combination of blue, yellow and brown. Not just in one spot but all over the disc. The disc face can do this as well as the disc edge. This can happen because the disc is used in an extreme situation such as racing, track day riding or stunting. It can also be caused by rider error if the rider is putting the brake on without realising it. By leaving their foot on the brake pedal for instance.

Then lastly and the street riders favourite, is sticking callipers caused by lack of maintenance. If the calliper sticks and the pads are constantly touching the disc then the constant friction will send the temperature sky high and this can happen very quickly. With a quality disc these are really the only ways you can get enough heat into a disc to warp it.Cheap low quality discs will warp at much lower temperatures than high quality discs!

If your disc isn’t warped and measures out of tolerance then you have a bent disc. A bent disc is a completely different problem. The disc remains the same silvery colour but is no longer straight or flat. This is usually caused by some sort of impact. The infamous ‘disc lock’ is a very common cause and has probably doubled the number of discs sold! Far more common though are bent discs caused by tyre fitters. Applying pressure to the side of the disc, whilst fitting a new tyre is by far the most common cause. It even happens in World Super Bikes believe it or not. The only cure is replacement. Better still, if you remove the disc whilst the new tyre is fitted and refit it afterwards it won’t happen!

With a high quality disc, general road riding will never produce enough heat to warp the disc. Perhaps with a fully loaded Harley Electra Glide, with ‘generous’ rider and passenger being ridden enthusiastically down the Alps with fixed discs you might manage it. Short of that it just isn’t going to happen and if the disc truly is warped it is almost certainly being caused by a sticking calliper.

If a disc is warping because of extreme use, such as racing or track riding, then the only thing you can do is replace it with a stronger one. Nobody will guarantee a disc against warping in racing but without a doubt the strongest discs out there are Brembo. Winners of practically every major race series practically every year!
- See more at: http://www.biketorqueracing.co.uk/btr-t ... jLfOe.dpuf" onclick="window.open(this.href);return false;

[johnp]

Sounds like a good idea but an idea which also can go wrong.

[MrGrumpy]

Sounds like a good idea but an idea which also can go wrong.

True, but if you your repair goes wrong, its not a major issue as the disc is knacked anyway.

[Steve_D]

Not a major issue if a bodged brake repair goes wrong??? I cant think of many issues more major on a bike!

Personally, I think that bashing a brake disc to straighten it out is a very dangerous practice and you are risking your life to save a couple of quid. What if your 'knocking it into shape' puts a hairline or virtually invisible crack in the disc? When you really need to anchor on and the disc under its greatest pressure you may find it shatters. Too risky for me but good luck anyway and I'll keep my fingers crossed for you.

[michaelphillips]

Not a major issue if a bodged brake repair goes wrong??? I cant think of many issues more major on a bike!

Personally, I think that bashing a brake disc to straighten it out is a very dangerous practice and you are risking your life to save a couple of quid. What if your 'knocking it into shape' puts a hairline or virtually invisible crack in the disc? When you really need to anchor on and the disc under its greatest pressure you may find it shatters. Too risky for me but good luck anyway and I'll keep my fingers crossed for you.

like going back to the stone age... take disk off ... put it on barbie for half hour, then bash it for ten mins....
i have to say, i hope your rear wheel to crankcase is unaffected, best to buy a new disk and use organic pads which wont heat the steal disk to extremes of warping, with any luck you have survived this remedy.. to reflect