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Brake Vibration (Causes and solutions)

Many riders confuse rotor warping, or warped rotors, with a condition called DTV (disc thickness variation). DTV occurs when a vehicle brakes are serviced and the brake rotor has runout in excess of 0.08mm . This runout causes the pads to contact the rotor when the vehicle is being driven "off brake" and after 3-4000 miles( Sometimes Much less), a thin spot develops on the rotor. The rotor runout itself does not actually cause a vibration. It is the effect of the thickness variation of the brake disc or brake rotor under braking that causes pulsation. Even small thickness variations such as 0.012mm or 0.0005" will exhibit itself as pulsation. A warped rotor is a very rare occurrence and in many years in business, we have seen no genuine cases of warped brake rotors.

The general guideline is that if the vibration happens immediately after install, there is a quite severe runout problem that needs looking into. Brake discs or rotors should be mounted on flat smooth rust and dirt free hub flanges without the use of coppaslip which includes small particles which have the same effect as dirt. Remember that even a small particle of 0.001" under the rotor surface can cause a deviation of 0.005 at the pad contact point.

 

Semi floating and fully floating discs are designed to have some "Free" movement to allow for heat expansion of the rotor.  

 

An Example

 Your wheel turns once every 1.9mtrs thats 842 turns per mile or

842104 turns per 1000 miles. If there is any runout Irregularity, on every turn of the wheel,

a minute amount of material is taken off the high spot as the caliper does not retract the pistons fully

each time the brakes are applied. In Time this will wear a thin spot altering the Parallel flatness

which then CANNOT be remedied, only by stripping and Re-machining the Rotor

Even a particle of DUST can measure .0005" 

 

If the vibration happens after 3-4000 miles and sometimes Much less, this is a clear indication that DTV has occurred which is not a warranty condition. The only solution for this is to remove the brake rotor, have it re-machined if possible, or replace it with a new rotor.

Every case of "Warped Discs" reported to us has been caused by NOT checking the Run-out when fitting.

 

Spring "Anti rattle" washer broken?

What causes washer to fail we cant be 100% sure but it is probably caused by uneven pressure of the opposing

brake caliper pistons. This puts too much pressure on one side of the disc causing premature washer failure.

 Every brand of brake discs on the market has this problem with the exception of Brembo (their washer is a special design which

is unlikely to fail). We have replaced rivets in Galfer, Braking & SunStar and others which have ALL suffered from anti rattle washer failure.

This is regarded more as a Caliper problem than a disc problem. 

 

Are Broken Anti rattle washers dangerous?

Not necessarily, its not as if the disc will fall off. It is still being held on with the Rivets which cannot come off.

Years ago Brembo used Aluminium "bobbins" on thier discs without any anti-rattle spring washer, this was known as

a "Fully Floating" disc. Mainly used for racing as it rattled and was very noisy for road use. Also the "Bobbin" as it was known then

was fixed with a circlip so there was a chance it could come loose and the bobbin could fall out. These are still used in racing as the 

discs are inspected before and after each race. This dosent happen with a road bike and its only when something goes wrong does anyone

examine the brake disc. 99% of front discs for motorcycles are "Semi Floating and have the spring washer. A small  % of discs are solid

such as Harleys Etc. Modern day bobbins are now called "Rivets" as they are actually riveted onto the disc also they are now made

from Stainless steel and not aluminium any longer.

 Rear Discs are 100% solid discs.  

 

 

Brake pad and Disc fitting instructions.

Brake pads and discs are important safety items and should be fitted by a competent mechanic.

Keep friction surfaces free from grease or other fluid contaminants which will reduce brake effeciency.

Fit pads with friction material facing the disc. Check calipers for free movement when changing the pads, badly worn or

grooved discs should be replaced by a competent workshop. Worn discs extend bed- in time and can cause severe reduction

or even loss in brake performance.Inspect brake pads regularly and replace when 2 mm of friction material remains on the

backing plate. Brake fade occurs more easily with worn pads.

 

When fitting new discs they must be checked to see if they are running completely true by use

of a DTI or Dial runout Gauge.If this is not done

Eventually DTV (Disc Thickness Variation) may occur which in turn will cause excessive Vibration and Judder.

 

Check calipers for free movement when changing the pads. This is most important and one of the

main causes of "warped discs" Or DTV is sticking caliper pistons.

Brake pads must be "bedded in" by starting with light use (Except in emergencies) until 80%

contact between pad and disc has been achieved, normally achievable within 100 miles or normal

road use. Motorway riding may take longer for brakes to bed in.

 

 

                                                                                                                              The final word on brake judder and “warped” discs.

                                                                            In simple terms brake judder is experienced by the Rider of amotorcycle as a pulsation through the brake lever

 or vibration of the handlebars under braking. The above symptoms can be frustrating,

disconcerting and result in rider complaints about “warped” brake discs. The phrase “warped brake discs”

is used almost universally by uninformed vehicle owners to describe the cause of brake judder. The actual

underlying causes of brake judder are, without a doubt, the most misunderstood aspect of automotive braking.

While it is possible for a brake disc to “warp” or distort (i.e. change shape) - disc distortion is responsible for

relatively few brake judder complaints in our experience. The overwhelming cause of brake judder is a

condition called Disc Thickness Variation – period! In other words the disc develops a lack of parallelism

between its inboard and outboard friction surfaces. I say, “developes” because even discs that are machined

to the very tightest tolerances during production can easily develop Disc Thickness Variation (hereafter

referred to as: DTV) due to incorrect fitment or driver abuse.

When the brake pads are pressed up against a disc that has developed DTV they will pass over a series of

thinner and thicker areas on the braking surface of the disc in rapid succession. Considering that the brake

pads are being pushed together with substantial force they will be forced down into the ‘cavities’ or thinner

areas only to be kicked back violently when reaching the bumps or ‘thicker’ areas. The frequency of this

‘bouncing’ action is typically over 100 Hertz when braking from highway speeds of around 70 mph. This

results in pulses that are transmitted through the caliper pistons, via the brake fluid to the rider, who

experiences them as brake judder..

Causes of DTV

Once you understand the causes of DTV it becomes clear that brake judder problems can be almost

completely eradicated by following a few simple rules. So, what causes DTV? DTV can be caused by a

number of factors including disc fitment errors, driver abuse and poor manufacturing processes. The causes

above are mentioned in order of their likelihood of occurrence.

DTV Cause No. 1: Failure to ensure that the mounting surface of the brake disc and hub are perfectly

clean prior to disc fitment.

One of the most common causes of DTV is the failure of the fitter to properly clean the mounting surface of

the disc and the vehicle’s hub. The smallest fragment of dirt or rust scale caught between the mating

surface of the disc and hub is magnified as you move towards the outside diameter of the disc. This results

in an unacceptable amount of axial run-out (inboard-outboard movement) at the friction surfaces of the

brake disc (the areas of the disc that come into contact with the brake pads). To put this into perspective,

the maximum axial run-out measurement that Blackshadow-uk will accept on a newly fitted disc is 0.08mm

(measured in the centre of the friction surface of the disc). A single spec of rust scale measuring only

0.05mm (50 microns) in thickness trapped between the mounting surface of the disc and the hub can easily

cause the axial run-out value to exceed this tolerance

 

Blackshadow discs are made of a proprietary high carbon content SUS420 stainless steel.

 This steel has many great characteristics but due to the carbon content of the steel.

 (which gives the rotor better memory retention and strength) some surface rust may occur.

To maintain your warranty, you must use New brake pads.

 Always use Factory Torque settings.

 We recommend getting your wheels rebalanced since many of our discs do not weigh the same as OEM units.

Break in period is normally within 100-200 miles Depending on road conditions.

 Do not over heat the brakes as this can cause irrepairable damage to the brake system.

 

 

Brake Drag and wheel binding?

 


Excessive brake drag is usually caused by one of several possible culprits:

1) Warped backplates;

if your pads aren't flat, you'll definitely experience greater brake drag as when the lever is released and the caliper pistons are

retracted from the pads, then you will still have rotor/friction material contact since the seals can only retract the pistons a very small fraction.

2) Misalignment;

If the wheel/caliper/fork assembly alignment is off, binding of the assembly

will often occur (bent axles and triple-clamps will be a problem here too).

This is particularly true if assembled and tightened while on a front wheel stand (attaching from the fork bottoms). Best way is to have everything

assembled but not tightened on the stand, then let it down and bounce the fork/wheel a few times to center everything, then tighten.

3) Poor Piston Retraction:

Poor piston retraction can be a major culprit and cause of rotor over-heating and distortion, accelerated pad wear,

and glazed friction surfaces (creating brake squeal, etc.). Check to make

sure all pistons are not only moving freely in their bore, but are retracting

as well (when the lever is released). You'll need to block the other pistons to isolate the individual your checking, alternate

one at a time. If then suspect, replace all piston seals (we recommend this regardless with a used or suspect caliper).

4) Excessive deposition layer build-up:

all friction materials impart a thin transfer layer on the brake rotors pad track. This is a normal part of the bed-in process. But some transfer more than

others, creating an excessive and/or uneven build-up that can cause problems with brake drag, brake judder and deteriorating performance.

 

 

 

 

Stainless steels come in roughly two types that are defined by the atomic structure.

Austenitic ones typically have high alloy content, low carbon content and exceptional corrosion resitance - but tend to be softer so less suited to high strength applications - they have a 300 designation for example 316L is one of the commonest here (this may not be true any more, this is the old BSI designation from a few years ago and many people are familair with it)

Ferritic ones (and the related Martensitic ones, this is the type we use) are very strong but have more of a tendancy to corrosion - they also respond well to heat treatment so can be made much harder, with a consequent reduction in corrosion resistance. These are designated as 400 series (We use 420) 

 

We have tried to give as much Information as we can to help you. Some of the Information

May have been Duplicated on our web pages. More Information is better than NO

Information.

If you cant do the work yourself or you dont have ALL the correct tools or Knowledge to complete the work correctly please have the work done by a Qualified Motorcycle Mechanic.