mechanical advice for motorcycle please?

Question

i am getting a major shuddering from front end when applying front brake the harder brake is applied the more severe shuddering is. have an idea what the problem is. brake disc is ok brake pads ok. any help/advice much appreciated.

other possible defect have a leaky shock absorber/fork leg on right side.

could this cause an inbalance in front forks resulting in shudder

Answer 1

I'm going to assume that you mean actual SHUDDER,,,and not vibrate,weave,wobble pull,pulsate,oscillate etc.

SHORT answer:Clean & Lube the brakes,,& Deep Clean Rotor&Pads
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Shudder,,,is a vibration-LIKE feel/sensation from the wheel assy,,that's NOT accompanied by pedal/lever pulsation.
You'll feel it in the bars,,not in the brake lever.

Primary Cause is NOT disk warpage,,,that creates Pulsation which IS sensed at the actuation lever/pedal.

It's a matter of "Hot Spots" on the disk,,,most of the time.

If You look Closely in bright light,,,and viewing from different angles,,,you'll see "Leopard Spots" on the disk surface.
It can be spots or streaks,,or coloration,,or texture differences.

The FRICTION COEFFICIENT of pad/rotor junction fluctuates,,,giving a similar effect to "Pumping the Brake".
But since there's NO Difference in Apply Pressure,,,there's No Pulsation feedback thru the control.

If you've ever experienced ABS activation Shudder,,it's precisely same effect.

In ABS(anti-lock brake sys)---the Apply Pressure is modulated every few degrees of rotation.
They DISTINCTLY shudder

In Heat Checking,,,Spots on the rotor become VERY HARD.
As the pads sweep the Rotor under a given,fixed amount of PRESSURE.....
The pads "SLIP" across the spots they cannot "Bite",,,and follow immediately into a Normal area which they CAN bite.

It Can also be Produced by Pads themselves which have become contaminated,,spottingly Glazed,,blah,blah,blah,,lottsa different stuff can happen to pads.

Sticky Pads in the calipers can cause it.

Sticky Caliper Piston ,,,Can,,but it's rare.
Usually Piston Induced Shudder is from extreme Wear in Caliper Bore or Piston...
Where they are no longer concentric,,,,they kokk in the bore and "Bite the piston".
(freaking Yahoo dont allow the word kokk,,,c-o-c-k)

Under apply pressure,,,ALLLLLLL Pads experience a certain degree of Knock-Back.
So the caliper/piston/Floating disk,,,whatever facilty is provided to accomodate that,,,DOESNT.
It STICKS,,,which creates a Alternating Bite/Release friction junction.

Any "Stiction" in the Floating system causes Apply Pressure to fluctuate at Friction Junction.

Less-Than 100% of apply pressure is being applied to Pad/Disk contact.
Because SOME is spent on overcoming the Float's STICTION.

More Actuation Pressure is required( I'm talking a MINUTE,Infintesimal amount),,,,but MORE is MORE.

You "Over-apply",,,and when any runout RECEDES,,,,the Piston Pops OUT,,,dropping apply Pressure.
Then when runout Advances,,,,,Disk is "Mechanically " applying ITSELF to the pad,,,,the way a Camshaft acts against a Lifter.
It's Doing so against a Static Line Pressure.
But,,,also against a Flexible INPUT Pressure(Your foot/hand)
If it happens to overcome that by .001 or .002",,,
Apply force DROPS.

Rotor Camming INTO Pad cause Friction to Rise
Rotor CRAMming into Pad--Fricton Drops because it finally Overcomes the STICKtion
Rider compensates----including an amount to overcome the Stiction........and the Cycle of Alternating apply pressure ensues

It creates a High Frqequency Vibration,,,and not a typical "Warped Rotor PULSATION"
Technically---it IS a pulsation.

But because it's NOT due to wide-runout over several degrees of rotation----you dont Feel it as a Yeng~Yang/In-Out Pulse at the pedal.

It's SHORT-Range wobble,,,over a very,very FEW degrees of Rotation.
And there's No Relief ,,,cuz the Float System cannot accomodate it .
Line Pressure actually Rises and falls

Instead of a sine- wave~~~~~~~~~~~~ from Runout Pulsation,,
You get a jagged,hi-freq sawtooth from PRESSURE MODULATION >/\/\/\/\/\/\/\

Shudder,,,not Pulse.

The Fix is to NOT target any specific area/problem.
Forget trying to isolate Exact cause.
Reason Why Not???
"Which Came First,,Chicken or Egg??"

Did Rotor Checking/HotSpots instigate a WEAR SPOT in a tiny range of piston travel.or float assy bearing point?.
Or Vice Versa,,,did float Stiction cause Rotor HeatChecking?

Simplest,Quickest,Cheapest,Most Certain approach is:
*Clean and Lube Calipers properly.....obviously,,inspect for abnormal wear & address that appropriately.
*Might as well replace the seals
*Dress the Rotor and Pads properly
*If Rotor happens to be a Floater,,,,deal with it's carriage &use correct lube

Easiest way to clean the rotor,,,is to make a sanding block from 1x2 lumber.
Cut 2 Pieces to a size that spans a Chordal Section of Rotor,an "inner and outer".
Drill hole through each end,,,put a Bolt/Nut to clamp them together.
Wrap them with 180Wet/Dry,tape it,staple it,,whatever.
Clamp the Rotor between your 2 sanding Sticks,,,
Let them butt against Fork Leg,Caliper,,whatever...
Spin the Wheel

Much more Uniform and Easier than Hand Sanding.
You need to take OFF metal,,,not merely "deglaze"
So,,,cut the livin' $#!+ outa the disk,,,6~8~10 Rotations...
that'll knock of 1~2 thousandths.
Switch Paper iif it gets "too Quiet".

Then before removing it,,,Makes a Couple or 3 Turns while Soaking it with Water.
"Wet Sand" for a better finish and to begin the cleaning

Take to rig off,,,,get a flat file and cut the OD Corners at 45~60*
Just Spin the Wheel while holding the file against it.
JUST the O.D. CORNERs.
If theres a factory Bevel or Blend from Disk Face to OD,,,,
Just use one of the sanding sticks & a few spins to make sure theres no edge resulted fron your sanding the disk.

It's easier than it sounds,,,all takes just a few minutes to prep the disk,,,even including Tool-fab time.

You MAY have to Replace the Disk,,,
But usually Not unless it's got a LOT of pre-existing wear.
Or extraordinarily heat checked.
If you see distintly Dark or Glassy Streaks/Spots,,might be rotor Replacement time.
Most WILL clean up,,,if you Cut them,,,and not merely scuff off the shiny surface by hand sanding

Clean it well with soap and water,,& rinse well/towel dry.
Wipe with WD40 on a towel to stop it from rusting till you can run it.

............................................................
Suspension faults will not produce Shuddering.
And certainly Not presuure variable symptoms.

There are all sorts of things to fool with,,,and even though many faults will masquerade via it's symptoms as being something else,,,,
keep in mind that each fault has it's own genuine & distinct syptoms.

Try whatever's easiest or sounds good to you,I'spose.
Could well be something else.

But if you continue having trouble with the Brakes,,,
The Brakes are what's going to need to be fixed

If it IS actually Pulsing the lever,,Go Shopping straight away for a Rotor.

But if actual Shudder,,You MIGHT luck out and be able forestall the expense of Rotor Replacement till it's actually needed.

***The RISKS of Shudder.
It's well known,,but while I'm babbling i might as well repeat it.
It the usual old Temp Flare>Sudden Fade thing during Braking.
When component temps suddenly Flare during an application to beyond the design/specs' capability.
"Trying to Stop 200 mph advance with 100mph rated brakes" effect

Even a 25% overheat at 50~60mph can be quite a thrill due to how instantly it occurs,,,after you've judged your stopping distance /shut off point and all seems to going well initially.

Not as severe & Sudden as popping a hydraulic line or seal,,,
but if approaching a busy intersection of cross-traffic at 40~50,,
The difference in effect is somewhat Moot.

Especially on Brake Probs,,,don't spend Too Much time "Chasing Ghosts" before fixing the Brakes...
Or ya just might catch up with some.

Good luck,,hope you get it sorted out & working well.

Answer 2

Unless you checked the rotor with a dial indicator, it could be warped enough to shudder and not appear warped to the naked eye. Is there any type of foreign substance on the pads? Also check the axle nuts for tightness.

Answer 3

Strange...severe shuddering from the front end usually indicates a bad disc or bad pads...is it possible the front wheel is slightly out of alignment? That's the only other thing I can think of...

Answer 4

Quite possibly if you do frequent hard braking you may have warped the rotor.

Answer 5

check your head race bearings at the frame ( Ithink the Americans call it the "triple tree") had a similar thing happen on my old BMW

Answer 6

check wheel bearings