Front Brakes Pulsing

[Jeffb]

I've got a '13 TTSE that I picked up last fall with 2800 miles.  I'm the third owner, and the thing is 4 years old, so there's no chance of any warranty.  When the front brakes started pulsing, I started searching the forum.  Since I had no warranty, and I didn't want to mess around with it, I just went out and bought EBC rotors and pads.  Guess what?  New rotors, new pads, still pulses.  I've seen someone suggest piston problems in the calipers, but that doesn't make sense to me (although, what else is there?).  At highway speeds (70-80 mph), if I lightly engage the front brake, it almost seems like a high speed clicking you can feel in the hand lever.  When I come to a stop, it's like something is out of alignment, and it grabs at the same point with each revolution of the wheel.  Any ideas?

[Coconut]

Use the SEARCH button for "bobbins" ... there are plenty of Topics about this !

Here's one of the latest : Front Brake Discs Warped

The front discs are "Semi-Floating" - they "float" on "bobbins" which are designed to allow the disc
to expand and contract, as they heat up and cool down, and prevent them from warping.

It seems that they are very prone to seizing up, which can mean the disc becomes seized
very slightly off centre / out of "true" and can exhibit the pulsing you ( and others ) describe.

I am sure that there are a number of Discs that have been condemned as "warped" and replaced
with new ones, when there was nothing wrong with them, other than seized bobbins !

Spray the bobbins with Brake Cleaner and physically rotate them in their mountings to free them up.

A suitable sized bolt with a washer under its head can be inserted through the bobbin,
then a washer and nut placed on the other side and tightened up - to clamp the bobbin.
A spanner or socket on the bolt head can then be used to rotate the bobbin and free it up,
or you could use a power drill to "carefully" rotate the clamping bolt if they are really bad !

This needs to be done to each of the bobbins on each of the discs.

In the Topic linked to above, I have mentioned that on my brand new Trophy
the bobbins can be rotated by hand by simply gripping them firmly between thumb and forefinger,
and rotating them - there is no detectable play when rotating them, and they rotate smoothly.

So that's an easy check to perform - if you can't rotate them by hand
then they need cleaning up and freeing off !

Once they are all free, and you've cleaned off all the crud etc that will come out
during the cleaning process, take the Trophy out on a good quiet road,
and carry out several heavy front braking runs, to re-centralise the discs 

Let us know how you get on !   

[Jeffb]

Coconut,   Thanks.  You missed that I replaced the Triumph rotors and pads with brand new EBC rotors and pads.  Before I did that, I did clean the bobbins, with no effect.  Since the original post, I've played some more.  With the bike on the centerstand, and the front wheel in the air, I grab the tire and rotate it.  It rotates freely like a mounted wheel should. However, when I let go, in one half of the revolution, the wheel will continue to spin briefly.  In the other half of the revolution, when I let go, the wheel stops turning immediately.  I'm beginning to think it's not brakes.  After mounting and torquing down the wheel, the shop manual says, "Check that the brake discs are centrally located to the calipers.  If not, apply gentle pressure to the fork to ensure the disc is centered with the calipers."  I don't know what this means.  Following the manual, everything is tightened down by now.  The only thing that comes to mind is when we were kids, we used to put our bicycle's front wheel between our legs, grab the handlebars and twist it straight.  Next step, I'm going to start pulling pads and see which caliper is grabbing the rotor.

[Coconut]

Hi JeffB,

I didn't knwo how long ago it was that you rerplaced the originals with the EBC ones,
hence the advice to check the bobbins.

"Check that the brake discs are centrally located to the calipers. 
If not, apply gentle pressure to the fork to ensure the disc is centered with the calipers."

I don't really understand that paragraph either, it's not at all clear what they mean !
( Page 16.8, Para. 8. within "Wheels and Tyres  Section of the Sevcie Manual )

In any event, even if the discs were not centrally aligned within the calipers,
providing the discs are running true they should not bind anywhere.

I'm thinking that this could be a Wheel Bearing issue 

At the point where the wheel seems to stop every time,
holding the wheel very lightly with your fingertips,
try gently turning it in each direction to see if you can "feel" any binding.

You could also try removing the pads completely and then spinning the wheel,
and if it still stops in that half a revoloution that you mention, at the same place every time,
you wiill know it's not a disc problem, and that it must have something to do with the Wheel Bearing !

Cheers 

[t552]

There have been cases where the disc face area on the wheel itself is not square to the wheel, or in other words out of true.
So remove the disc and use a "clock" to measure the surface area to see if it is flat.

[Jeffb]

Thanks t552.  It has certainly entered my mind that my wheel may not be true.  I'm not familiar with the procedure you suggest though.

[silverstripes]

When T552 mentions "clock" I think he is talking about a clock or dial gauge. This is as it says a gauge with a dail and calibrations in MM or thou (Thousands of an inch). It has a probe sticking out which drives the gauge. So the process is mount the gauge on the fork leg as this is solid and remains constant. Run the probe on the disk and then let the wheel rotate and note the variation known as run out.

If you do not have such and item then secure  a probe (Small screwdriver or similar) to the fork leg and just keep it off the disc say 1mm. Then rotate the wheel and see if this gap narrows or widens. You will then see if the disc (Rotor) is running true.

I'm am sure the engineers may have a better explanation. 

[earthman]

Did you check/clean the area of the wheel after removing the original disks? Years ago I made this mistake myself on a 4 year old bike, had similar braking problems,...removed disks and used a fine sanding block to properly clean the mounting surfaces. There really wasn't much for the eye to see but after doing so, braking problem disappeared