Pulsating new front rotor

gatsby

gatsby

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Hi,

I recently installed a new rotor, and new pads. I am getting pulsating when I stop. It appears to be seated properly on the hub. Does the new rotor need a run in, or am I missing something? It is a vented Girling. Thanks!
Gatsby
 
gatsby said:
Hi,

I recently installed a new rotor, and new pads. I am getting pulsating when I stop. It appears to be seated properly on the hub. Does the new rotor need a run in, or am I missing something? It is a vented Girling. Thanks!
Gatsby
Click to expand...
I assume it is cross drilled and floating but not "vented"? Vented usually refers to two braking surfaces separated by radial webs between them, allowing for air flow for cooling.

Have heard that original type Norton rotors can need to be test fit against hub and rotated to other bolt alignments to get best flatness to hub.

With floating rotors, sometimes the spindles are too stiff to allow proper centering. Try manually moving disc at each spindle to work them a bit.

Also heard some Lockheed calipers and rub on the floating Girling type rotors and need a little clearancing where the spindles rub.
 
Fellow Canuck . Appears to sit against hub is not good enough . Could be former rust or particles in there to create a questionable seating home situation for the disc . You must be scrupulously clean . Try again .
 
Did you clean the new disc with brake clean ? , otherwise get a micrometer and measure around its diameter and see if the thickness is the same if it's not , maybe return it this causes pulsing ..A small amount of measured run out measured with a dial indicator, of disc is ok for pad knock back , maybe a couple of thou , this wont cause pulsing .To run in pads and disc , do approx 10 60mph down to a slow speed, not a dead stop as you can warp the disc , this general info .cheers
 
As per Torontontian's advice make sure disk and hub are clean, and there are no raised surfaces around the holes in the hub and disk. Hand run a countersink etc remove any raised edges and burrs.

If you have a dial indicator, check the runout.

If not, unbolt the disk and rotate it one bolt hole at a time, retightening each time. You will probably find one location which has lower runout than any other. Ride the bike and see if it is any better. If not, you probably have a warped disk issue.
 
Pulsing brake lever usually means the disc is not parallel. Check all around the disc with a micrometer. Should be the same reading all the way round. If not, the disc needs truing up. I have come across this many times with second hand, chrome worn discs, and occasionally, with new discs. Some of which are supplied thicker than what was originally fitted.
 
As already stated
Make absolutely certain the mounting faces are clean
If they are try a dti guage on the hub face and if that is true with no high spots it's your new disc at fault
What's the history of the bike? IE was the old disc ok?
 
Discs need to be tightened down evenly and finally torqued in a "crucifix" manner and now circular....
make sure all the mounting faces are free from dirt. debris etc & if you have access to a clock gauge check the run out
I purchased my drilled disc from RGM and fitted without issue
 
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this is a floating rotor check the stainless bobbins are not tight or fouling on the caliper mouth
 
Don't forget this is a Wassell part... runout is by design!

Joking aside, I had spacing issues, which was put down to a 'bad batch' - they offered to swap it out for another, but I didn't fancy chancing it so went back to a standard one instead.
 
Hi,

I recently installed a new rotor, and new pads. I am getting pulsating when I stop. It appears to be seated properly on the hub. Does the new rotor need a run in, or am I missing something? Thanks!

I rolled my bike with the front brake slightly pressed. When I reached the point that my candles compressed slightly, I marked my rotor with a marker. I then measured with my digital calliper. I measured at each trio of drilled holes, at the same depth, using the last hole as a guide marker. The thickness of the disc was consistently 6.65 mm, and dipped to 6.57 mm where I marked the disc.

Would this be enough difference to be the cause? Many thanks to everyone who replied.

Cheers,

Gatsby
 
Back in the day I worked on a BMW K75 that had a pulsing front brake. It was pretty savage. I ran it down to the owner using Armorall on the front fork sliders. He had let a small trickle run down the disk and that was enough to give it a slick spot. I am not saying that this is your problem but weird things happen.
 
Big_Jim59 said:
Back in the day I worked on a BMW K75 that had a pulsing front brake. It was pretty savage. I ran it down to the owner using Armorall on the front fork sliders. He had let a small trickle run down the disk and that was enough to give it a slick spot. I am not saying that this is your problem but weird things happen.
Click to expand...
Could be a small seep out bottom of right side fork where the damper rod retaining bolt goes. That will reach the disc on one side only.
 
gatsby said:
Hi,

I recently installed a new rotor, and new pads. I am getting pulsating when I stop. It appears to be seated properly on the hub. Does the new rotor need a run in, or am I missing something? Thanks!

I rolled my bike with the front brake slightly pressed. When I reached the point that my candles compressed slightly, I marked my rotor with a marker. I then measured with my digital calliper. I measured at each trio of drilled holes, at the same depth, using the last hole as a guide marker. The thickness of the disc was consistently 6.65 mm, and dipped to 6.57 mm where I marked the disc.

Would this be enough difference to be the cause? Many thanks to everyone who replied.

Cheers,

Gatsby
Click to expand...
Yes. That translates to over .003" difference in thickness. Your disc needs machining to get it parallel.
When i machine discs, i do both sides of the disc without dismounting it from the lathe, this guarantees that it is perfectly parallel.
 
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dobba99 said:
Yes. That translates to over .003" difference in thickness. Your disc needs machining to get it parallel.
When i machine discs, i do both sides of the disc without dismounting it from the lathe, this guarantees that it is perfectly parallel.
Click to expand...
Thanks for the tip! I do not have a lathe, but I know someone who does. Looks like I have a job for him. Thanks!
 
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