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Front Wheel Pulsing

There is another cause but it’s unlikely in most cases of pulsing. When new or freshly machined rotors are installed, the brakes need to be properly bedded in to work as they should. This involves repeated sequences of high speeds and then very hard braking which gets the rotors and pads very hot which transfers pad material to the rotors.

If that coating on the rotors is somehow worn away or otherwise removed in areas, it creates areas of different coefficients of friction, and because less slippery and more slippery areas are passing thru the pads, pulsing can occur. In that case, bedding the brakes again will cure the problem. Doing this,’of course, is much less risky in a 4 wheeled vehicle.
 
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I had a mystery pulse once in tune with the front wheel rotation under brakes.

I scrubbed the rotors with red scotch brite, cleaned them with brake cleaner, re-torqued the calipers with the brake lever on, no change.

Then I pushed sideways on the rotor buttons. The rotor buttons had the little springs, not full floaters. Some of the rotor buttons were "stuck" and pushing on them loosened them up for free sideways motion. Problem solved.
 
What part of your body did you use to detect the pulsing?
 
Not really guessing. If you don’t feel the pulsing through the brake lever, it has to be caused by different regions of differing coefficients of friction on the rotor as they pass through the pads. And there are two main causes for this. 1. Contamination of the rotor or 2. Uneven deposition of pad material.

Cures: For 1., clean the rotors. For 2., bed the brakes again.

It’s knowledge and experience speaking. Not guessing.
 
FYI, I’m 74 years old and a retired engineer. I do know a few things.
 
And if the OP would simply clean his rotors thoroughly, we’d have a much better idea of the cause of the problem. It’s easy and quick to do.
 
Also, the oils on your mechanics hands and fingers could be the cause of any contamination of your new rotors.
 
No luck, Pulsing still there, almost feels like it's getting worse, more likely I'm getting increasingly annoyed. Can anyone recommend a solid mechanic or shop in the bay area that does wheels, more than just the basic stuff. In the event the wheel may need a rebuild or something along those lines? Thanks in advance!
 
augustiron said:
This is a known problem on the KTM 790 adv.
Most replace the rotors with aftermarket.
There is a lot of discussion of it on KTM adventure specific forums.
Some of the threads might be older as I don't think it is as prevalent on the 890s of the last few years
There is also a front brake recall for certain years.
A quick Google search Will give you all kinds of leads to follow.
Click to expand...
Thank you, I will research this and see if this bike is being affected similarly.
 
ST Guy said:
FYI, I’m 74 years old and a retired engineer. I do know a few things.
Click to expand...

FYI, that doesn't give you an expert knowledge of this problem because I suspect you did not take a class in motorcycle brake rotor maintenance. Would it matter if I said I have science degrees in Physics, Applied Engineering, and Mathematics, and I am actively working for a leading global tech company?

But I don't doubt there is some issue around the rotor, whatever it may be.

Here's a thought. This bike has ABS, right? Well, on my ABS bike, there has been many complaints of front brake pulsing, but it's faint and rapid, and can be felt in the lever. The experts like yourself claim it's in our minds...
 
ctwo said:
FYI, that doesn't give you an expert knowledge of this problem because I suspect you did not take a class in motorcycle brake rotor maintenance. Would it matter if I said I have science degrees in Physics, Applied Engineering, and Mathematics, and I am actively working for a leading global tech company?

But I don't doubt there is some issue around the rotor, whatever it may be.

Here's a thought. This bike has ABS, right? Well, on my ABS bike, there has been many complaints of front brake pulsing, but it's faint and rapid, and can be felt in the lever. The experts like yourself claim it's in our minds...
Click to expand...

I am more qualified than you know.

And I have personal experience, backed up by high end brake manufacturers. I wouldn’t dismiss my suggestions off hand.

Odds are in my favor that if the OP would simply clean his rotors, the pulsing would disappear.
 
ST Guy said:
I am more qualified than you know.

And I have personal experience, backed up by high end brake manufacturers. I wouldn’t dismiss my suggestions off hand.

Odds are in my favor that if the OP would simply clean his rotors, the pulsing would disappear.
Click to expand...
Sadly this is not the case.

Rotors cleaned with brake cleaner and rags, no abrasives. Pulsing is absolutely still there. The pulsing is strongest at slow speed right before stopping, like 15mph to zero.

Nothing visible on rotors so I’m not inclined to use abrasives.

Still hoping to find a skilled wheel person in sf Bay Area. I’m pretty sure the hub has a rotational runout that is measurable. I may reach out to KTm directly but I’m betting they will tell me to F-off as bike is 7+ years old, although low mileage (<15k).
Appreciate you all and your advice, try not to flame each other so much. I don’t think anyone is actively trolling afaik.
 
richardault said:
Sadly this is not the case.

Rotors cleaned with brake cleaner and rags, no abrasives. Pulsing is absolutely still there. The pulsing is strongest at slow speed right before stopping, like 15mph to zero.

Nothing visible on rotors so I’m not inclined to use abrasives.

Still hoping to find a skilled wheel person in sf Bay Area. I’m pretty sure the hub has a rotational runout that is measurable. I may reach out to KTm directly but I’m betting they will tell me to F-off as bike is 7+ years old, although low mileage (<15k).
Appreciate you all and your advice, try not to flame each other so much. I don’t think anyone is actively trolling afaik.
Click to expand...
The symptom you’re describing will only have a few possible causes. Varying coefficient of friction is one and while it might not be absolutely ruled out by cleaning, you’ve done a lot to ensure that it wasn’t caused by contamination. Varying deposition, maybe, but you can move on to something more definitive to narrow down the problem.

Variations in rotor thickness are a common cause. To find out if this is an issue, get a micrometer and measure the thickness of the swept area in several places around the disk. If the measurements differ by more than .015mm, this is probably why the brakes are pulsing.

This will rule in or out disk thickness variation as a cause. If this is the cause, the likely cause of *that* is runout. Sometimes the wheel hub has runout, as you’re wondering about, but sometimes there is runout at the mating surface of the rotor carrier or the outer portion of the carrier, where it connects to the disk. A shop can check for this, and if you have a dial gauge with a rigid mount, you can too.

Once in a while, both the hub and the carrier have runout. There are cases where their relative alignment can be additive or subtractive. Changing the orientation of the carrier to the hub can result in minimizing the runout at the outer edge of the carrier to acceptable limits. That’s ultimately the only surface that matters.

Run out will create disk thickness variations over time, as the disk wobbles as it rotates, whisking against the pads in some places with each revolution, while not contacting other parts of the disk at all. You could either machine or replace the disks if yours have the variations, but if there is any runout, the problem will eventually recur.
 
You can remove one disc at a time to test which disc is bent... ante up a new disc to cure the pulse...

My RC45 front disc was bent by the previous owner... the lever would pulse
during braking... I chucked the disc in the Lathe and cut a new surface... but
pules was noticeable smaller but you could still feel it pules... I tried bending
the disc in a press but no joy... I sanded the disc and the pulses got noticeable
smaller but again you could feel a pulse especially when braking from 140
mph... I gave up and anted up $2,500 for a set of Jeff's Ceramic Matrix
Composites disc... now I enjoy not only great pulse free braking but also
saved 1 lb 14oz (849gm) savings over each stock Honda steel...

Unless you have access a magnetic chuck I don't recommending machining
a narrow motorcycle brake disc... first the surface tends to bend away
from the tool bit at the weak holding points and second if surface the
has holes or slots the tool bit will momentarily unload and create a
bump which will be felt as a pulse at the lever... the simple way to
erase unwanted groves in either stainless steal or cast iron rotors is
to remove it from the buttons... then chuck it in the Lathe... work a
180 grit sanding disc against the surface evenly until the groves are
gone...

423834488_35781b3ed8.jpg


The solution Ceramic Matrix Composites...

3193188896_9d34585b46_o.jpg


3193188902_d61cb52189_o.jpg
 
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Thank you all for this information, it's given me a lot to consider. I've tried what I can with regards to some of these suggestions, but problem NOT solved.

Updates

Back in September I left the bike with Scuderia for a major service and an examination of the brake issue. We collectively decided to replace the front rotors with OEM parts from KTM. And voila the pulsing was gone... for a while. Maybe around 400 miles of commuting, in little 8 mile (round trip to work) chunks, and then the pulsing came back.

Just last week I took it back to Scuderia and they bled the front brakes and replaced the pads as they could not detect warping or a variation in thickness in the front rotors (although I'm not 100% certain they gauged this). Regardless, this did not solve the pulsing issue. |

So my question to the forum are these?

1. What could be causing the pulsing in the front brakes?

and if the rotors are warped or somehow developed some variation in thickness from riding...

2. What could be causing this warping or what is developing the variation in thickness on the rotors.

Keep in mind, the only solution up to this point was replacing the rotors, and that is only lasting a brief (~400 mile) period of riding.

I am not tracking the bike, so it's unlikely I've overheated the rotors to cause warping. What other factors could be warping them, or is this some other source? Electronic or otherwise?

Thanks to everyone dearly, I'm truly losing my mind, as braking is getting increasingly hectic especially as we move into the wet season.

I'm asking here because I'm pretty confident Scuderia will ask me to consider replacing the calipers, or electronics, or the front wheel. Which I'm unwilling to do until I have a clue as to why it's happening.
 
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