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Front Wheel 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.
 
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.
 
My 2c

Pulsing is not the master cylinder, lines, bleeding or the calipers.
A hydraulic system does not induce pulsing on its own. It is fairly dumb, there is either no pressure, some pressure, or a lot of pressure, it does not induce varying pressure and feedback to the pump mechanism (master cylinder)

An ABS pump can induce pulsing into the hydraulic system, but that is a whole separate issue.

The pulsing you are feeling is mechanical variation either causing 1) vibration of the entire bike 2) pulsing into pump ( the master cylinder lever) or 3) both of the above.

Why? Couple of ideas
Run out or friction issues

Run out - Something is out of flatness spec causing excessive run out of the rotor at the braking surface causing the calipers to send pulsing feedback as they try to squeeze something that is essentially wiggling instead of running straight and flat.
There are really only two things that affect this, the mounting surface of the rotor on the rim, or the rotor itself.

Friction - there is some variance of the friction surface that is altering the friction coefficient as the circumference of the rotor sweeps through the pad contact breaking area leading to more - less - More - less, etc friction causing a pulsing/vibrating feeling.

New rotors, if they were the problem, would fix both of these.
New rotors temporarily fixing this shows that the rotors were partially at fault, but the underlying condition caused them to fail as well.

Why?
- defective quality rotors?
This is why a lot of owners replaced the rotors with aftermarket pads and rotors.
- slightly out of tolerance rim rotor mounting surface? Possible

I highly doubt it is anything to do with the remainder of the hydraulic system. This is a mechanical issue.
 
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Sadly it looks like there were two recalls on this bike filed with the NHTSA, and 12 complaints, many about front brake pulsing. At this point the bike is out of warranty but I wonder if there is a way I can pressure KTM into replacing aspects of the front brake system to relieve this safety issue? Does anyone have experience with KTM US?
 
A recall stands valid regardless of where you are in your warranty, they are separate things.

I don't have specific experience with KTM corporate, but I have read a lot about how they are handling the cam issues and it is really hit or miss depending on how hard your dealership representatives are willing to push the issue for you.
 
I don't know if I mentioned it in this thread or elsewhere with somebody talking about pulsing brakes, but ....
my old Ducati st3s had pulsing brembo brakes and the fix was to grind off the buttons between the rotor and the carrier and put in aftermarket ones that allowed more float of the rotor relative to the carrier.
Some people found it unnerving that there is a little ching ching sound from the rotor moving on the carrier so much, but the brakes were fantastic after that.
It just allowed more lateral movement, not radial, so there was no slop in the braking feel.

I haven't seen that discussed as a fix for the ktm specifically but I haven't spent a lot of time looking, but the principal holds the same.
 
I dunno if this was covered, but, how were the new rotors and pads bedded in? Only time I've run across pulsing I thought it was a bent rotor or stuck floating buttons, but after cleaning up the rotor and replacing pads coupled with a proper bed in the pulsing went away entirely.

Edit: never mind, I see this is a recall thing. Wonder if it has to do with where the rotors mount to the wheel, too much paint making a not so flush mounting surface or something along those lines?
 
I think I read somewhere that if you really heat the brakes/rotors through many agressive stops, and then keep them applied when stopped such as waiting for a signal light, it can affect things in this manner.
 
More so during bed in, the pad material can get transferred to the rotor unevenly when they're hot and fresh is my understanding.
 
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