pulsing front brakes

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PBRnr
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pulsing front brakes

Postby PBRnr » Tue Dec 12, 2017 9:12 am

Searched quite a bit and followed various past suggestions to resolve pulsing front brakes, but still with the issue. Took the rotors off, inspected the wheel for casting defects (none apparent), lightly sanded both sides of the rotors, re-torqued rotors back to wheel w star technique, even spun each of the floater 'buttons'

I don't have an accurate way to measure run-out but visually cannot see any obvious warp to the rotors when I spin the front wheel up on the stands...considering the bike has <6k miles on it, i find it hard to believe the rotors could be warped, but is there any other cause for the pulsing outside of what I've already looked into?

I'm reluctant to buy new rotors unless i've gone over every potential cause w these oem ones first
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Re: pulsing front brakes

Postby No. 47 » Tue Dec 12, 2017 10:02 am

Are all the caliper pistons freely moving back and forth?
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Re: pulsing front brakes

Postby The Gin Reaper » Tue Dec 12, 2017 11:53 am

PBRnr - you can crudely measure if there is any run out using a sharp pencil. Place tip against the disc and shaft of the pencil braced against suitable surface that wont move like the fork leg or brake calliper. Then rotate the disc slowly and see if the tip moves off the disc or breaks off depending on if the disc moves away or toward the pencil......

its crude but it works - may take a couple of attempts to brace the pencil properly.
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Re: pulsing front brakes

Postby PBRnr » Tue Dec 12, 2017 3:08 pm

Good ideas, will check pistons and pencil runout method. Cheers!
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Re: pulsing front brakes

Postby Aphex » Tue Dec 12, 2017 3:38 pm

The Gin Reaper wrote:PBRnr - you can crudely measure if there is any run out using a sharp pencil. Place tip against the disc and shaft of the pencil braced against suitable surface that wont move like the fork leg or brake calliper. Then rotate the disc slowly and see if the tip moves off the disc or breaks off depending on if the disc moves away or toward the pencil......

its crude but it works - may take a couple of attempts to brace the pencil properly.


Good idea, I used a sharpie on my super moto when truing the wheels to mark any high spots.
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Re: pulsing front brakes

Postby The Gin Reaper » Tue Dec 12, 2017 6:49 pm

Also - have you changed the front wheel recently?


Ignore this - i've just reread your post
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Re: pulsing front brakes

Postby Savage » Wed Dec 13, 2017 6:42 am

I had the issue and nothing showed any signs of warping or Ill fitting rotors.

I went ahead and filed the castings and refitted the rotors, no more issues.

I think sanding is not going to help, you need to use a file.
I used a small hand smooth file and that did the trick for me.

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Re: pulsing front brakes

Postby PBRnr » Thu Dec 14, 2017 7:52 am

Savage wrote:I had the issue and nothing showed any signs of warping or Ill fitting rotors.

I went ahead and filed the castings and refitted the rotors, no more issues.

I think sanding is not going to help, you need to use a file.
I used a small hand smooth file and that did the trick for me.

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Borrowed a wheel truing gauge (for lack of better term) and ran the rotors under it...both look VERY straight. I think the dial units were 1/5000 in or something and the right rotor ran +/- 3, the left +/- 2. Not sure what the spec is but I still need to pull off the calipers to check pistons...may as well give them a deep clean as well

The 990 front wheel has a flat, machined surface for the rotor to sit upon unlike (I assume from various pics) the 1290 has. Considering I didn't see/feel any clear defects, I didn't dare file/sand away blindly because it would certainly cause the rotors to sit out of parallel to each other and the rim.
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Re: pulsing front brakes

Postby DaveNZ » Thu Dec 14, 2017 8:19 am

A build up of pad material on the high spots of your disc can cause pulsing, also if your worried with the alignment of the callipers to the disc, loosen the calliper bolts, hold your brake (brake lever) hard in, so pistons lock to disc, then tighten the calliper bolts while the brake is locked on, you could put a zip tie on the brake, or get someone to hold it on.
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Re: pulsing front brakes

Postby Aphex » Thu Dec 14, 2017 3:32 pm

DaveNZ wrote:A build up of pad material on the high spots of your disc can cause pulsing, also if your worried with the alignment of the callipers to the disc, loosen the calliper bolts, hold your brake (brake lever) hard in, so pistons lock to disc, then tighten the calliper bolts while the brake is locked on, you could put a zip tie on the brake, or get someone to hold it on.


This is good advice, whenever I remove the front wheel I always jam the brakes and pump the forks to get everything lined back up.

I think you're on the right path PBRnr, last time I cleaned my calipers half the pistons were doing most the work and it took ages to clean them and get the pistons to extend at roughly the same speed/distance per pull of the brake lever. I only used warm soapy water and a soft toothbrush though, so maybe there is a cleaner that will make it go a little faster.
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Re: pulsing front brakes

Postby PBRnr » Fri Dec 15, 2017 8:15 am

thx. I forgot to say I lightly sanded the rotors when they were both off the rim. Just today cleaned off the pistons. maybe 1 of 4 were slow but all were mobile initially. Didn't have time to take a test ride after bolting things back together today

Fingers crossed.

Maybe the next step would be to swap out the brake pads tho the oem brembos on there right now have lots of meat left...
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Re: pulsing front brakes

Postby battleshaft » Fri Dec 15, 2017 9:08 am

PBRnr wrote:thx. I forgot to say I lightly sanded the rotors when they were both off the rim. Just today cleaned off the pistons. maybe 1 of 4 were slow but all were mobile initially. Didn't have time to take a test ride after bolting things back together today

Fingers crossed.

Maybe the next step would be to swap out the brake pads tho the oem brembos on there right now have lots of meat left...


I was in a similar situation to you with my 990. Bike had only done 8k miles, but it turned out to have a warped disc. I replaced the discs and pads (used EBC after reading those stories about the OEM Brembos de-laminating) - problem solved. I went through all of the other logical steps first though: checking disc buttons were all free moving, full caliper and pad clean, disc clean etc.
On my bike you could hear where the disc deformity was by lifting the front on a stand, and spinning the wheel by hand while lightly applying the front brake.
It was a joy to have smooth, sharp brakes in the end!

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Re: pulsing front brakes

Postby PBRnr » Fri Dec 15, 2017 5:52 pm

Good to know. I don’t understand why brembo pads seem to be so harsh on rotors...on my ‘83 bmw, they eventually wore grooves into the rotors around the cross drilled holes. Maybe they’d do better on higher grades of steel? At that rate probably higher performing pads out there as well...
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Re: pulsing front brakes

Postby PBRnr » Fri Dec 15, 2017 11:04 pm

Tried to start bike, dead battery. Wanted to swap the lead acid for my shorai from the previous bike anyway, so did that. Took the bike to the shop to get a toolkit as the bike was missing it when I bought it.

Good news, no pulsing brakes! I think the cleaning of the rotors and pistons seems to have worked.

Bad news, bike died about 2 miles from home

Doesn’t appear to be charging the battery as it ran flat and now has not enough juice to run over.

Sigh
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Re: pulsing front brakes

Postby PBRnr » Fri Dec 15, 2017 11:06 pm

One kicker is that the oem toolkit doesn’t include a 5mm Allen key to even take off the battery fairing! KTM saw fit to include a bottle opener though as a final F U it seems as I sit here without power and without beverage
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Re: pulsing front brakes

Postby Willh » Sat Dec 16, 2017 1:06 am

PBRnr wrote:One kicker is that the oem toolkit doesn’t include a 5mm Allen key to even take off the battery fairing! KTM saw fit to include a bottle opener though as a final F U it seems as I sit here without power and without beverage

The torx bits should fit.
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Re: pulsing front brakes

Postby PBRnr » Sat Dec 16, 2017 3:08 am

I tried but didn’t want to chew up the bolts so decided not to...
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Re: pulsing front brakes

Postby DribbleDuke » Sun Dec 17, 2017 3:20 pm

PBRnr wrote:One kicker is that the oem toolkit doesn’t include a 5mm Allen key to even take off the battery fairing! KTM saw fit to include a bottle opener though as a final F U it seems as I sit here without power and without beverage

I do remember having a conversation that covered topics like this on another thread. It went something to the affect that there is nothing on this bike that money won't fix.
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Re: pulsing front brakes

Postby PBRnr » Sun Dec 17, 2017 6:46 pm

No wonder there’s more black and orange around my home than green ;)
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Re: pulsing front brakes

Postby Varinn » Fri Jan 26, 2018 5:10 pm

I've got pulsing fronts on my 990 that I am trying to look at right now. First thing I noticed when I took the wheels off the bike is that the rotors have lots of thickness left but they have some grooving going on, to me it seemed normal from car experience.

I tried checking all the rivets connecting the discs to the hubs and found that both front rotors had an uneven gap between the hub and disc portion, with half of the rivets spinning freely and say a 2-3mm gap between the disc and hub. The other half they either spin with lots of resistance or not at all, and the gaps can be smaller with some looking to be around 1mm. In other words it seems like the discs have shifted a bit.

I don't mind popping calipers out and dropping in a rebuild but with the meat left on the rotors I'm hesitant on dropping $500+ on a new pair of discs. Is there any PM work that I need to be doing to stop these rivets from getting stuck how they are? Does it even matter? I'm thinking if the rotors aren't gliding on them smoothly they might not be running true to the wheel and pushing the caliper pistons back in.

Rotors have some but VERY minimal pad deposits and nothing significant enough to make me suspect them, I've gotten way worse on my track car without any pulse.

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Re: pulsing front brakes

Postby No. 47 » Fri Jan 26, 2018 6:48 pm

The discs are semi-floating and, afaik, the bobbins connecting the outer and inner parts of the disc should spin and move freely to allow true alignment of outer part of disc with caliper pads/pistons when brakes applied - if not, disc can’t move to align, hence pulsing.
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Re: pulsing front brakes

Postby PBRnr » Sat Jan 27, 2018 5:43 am

when I was dealing w my rotors, the bobbins were able to spin evenly on both rotors and the spacing between the rotor and carrier was even all the way round.

strange that you are getting varied spacing of the rotor and carrier. I've never heard of rotors warping along the plane of the rotors themselves...does this suggest that they are not exactly circular? I'd also guess that if there's +/- 1mm difference in rotor orientation about the carrier, you'd be able to visually see that kind of deviation when the wheel spins...rotors appear to be hopping up/down? strange. Unless I am misunderstanding what you wrote.
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Re: pulsing front brakes

Postby Varinn » Tue Jan 30, 2018 5:47 pm

I think the eccentric gaps were a bit of a trick of the eye actually, I had the wheels off for new rubber so I had a good chance to inspect. I went and cleaned the bobbins and found some were more stuck than others but even post cleaning I get a good side-side movement of the disc though the bobbins don't spin for shit by hand (easily with the bolt trick though). The uneven gaps turned out to be brake dust/dirt that made them look smaller/larger in different points.

I've already punched out my old bearings for front and rear so I'm waiting for the replacements to show up before I can put them back on the bike and see how they sit. Some time in the next couple days I should get a chance to clean the calipers up which is where I'm expecting to find the most issue with the front wheel as I haven't had them apart before.


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