Back to Pulsating Brakes!

[Tony/CT]

I've been looking at new rotors for the 09 Vintage to address the pulsing, like riding a bucking horse, brakes. But before I invest, I'm wondering if something else could be causing the problem. The pads look good. The previous owner installed speed bleeders on the bike for ease of changing the brake fluid. I'm wondering if that could have something to do with it. If there isn't sufficient brake fluid in the line wouldn't that cause spongy brakes and not the bucking action? These are floating rotors. My EV has solid rotors with no problems at twice the mileage. Is it a bad idea to replace the floating rotors with solid rotors? The front brake alone is the worse. Not so bad with the foot brake, although there is still a bit of pulsing. I'm thinking it is the other front rotor in the linked system and not the rear rotor which is solid!

[NCAmother]

If you have the time and patience, you could mic the rotors, depending on your readings you could get them turned.  You don't have to remove the wheel if you get a cheap harbor freight dial indicator with magnetic base.  Hopefully they aren't warped, and most hopefully the rim/tire is true

[Triple Jim]

The thing that will cause disk brakes to pulsate with just a couple thousandths of error is thickness variation of the rotor.  When it's happened to me, it's happened because the rotor developed a hard spot from getting too hot.  The hard spot doesn't wear as fast as the softer areas, so as the disk wears, the pulsing gets worse and worse.  Turning the rotor(s) helps only temporarily, unless you can turn all the way through the hard area.  Measuring the thickness around the rotor in several places with a micrometer will identify a thickness variation.  I've read that variation as little as 0.001" can be felt.

I understand that floating rotors can get stuck and cause pulsing too, that's a different problem that I have no experience with, but it takes quite a bit more runout (side to side wobble) to cause pulsing than it takes thickness variation.  My Mille has non-floating disks, and the hand lever operated front one has about 0.008" runout (warp).  The caliper tracks it fine and there is no pulsing at all.

[Late to the party]

Should it become necessary to have the rotors re-ground... given how important brakes are, it sounds like this might be a good time to do that... I know a very competent man in Michigan who does this sort of work. Grinding motorcycle disk rotors is all he does, and he does an excellent job.

Mr. Thom Tokarz
True Disk, LLC.

Google it.

Lateness

[Tony/CT]

I hadn't thought about the rim not being true. I guess I will also have to consider that in the equation. If I can determine that the problem is with the rotors, I will consider sending them out and having them reground. Thanks for the information.

[fotoguzzi]

I bet the stock rotors are too thin to grind any off..
you have an EV with solid mount rotors? Most EV's I've seen had floating rotors that didn't really float because the button fill up with dirt/dust and don't function as they should.

The thing that will cause disk brakes to pulsate with just a couple thousandths of error is thickness variation of the rotor.  When it's happened to me, it's happened because the rotor developed a hard spot from getting too hot.  The hard spot doesn't wear as fast as the softer areas, so as the disk wears, the pulsing gets worse and worse.  Turning the rotor(s) helps only temporarily, unless you can turn all the way through the hard area.  Measuring the thickness around the rotor in several places with a micrometer will identify a thickness variation.  I've read that variation as little as 0.001" can be felt.

I understand that floating rotors can get stuck and cause pulsing too, that's a different problem that I have no experience with, but it takes quite a bit more runout (side to side wobble) to cause pulsing than it takes thickness variation.  My Mille has non-floating disks, and the hand lever operated front one has about 0.008" runout (warp).  The caliper tracks it fine and there is no pulsing at all.

excellent description  of the problem.

[normzone]

Interesting. I have looked at the front rotor controlled by my foot brake pedal on my '99 Bassa, since that is the pulsating one, and there's no way in hell that design could allow much float on it's best day.

What kind of precision measurement are we talking about here?

I have calipers that discriminate to .001 but I'd have to go borrow a micrometer if we are serious about thickness variation of .001 making a difference. And remember, discrimination is not the same thing as accuracy or reliability of measurement. If a thousandth of an inch can make a difference then you should be measuring with something that reads down into .0001

[NCAmother]

I believe your dial caliper that measures in increments .001 would suffice.   Again, I recommend you check that your rim and tire are true.

[sonicboom]

Had a twin disc 1200R sportster that pulsed after new pads installed.

I just ran it hard down a mountain road and it went away.

[Cam3512]

Could it be the brake pads?  Remember, those are the originals.  If a possibility, try switching them out first.  You'll need to do that soon anyway, and it might be the easiest fix.

[rodekyll]

It takes a 'C" mic to do a rotor because a caliper only measures the thick points -- it can't get past the ridges to measure the grooves.  The real-deal mic has pointy jaws to find the thin places/

[Wayne Orwig]

Any time I've had a problem with pulsing brakes it is simply a contaminated spot on the disk surface that grabs the pads at that one spot.
I take a 3M Roloc disk in a grinder and clean off the disk surface. Problem solved.

[Zoom Zoom]

As I mentioned before, ditch the semi floaters and replace with full floaters. Done! you will never have that trouble again.

Might be dirt getting in the buttons, or warpage, or both. Unless they changed them, the stockers are/were 4.5mm. The replacement FF's are 5mm and I think I may have seen 5.5mm but don't hold me to that. Thicker rotor helps resist warpage as it can dissipate heat better with more material, along with simply being thicker.

When I think about how long I lived with the originals on my old EV, I cringe. I would clean them and they would be better but never entirely great. Eventually no amount of cleaning would resolve the pulsation. I finally could not stand it anymore. My only regret was not having done it sooner. If the time comes when the disc on the LeMans or Stelvio warp, they will be changed post haste. I will not screw around with a temporary stop gap ever again unless I have no choice. I have cleaned the buttons as well as the surface of the disc. It only works for a while. At least that has been my experience. No doubt others will disagree, but you asked this before so I would suppose you have already gone the route of cleaning.

My 2 cents.

John Henry

[Paul_Tim]

When I bought my 08 Stelvio last year the brakes were pulsating, tried freeing all the bobbins to no avail so tried to measure the run out. One disk had 0.03" run out and the wear p[attern agreed with my readings, got a set of rotors from a Griso (gold centers but otherwise identical) and the problem went away.
Took the 'warped' disk into the machine shop and after some investigation involving a surface plate and some fancy measuring equipment it turned out not to be the disk rotor itself but the rotor carrier that was bent, (probably caused by being 'lent on' when having a tyre changed).

[rocker59]

The 320mm Brembo rotors are semi-floating.

Usually, pulsing is caused from the buttons getting stuck.  Some spray brake cleaner will usually help.

Two other options, though unlikely are:

1)  The stainless blade is warped
2)  The steel carrier is warped

It is possible to bend them when changing tires, if someone is ham-fisted.  Unlikely, though.

My bet is the buttons have gunk in them and need to be cleaned to be freed-up.

Oh, and your '98 EV had 320mm semi-floating rotors.  Just the carrier was different.

[rocker59]

Interesting. I have looked at the front rotor controlled by my foot brake pedal on my '99 Bassa, since that is the pulsating one, and there's no way in hell that design could allow much float on it's best day.
 

The buttons that the blades float on have springs on the back.  That makes them "semi-floating".  The rotors can definitely move, though the springs are pretty stiff.

This semi-floating Brembo rotor first showed up on Ducati's 900SS and 851/888 of the early 1990s.  Stainless blade and painted steel rotor is the basic package, and that's what Guzzi still uses.  Brembo also offered full-floating versions in both cast iron and thicker stainless.  Also available with aluminum carriers.

It's really easy to upgrade from the bottom of the line Guzzi Brembo units by searching Ebay and buying Ducati or Aprilia take-offs.

The "Snowflake" version is the one to have, if you want stainless blades.  They have thicker blades and aluminum carriers.  And, they work really well.




I went with the full-floating cast-iron w/ aluminum carrier version when I replaced the rotors on my Sport 1100.  They rock!

[normzone]

Damn, you guys are awesome. The only things you haven't done for me is buy the parts, install them, and ride the bike for me. And then what would I do with my time and money?

Much thanks. I going to leave work and join the dance on the freeway. Cheeseburgers tonight at the lady's request.

 ;D

[Tony/CT]

I did clean the bobbins with brake cleaner until they turned freely. That did not solve the pulsing brakes.

[rocker59]

I did clean the bobbins with brake cleaner until they turned freely. That did not solve the pulsing brakes.

Might be time to pop for some "snowflakes".   ~;

[Uzidzit]

now remove the rotors and re-scuff them with scotchbrite, and re-bed or better yet replace the pads....any time you change the pad maker or the compound from the same maker you have to clean the rotors, this measns scrubbing about .0005 worth of old pad deposit and rotor off to get below the contaminated surface. go in small circles and work around the disk,  150 grit aluminium oxide also works well for this.  DO NOT use black silicon carbide wet or dry paper it embeds in the disk  I have only seen a very few truly warped rotors, 99 percent of the "warped " rotors are just contaminated or have stuck bobbins.

always cool your brakes btw, if you come off a very long hard run (like 90+ down the chero on the downhill side) don't just stop at he side of the road after max brake, run a mile or two with little braking.  that blazing hot rotor will make a spot of heavy build up where it sits between the pads if you do max brake and then just stop and let the front wheel just sit in one spot....

clean your calipers with ivory dish soap and water and a tooth brush regularly, if they are dragging a tiny amount that leads to heat and the heavy deposits in one spot when you stop as well

[Cage Free]

Any time I've had a problem with pulsing brakes it is simply a contaminated spot on the disk surface that grabs the pads at that one spot.
I take a 3M Roloc disk in a grinder and clean off the disk surface. Problem solved.

I did something similar to that on my Bandit 1250 when the brakes started pulsating. I had read an article in cycle world about contamination on the discs causing pulsating and used brake cleaner and 400 grit wet and dry to clean the discs, worked as advertised, pulsating gone.

[rodekyll]

I have a set of almost-worn-out pads for my iron rotors that I glued sandpaper to.  When the rust on the rotor leaves that little pad-shaped ridge I pop in the pads and give the wheel a spin.  I suppose a guy could install them and go for a short ride if the ridge is stubborn, but I've never had to do that.

I'm thinking maybe that 0.0005 of sprucing-up on the SS rotors might be more easily and EVENLY accomplished with this method.

[JohninVT`]

Easiest way to free bobbins;
Slide a bolt through the bobbin from the inside, out.  Screw a nut onto the bolt until it's snug against the bobbin face.  Screw the chuck of a cordless drill onto the remaining threads of the bolt and....pull the trigger.  Rinse, lather, repeat.  

[Uzidzit]

Easiest way to free bobbins;
Slide a bolt through the bobbin from the inside, out.  Screw a nut onto the bolt until it's snug against the bobbin face.  Screw the chuck of a cordless drill onto the remaining threads of the bolt and....pull the trigger.  Rinse, lather, repeat. 

one step faster use an easy out ;-T

[1Sourdough]

Pro'ly not related but when I bought the Strada and started riding it home from Virginia the integrated brakes pulsed, and the forks vacillated when the pedal was pressed.  The motor had fresh Pirelli Sport Demons, with the wavy center rib, and I thought that might be causing it.  Finally got curious enough to inspect the front wheel and found several balls missing from the left bearing.  Could the right bearing be not up to snuff on your machine?

[Triple Jim]

I did clean the bobbins with brake cleaner until they turned freely. That did not solve the pulsing brakes.

I'm curious to know if you measured the rotor thickness in a few places yet, and what you found if you did.

[normzone]

AND HERE WE ARE AGAIN...

Having just returned from having my local heroes put tires on the bike and check out the brakes. Tim verified all bobbins turn. The float designed in is minimal - he showed me a full floating on another bike, and the difference is dramatic.

Survey says:........Rear disc, flat within .003, front right disc within .003...front left disc, the one linked to the foot pedal...out by .010 for about half the disc diameter.

It was that way when I bought it - the front fender shows a ding on the left corner, so it could have been a fall, or a careless tire change, or the shop owner said some of their older tables can clamp on the disc if you're not paying attention, so maybe a sloppy service somewhere betwixt the two previous owners services.

I came here looking for a cost on replacement disc. For the nonce, I have new pads, and (expletive deleted)! The brakes were good before, and they got turned up to eleven now. But still shopping for a disc.

[Orange Guzzi]

Front brake rotors are mounted just a few inches from the road and the nearly the first thing to catch road grime and stuff in the air.  We all see how dirty a motorcycle can get after just a few miles of riding.  I would suspect that many brake pulse, grab issues can be traced back to contamination of the rotors and pads.  I recently had an issue with this on one of my bikes.  I went thru the cleaning, sanding, dial indicator inspection, button cleaning only to continue having a pulse.  I found new rotors, new buttons and then put off buying them.  I continued riding the bike and found that the pulsing has nearly went away after a few hundred miles of riding and braking.  I suspect that dirty is the problem. 

[normzone]

I've made some efforts to clean, and am wondering if an attempt to beat it back into something less than .010 while on the bike would risk damaging the wheel if done carefully. .010 seems outside the scope of "dirty".

I wonder if I ground some off of the high side if the disc would respond positively, or if it's memory would make it respond oddly.

Bear in mind at this writing anything I do will be with the wheel on the bike. I'm not yet setup for more intensive surgery.

[canuguzzi]

now remove the rotors and re-scuff them with scotchbrite, and re-bed or better yet replace the pads....any time you change the pad maker or the compound from the same maker you have to clean the rotors, this measns scrubbing about .0005 worth of old pad deposit and rotor off to get below the contaminated surface. go in small circles and work around the disk,  150 grit aluminium oxide also works well for this.  DO NOT use black silicon carbide wet or dry paper it embeds in the disk  I have only seen a very few truly warped rotors, 99 percent of the "warped " rotors are just contaminated or have stuck bobbins.

always cool your brakes btw, if you come off a very long hard run (like 90+ down the chero on the downhill side) don't just stop at he side of the road after max brake, run a mile or two with little braking.  that blazing hot rotor will make a spot of heavy build up where it sits between the pads if you do max brake and then just stop and let the front wheel just sit in one spot....

clean your calipers with ivory dish soap and water and a tooth brush regularly, if they are dragging a tiny amount that leads to heat and the heavy deposits in one spot when you stop as well

And I was told I was being paranoid because I check for oil leaks with a paper towel. :D

The brake cool down is spot on though.