Not Ducati related but………… Is there anything that could be wrong with forks that could cause a front end vibration whilst braking? I rebuilt the forks on my Gsxr 1000 K9 road bike and after I noticed this vibration whilst braking, at first I thought it was something that I had done wrong but then realised it must be the discs etc as I hadn’t long done a track day. But I did everything by the book, oil, oil level etc etc. I’ve done many forks as well and I just can’t see it being anything to do with them, just co-incidental more than anything. I checked wheel bearings, I checked head bearings, I checked the front wheel, fork alignment etc, even the trick with the calipers not being fully tightened and applying the front brake then tightening them up. I checked all bolts on the triple tree, absolutely everything. I was so convinced more than anything that it was now to do with the discs being warped. So I tested them for run out and they are within spec, the service limit is 0.3mm and one disc is 0.17mm and the other is 0.23mm There was also an advisory at the start of the year for the front wheel bead being out of straight or whatever it was called so I checked the axial run out and that was within spec also. Limit is 2mm and it was something like 0.94mm one side and 0.66mm the other side. Scratches head!
Could be road film build up on disc - it would give irregular friction against the pad and not necessarily be visible. Maybe give the disc faces (both sides) a good scouring and use some solvent (checking that it wont adversely affect the pads of course!). I have this on my daily motorway use bike from year to year.
Its not a change in disc run out, its more of an extremely thin coating of baked on road shite that has a different frictional value to the 'clean' disc surface. Others here may have other ideas - but mine wont cost to try and I have found that it has helped on my bikes in the past. Usually I'll fit fresh (sintered) pads in the spring to clean off the disc if scouring hasn't helped.
One area to check is that all the disc bobbins can rotate freely. If they become seized or slightly seized in place through road dirt or whatever, they will give that vibration feeling under braking. You can check with a bolt, nut and washers through the bobbins to either free them up, or check they all rotate with a spanner That is of course, after checking they are straight . If you had the discs off the bike, then it can also be caused by corrosion or paint on the disc mounts and/or the wheel mount area where the bolts affix it to the wheel. Corroded bolts also can chime in if they do not sit correctly. Check and clean all those too. I had this exact dance with a ZRX1200. I changed the entire front end in pieces, wheels, discs, forks, bolts, bearings, pads, everything and never cured it ...turned out my headstock had the slightest of twists from an accident before I bought the bike. Not enough to put things out of line for an MOT test, but it was the only explanation left over.
Forgot to say, bobbins are free, checked them and they are fine. Ah I see what you mean. I might pull the trigger on new pads and discs just to see how it goes, can’t go wrong with that anyway unless the problem is still there, that would be a kick in the cock.
We have a similar thing with a Daytona 675R we ran in Jerez, I've got some video's of it, can barely hold on to the bar when I hit the brakes. we have changed discs, and it still does it, so like you we are scratching our heads a little. We thought maybe the forks are bottoming out, but we are even looking at things like the Sigma slipper clutch to see if we are basically getting clutch chatter where it's out of spec. Does it get worse the harder you brake? for us, you can just push through and brake harder and harder and it doesn't get 'worse'. We checked the forks (they have been rebuilt) and we checked head bearings, wheel bearings and even the bobbings on both sets of discs.
you might have answered yourself in your last sentence Wull, if it was enough for an MOT tester to give you an advisory then I would try another wheel for starters if you can, just to rule it out. Careful studying of disc surfaces with good lighting can reveal a lot sometimes.
Axial and radial run out of rim checked?Tyre not seated properly. With Chris on this one. Distorted wheel Tyre balance unlikely to be correct if not seated. Tyre badly worn? I-regular wear.
Only thing with that is there was never any problems until much later. So only way I’d know for sure that it could be related is if I had done the axial run out check back then versus now. The readings now are 0.94mm and 0.66mm which is well within spec which is 2.0mm. The hub is perfect and that has a tolerance of 0.25mm. I’m fairly certain this issue appeared after I did the forks.
Both good, tyre balanced and seated correctly. Problem was there with the last front as well. Thing is it’s only whilst braking which is telling me it’s more brake related than the wheel itself but I’m no discounting anything. There isn’t anything shouting out at me because I’ve checked it all.
Headstock bearings? Wheel bearings? Brake pads seated correctly. Rare but found a detached pad from backplate once. Bike had been stood a longtime brake piston stuck on freed off and sintered pad had a clean through crack. is it same poorly seated tyre found at MOT? Or new?
Wheel bearings and head bearings are fine. haven’t removed the pads just visually looked, they looked fine but I’ll remove them just to see. The advisory was “front wheel has slightly distorted bead rim” so wheel itself not tyre.
Could you remove one disc and test? Then swap to removing the other. This would potentially tell you that the problem is at least disc related...
