I was thinking a warped rotor too. can I check that with a straight edge? or how would you go about checking that?
The wheel weight was still on in the correct spot.
Before checking the disk confirm the following:
- The wheel balance is still correct (and yes, I know you say the wheel weight is still in place)
- The fork oil volume is correct and has been replaced since Sinatra was at #1.
- Head bearings are correctly torqued.
If it is a disk related issues there are four things you need to consider:
1) Have the disk's glazed? Unlikely to cause judder, more likely noise.
2) Are they sitting square on the wheel flange. Unlikely to be the issue unless you have recently taken them off or replaced them.
3) Disk run-out.
4) Disk thickness variation.
3 & 4 can cause juddering. With 3) The calliper pistons get pushed in on one side but the opposite pistons come out. Therefore you need a (relatively) large distortion to cause an issue.
Conversely, with 4) both pistons are pushed out thus less variation will give rise to judder.
On that basis I would check both.
For a quick run-out check lift the front wheel and arrange a pointer so it I within (say) 1 mm of the wheel.
Spin the wheel and any warping will show as a variation in the gap between your pointer and disk face.
Accurate check: use a Dial Test Indicator (DTI) to measure any run-out.
For variation a micrometer is needed (vernier callipers are best avoided in all but a brand new disk because as the pads wear the disk it will leave a lip which most callipers can't bridge. It is the swept area of the disk you are measuring).
Maximum run-out is 0.15 mm (vented type ) and 0.3 mm (solid)
For thickness variation <0.008mm
If you want to become a brake Guru then you could do worse than committing
this to memory. Pages 30 & 31 are particularly relevant.