Okay rocket scientists need help with this one

[lowlife]

Front brake grabs and lets go rhythmically like a warped rotor. all rotors have less than .005 of runout and has no deviation on thickness. Parts are all tight. this is driving me bug **** as its very disconcerting in a corner. i spose I can go out and measure runout again. I am watching the upgraded caliper thread very closely, as this may be my next upgrade to the bike.

 

[zlMark]

I'd let the front hang and check for drag on caliper. It may be heating up and warping when hot. and check wheel bearing play. Caliper slides need to be free. I use silicone based brake lubricants only!

 

[MachIV]

ZRXs have been known to do this and it`s usually
because they need a good cleaning.

 

[bigjeffie]

both tips are correct.
thoroughly clean all components, disassamble and flush calipers, even master cylinders. how old are the lines?
20 years was enough time to fill my system with junk.
if you replace all or most of the seals etc and wipe all that crud out of the calipers, there will be an immense improvement in performance