Modern Vespa

On the used 2009 GTS I recently bought, the rear disc had cracking and seemed to have a high spot when the tire spun almost all the way around. I bought new rims (13") with new tire, replaced the disc brake and bought a new caliper with new brakes included. Brakes were really tight on install so I sanded the brake pads a little and everything seemed fine.

Well after about 100 miles, the rear disc seems to have developed that high spot again, where the wheel rotates freely until it hits that spot. If I go for a spin without using the rear brake, both the caliper and disc are very hot to the touch?

Other then maybe replacing the hub or the hardware spacers that hold the wheel on, I am unsure how to fix?

Any recommendations would be appreciated.

Only thing I can think of off top of my head is a problem in master cylinder.

Not familiar with the design of a GTS master but most all masters I have seen on motorcycles and other applications have a small hole in the bore just toward the pressure side of the piston. If this hole is plugged or the lever for some reason does not let the piston back far enough to uncover the hole there can be pressure held in the line and caliper that will cause the brake to drag. It can get to the point the bike/scooter will not move.

The hole is hard to see in this picture but it's the one above the red arrow. The other hole is much larger. Very possible that a tn year old scooter has sat too long and crud has plugged the hole!

I would try applying rear brake several times while on center stand and see if it gets hard to turn by hand. Then crack the bleeder on the caliper and without touching the brake lever see if the wheel now turns. If it now turns free there is about a 90% chance that hole is plugged or there is a problem with the lever that operates the rear brake.

Thank you! I will play around and see what I can do about it.

Overfilled reservoir? Another possibility.

Yes that could be a possibility, no room for normal expansion. Never had it happen, but "Never say Never!"

Thanks -- I am going to do a fluid bleed tomorrow and see how the fluid looks, since I feel like I have been boiling that rear fluid with the high temperature of the caliper. Long term plan is to replace the rear bearings, hub and the spacers to see if that helps a little bit. Might almost try to sand the brakes a little bit more. I guess the challenge I really have is that I don't know how freely the wheel should spin and what the rear should feel like when accelerating since this Vespa was really beat up when I bought it. Right now it sorta feels like it is dragging and I don't believe that is normal.