I have a weird issue where I can use the front brakes no problem, but as I ride or as the ambient temperature warms up the pressure increases in the brake system until it locks the front brakes down and the brake lever is hard. I can then crack the bleeder and everything returns to normal for about 10 to 15 minutes depending on how hard I am riding before happening again. Have you ever experienced this or have any ideas of what it might be?

 

Yes it is a master cylinder fault. Usually the piston is not returning fully, so the hole between reservoir and cylinder is always covered by the piston. As fluid expands, it can't flow back into the reservoir, so puts the brakes on, creating more heat, so fluid expands more and puts them on harder.

 

Yes like merryman says front master cylinder is issue most likely gummy brake fluid and return hole is blocked inside could try to fluid and bleed system real good if not may have to take master cylinder apart clean,and it rare brake line issue

 

I will order the stuff to do a master cylinder rebuild. Any recommendations on a good online supplier? I really hate using cheap Chinese stuff if I can avoid it.