My rear tires/rim be locking on me randomly when i drive.. when it first started i pop my hood open and saw that the proportion valve was leaking and had it replace.. and bleed the brakes.. it stop locking for a day then it locked again the next day.. i did a disc brake conversion because i found out my brake drum was warped.. when i did the conversion i re-bleed the brake and did everything properly.. it was riding good, no locking or what so ever.. for about almost a month now.. and then it started locking on me again recently.. but when my nephew test drove it for two days straight it doesn't lock.. then i drove it earlier it was cool.. then coming back home it started locking again? theres no leaks.. can it be the caliper? or brake booster and master cylinder? help.. oh yeah my car is a Honda Civic Hatchback 92' stick shift..

 

Make sure the system isn't contaminated with a substance other than brake fluid. Oil-based materials will destroy all the rubber parts in the system, leading to lots of problems. Check the rubber seal under the cap on the master cylinder reservoir is not swelled and distorted.

Dragging will occur if the master cylinder does not return to the fully out position when no one is pressing the brake pedal. Often you can try just adjusting the stop light switch so the pedal comes up a little higher. There is also an adjustment nut on the pedal side of the booster.

 

thanks for your help, i'll do that tomorrow after work