I recently reworked my entire brake system and did install residual valves and proportioning valve. I have 4-wheel drums and don't need the prop vale now but put it in so I would be ready when I go to front disks in the future. I have ready many posts on different forums regarding needing or not needing residual valves but I put them in anyway. The system works well (considering it is all drums). I'm not sure it is better now than before when it didn't have the residual valves.
The reason for them is if the master cylinder is lower that the caliper or wheel cylinder, gravity allows enough back flow to allow the caliper to retract and the pads won't remain against the rotor, same for the wheel cylinders. It adds petal travel and can allow brake pad chatter, noise. That's the theory.
Duh! I confused the post... Sorry for misleading anyone!You are thinking of a residual valve, which works like a check valve.
When I decided to go with them, I understood that they should be as close to the mc as possible for that very reason, talking about the residual valves.So if you have a brake line that is for example 3' long, and you put a residual valve 12" away from the wheel cylinder or caliper. This is going to cause the 12" of line to maintain pressure. I get the feeling here that people are expecting a portion of the fluid in the remaining 24" of line to drain back to the master cylinder. If that happens, what replaces the drained back fluid that has left the 24" line. Air? Vacuum? I think I have to agree with @lincolnuT on this one.
Wait, we were talking about residual valves, somehow things got jumbled, lol.Duh! I confused the post... Sorry for misleading anyone!