ok i just did the IFS brake swap on my 85 runner and i replaced the master cylinder and now i have no brakes except for the rear. i bench bled the new master then stuck it on and bled the lines, ive put 3 bottles worth of fluid through it and still no pedal. you can pump the pedal up and get pressure but when you release it and let it sit for 1 second it will lose all pressure again. also you can pump the pedal and watch the fluid in the reservoir go down, then when you let off the fluid fills right back up, like theres some void being filled then released?? i even changed back to the old master cylinder to see if the new one was messed up and the same thing happens. i just dont get whats going on. could the vacuum pump be messed up? it cant be air in the system, ive bled the hell out of everything. anyone got any ideas?

 

Check your metering and proportioning valves. I think this will lead you in the right direction.

-Wrench

 

ok i bled the rear proportioning valve, overlooked it the first time and still no change. by metering valves are you talking about the little junctions on the passenger side above the frame rail?

 

Ummm, I'm not entirely sure of your set up. You mentioned that you did a brake swap? I take it this means that you changed the front calipers? If so and then you changed the master cylinder too? By changing component sets you have to factor in just how hydraulics work. If you change the relationship between the size of pistons inside the master vs your wheel cylinders or caliper pistons you are bound to have some problems. Are the bores of equal or unequal size?

Don't fret, this is usually a simple fix. You may need a different master or you may need to go with an adjustable rate proportioning valve, that is, a racing type p-valve. These are available at most hi-performance shops. I would try and contact someone who has done your exact swap (and someone with the same original set up) and see what components they used or had to change. Hope this helps.

-Wrench