son has a 91 land cruiser, brake pedal goes to the floor and no pressure will build to bleed system. Master cyclinder was replaced with no change in pedal effect. Have found no leaks past the master cylinder.

Did you properly bleed the master cylinder? Did you bleed the entire brake system, LSPV and all?

You must make sure that you bleed the system in the correct order. I'm not positive, but I think that I started with the farthest line, ended with the shortest line, and then bled the LSVP. correct me if I'm wrong. But if you don't bleed in the correct order, then you won't have proper pressure. (or any in my case)

1. Drivers side rear
2. Passenger side rear
3. Passenger side front
4. Drivers side front
5. LSPV (Load sensing proportioning valve)

there you go, I had it backwards. But you have to bleed in that order. good luck.

So you have to bleed in that order (starting with the right rear) or else you won't get any pressure at all?

No, you can bleed it any way you want and still have OK brakes, but in order to get ALL the air out, you should bleed it in that sequence.

Thanks for the info. Is it SOP with this system that no matter how much you pump the brake pedal, it will not build up pressure until the sytem is bled in the right sequence. I'm talking, the pedal goes to the floor time after time. Usually a system can eventually build up pressure with air in the line with enough pumping.

I agree, you should have SOME brake pedal.

You never did answer though, did you bleed the master cylinder properly BEFORE installing it in the truck?

I guess it's possible you got a bad master too.

Maybe try gravity bleeding the brakes. Basically just open all the bleeder valves and let the truck sit for a while, may take 30 minutes, might take an hour or 2. You can even park it uphill to let the fluid drain back. Just keep an eye on the master cylinder, don't let it run dry or you will introduce more air into the system.

im just throwing it out there, but have you checked the condition of the brake lines? a couple of months ago, i pulled my truck to the back of my grandfathers lot. when it came time to leave, i asked my girlfriend to move the truck out front, so i can close the gates and finish everything up. when i got up there, she said that the brakes didnt work, and that the pedal had gone to the floor, and she had to use the parking brake to stop. i figured 250,000 miles on it, i must need a new master cylinder, as i had just done a brake job (new pads, shoes, turned rotors and drums). took it to school, replaced the master cylinder in about an hour and a half, after bench bleeding it, and tried it. still went straight to the floor. after goin through about two quarts of brake fluid trying to bleed it, a friend noticed a large, growing puddle under the truck. i looked, and asked a friend to push the brake pedal. beside the front left wheel, i was squirted by brake fluid. i inspected the brake line, and found that the exhaust manifold had melted through one of the hard lines, and the fluid was spraying out, and hitting me. ordered the line, replaced the line, and all was fine! so, like i said, check all the lines, hard or soft. <img src="/forums/images/graemlins/kewl.gif" alt="" />