I have chevy 1/2 ton runner gear under my 88 4 runner and when the runner is not running it has good break peddle but when you start it up the brakes go to the floor. Anyone have any ideas? new mastercylinder? eliminate the porportining valve?? thanks

 

I believe you have air in the system. From this site here is this:

The proper order for bleeding the system is to start with the longest hydraulic line and work around the vehicle to the shortest line, and then do the LSPV last. So in this case, the order is: driver's rear wheel, passenger rear wheel, passenger front, driver's front, LSPV.

And about LSPV removal, it's fairly straight forward. There are plenty of threads on here. Also do a Bing search.

Also more detail about what's going on will help with us giving you help.

 

X2. More than likely you have air in the lines. Start the truck have a buddy pump the breaks till there is some pressure. Keep pressing on the pedal. You open the blending valve let the fluid run out a sec. Close the valve. Have your buddy let the pedal off the floor and pump the pedal same as in step 1. It helps to get a fluid catching bottle of some sorts with a hose that slips over the bleeder valve this lets you keep the old fluid off the ground and lets you see when no more air is coming out the valve. Follow the right bleeding order and you should be good to go. Some times it takes a little bit but you will get there

If you already know this then disregard