Hi new to the site here very helpful in the past so I thought I would join. My son has a 97 4runner sr5 and we did a brake job this weekend on it. Two new wheel cylinders and new calipers. I also installed a new master cylinder. Bench bleed the ms then all four brakes in the proper order. There are no air bubbles in the tubing when I bleed the brakes. Get good pedal pressure with the truck off but when I start the truck the pedal sinks to the floor. There are no external leaks. I need some help!!! Thanks

 

Connected vacuum lines back up correctly? Im assuming you pumped pedal after start up?

 

Yes lines are hooked up correctly. Yes pumped the pedal up after started engine but the pedal will hold pressure for a short time then goes to the floor.

 

Well if thats the case i would look at the master cylinder. Is it an oem part?