Brake pedal sinks to floor engine on

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AZ Highlander

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I had the same problem. Replaced everything associated with brakes and then replaced the master too. A wise friend told me to have someone pump the brake pedal while I take my rubber gloved thumb and finger to plug the ports on the master while the friend pumped the brakes until fluid came out and forced my fingers away from the ports enough for brake fluid to leak out the master at those ports a little. That’s the only thing that worked. I tried all kinds of ways to bench bleed two different masters, but with all the air stuck in spots, the fingers as temporary plugs is all that would actually fully bleed the master.
 

Mark Ugrich

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Make sure the check valve on the booster is working correctly.The pedal should be hard with the engine off, then with pressure on the pedal, start the engine and the pedal should drop slightly.that is the procedure to check the booster. If everything checks ok but the pedal still goes to the floor, you may have a defective booster.
 

Cyrillious

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Don't know if this helps but did you check the proportioning/prop valve? (Brass looking part under the radiator). If your brake warning light is on check it. The spool may have shifted.
 
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Cdog_96

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I have metal fittings plugged for when I am doing this operation, but light pressure is all you need to do a quick test, so the plastic plugs should be sufficient.

One thing I've not seen discussed yet is whether or not the fluid level in the master stays the same after several dozen pumps with the engine running. My thought process wonders if the master is leaking out the piston seals and into the booster. Tbe odds are really slim, but it is something to consider if the pressure check comes up empty.
It stays the same level, I'm going to try process of elimination and plug off the ports and see what happens, part of me thinks the rears aren't adjusted properly which could be my issue
 

Radiohead

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Severely unadjusted rear brakes would allow excess pedal travel. I'm sorry, I thought that was eliminated earlier or I might have mentioned that. Keep us updated.
 

Cdog_96

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If I don't have plugs I just pound an old line shut with a hammer,fold it on itself pound it shut again. I'm too lazy to break out the oxyacetelyne.
So with rear port plugged off and front line still in, the pedal felt better and came to a stop. With the front port plugged off and rear line still in, pedal felt the same sank to the floorboard. I had one double threaded plug available so I couldn't plug both off at the same time
 

CountKrunk

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I assume you'll need to plug up both rears to rule out issues in the rear.

And
I had the same problem. Replaced everything associated with brakes and then replaced the master too. A wise friend told me to have someone pump the brake pedal while I take my rubber gloved thumb and finger to plug the ports on the master while the friend pumped the brakes until fluid came out and forced my fingers away from the ports enough for brake fluid to leak out the master at those ports a little. That’s the only thing that worked. I tried all kinds of ways to bench bleed two different masters, but with all the air stuck in spots, the fingers as temporary plugs is all that would actually fully bleed the master.
This is what VGG does I'm pretty sure.
 

Radiohead

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Doing it one system at a time is exactly the right way to eliminate the good parts. Are the rear shoes truly adjusted up?
 

Cdog_96

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So we know the problem is in the rear,double check adjustment,shoe placement( if 1 shoe is bigger it goes on rear position,and look hard for leaks.
Rear brake shoes were way out of adjustment, rubbed my thumb raw spinning the adjuster wheel and got the drum snug against the shoes. Decent pedal now with engine running but still doesn't feel right, bled all four corners again no air so it might just be in my head. Will test drive this weekend I appreciate the help
 

Ricko1966

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Rear brake shoes were way out of adjustment, rubbed my thumb raw spinning the adjuster wheel and got the drum snug against the shoes. Decent pedal now with engine running but still doesn't feel right, bled all four corners again no air so it might just be in my head. Will test drive this weekend I appreciate the help
Backup and stop multiple times on your test drive. I'll bet with a little driving your brakes will self adjust and feel good.
 

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