Brake Pedal Sinking to floor

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Toyocel
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Brake Pedal Sinking to floor

Post by Toyocel » Fri Jan 29, 2010 9:02 pm

My brake pedal goes all the way down to the floor with very little resistance. I just changed the brakes (pads, calipers, drums). The fluid level is the same so I know there is not a leak. I checked on the interwebs and most of the sites say if the pedal slowly sinks to the floor it is the master cylinder but my pedal sinks to the floor with barely any force on it. Any ideas? Or is it just the master cylinder?

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ARCHINSTL
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Re: Brake Pedal Sinking to floor

Post by ARCHINSTL » Fri Jan 29, 2010 9:21 pm

You don't mention it - but did you bleed the brakes? To change the calipers (rear cylinders, too?), you do have to disconnect the lines and do the bleeding. If it worked OK before the work, it should work now. I've never had this problem myself on the T4WD, though - but after brake work I automatically renew the fluid while bleeding.
Except - a possibility is having the rear shoes way too far away from the drum; I had this on my Dodge/Mitsu truck until I realized my setup error.
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Toyocel
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Re: Brake Pedal Sinking to floor

Post by Toyocel » Sun Jan 31, 2010 8:00 am

I had the same problem before I bleed the brakes. I'll try tuning the drums. But the left caliper on the front clamps but not with a lot of force, when I apply the brakes I can turn the wheel with my hands with little effort.


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blade
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Re: Brake Pedal Sinking to floor

Post by blade » Sun Jan 31, 2010 10:12 am

well if you can still turn the disk on the front one i would say that the master is tost unless the is a leak some where of there is air in the system

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Petros
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Re: Brake Pedal Sinking to floor

Post by Petros » Sun Jan 31, 2010 11:19 pm

when you bleed the brakes there is a procedure you have to follow or you will not get all the air out and it will act like this. It is possible your master is bad, but you will not know for sure unless you get the air out.

Usually if the master is bad you can pump up the brakes, but if you hold your foot on it the pedal it SLOWLY sinks to the floor. IF you can not pump up the pressure, it sounds like air trapped in the system.

To bleed your system you have to first bleed the master at the line, have someone pump up the pedel and hold it while you crack the flare hose nuts on the master, than close them before they left off on the pressure. Once you get a clear stream of brake fluid from each line, than you go the rear wheels and bleed them the same way at the bleed valves, and than the front wheels. you must close the bleeder valve before you allow the person holding the pedal to let it up again to pump it back up. And keep checking and topping up the master, if it gets low you will pump air back into the system and you will have to start over.

Study the procedure in the FSM on the link from this site.

Good luck.
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artictercel
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Re: Brake Pedal Sinking to floor

Post by artictercel » Mon Feb 01, 2010 1:22 pm

A way to test where the problem is

You can take 4 pairs of vise grips and pinch each brake line on the rubber part. It the pedal feel right after you do that then the air or leak is somewhere downstream of the clamps. You can remove on clamp at a time to find the problem. If it is still mushy with the clamps on the brake lines then there is a problem with the master cylinder. If it pumps up as the previous poster stated then your master is shot. If it doesn't pump up then there is air in the system. I usually bench bleed a master before I install it. But it can be done on the car too. Remember to used the right brake fluid! Good luck.

4wdchico
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Re: Brake Pedal Sinking to floor

Post by 4wdchico » Mon Feb 01, 2010 2:57 pm

artictercel wrote:A way to test where the problem is

You can take 4 pairs of vise grips and pinch each brake line on the rubber part. It the pedal feel right after you do that then the air or leak is somewhere downstream of the clamps. You can remove on clamp at a time to find the problem. If it is still mushy with the clamps on the brake lines then there is a problem with the master cylinder. If it pumps up as the previous poster stated then your master is shot. If it doesn't pump up then there is air in the system. I usually bench bleed a master before I install it. But it can be done on the car too. Remember to used the right brake fluid! Good luck.
Just be sure to replace all of the brake flex hoses that have been pinched right away. LOL- great way to cause a hose blowout!

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Petros
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Re: Brake Pedal Sinking to floor

Post by Petros » Mon Feb 01, 2010 6:06 pm

it seems crushing the flex hose enough to pinch off the pressure would be ill-advised, espcially with an older hose. Not a good idea, you would have to replace the hoses as 4wdchico says, and than bleed everything out again anyway.
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'84 Tercel 4wd (daily driver, with on going mods)
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artictercel
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Re: Brake Pedal Sinking to floor

Post by artictercel » Mon Feb 01, 2010 11:49 pm

On a car this old I would be replacing the brake lines anyway. They are easy to replace. But if you want to find where the problem is it is the easiest way, if I was afraid that my brake line would "burst" after they had been pinched lightly for a few minuets.... Id be a bit afraid to drive the car.

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Re: Brake Pedal Sinking to floor

Post by takza » Tue Feb 02, 2010 3:55 am

If I recall right...I had about the same thing when I replaced my brake lines and MC....thought I was up sh*t creek. Ended up using a vac pump to bleed them out right...couldn't manage it with the typical method. Need to loosen the lines at the MC a bit and try to bench bleed it first...then go from there?
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