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brake pedal drops slowly under pressure??

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Old 01-08-2012, 02:47 PM   #1
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brake pedal drops slowly under pressure??

1997 4runner 3.6 v6 auto 4wd stock rims and tires with abs. I have replaced the rotors with oem and added a set of duralast creamic based pads with new shoes and drums on the rear. Master cylinder and reservoir are new also. I have visually inspected all the hard lines and checked each wheel for leaks and the level in the reservoir hasnt dropped.

The entire system has been bled completely a couple of times using new fliud and no air bubbles remain at the wheels. When the engine is off you can pump the pedal 3 times and stand on it and it does not move. With the engine running if you let it sit for a short time and go for the pedal it drops almost to the floor (within an inch or so) then if you push it again it firms up but then slowly drops to toward the floor under pressure. The truck stops very well when you have a chance to pump the brakes first but that first push it feels like theres nothing there. This is my wifes daily driver and I have the same setup on my taco with no issues only diffrence is I have no abs. Please if you have any suggestions let me know!!!!! Im not sure what to do next.
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Old 01-08-2012, 03:49 PM   #2
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Check for loose wheel bearings. "Play" in a wheel bearing can allow the rotor ( and hub and wheel) to deflect from its normal rotation. This will push the break pads further back into the caliper than normal. Your first pump makes up this distance and the second gets the job done. (Assuming your calipers are tight) Sometimes wheel bearings can get pretty sloppy without making a lot of noise and a symptom like this can be the first hint that something is wrong. Unfortunately these bearings are a pain to change ( pressed in non adjustable and "sealed") If this is your problem, and you want to "DIY" , do a search, there are several REALLY GOOD write ups.
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Old 01-08-2012, 07:48 PM   #3
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Quote:
Originally Posted by micropiper View Post
1997 4runner 3.6 v6 auto 4wd stock rims and tires with abs. I have replaced the rotors with oem and added a set of duralast creamic based pads with new shoes and drums on the rear. Master cylinder and reservoir are new also. I have visually inspected all the hard lines and checked each wheel for leaks and the level in the reservoir hasnt dropped.

The entire system has been bled completely a couple of times using new fliud and no air bubbles remain at the wheels. When the engine is off you can pump the pedal 3 times and stand on it and it does not move. With the engine running if you let it sit for a short time and go for the pedal it drops almost to the floor (within an inch or so) then if you push it again it firms up but then slowly drops to toward the floor under pressure. The truck stops very well when you have a chance to pump the brakes first but that first push it feels like theres nothing there. This is my wifes daily driver and I have the same setup on my taco with no issues only diffrence is I have no abs. Please if you have any suggestions let me know!!!!! Im not sure what to do next.
Did it do this before you did all the brake work? It possibly could be the brake booster, the diaphram is ripped/leaking.
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Old 01-09-2012, 04:12 AM   #4
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Quote:
Originally Posted by Buggys3sgte View Post
Did it do this before you did all the brake work? It possibly could be the brake booster, the diaphram is ripped/leaking.
This is what I was thinking, this or the master cylinder seals are leaking by. If you don't have a leaking wheel cylinder, and your pedal slowly makes its way toward the floor at a stop light, one of those two things are bad.
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Old 01-09-2012, 05:07 AM   #6
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The front wheel bearings are less then 6 months old. Yes the pedal has been spongy since i bought the truck. Everything Ive done has made it better but its still not right. Is there a method for testing the booster or the seals in the master?? Thanks for your replies guys!!!!!
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Old 01-09-2012, 05:29 AM   #7
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There is another thread that is the same issue. In my case, it was the actuator. Read up on this thread:


http://www.tacomaworld.com/forum/2nd...2009-taco.html
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Old 01-09-2012, 05:08 PM   #8
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ok so it ended up to be your abs actuator? I will go and check if the rear shoes are close enough to the drum hat. That is something I had not checked. The master cylinder is less then a month old and is new not refurbished. Is it possible I got a bad one???? Again thanks !!!!!
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Old 01-10-2012, 03:31 AM   #9
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Quote:
Originally Posted by micropiper View Post
ok so it ended up to be your abs actuator? I will go and check if the rear shoes are close enough to the drum hat. That is something I had not checked. The master cylinder is less then a month old and is new not refurbished. Is it possible I got a bad one???? Again thanks !!!!!
Did you install it ??? If so, did you bleed it properly ? A master cylinder needs to be bench bled before installing, then I usually go around and bleed each wheel to be sure any and all air is out. Boosters rarely go bad, less often than master cylinders anyway. I suppose it is possible you got a bad master cylinder. But I would bleed the hell out of all lines first. I'll have to get back to you on a possible bad booster, I've never experienced one myself, I'm sure there is probably a vacuum check you could do on it, maybe someone else with experience could chime in.

Edit: Forgot to add... A wheel bearing, brake rotor, etc etc... has nothing to do with a spongy or fading brake pedal, I don't care what anyone says, it's completely and totally unrelated. However, a bad bearing could cause a vibration in the pedal as your are slowing down, and a warped rotor will cause a pulsating pedal which most people have experienced at some time or another. Once you are stopped, and the pedal starts going to the floor, something is leaking by.
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Old 01-10-2012, 03:57 AM   #10
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Ok, got confirmation on the booster... Get a little vacuum hand pump with a gauge if you don't already have one and make sure it's holding vacuum.

Adjust your rear shoes as mentioned. Make it so they're JUST free enough to allow the drum to spin by hand, even if they're rubbing just a touch that's ok as long as you can spin the drum.

If your cylinder was properly bled and you're sure there is no other air in the lines, you have a defective master cylinder.

One other suggestion is use a hand pump to do your bleeding if you're not already. It's the best way to make sure you're getting all the air out.

I hope this helps you bud !!!
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Old 01-10-2012, 05:27 AM   #11
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Yes I installed the master and bled it before according to the instructions included in the box.No air remained in it when reinstalled. I will go get a vacuum gauge and chek the booster for pressure. Thanks everybody TW rules!!!!
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Old 01-10-2012, 05:44 AM   #12
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Quote:
Originally Posted by micropiper View Post
Yes I installed the master and bled it before according to the instructions included in the box.No air remained in it when reinstalled. I will go get a vacuum gauge and chek the booster for pressure. Thanks everybody TW rules!!!!
If you go to sears, they have a nice little kit that includes the pump and some attachments, you can use it to check vacuum as well as bleed brakes or whatever. Harbor Freight has one for cheaper, but that one didn't last me very long.
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Old 01-15-2012, 06:00 AM   #13
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To update

It was the rear brakes not adjusted properly. I jacked up the rear and pulled the e-brake and spun the tires and thet just rolled. Thanks to everybody for the suggestions.
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Old 01-17-2012, 10:53 AM   #14
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Quote:
Originally Posted by micropiper View Post
It was the rear brakes not adjusted properly. I jacked up the rear and pulled the e-brake and spun the tires and thet just rolled. Thanks to everybody for the suggestions.
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