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Spongy brake pedal??


Toymota2
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Galant VR-4 org Post #: 996254 posted 05/30/11 02:14 AM     Remind Me!  Send Private Message   Edit Post      
My 89 ZR4 has factory ABS brakes which has been unplugged and sensors removed by the previous owner. The problem i am having is the brake pedal is very soft and can pretty much push it to the floor!!
I have changed the pads and bled the whole system with no improvement. Am I missing something here? Could it be my brake booster or master cylinder bypassing?

Any ideas would be appreciated.

Thanks.

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gsxconvert
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Galant VR-4 org Post #: 996262 posted 05/30/11 03:20 AM     Remind Me!  Send Private Message   Edit Post      
leaky line or caliper. or on the ABS unit itself. possibly the brake master itself see if its leaking between it and the booster.

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thedsmguy
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Galant VR-4 org Post #: 996310 posted 05/30/11 01:40 PM     Remind Me!  Send Private Message   Edit Post      
My car recently had the same issue and it was the master cylinder.

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toybreaker Galant VR4.org Moderator
it's peace of mind at 100 mph plus
1990/2000


Galant VR-4 org Post #: 996335 posted 05/30/11 03:33 PM     Remind Me!  Send Private Message   Edit Post      
A good way to narrow things down in this situation is to check and verify the various components as much as possible before tearing things apart.


To verify the booster is working correctly, hop in the car, and with the engine off, pump the brake pedal ten times to use up the residual vacuum.

The pedal will seemingly rise up and get harder to push as the vacuum is used up and "assist" is lost from the booster.

Now, hold the brake pedal down and light up the car.

The pedal should drop noticeably.

This quick test will indicate the booster is functioning correctly.



If it passes this test, you can verify that the master isn;t bypassing internally by just holding pressure on the brake pedal for a minute. If the pedal drops, fluid is bypassing around the cups in the master and it's probably junk.


If the pedal doesn;t drop, then it's time to look at the other components of the system.



Air in the system will give a spoongy feel.

Had any part of the hydraulic system been opened, or components replaced before the problem appeared or did you buy the car in this condition?

[edit] I see that you bled the system, are you sure you got all the air out?

Did you bleed the master?

Did you bleed the abs valve body?

/edit


A siezed slider/pin on a caliper can also give the pedal a spoongy feel.


Does the car pull/feel weird under hard braking?

Are any of the wheels significantly hotter/cooler than the rest?
... bear in mind the rears will be somewhat cooler than the fronts, but they should be approximately the same side to side, ... do NOT touch the rotors, (that shit is HOT!!! ) ... just feel the wheels.


At this point, you have to start somewhere, so please, check the booster and master cylinder as outilned above and update the thread so we can advise you further.


Edited by toybreaker (05/30/11 03:42 PM)

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Toymota2
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Galant VR-4 org Post #: 996594 posted 06/01/11 02:59 AM     Remind Me!  Send Private Message   Edit Post      
Thanks for the replies guys!

So I have just done the checks you suggested toybreaker and the pedal pumps up very firm with car off and as soon as fired up it sinks away as it should do but it is very soft and with a bit of effort I can push it right to the floor .

The pedal has been soft since I have owned it but only drove it a couple of times as I am trying to get it road certified which it has failed on due to brakes been crap!

I can see no sign of leaks from the master cylinder, abs unit, calipers or lines. So to me it points to either master cylinder issues or the abs unit playing up due to been not plugged in? I have a 2nd hand master cylinder lying around which I might give a try.

Quote:


Air in the system will give a spoongy feel.

Had any part of the hydraulic system been opened, or components replaced before the problem appeared or did you buy the car in this condition?

[edit] I see that you bled the system, are you sure you got all the air out?

Did you bleed the master?

Did you bleed the abs valve body?




I bled the calipers rear to front then bled the abs unit with no sign of any air bubbles after giving the pedal 10 pumps on each.

Thanks again.

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chrisfullwood
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Galant VR-4 org Post #: 996863 posted 06/02/11 10:55 AM     Remind Me!  Send Private Message   Edit Post      
OK this might be a stupid answer/question but you said 10 pumps at each corner, are you using speed bleeders, or did you actually close off the bleed screw during pumping?
Again i know it may be a stupid question / answer, but the only stupid one is one that didn't get asked right.

If you just leave it open while pumping, it will suck air back in and force bubbles further up the system, so you might be in a situation where your forcing the fluid out, but bubbles are still part way in the system. especially the back, remember there is a deceptively large amount of fluid, and a long way for it to go to the back wheels.

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Toymota2
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Galant VR-4 org Post #: 996962 posted 06/02/11 09:47 PM     Remind Me!  Send Private Message   Edit Post      
I use a tool which has a one way valve in the line so I am thinking using this I can just pump away with the bleeder cracked open then shut it off once done?
I have used it on many other cars before with good results. Thanks for your input though, if all else fails I will go back and try it that way.

This afternoon I swapped the brake master over to the 2nd hand one I had lying around which seems to have made the pedal a little bit harder but not a hell of a lot. When the car is revved up the pedal feels good, just when idling it feels soft.

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Nabeel
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Galant VR-4 org Post #: 997111 posted 06/03/11 06:56 PM     Remind Me!  Send Private Message   Edit Post   
It sound needs proper bleeding only.



91 VR4
09 GT eclipse
91 Cefiro

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