S 10 brake booster causing spongy pedal? (Page 2/3)
Rickady88GT OCT 08, 12:02 PM
All 4 calipers appear to be working fine. I religiously use my parking brake. It is in good working order. They wear the pads about the same, left to right and front to rear. With the exception of the rears have slightly more wear on the outside pads. But rears wore exactly the same.
I do not remember attempting to bleed the proportioning valve?
82-T/A [At Work] OCT 08, 12:58 PM

quote
Originally posted by Rickady88GT:

My 88 has a good pedal feel with engine off, but start the engine and the pedal gets spongy. I know the booster takes out some petal feel, and that the pedal will go down a bit, but this seems extreme. So does the booster go bad like this?



Lots of things, but I basically concur with everything Ogre has said. Here are some instances where I found spongy brakes to be caused:

1 - Old flexible brake lines (between the steel lines and the calipers.
2 - Worn pads = greater distance
3 - Air in brake lines
4 - Failing master cylinder, e.g. the piston seal is corroding allowing fluid to escape.
Rickady88GT OCT 08, 01:18 PM

quote
Originally posted by 82-T/A [At Work]:


Lots of things, but I basically concur with everything Ogre has said. Here are some instances where I found spongy brakes to be caused:

1 - Old flexible brake lines (between the steel lines and the calipers.
2 - Worn pads = greater distance
3 - Air in brake lines
4 - Failing master cylinder, e.g. the piston seal is corroding allowing fluid to escape.


Yah, I also agree in theory, but in practice it is a little more difficult to trace it down. The lines are SS, and the pads look new with no visible gap. VERY slight drag on every disk, only enough to hear it drag. The park brake holds the car in place on an incline.
Air in the master or proportioning valve is a possibility as well as bad cups in the master.

[This message has been edited by Rickady88GT (edited 10-08-2021).]

mmeyer86gt/gtp OCT 08, 02:36 PM
how old are the ss brake lines
Rickady88GT OCT 08, 03:45 PM

quote
Originally posted by mmeyer86gt/gtp:

how old are the ss brake lines



10 years?
theogre OCT 08, 04:27 PM

quote
Originally posted by Rickady88GT:
If the bar moves, shouldn't I be able to use an Ohm multimeter to check it, without removing it? It reads open right now, this is what I expect from a normal poison. If the bar moved shouldn't I get resistance?

Yes. The 2 pins Will show a "short"/close reading 0Ω when the bar moves.

Bar middle is sealed by "o-rings" and never get brake fluid there so the Switch never sees system pressure.
Can check/replace w/o causing other brake issues But don't leave switch hole open to air for hours to days either.
Any Tiny amount of fluid getting in the bar middle draws water from air and can drop crap in there.
82-T/A [At Work] OCT 08, 10:31 PM

quote
Originally posted by Rickady88GT:

10 years?



My thought also here... I wouldn't go replacing them necessarily... but they technically aren't stainless steel, but instead rubber hoses with steel braiding around them. They can still swell and expand.

My thought though... master cyl... the "cups" as you said (didn't know that's what they were called). I had a Fiero sit for a long time, and I reused the same master cyl (which was new a couple of years before I let it sit) and no matter how much I bled the lines, it still felt spongy. Just a thought...
theogre OCT 08, 11:47 PM

quote
Originally posted by 82-T/A [At Work]:
My thought also here... I wouldn't go replacing them necessarily... but they technically aren't stainless steel, but instead rubber hoses with steel braiding around them. They can still swell and expand.

Not when have "real" SS soft lines because inner core is Teflon tube.

That said... SS soft lines in street cars have never been good idea no matter how much BS is published by the makers.
And while newer ones labeled as DOT sets, that cert is Voided as soon as you add anything to support/protect the hose like many use zip ties and other things to keep the hose away from tires etc. That also Voids most SS soft line Warranties too even when they come w/ the hoses.

When replace old OE "Rubber" or SS lines get sae j1401 "rubber" hose.
Uses same hardware as OE w/ much better "rubber" hose. Often sold as "pro grade" parts.
See https://www.fiero.nl/forum/Forum2/HTML/129208.html
82-T/A [At Work] OCT 09, 09:34 AM

quote
Originally posted by theogre:

[QUOTE]Originally posted by 82-T/A [At Work]:
My thought also here... I wouldn't go replacing them necessarily... but they technically aren't stainless steel, but instead rubber hoses with steel braiding around them. They can still swell and expand.

Not when have "real" SS soft lines because inner core is Teflon tube.

That said... SS soft lines in street cars have never been good idea no matter how much BS is published by the makers.
And while newer ones labeled as DOT sets, that cert is Voided as soon as you add anything to support/protect the hose like many use zip ties and other things to keep the hose away from tires etc. That also Voids most SS soft line Warranties too even when they come w/ the hoses.

When replace old OE "Rubber" or SS lines get sae j1401 "rubber" hose.
Uses same hardware as OE w/ much better "rubber" hose. Often sold as "pro grade" parts.
See https://www.fiero.nl/forum/Forum2/HTML/129208.html[/QUOTE]


OGRE, are there any "stainless" brake lines you recommend at all for a car that you were completely restoring / rebuilding? Or would you just use the rubber lines you mentioned in the link?
Mickey_Moose OCT 12, 02:11 PM
I recently had this problem as well. I just had to remove the master and bench bleed it properly - all is good since doing that at the start of the year.