What would cause spongy brakes besides air in lines? - Third Generation F-Body Message Boards

MrsLottaBallsCamaro · 03-24-2002, 08:50 PM

I have 4 wheel discs on the IROC, and ever since I got the car in January, the brakes have felt spongy. The first half of the brake pedal does absolutely nothing. I bled the brakes, but there was no air in the lines. What else would cause the the sponginess? I was thinking maybe the master cylinder.

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fbodyfreek · 03-24-2002, 09:36 PM

I think your right about the the master cylinder. Thats the only thing I can think of unless you have a leak somewhere.

86iroctpi · 03-26-2002, 12:05 AM

I have the same problem. I have tried replacing the master cylinder twice, both front brake lines, rebuilt the rear calipers, bled the lines numerous times, and I still have the problem. It is better, but it still isn't as good as I would like. Any other suggestions on solving this problem would be greatly appreciated.

racereno · 03-26-2002, 08:19 PM

My first guess would have been the outer brake lines. But let me open up a good can-o-worms, how about worn out brake fluid?

TomP · 03-26-2002, 09:50 PM

Uh oh; should I yell "rear caliper recall!!!" again? See my last message to 86TpiTransAm about the prop valve... my brakes were so spongy I had to double pump my pedal to get any decent braking.

racereno · 03-26-2002, 09:56 PM

Good call TomP. I've heard those units can act pretty nasty when they go.

I still wonder how many thirdgenrs have replaced their brake fluid ever.

turningfast · 03-27-2002, 12:23 AM

Tom P (uh oh: should I yell "rear caliper recall!!!" again?) is right, when the pads wear and the pistons come out of their bores further they use more fluid. You may not have found it or seen any posts yet, but this is a big problem with the early disk set up for these cars. Take a look at the rear pads, if there is a lot of space, like an eigth of an inch or more this is the cause. Look more at the piston or inboard side, since the sliders could be sticky.

LottaBallsCamaro · 03-28-2002, 11:57 PM

racerreno- I cant find that post, sould you post a link to it? Thanks!!

fixomatic · 03-28-2002, 11:59 PM

NEW to this board,but i logged in to post about this very problem about spongy brake i have an 88 firebird with a v6 that i'm selling and i just bought an 84 with 305 both have the same problem..and it would be nice to fix this problem two master cyl i have bleed the S out of them i have been working on cars for years and never had such a problem as this i have pulled apart the porportional and every thing looked good i made plugs out of cut brake line and welded the ends capped the master cyl opennings one at a time and have narrowed it down to the front brakes being spongy. i have removed the calipers and used a C clamp to hole the pistons and bled the brakes and holding the calipers for the best possible way for air to escape from them.........so do i change the porportional valve or are the braks on theses car spongy???????

MrsLottaBallsCamaro · 03-29-2002, 01:13 PM

Our 91 RS has front discs and back drums and it braked a hell of a lot better than the IROC with the 4 wheel discs! And I don't think that the back brakes on my car is what is causing the sponginess, either.

TomP · 03-29-2002, 05:55 PM

If the rear pads aren't as close to the rear rotor as they should be, then the "first half of the brake pedal" is wasted on moving the rear pads closer to the rear rotors.

I actually had to double-pump my brakes before I put the rear caliper recall kit on. The first pump moved the rear pads to touch the rear rotor. Then I'd let off the brakes quickly, and do a quick second pump- the pads never got a chance to retract, and all of a sudden, the car would brake nice and hard.

Try that! Try double-pumping the brakes when you're driving. The first pump should be a quickie, then on the second pump, keep your foot down. If you suddenly stop really well, it's probably that damned recall again. Here's a link to the message I mentioned: http://www.thirdgen.org/techbb2/show...threadid=94532 (Where exactly is the proportioning valve??)

And fixomatic, those cars have the rear drums, right? If there's sponginess in the front brakes, don't forget that these cars have the quick take-up valve in the master cylinder. That thing's a bitch to bleed and get alll the air out of. You might want to look into replacing the front hoses. Over time, brake hoses crack on the outside, and deteriorate on the inside, and mess up the brakes. You might have partially clogged front hoses! Did you use a sealer resistant to brake fluid on the cap of the prop valve when you put it back together?

Also, that '84 probably has a cast-iron master cylinder body. GM moved to aluminum bodies in later years, since the cast iron jobs can rust inside the bore. A little rust and a rubber seal = torn seal.

fixomatic · 03-29-2002, 09:40 PM

tomP thanks for the input, but i feel for the most part the master cyl is ok. if you cap both holes you get a hard pedal. and on both cars they are alum. i had a friend step on the brake and i just held the lines to see if they would balloon up at all and i could see no sign of a problem......but i will not rule it out.........i have replaced lines in the past on cars that had problems like pulling to one side and found that they had colapsed....and what about this i has one car i fixed that you would step on the brake and it felt fine but when you release your foot the brake on the right side would not release .......bad brake line it held pressure after you let your foot up...i will post on what i find

racereno · 04-01-2002, 09:29 PM

LottaBallsCamaro sorry so long to repost but I've been waiting on parts. Just got some PA Racing tubular a-arms and an Edelbrock STB. Pheonix Injector bleed system is coming so I'll know more about the brake situation then.
The reason I mentioned brake fluid before was I've had some small caliper problems the last couple of years. Upon disassembly I noticed the piston was sticking because of a "rusty" spot or two in the cylinder. I've replaced calipers twice so this time I got new hoses and calipers and will flush and replace the brake fluid (the stuff looks nasty). Cya guys soon.

86iroctpi · 04-02-2002, 12:54 AM

I installed the recall kit in my rear callipers, and still have spongy brakes. The brakes catch early when I hit the pedal, they just don't seem to want to stop.

BlownBird · 04-02-2002, 10:05 AM

TomP, You are the man! I have had bad brakes for over a year now. I have tried everything, I now have an aftermarket master cyl, Aerospace brakes, new lines, and still had a problem! I went out to the garage after reading this post (and the linked post) and I'll be damed, the pass rear caliper was a 1/2" away from the disc. I want to thank you for answering "the unsolved brake problem" that has plagued me, an many others. You are the man! :hail: :hail: :hail:

TomP · 04-02-2002, 07:55 PM

Beautiful! Glad I could help!! It's my way of "getting revenge" on those brakes for all the times I wasted bleeding them.