Brakes : Pedal going away

[maxrevs85]

Today I drove my car to work. On the way home I was loosing pedal . It was going soft . I was in traffic and conditions where the same as usual and the temp has been the same . I mension temp because the brake lines get pretty hot by the headers on the drivers side and the master cyl gets pretty warm too. I don't think much more so then any other vette. I'm wondering if the mastercylinder is going bad . Fluid is full , it is dirty and needs to be flushed. But it seems to go all of a sudden and then got worse . By the time I arrived home the pedal was practicly on the floor. There are no visable signs of leaks at any wheel or at the mast cyl. Any ideas?

 

[ErnieN85]

Most likely needs a new master cylinder. internal leaks show up as the pedal going soft or away! change it soon if there is no indication of leaks elsewhere.

 

[maxrevs85]

Thanks Ernie , That was my take on it too.....strange how it went so quickly....

 

[Vettelt193]

if the pedal is ok when the car is cold, it is the fluid... you would be surprised how much a fluid change can change your brakes

 

[Fiddler's Gold]

Yeah, looks like a problem!

Well, it sounds as if your fluid has broken down and it is simply not providing what you need to "do the braking" -
The heat that builds up in your drums and rotors (in certain cases the surface temperatures of which can exceed 1333 degrees fahrenheit) also causes the brake fluid to heat up. This is why DOT #3 and DOT #4 brake fluids usually have a boiling point which surpasses 401 degrees fahrenheit. DOT #3 and DOT #4 brake fluids are made from Polyalkylene Glycol Ether which, by nature, has a very strong attraction to water (brake fluid is hygroscopic). Water contaminating brake fluid makes its boiling point drop which causes bubbles to form in the brake fluid (imagine sprinkling water into a frying pan full of hot oil). Bubbles and water are more compressible than brake fluid which makes it more difficult for the master cylinder to compress the brake fluid and in turn, compress the calipers and brake drums. A sign of this may be a low, soft, or spongy brake pedal feel (caused by the the contaminating bubbles and water compressing before the brake fluid does).

Liekwise, DOT #5 brake fluid, on the other hand, is formulated from silicone. While silicone is not hygroscopic and has a higher boiling point than DOT#3 and DOT #4 brake fluid, any water that gets into the brake system will sink to the lowest point of that system (water being heavier than silicone) and may potentially find its way to the calipers, boil at 212 degrees fahrenheit and cause a vapor lock which could cause brake failure.

You need to determine, what color or how you are determining the "dirty fluid" --- The color of the brake fluid itself, offers a clue. New, clean brake fluid usually has a golden color (unless it is DOT #5 which may be purple or yellow), while dirty old brake fluid is brown or if heavily contaminated, black. A brake fluid moisture tester can also be used to gauge the purity of the fluid in your brake system. So for the record, draining and replacing your brake fluid helps to remove contaminants (such as water and rust) and to lubricate the metal and rubber parts of your brake system (like the master cylinder, brake lines and seals, valves, wheel cylinders and caliper pistons) which may help them last longer.

HTH,
Andy
-=The Fiddler=-

 

[Fiddler's Gold]

One more thing...

The extra heat generated and being expelled near to the brake lines may just be enough to cause the heat problems and/or overheating of the fluid and thusly the soft brakes. Additionally,
the heat generated from braking & potentially the brake lines in the engine bay near the headers, etc may be causing the chemical composition of the brake fluid to change. Gasses are boiled out of the brake fluid and since these gasses are more compressible than the brake fluid they came from, you will notice a soft or spongy brake pedal feel.

Probably exactly what is causing your problem. Might want to replace the fluids and get a a therma-scan of the C/F degree test of the lines during normal or traffic operation.

HTH.
Andy

 

[JonM]

If I were you, I would also change the break pressure switch on your MC. Your break light should have gone on if the preassure was uneven.

 

[maxrevs85]

Thanks guys for the info . If you have followed my 85 engine project thread ,which is not my 85 engine breakin thread, you'll know all the things ive done to the car. The brakes were to be my next off season project . I basically was driving it to get a few miles on it and get some of the bugs out. I'm not surprised of this condition. Its one of them normal repair items . I have 114000 miles. I believe the heat could be a contributing factor even though I've drove it under the same conditions before. I know from my racing days what heat can do to fluid. I'm going to insulate the lines when I do the entire job. Thje dirty , very dark fluid surely isnt good either. The flush and refill was to be done next.But i figure for $150 i can put a new master cylinder on and be done with that part. Then Braided lines and any other upgrades I can afford. The rest of the chassis has been upgraded.I would realy like to do the BIG brake ugrade,but then its new wheels and tires etc..........

 

[vigman]

Had the same on my 84 & 88

As the fluid gets funky..it chews the O rings
( not to mention the bore ) and the FIRST place I would look it the back of the master on the Vac booster underneath... you MIGHT see a bit of sweating brake fluid which means the rear seal is GOING.

If the pedal fades.. and you can pump it up it's typically the master.

Put on some gloves, run your fingers around the inside of the rim

Just dust...cool

Black gunk...not cool, leaking wheel cylinder.

Are you loosing fluid?

If it's the fluid.. try this trick

Steal a turkey baster.

Check the pedal... soft?

Suck all the old fluid out.. take a paper towel wipe the inside of the resivoirs.
Put new fluid in. Only fill 1/2 way
( both front & rear resivoirs).

... Have somebody pump the pedal 2 or 3 times... did the fluid turn color again?

Do it again till semi clear

Got pedal?

If yes fluid is VERY BAD....
If same... bad master..( or leak someplace else in system.)


Vig!

 

[maxrevs85]

Vig, previously i did draw the fluid out of the res. and refilled . It turned bad again . Also the pedal wont pump up. I agree that the fluid as taken its tole on the o-rings and the bore . Since i have been refurbishing everthing on the car anyway I would feel better installing a new one and crossing that off the list. I'll address the calipers at that time too. I dont drive it every day and it was purchased have fun with and that includes the work involved too. I've been involved in cars all my life . If I had to pay to have it all done it wouldnt be the same for me .I also enjoy comparing notes. There is always something to learn .... oh yea, where's your buddy shadow? been kinda quiet. :L

Oh yea , I'm not losing any fluid anywhere, dry as a bone at all corners.

 

[Vettelt193]

looks like shadow quit, or got the boot from CAC... he is no longer in the members database

 

[vigman]

It was a joke

He got the boot!



Vig!

 

[Vettelt193]

i didn't get the memo!

 

[maxrevs85]

No e-mail either......

 

[vigman]

But Rob DID post a letter

Gotta find it
BRB!

Vig!