Brake Pedal Fade Yikes!!

[69vettester]

My bakes are stock manual and work just fine at sea level , where I live. but if I go up to 4kft elevation + the brake pedal wants to almost touch the floor, and I have to start pumping them or my brake like will come on. Man it's scary comming into a town at 50 with the brakes being puny like that. They return to normal as I come down in elevation! any advice short of brake upgrade.
Thanks..
TomC

 

[Yoda]

Brake Fade.. I know of this FIRST Hand..

Tom,

I had this very same problem, rather than go into a lengthy reason why it happens, I'll let you know what I did to remedy the problem.

I tried to bleed the brakes.. there was so much gunk in the lines that very little fluid would come out. I took it to a brake shop (mom and pop type) and explained my problem, and not being able to bleed the brakes??? The ole boy there asked if I could leave the car.. I said sure...

He power bled the brakes, cleaned the master cylinder really good then filled them with DOT 3 and power bled them.

He told me that the only clear looking fluid was in the master cylinder. I drive mine up to Lake Tahoe and Reno both over 8,000 feet and have had NO problems. His explaination had to do with small air bubbles, gavitation and about 10 more minutes of explaination, bottom line was the brake fluid had probably been in the lines since 1981 and was useless over 2,000 feet

I recommend NEW Brake fluid...

 

[Eric]

Same thing happened with mine and, like Bud, I flushed with new fluid and saw some pretty disgusting gunk coming out of those lines. The flush was in preperation for a complete brake system overhaul but now I'm wondering if I need it because the fluid flush made a HUGE difference.

Here's a thread discussing the different fluids available. I used Valvoline SynPower dot 4 on the advise of some other CACers. http://www.corvetteactioncenter.com/forums/showthread.php?s=&threadid=4145

 

[69vettester]

OK, That makes sense, Ill flush and refill. Looks like Ill need to research for the best fluid?

THanks Guys
Tomc

 

[69vettester]

The plan..

Im not good with brakes so my plan is to take it in to the same shop that hung my exhaust(excellent job). A guy there was also the one that welded the cracked strut mount bracket for me(another excellent job). I have no doubt they'll do as good as can be done. The fluid will be dot4 high temp "no" silicon. Got that part of the plan from the link above, thanks 71Shark.
Ill post whens all done and what the fluid looked like that came out ect.
TomC

 

[69vettester]

what a hassle...

Well racer78, he's not my mechanic, he works in a specialty shop , brake and exhaust. they did the weld when I hand carried the bracket in. they would't have touched the job if they had to do the remove or reinstall. thats great, I want to do all the work on my car that I can, but I have limitations.

I just returned from seeing if they would do the flush and refill, they said they would do the job but their flush pump is set to do with dot 3 and dot 4 was not an option, I said goodby. The next place made a huge deal about the peculiarities of corvettes and how they have years of experience on "these cars" (made a brake flush and bleed sound Like rocket science) , that was fine but led to their open end price of "we'll start the job for $70 ". I said goodby. finally found a place that wants the car all day they will do a complete flush and refill with dot 4 high temp for $70. I take it in the 2nd and will post the results
TomC

 

[69vettester]

Yep, a Power bleeder... he said " its hooked up to dot 3 fluid and thats that. Their so used to dealing with a public that doesnt know the difference. so they just do what they want and arent flexible about what I consider real important stuff!!ad
Oh well I found a good brake shop,and they'll do a fine job
TomC

 

[sscam69]

what the mechanic was refering to

I am not actually to keen on how a brake booster works but from your description of what the mechanic talked about "gavitation". I think he meant cavitation. Basically cavitation is a million dollar word for boiling. If the pressure of a fluid flowing in a pipe, take water for example, gets low enough it starts to boil. It does not have to be 100 degrees for that to happen as is the case with water. Most fluids are considered incompressable (by engineers), or at the very least they compress so little that it is considered negligable. Air on the other hand is considered a very compressable fluid. Well basically if the fluid starts to boil you have air in your lines and it gets compressed, hence your brakes don't work so good! As you go to a higher elevation atmospheric pressure drops and i am assuming that it dropped low enough that the fluid in your lines started to cavitate.

I hope that helps explain things a little.

sscam69