hi to all, is that time once again to take my babe out for a spin, after a "way too long canadian winter" ...
but i'm going mad,
i've spent already 4 litters of brake fluid trying to bleed the bloody brakes and still...i'm not satisfied, i did replace the master cylinder thinking that was the problem but, its still the same, it works fine for about 10 minutes of driving and then it becomes spongy again, bleed again and same results 4 litters after, no change, there are no leaks, the only explanation i got is...air is entering the system, but doesnt make no sense,
please guys, is there any tech article or something that can guide me thru? before i end up talking to the "shrink"? or the psyquiatric hospital?
thanks to all for your understanding. :hail:
Fernando.

 

How about the brake lines, did you replace them too, or are the originals still on?

 

i did just replaced the section aft right, it doesnt leak, but now i`m wondering, the main supply line to the back wheels passes about 2 inches from the headders, it could be a vapor lock...i wander
Fernando.

 

Vapor lock could be the issue if you got water in the system or left the cap off the bottle on a humid day and then filled the system with it. Aside from that, all I can think of is either a leak (which you say you don't have one) or the master cylinder. Did you bench bleed it before putting it on?

 

could be the booster. ive seen it happen on a firebird

 

dear KC, sure its not water, so we can now discard the vapor lock theory (4 litters after).
carlover, good idea, but still not, the hizzing sound of vacuum being filled is loud and clear when i disconect the vacc line and the check valve is ok, BUT, one good point... for the carbed guys, where exactly is your vacc line connected? straight to the manifold? mine is connected to the carb base (lower aft side of the carb itself) edelbrock 1406, i have seen some older cars conected straight to the intake manifold, i wander if theres any diference.
Fernando.

 

Did you "bench bleed" the master cyl?

The lines don't attach to it at th ehighest point. So if you didn't, you can bleed them from now until the 2nd Coming, and they'll still be spongy, because the air that gets trapped at the highest point in the master cyl has no way to get out.

 

bench bleed?
SOB, ok bro tell me more please, how do i do that?, sure i didnt, i just put it all together and started bleeding,
please again brother, teach this poor analphabet the good old know how.
i'm not kidding, i had no idea about bench bleeding but makes sense, never done it before.
amazing how after this many centurys, good old Socrates is still right "all i know is...i know nothing"
please RB, tell me how or point me to a step by step site.
thanks a million brother.
fernando.

 

You have to bleed the master cyl while it's being held level.... "bench bleeding" refers to clamping it in a vise and hooking up the bleeder apparatus to it, mYbe tilt it a little bit one way and then another to make sure that any air that's trapped gets its chance to make it to the fitting; then with the bleeder stuff still hooked up until the last possible instant before hooking up the lines, WITHOUT LETTING ANY FLUID COME OUT OF THE BLEEDER LINES, install it on the car. Makes an astounding difference.

On some cars you can accomplish that by parking it on a hill or jacking up the rear end; but on these, the MC sits at too much of an angle for that to be practical.

 

LOL, I asked this yesterday!

 

Somebody should make simple common ordinary repair stuff like this into a tech article and/or a sticky, to prevent these repetitive posts.

I gave the same answer yesterday of course.... I hope I did anyway.

 

Bleeding Master Cylinder on the car.

 

That won't work on these cars..... the fitting isn't at the highest point..... there will still be air trapped in there.

Only solution is to bleed it while it's being held level, which is not possible (or at least not practical) after it's been installed.

 

If it won't work on these cars, why did GM put it in the manuals for them? It worked on my car and it is a 1989 Iroc. :werd:

 

whatever the case...
i love you all guys :hail:
thanks a million times, i'll do so and will keep you posted.
Fernando

 

Because it's just generic boilerpate text that they put in all of them whether it applies or not. Just because they stuck it in the one you have too doesn't alter the laws of physics for this universe.

Lorem ipsum dolor sunt......

 

Thank you for the enlightenment. BTW, the instructions that came with the new master cylinder I put on my car also included that procedure. I guess they don't know the laws of physics either. Whatever works best for you do it, that procedure worked great for me. Maybe I was just lucky since I have had no problems with it..

 

Maybe you're lucky you haven't noticed the problem you have, if you didn't bench bleed it; or maybe you just don't realize how well they could work if you got the air out that you left in there. Whatever. It's your car. As long as you don't run over me with it because the brakes failed outright, it doesn't matter to me.

I'm not particularly interested in getting into some stupid argument over why GM included their generic boilerplate in a manual for a car that it doesn't apply to. It hardly matters. I'd prefer to concentrate on how things really are, instead of second-guessing somebody else's technical proofreading. So: go take apart a master cylinder and see how it's put together. Notice while you're at it that the fittings for the lines enter the cylinders proper at the middle NOT AT THE END, and it will immediately become obvious why air gets trapped in there and can't get out through the fitting after the cyl is installed at a 20° angle on a car. There's at least a couple of cc's of air that will remain at the highest point of the cyl. I guess it must be air that hasn't read the manual.

 

ok my brothers, lets cool our jets...
one thing i remember, it was bleeding at the master cylinder as well but not as described in the manual and more, no bench bleeding, in any case, i will first follow the procidures to the letter and if its still the same (i think it will be) then i'll remove it and bench bleed the sucker.

thanks to all of you for your time, this is the best forum ever, and more, from the cars we all love.
Fernando

 

Yeah.... unfortunately no manual is perfect, not even a factory one. My several little brothers that have worked in parts depts and service depts at dealers all tell good stories about manuals, parts blowup diagrams, parts listings, etc. that are just plain, out-and-out wrong. And that includes among their employers over the years, most of the GM divisions, and a couple of Asian brands, and several European brands.

I didn't mean to sound mean, i apologize if I came across that way, maybe I should take a lesson from ede and use lots of smilies.

In any case, the factory's write-up on that is wrong, and should not be believed, since it is in every manual they print for every car, and doesn't really apply to these cars.