78 Corvette brake conundrum...

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j par

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Helping a customer with his 1978 Corvette. We put four new brake hoses four new brake calipers 2 front rotors and bearings. Brand new master cylinder bench bleed. Vacuum bleed all the brakes starting with passenger rear ending with drivers front. Then to make double sure did a short gravity bleed on all four just to make sure. NO BRAKES...???...:BangHead:...
 
Helping a customer with his 1978 Corvette. We put four new brake hoses four new brake calipers 2 front rotors and bearings. Brand new master cylinder bench bleed. Vacuum bleed all the brakes starting with passenger rear ending with drivers front. Then to make double sure did a short gravity bleed on all four just to make sure. NO BRAKES...???...:BangHead:...

Who did the master come from?
I had a couple parts store units a few years ago that wouldn't push fluid. Brand new, right off the shelf, something was up with the piston bypassing fluid. Sucked!
 
Who did the master come from?
I had a couple parts store units a few years ago that wouldn't push fluid. Brand new, right off the shelf, something was up with the piston bypassing fluid. Sucked!
Right now this is the best that I can think of is well that he just got a bad overseas part... Like I told him autoshop 101 just because it's new doesn't mean it's going to work..
 
So I take it the system won't build pressure. Is that what your saying ?
PS I figured I'd bust your nads right out of the gate. lol
 
So I take it the system won't build pressure. Is that what your saying ?
PS I figured I'd bust your nads right out of the gate. lol
Yeah when I took the lid off the master cylinder and had him slowly push the pedal of blerp came out of the front but not anything out of the back...
I got to say when I was bench bleeding it it did act a little odd... Almost like aerating the fluid.. if that makes sense...
 
Did you try pumping the pedal to build pressure.
 
Well then, why are you asking. It's obvious the master is the problem. lol Geez...
I know I've done this more times than I can count and I'm just a little frustrated coming home from such a simple task and not having the results thjat I should...
 
You will get it fixed :thumbsup: seems like in today's parts world the second time is a charm.
 
Pushrod length?
If the piston doesn't come back far enough, the C-port won't be open and she can't reload.
Just got off the phone with a high school buddy of mine who's been working at the local cab company as a mechanic for 30 years. Needless to say he's changed a couple breaks LOL I think on the contrary to what you're saying I may have over pushed the piston when bench bleeding. He said that that was a normal practice to bench bleed but now he said he doesn't do that at all. He just puts it on hooks it all up gravity blades and then does the old pump pump hold on all four to make sure and that's it...
So when I go back to that customer I Monday I plan on giving the old one more try with the bleeding and if that doesn't work off to get the master cylinder warrantied. Then I may just put it in the car and bleed it from there only being able to push the rod as far as the brake pedal will take it...
 
If the pushrod is too long, the C-ports are closed, and it will not gravity bleed. It cannot bleed at all because the ports are closed!
On another note;
If the master cylinder is higher at the front than at the back, it can trap an air bubble in the high point, that is gonna act like an airspring, When you push the pedal down the fluid will go down the line, and then when you let off the pedal, the air bubble will push the fluid back up into the reservoir. If you pump the pedal rapidly allowing it all the way back on each stroke,then hold it for a half a minute; then you can beat the bubble at his game and drive the fluid past the bubble. You can repeat that until you get a spongy pedal. Then you go to the calipers and force the pistons back into the bores, both of them, and make sure you clamp the offside one down. This will drive the bubble (hopefully) back into the reservoir.
Alternatively, you can have a helper crack the line as you are forcing the pistons back and drive the bubble to atmosphere.

You can know that you have a bubble, by the size and power of the fountain that spouts from the reservoir when you gently leave off the pedal after having pumped it several short pumps and hold on the last one;
No fountain probably indicates a closed or severely restricted C-port.
A flipping huge fountain spewing fluid 4 ft high,all over the underhood area, indicates the rear shoes need adjusting,lol, or shazzam that's a big bubble.
On a properly bled and working system, the fluid will just roil around in the reservoir with perhaps a small fountain no more than .75 inch high.
As you know,brake fluid eats paint, so take appropriate precautions
 
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Master cyl is unhappy...there is more to bench bleeding a master cyl then pumping...the worst thing is those plastic fittings and rubber hoses...every time I sold a master cyl with that kit in the box there was a 75% chance it was coming back to me as defective.I've sold over 10000 master cyls probably more...it takes 3 pumps..that's it.
 
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