I have been having trouble with my brakes ever since I replaced the MC. Anyway the system has beed bled three separate occasions and still have the spongy pedal. Last night I decided to get to the bottom of this so I bled the system again with a Motive Bleeder. Went through a quart of fluid with no air. Sat in the car and the pedal fills the same way. So today I decided to do it the old fashion way with a helper. Here's the thing, as I'm bleeding the rear it's doing what it's suppose to do. Brake pedal goes down half way until the bleeder is opened then goes to the floor then repeats. But for the front, to start with the pedal was half way crack the bleeder pedal goes to the floor. But then when the pedal is released to pump again it drops to the floor. And I'm getting very little fluid from each bleeder for just the front. What does this mean? Do I need to re-bleed the MC in just the front?

 

That's not correct. since the system had been bleed before, the pedal should not go half way down, it should be pretty hard from almost the top and fall only with the bleeder open.

Sounds like you differential valve is tripped.

 

What does that mean?? Please explain.

 

http://apicdn.viglink.com/api/click?...hid%3D36760007

Look at squirting vs dribbling.

 

You are closing the bleeder before your helper releases the pedal correct?

 

Spongy pedal and halfway down means you still have air in the system. Did the car sit for a long time? It is possible there are deposits in the calipers that are blocking flow. If not, you need to thoroughly bleed the entire system.

Start at the master cylinder. Crack one bleeder at a time and look for air to escape. If none, then put pressure on the pedal and crack one slowly. HAVE YOUR FENDER COVERED!

Do this a couple of times with each until you have clean flow with no air bubbles.

Now go to the right rear caliper. Remember, there are TWO bleeders on each. Since you have fluid in the system, I'd recommend gravity bleeding. Have the car on four jackstands, remove all four wheels, and crack open ONE bleeder on the right rear. Let it sit 20 minutes, checking for air bubbles. A slight tapping on the caliper may help dislodge any. Be sure to keep an eye on the master cylinder and keep full.

Repeat for the other bleeder.

Move to the left rear and repeat.

Move to the right front and repeat. There is only one bleeder at top. If it is at bottom, your calipers are messed up.

Move to the left front and repeat.

Check your pedal. If not a somewhat firm pedal near the top of the stroke, repeat all four.

Now DOT 5 will be somewhat spongy, especially if you poured too fast and introduced air bubbles in the fluid.


If you still have problems, then you probably installed the master cylinder wrong. The rod must just barely touch the piston in the MC when tighten to the mounting bolts. Frequently this is too long (pushes in) and so the rear piston is actually partially on the stroke and the system won't bleed.

 

Yes

 

My M/C does not have any bleeders or are you talking about the two brake lines leaving the M/C?

 

Ok I just went and bled the front reservoir and did have a little air in it. After that I re-bled the front calipers but nothing is coming out. What the heck is going on??

 

Did you bench bleed the MC before installing?

 

I did but did it again on the car.

 

If the brake system is in order you can gravity bleed the fluid. Open the bleeders and just let the fluid flow out. (I use Dot5 so I do not have to worry about paint damage on the suspension parts.) See what happens when you do this. No fluid comes out from the front calipers when a helper pushes the pedal and you open the bleeder? mike...

 

Yea it's crazy, the helper pushes down on the pedal and I open the bleeder and nothing??? I did power bleed it after that with the Motive and got alot of fluid out. I re did the whole system and to me it still just don't feel right.

 

OK. So no flow from the front calipers at all? If so, I would be back tracking to find the blockage or lack of pressure from the MC. Pretty simple in theory but can get complicated at times. Wish I could see it in person. mike...

 

Well Mike I can get plenty of fluid through the Motive bleeder on the fronts but not the other way.

 

OK. I would take off the brake line for the fronts from the MC. Place my thumb over the hole and have the helper push on the pedal. It should pass fluid no problem. If you can hold in the pressure then the MC is the problem. Again, this is trying to fix it over the keyboard. mike...

 

Well I know that's not the problem because I just bled the front master cylinder by using the plastic fitting with hose. I actually saw bubbles as my helper depressed the pedal. Yoou know what I mean where you take the hose and submerge it in the fluid. Same thing as bench bleeding but did it on the car.

 

Yes, I understand. If the MC is producing the required pressure then you should have pressurized fluid flow when you open the bleeders with helper pushing pedal. Either the MC is not producing the pressure or you have an obstruction. You should not be able to hold back the pressure from the MC while holding your thumb over the outlet hole with helper pushing on pedal. Sorry I can not offer more help. Frustrating when I can not get my hands on the car. mike...

 

Ok I'll try tthat.

 

Today I went out to check the bleeder screws to see if they were wet or not and all six of them I could swipe my finger where it threads into the caliper and had fluid present. All bleeders are tight. The backs are new speed bleeders as well. I called a Corvette shop and without seeing it he thinks the calipers need rebuilt.