Squishy Brakes

[RHarms]

My Cobra has been on the road for several years. The brakes have always been- adequate.
Recently the line entering the master cylinder, front, started to leak. Inspection revealed that the flare had broken. Long story short, master cylinder replaced and bench bled, line replaced, and a modified brake pedal was installed, to improve the pedal ratio. The brakes were bled.
The length of the rod between the power booster and master cylinder was not changed. ( I adjusted it incorrectly once, after driving about a 1/2 mile, the brakes locked. Very exciting)

Results:
1. Engine off, the pedal goes 9/10 of the way to the floor.
2. Engine on, the pedal goes all the way to the floor. Pumping brings it back, a very little.

For now, I assume the following,
1. Rebuilt master cylinder not leaking internally,
2. Bleeding done correctly,
3. Power booster OK.

Any ideas on what I should look at first? See above, I really do not want to mess with that power booster to master cylinder rod, but I suspect that needs to be lengthened.

By the way, the car was built and registered in New Jersey. I now reside in California. I am keeping my fingers crossed, re: registration.

Thanks

[xlr8or]

push through mushy pedal = air in the lines or leak.

[rdorman]

I know Don will chime in on the pedal, pushrod, booster relationship since he created the mod so I will go elsewhere. But it does seem as though it could be part of the problem, depending.

Tell me this, when you do push the pedal down to the point you get a firm pedal (and not because it is on the floor!), does the pedal stay there or slowly sink?

If the pedal stays put, I am going to go for bleeding. If it sinks, leak. At least that is where I would start. Of course, if the pushrod being way to short.......

Bleeding a previously open system can be pesky. Every time the line rises and then falls is a great place for the bubble to reside. Did you open the bleeders to far? I see people do it all the time. I open mine only about 1/4 to 1/2 turn. Open them further and you suck air back in around the threads on the pedal return stroke. I don't know how you bled them so you might compare notes with some others around here. With the master cylinder higher than the calipers, they will pretty much self bleed. Pump the peddle slowly by hand.

Rick

[relaxinrob]

You have air in the lines somewhere.

[RHarms]

Thank you for the incredibly fast responses.

I used two methods to bleed.
1. My wife pumped the pedal as I opened and closed the bleeders ( 1/4 to 1/2 turn) I think we stayed coordinated during that process.
2. Being mushy after that, I used a hand vacuum pump. I kept refilling the master cylinder, making sure it never got too low, and bled and bled. I bled about 2 pints of fluid.

By the way, once the pedal stops, it stops. So, problably still has air in the lines.

I have a line lock on the front brakes, which I have never used in 10 years. I think I will remove it, one less place for air to hide. There is also a front/back balance valve, located above the master cylinder. Maybe I should try to relocate it lower. A challenge, but probably worth it.

You all have answered, indirectly, my primary concern, a broken/leaky booster will not cause the symptoms I am seeing. Air, Air,Air, that is the problem. The challenge, getting rid of it. I will bleed again. This time, maybe blood. :-) Thank you.

[Eljaro]

Rhams, you should check your rod moving the piston inside the master cylinder. If you position it wrong you lock the brakes (like you experienced already) or you could be pumping the brake fluid back into the reservoir instead of into the brake calipers. I had a similar problem when bleeding my clutch circuit.
In the brake rest position the rod must not be adjusted to hit the inner stop in the master cylinder, but needs a little preload.

[RallySnake]

RHarms,

I went through that exercise a few years back. I could not get all the air out with normal bleeding methods. I got a large syringe from the wife (she's a nurse). I removed the bleed nipple from the right from caliper. I wrapped a little plumber's tape around the theads and screwed in back in the hole enough to seal the threads, but not enough to bottom out. I filled the syringe with brake fluid and connected it the the prepared nipple with a short length of tubing. As I slowly forced the fluid in, I could see all the bubbles coming out through the brake reservoir in the engine compartment. When they stopped, I stopped. I removed the plumber's tape and bled all the fitting normally. Worked great!

Paul

[dscott]

Sure sounds like air to me. The adjustable valve could be trapping some air. You should also check the rod between the master and the booster. You should have about a 1/16" gap. The best way to bleed brakes is with an injection system but they are expensive. I usually try drip bleeding the brakes. If you try the pump and open system sometimes you can create bubbles if you pump too fast. To drip bleed I start with the brake farthest away and open the bleeder so it drips about 1 drop every 2 or 3 seconds. I do that for about 15 minutes and proceed to the reat, 1 at a time. If you have the Cadillac rear disc calipers you will need to take them off to properly bleed. The bracket they bolt to sets the caliper bleeder below the top so you never get the air out. The other critical item with those calipers is the parking brake adjustment. It must be properly adjusted or the pedal will set low and never come up.
Don

[Double Venom]

Any doubts on the brake rod, grab the wife again, have her watch the rod in the master. You should be able to move the brake pedal just under a 1/4" and the master cylinder shaft should start to move, any more than that then lenghten the rod.

Still convinced it's air though. Force filling from the bleeder works everytime. "Mighty Mite" makes a neet little kit for this. And you wont have to track down a nurse!

Bias valve should be just fine, as well as your front line-lock. But if you want to move or delete, your call, but not the bias valve .
DV