"Mushy" Brakes

[Floyd B.]

Completely rebuilt the brakes on my '73. Rebuilt calipers, new brake lines, new linings. Used the old master cylinder (it looked quite new) and combination valve. I thought I had bled them thoroughly, but I had to do it manually without the use of a vacuum pump or bleeding kit.

The brakes are now very mushy. The pedal will go all the way to the floor and barely engage the linings to the disc. If I first pump the brakes with two quick strokes before attempting to stop, they work pretty well.

Does it sound like I failed to bleed all of the air from the lines? I've done this several times and I'm not seeing any air bubbles. Or does it sound like the master cylinder is malfunctioning, or perhaps something else?

[Mike M.]

Re: "Mushy" Brakes

most likely still air in system. kepp at it. good luck, mike

[Jim T.]

Re: "Mushy" Brakes

Auto Zone's free tool loan program has a vacuum pump for your use. I don't know if the unit Auto Zone offers has the brake bleeding cup or not. I do know that one you get the firm pedal and your brake pads broken in, the C3 braking system with power brakes is impressive.

[Duke W.]

Re: "Mushy" Brakes

"Used the old master cylinder (it looked quite new)"

What does this mean? It looked new on the outside? You disassembled it and did a thorough inspection then put it together with the old cup rubbers?

You symptoms could be a failed M/C due to an internal leak.

You didn't "completely rebuild the brakes" unless the M/C was part of the process.

Duke

[Harmon C.]

Re: "Mushy" Brakes

Floyd Just for fun did you bleed two places on each rear? Lyle

[David N.]

Re: "Mushy" Brakes

Floyd, I had similiar problems on our '69 BB convertible. I tried the vacuum bleeding method, but it just did not get all of the air out of the corvette's brake lines period. They only way I could get 100% solid pedal was with use of a pressure bleeder system. Fortunately for me, my brother has such a pressure bleeder at his house. All manufacturers use a pressure bleed system. Guaranteed full perging of the brake lines. If you can locate one at a local tool rental shop or at one of the major auto parts store, that is absolutely the very best way to go. I spent unknown hours trying to manually bleed then unknown additional hours trying to "vacuum" bleed the system(it just seemed to suck the fluid past the seals every time.) Pressure bled them once, and viola! presto, solid brake pedal on the first try.

David Nims member 19639

Save the wave ~~~~~~~~~~~~~~~~~~

[John H.]

Re: "Mushy" Brakes - Trivia

Although pressure bleeders are used universally for repairs in dealerships and brake shops, they aren't used in assembly plants (except for repairs). The bleeders aren't touched in an assembly plant - an adapter is clamped on the master cylinder, a vacuum is drawn in the system through the two little compensating ports in the bottom of the reservoirs, and brake fluid is injected through those two little ports at 40 psi while the system is under high vacuum. Result? High, hard pedal, no fluid mess anywhere; this "evacuate-and-fill" process has been used in assembly plants for 35+ years (also used for coolant, power steering fluid, and A/C refrigerant). Hydraulic clutch master and slave cylinders are received as a pre-bled and pre-charged system; you just connect the fittings.

[Al C.]

Re: "Mushy" Brakes

Floyd -
I had a devil of a time bleeding my '58 (totally rebuilt system) until I did a "bench bleed" of the master cylinder. Make a 12" brake line with connector to mount on the m/c output port, bend it so it squirts back into the filler port (cap off), and pump multiple times to get trapped air out of the m/c. I forget, may need "nose down" or "nose up". Reconnect to car brake line and proceed to bleed system.
... Al '58 245hp

[Floyd B.]

Re: "Mushy" Brakes

Good points and I stand corrected. I rebuilt everything up to, but not including the master cylinder. It looked brand new on the outside and the brakes were working before I started the restoration project, though the pads and rotors were metal-to-metal. It looked like the previous owner had replaced the M/C, so I figured I would be better off just leaving it alone.

The brake lines were passable, but since I was doing a restoration, I decided that it would be a good time to replace them. The calipers were in definite need of a rebuild and the rotors were shot.

[Floyd B.]

Re: "Mushy" Brakes

No I did not. If I understand what you are suggesting, I only bled the bleeder values on the forward end of the caliper. The ports on the back do not have bleeder valves but are plugged with a hex-shaped plug. Since the brake line connects to the caliper on the opposite corner from the bleeder valve, I did not think it would be necessary to install a valve in the other port. Do you think this is a bad assumption?

[Floyd B.]

Re: "Mushy" Brakes

Thanx to all who responsed. What I take away from this thread of posts is that I need to take the suggestions I received and work harder at getting the air out of the lines. If I can't get satisfactory results on my own, I should probably brake down (no pun intended) and take it to a brake specialist and have them power bleed the system.

[Harmon C.]

Re: "Mushy" Brakes

Floyd The fronts only have one place to bleed and the other is pluged but the rears have two bleeders on each side and you need to be bleed both. Lyle

[Terry F.]

Re: "Mushy" Brakes

Something that worked for me was to raise the rear end while bleeding the brakes. Leave it in that position over night or longer if you are not doing anything. Then bleed the furthest cylinder and work toward the front. After you finish the rear, lift the front end very high and do the same. It seemed to improve my brakes a lot. Terry