Spoungy brake pedal on my '65 non p/s car.

[Tony S.]

I've got a long spoungy brake pedal on my '65 non p/s car and I'm not sure why. Any insight would be appreciated. Here's what I've done and where I am:

I have a rebuilt master cylinder with a new 1" rebuild kit in the m/c. I have pumped down the brakes to where there is no bubbles in my brake lines. The master cylinder piston is traveling freely. Yet, when I depress my brake pedal, I get a long slow spoungy pedal. If I pump the pedal 2 or 3 times, I've got a pretty good pedal but not with the first pedal push. I've run plenty of fluid through the lines and have verified that I don't have any air in my lines.

Any suggestions?
Tony

[Timothy B.]

Re: Spoungy brake pedal on my '65 non p/s car.

Anthony,

Are the lines original, If so could there be a pinhole. Look for seepage at a connection, espacially if the lines are stainless steel.

[Tony S.]

Re: Spoungy brake pedal on my '65 non p/s car.

Brand new steel lines all around.

[Edward J.]

Re: Spoungy brake pedal on my '65 non p/s car.

Tony, from what your saying its sound like theres air trapped in the system somewhere, or air is being drawn into system by a fitting not tight enough.

Did you bench bleed the master cylinder before instalation ? on the rear calipers did you open bleeders for the inboard and out board when bleeding? did you use the correct order when bleeding calipers? where any of the lines replaced or parts of the system opened other than the m/cyl.?

[Rich P.]

Re: Spoungy brake pedal on my '65 non p/s car.

First question I would ask is are you useing silicon fluid? It is more work to get a good pedal with silicone.

Rich

[Richard J.]

Re: Spoungy brake pedal on my '65 non p/s car.

I had that same issue a few months ago. I changed mc and a caliper... fully flushed system... bench bled mc twice... power bled system 3 times.... was pulling my hair out trying to get a decent pedal.

Finally in desperation... got my wife in the car and bled the system by hand the old fashioned way. Pedal came up and fine ever since.

I always thought a power bleeder (SnapOn - I used to be a Dealer before I retired) was the way to go... Now I think they just get you in the ball park, especially if you've had the system totally apart.

just my 2 cents worth...

[Tony S.]

Re: Spoungy brake pedal on my '65 non p/s car.

Guys. I'm using a dot 4 product. I've had the mc off and replaced the piston assembly in the mc. In bleeding out the air, I started with the right rear caliper, moved to the left rear, then the right front. Finally went to the left front. I pumped the pedal while my friend Herb bled the brake calipers. I noticed that when I removed the cap from the mc and lightly pump the pedal by a couple of inches down, I could see air being discharged in the mc, so it makes the fluid bubble up.

[Don H.]

Re: Spoungy brake pedal on my '65 non p/s car.

Hi Tony,
What has worked best for me is someone doing the pedal very slowly. Also opening both rear bleeders on each caliper then the front. If necessary doing multiple times. Good luck, Don H.

[Joseph P.]

Re: Spoungy brake pedal on my '65 non p/s car.

Hi Tony, I have a 65' that had the same problem. I would be driving down the road and hit the brakes and it would go from side to side and would have to pump the brakes. I replaced the MC and the lines and it didn't help. I rebuilt the calipers. I found one of the calipers that looked pretty bad. Once I rebuilt the calipers and bled the brakes it works like new. I have a full pedal and never had another problem. Good luck. Joe

[Edward J.]

Re: Spoungy brake pedal on my '65 non p/s car.

Anthony, wipe down all the fittings and pump brake 10-15 times to make sure none of them are leaking, sometimes when so many lines get replaced there always seems to one or two that leak, this will cause air to be drawn in each time the pedal is released, I find that new lines sometimes require extra torque to seat the lines.

You have the correct seq. for bleeding, keeping it simple air generally on corvettes tend to get trapped in the rear because of the length of the lines and the rear calipers have two bleeders on rear.

[Paul J.]

Re: Spoungy brake pedal on my '65 non p/s car.

Tony;

I would first follow the advice in the previous posts, looking for leaks at the fittings, and aound the seals at the caliper pistons. If you still can't find the problem I would replace the hoses (if you did'nt do this when you changed the lines). Old hoses can collapse inside. This causes the car to pull side to side during hard braking and can also cause a spongy pedal. This does'nt happen very often on cars, but it is prevalent on full size GM trucks.

Paul

[Tony S.]

Re: Spoungy brake pedal on my '65 non p/s car.

Thanks guys. I appreciate all of the good advice. I'm trying to finish things up for the Heartland Regional. This restoration may turn my hair gray if I'm not careful (whoops, it already happened ).

Best,
Tony

[Mark L.]

Re: Spoungy brake pedal on my '65 non p/s car.

Tony,

When we did the brakes on our '65 non P/B car I used the gravity method, one wheel at a time. It takes a while but works. Good Luck.