Low Brake Pedal on 65 with Power Brakes

[Elliott P.]

My 1965 L79 with power brakes has a very low brake pedal, after all linkage adjustments and brake bleeding. I have been told that this is typical of these cars by several persons. Is it unique to the one-year-only master cylinder (first dual-cylinder), or anything else unique to this year? Even if it is correct, I do not like it. How do I fix it?

[Frank D.]

Re: Low Brake Pedal on 65 with Power Brakes

Can't say on a '65 but when I changed my 63 to power brakes using all factory original parts (the one year only power boosters bring eye-watering prices), I thought the pedal travel was beyond scary and I'd done something wrong. In reading the 63 manual it said if the pedal on power brakes was 1" off the floorboard its within specs. That's a gut-wrenching amount of pedal travel and I couldn't deal with it.

I bought a different clevis rod from McMaster's for the pedal and I now have about 3" off the toeboard when the pedal is fully depressed. The car stops with conviction and without giving the driver heart palpitations...

McMasters #6071K14; I had to cut about 1/2" off the threaded clevis end to "dial it in" to perfection. I do NOT know if this will work on a '65 however.

[James G.]

Re: Low Brake Pedal on 65 with Power Brakes

Bleeding can be a real problem. A common problum is one caliper still has ''air trapped'' in one one of the pistons. Starting from the caliper furtherest from the master, the RR, OPEN each bleed screw by itself and let it gravity drip after using a pressure bleeder on the master. There are bleeders on the market today that let you pressure bleed each caliper. Make sure the fluid is clear and clean. Move to each claiper and bleed each side carefully.

Then disconnect the pressure bleeder, fill the cylinder with clean fluid and take the car for a road test.

If the problen has not been corrected, use the old fashion two people, one in the car on a hoist with the car in the air pumping and holding while the the other is under the car releasing the bleed value while the person holding the pedal down. You have to talk to each other, saying ''pumping........holding........., now release the valve.......close the valve and back to pumping.

It may take ''THREE ATTEMPTS'' to get all the air out.I can assure you that once all the air is out, the factory system will work properly without having to buy other fixes like suggested above.

[Harry S.]

Re: Low Brake Pedal on 65 with Power Brakes

Drum brakes or Disc brakes?

[James G.]

Re: Low Brake Pedal on 65 with Power Brakes

Harry, you could only get POWER BRAKES on disc in 1965.

[Harry S.]

Re: Low Brake Pedal on 65 with Power Brakes

Ug, that new fangled technology!

[Elliott P.]

Special brake bleeding requirements for 1965 Corvette with power disk brakes:

1. Before bleeding, turn off engine and depress brake pedal several times to deplete vacuum reserve.
2. Attach pressure bleeder to master-cylinder front reservoir and bleed each front caliper asm. at inboard bleeder valve while tapping caliper asm. lightly with rawhide mallet. Remove pressure bleeder and adjust brake fluid level in front reservoir
3. Remove rear wheels. Attach pressure bleeder to master-cylinder rear reservoir and bleed each rear caliper asm., first at the inboard bleeder valve and then the outboard bleeder valve and then verify at inboard bleeder valve, repeat outboard/inboard until no air, all while tapping caliper asm. lightly with rawhide hammer, on one side of the car; then repeat sequence on the other side of car. Remove pressure bleeder and adjust brake fluid level in rear reservoir. Install rear wheels.
4. Start engine and test for firm brake pedal.
5. If brake-pedal height is too low with brakes applied, adjust brake push-rod at the clevis-pin by loosening clevis jam-nut and turning push-rod in or out until there is virtually no play in push rod with the brake pedal fully retracted against fixed rubber stop. Hold push-rod so it cannot turn, and tighten clevis jam-nut.
6. If brake pedal is still not firm, or has excess travel, then further repairs will be needed on brake system.

Does all of this seem reasonable? It seems to me that some play must be left in brake-rod so that the brakes are not partially engaged due to temperature changes that may affect that clearance.

BTW, I gotta say, the Kelsey-Hayes 4-piston disk brakes (front only) that first showed up on my 1965 Lincoln were far better designed than these Corvette stoppers. And no sleaving was required because piston ring was grooved into cast-iron caliper, sealing against smooth S.S. piston. Never had a problem with bleeding either. And, oh yeh, the Corvette is more fun to drive.

[Mel S.]

Re: Low Brake Pedal on 65 with Power Brakes

I have a 66 with power brakes and they work great. I rebuilt the calipers with the "O" rings on the pistons and new pads. I originally had the seals but they leak. I also had the master rebuilt and put in a new booster. I have had the car since 1976 and had issues then but now it is good to go.
Hope this helps
Mel

[Richard G.]

Re: Low Brake Pedal on 65 with Power Brakes

Harry's question was valid.
True Most 65 Corvettes came with disc brakes.
GM offered credit for drums, if you wanted the lowest price Corvette possible
Or didn't want to mess with the newfangled stuff you could have drum brake 65.
A friend of mine used to have a Mossport Green 65.
It had one option, a radio.
Three speed transmission to boot.
It is the only one I have ever personally seen.
Rick

[Duke W.]

Re: Low Brake Pedal on 65 with Power Brakes

My 1965 L79 with power brakes has a very low brake pedal, after all linkage adjustments and brake bleeding. I have been told that this is typical of these cars by several persons. Is it unique to the one-year-only master cylinder (first dual-cylinder), or anything else unique to this year? Even if it is correct, I do not like it. How do I fix it?

Your symptom could be an indication that one side of the m/c has failed and will not hold pressure.

Duke

[Elliott P.]

or is not properly bled of air, you will get significant pedal travel before two pistons in MC contact and give a firm pedal on good circuit. Which leads me to suspect improper bleeding of rear calipers. I wonder how many experts forget about the outboard bleed valves on these Corvette rear calipers, requiring removing of rear wheels? I will have that checked out.

[James G.]

Re: Low Brake Pedal on 65 with Power Brakes

Thanks Duke. You may have hit on the problem. At least you got my old noodle noodling. I don’t think one side has failed, because there is no leakage anywhere (there is one seal that could fail in MC without leaking). But you got me looking hard at that dual MC. These early dual MCs did not yet have mandated CHECK BRAKE differential switch for failure warning. This particular system also does not have any proportioning valve to muddy the waters. But, the two cylinders are not truly independent. If one side fails, or is not properly bled of air, you will get significant pedal travel before two pistons in MC contact and give a firm pedal on good circuit. Which leads me to suspect improper bleeding of rear calipers. I wonder how many experts forget about the outboard bleed valves on these Corvette rear calipers, requiring removing of rear wheels? I will have that checked out.

Duke has a point, and your comments are valid also. I think if you send the power boster out for rebuild, the problem will be corrected. And maybe the master cylinder needs a re build as well. The car is 54 years old. And YES, remove tires when bleeding.

[Elliott P.]

[Tom B.]

Re: Low Brake Pedal on 65 with Power Brakes

Have your rear rotors been drilled out of the spindle hub? If they have you need to dial indicate the rotor runout in the 5 different stud positions to get the lowest amount of runout otherwise this can cause your rear calipers to self pump air and you will always keep getting a low pedal .

[James W.]

Re: Low Brake Pedal on 65 with Power Brakes

Is it lower than this? Just finished having my master cylinder sleeved and booster rebuilt. Put everything back as I marked it when I disassembled it. I then gravity bled each brake for several minutes using DOT 4 fluid.

Regards,

James