"Hard Brake Pedal" on my 1967

[Gerald C.]

My manual brake car has a "hard" pedal and doesn't stop as well as it should, but eventually does and I'm looking for thoughts on what's causing the problem and steps I should take or look for to correct the problem.

Thanks
Jerry

[Duke W.]

Re: "Hard Brake Pedal" on my 1967

This is a common complaint on manual disk brake C2/3s. GM didn't want to include a vacuum booster with base equipment, and they specified a whooping 120 pound pedal force for a 1 g stop. That would be considered totally unacceptable, today. I don't know the drum brake spec, but I bet it's less.

Modern cars probably require no more than 40-50 pounds for a maximum performance stop or ABS engagement. Consequently when you go from a modern car to a vintage Corvette with manual disc (and even drum) brakes, it feels like "no brakes".

You either accept it or add a vacuum booster. Be sure the brake pad Cf rating is at least FF. GG would be even better, but may not exist. Pads can also develop a glaze that lowers the Cf. The solution is an "Italian tuneup" for the brakes. Find a road, especially going down hill that you can get the car going fast and then heavily brake down to low speed. Do this at least a half a dozen times to break the glaze.

Duke

[Gerald C.]

Re: "Hard Brake Pedal" on my 1967

Duke,

Would it better if I pull out the pads and see if they are glazed over then clean the glaze and reinstall? Can you explain the cf rating to discuss and where would I buy the FF pads?

Thanks

[Gerald C.]

Re: "Hard Brake Pedal" on my 1967

I just thought disc brakes around would stop better than they do!

[Larry E.]

Re: "Hard Brake Pedal" on my 1967

[QUOTE=Duke Williams



. The solution is an "Italian tuneup" for the brakes. Find a road, especially going down hill that you can get the car going fast and then heavily brake down to low speed. Do this at least a half a dozen times to break the glaze.

Duke[/QUOTE]
Very funny Duke; kinda reminds me of what some mechanics call a "Fiat">>
"Fix it Again Tony," Larry

[Gerald C.]

Re: "Hard Brake Pedal" on my 1967

I think I would rather replace the pads! Any vendor suggestions??

[Leif A.]

Re: "Hard Brake Pedal" on my 1967

Gerald,
These Delco pads are FF...they work just fine. Be sure to "bed" them in once installed.

[Gerald C.]

Re: "Hard Brake Pedal" on my 1967

Leif,

Can you explain what you mean by "bedding" the pads?

Thanks

[Jim D.]

Re: "Hard Brake Pedal" on my 1967

Leif,

Can you explain what you mean by "bedding" the pads?

Thanks

These are the instructions for the PowerStop ceramic pads I installed on my 65. They are low dust and once bedded in properly, the pedal feel is not hard at all.

"IMPORTANT: BREAK IN NEW FRICTION USING THE PAD BEDDING PROCEDURE AS FOLLOWS. PROPER PAD BEDDING CAN PREVENT ROTOR WARPING.The break in procedure is critical! If you do not break in the pad properly, it can result in brake pedal pulsation and thermal shock to the rotor causing stress cracks. Break in the pads as follows: 5 moderate to aggressive stops at 40 mph to 5 mph without letting the brakes cool and do not come to a complete stop. Then do 5 moderate stops at 25 mph to 5 mph and let the rotors cool after each brake application. You should expect to smell some resin as the brakes get hot."

[Gerald C.]

Re: "Hard Brake Pedal" on my 1967

These are for front and rear with the same AC Delco part #17D8?

[Leif A.]

Re: "Hard Brake Pedal" on my 1967

These are for front and rear with the same AC Delco part #17D8?

Yes. And, Jim answered the bedding question to a "T".

[Gerald C.]

Re: "Hard Brake Pedal" on my 1967

Thanks for the feedback. I'll check the pads out in the morning

[Jeffrey S.]

Re: "Hard Brake Pedal" on my 1967

Has anyone worked on your master cylinder / ? if so check to see which half of the master is going to the front brakes / the front half is for the front brakes the rear for the rear / if the lines are reversed ( easy to do ) your brakes will take much more effort and will not stop the car as they should / I deglazed my pads / scuffed the rotors / all with no effect / then I looked at another 67 and I notice the lines reversed on the master / swapped the lines all better . I know this doesn't happen often but it does happen. Hope this helps. Jeff Believe me non power brakes do stop these cars .

[Duke W.]

Re: "Hard Brake Pedal" on my 1967

Leif's photo shows the pad rating, which is promulgated by the Friction Material Standards Institute (FMSI). The letters indication the Cf range, and IIRC F is 0.40-0.45. G is .05 higher range and E is .05 lower range. The first letter is the Cf when "cold" like near room temp and the second is "hot" something like 300C, so FF would not fade as much as FE.

Also of note is that all disk brake systems have a FMSI assigned "D-number" indicating the basic pad geometry. The C2 Corvette system is D8, which indicates a very early system design. New cars today up in the several hundreds. Most replacement pads incorporate the D-number into their part number.

You could remove the pads and sand them on a flat surface with some fairly course paper like 100-150, but the Italian tuneup would be easier and more fun, so try that first.

Regarding break-in, most shops want to turn rotors when they install new pads because they "break-in" in the first couple of stops. When installing new pads on used rotors I prefer a slow break-in consisting of 200-300 miles or "normal" braking. This is how I broke in new front pads for my Cosworth Vega back when I did track events from the early eighties to the late nineties. I went through at least six sets of Delco OE replacement semi-metallic pads for Monza brakes. (vented rotors with larger piston calipers v. solid Vega rotors with smaller piston calipers). The rotors are scored silly with numerous short radial cracks. A brake shop would consider them junk, but they are still over minimum thickness and not warped, and the brakes work great!

Ford had the same rotor cracking problem during the sixties GT development program, which is why they developed the quick change rotors, but in the end they concluded that the short radial cracks were no problem. This is documented in a SAE paper, and based on that I didn't worry about the short cracks and they never became a problem.

Duke