67 GT - hard brake pedal

[Mike72ss]

I am helping a friend of mine try to diagose a hard brake pedal on an original 390 4 speed, 67 GT. We are both at our wits end and just about given up on this problem. The car came standard with front dual piston discs. This car has also had a full restoration, meaning all new stainless brake lines, brake cylinders, calipers, distribution block, rubber hoses and of corse a new booster and master. He first took it to a repair shop here in the Detroit area that specializes in Fords. They sent the booster out to Booster Dewey in Oregon to have rebuilt, tried another master cylinder, still no luck. Today, we pulled the master off again an readjusted the brake pushrod, thinking it was not pusing the master cyclinder far enough and rebleed the brakes, with the same hard pedal results. I checked manifold vacuum and read 12 inches, a liitle low , but I think should work.

If anyone has a clue what could be wrong, We're open to suggestions.

Thanks!
Mike

 

[2nd Mustang]

If you mean the pedal feels like you're pressing on a rock and it is moving very little, sounds like the booster isn't working. Maybe the vacuum source is not a manifold vacuum source or the check valve in the booster is bad. When the booster is working correctly, the pedal should have almost an initial soft feeling.

My 67 coupe has 12 inches of vacuum at idle and my power booster works okay.

 

[jcode68]

I feel your pain, I went thrus this a couple of months ago when I converted to power front disc brakes. Turned out that the brand new booster I bought was junk, the replacement worked perfect. Many lost hours troubleshooting this one. Couple of things to check:

1)If you have a MightyVac (small hand operated vaccum pump) you can hook this up to the check valve on the booster and make sure any other ports on the valve are plugged. Pump it up until you reach about 15 inches of pressure and see if it holds for at least a couple of minutes. If it fails to hold, your problem is with the check valve, which can be replaced.

2)if it passes (mine passed too) then there is most likely an internal problem withing the booster. To determine if the booster is having any affect at all, start your car with everything hooked up per normal and DO NOT touch the brake pedal. Shut the car off, then apply pressure to the breake pedal and hold it. With your foot still on the pedal, start the car. If the booster is working at all, you should feel the pedal go down at least slightly. My booster did not, even though I had 18 inches of vaccuum.

3)If the booster seems to have some affect, it's time to look at your pedal setup. I'm assuming based on your post that you had power brakes before and simply replaced the booster with new (if this is incorrect, it could simply be that you need to get a new pedal which is made for a power brake application). If you disconnect the pedal from the brake rod that comes thru the firewall, hold the pedal up (toward the driver) as far as you can. Does the brake rod reach the pedal at it's highest point? If not, then you need to adjust it to within 1/8" of the top travel of the pedal. I spoke to a tech who did a lot of work on Mustang power brakes and he said he wrestled many problems like your which turned out to be poorly adjusted brake rod to pedal assembly. Look forward to your response - good luck and don't give up.