Brakes

[67 GT350]

I have a nice restored 67 GT350 that I bought out of Texas. Question I have is  about the brakes. The front brakes are so tight. I do not drive the car often, so do I just need to drive it and break them in? The front brakes are hot, the reads are cool after a 10 mile drive. In fact when I start it up in the garage, it is actually hard to move. Can the proportioning valve be that bad that it makes the front brakes tight? WHAT IS THE GIG? I know that 67 brakes are "touchy" but a Shelby I had years ago would lock up the rears easily, but this car locks up the fronts! DANGEROUS!

[Tom Honegger]

Pistons are probably frozen (or partially) in the calipers.

[67 GT350]

I am not sure of that, because I was able to move every piston. It seems when I started it up after sitting, I mashed the brakes, (just to make sure I had pedal, and they were on, after a short drive they were better, but still would hold the car slightly. Someone told me it could be a "collapsed brake hose"

[Shelbypat]

Open the bleeder to check if there is presure when brakes are tight. If so, check the master cylinder rod adjustement to be sure the orifice is free to allow backflow into  your master cylinder. If no pressure when open bleeder, you may have calipers issues.

Patrick

[Darrpo]

I have had this happen and found the front rubber brake hoses were the cause. They would not let the fluid flow back.

[67 GT350]

Yes, your the second one to say that, I will investigate that and the post from ShelbyPat! Thank you guys, this is a start! I find it interesting that nobody has mentioned the proportioning valve, I was think it was that, but I think that only controls the rear brakes.

[Bob Gaines]

Yes, your the second one to say that, I will investigate that and the post from ShelbyPat! Thank you guys, this is a start! I find it interesting that nobody has mentioned the proportioning valve, I was think it was that, but I think that only controls the rear brakes.

That is because it controls fluid to the back brakes as you suspected.

[shelbydoug]

In the master brake cylinder for drum brakes there is a check valve in the line. When you use it with discs, you remove it.
The check valve keeps the pistons from returning to a full off position.

Normally this would not be an issue (in the old days) but it is something really simple that the current generation wouldn't be aware of in installing "the wrong" master (drum brakes) vs.discs.
Current parts listings would use a "universal" application and have a note in the instructions that if you are going to use it with disc brakes, to remove the check valve.

What? Who? Where? Instructions? Read? Look at the pictures? Huh? Nah.

I suspect this is your issue. The check valve is just a little plastic thing that plugs into the output port of the master. It's one of those ten cent throw away things that a mechanic would need '60s hands on knowledge of to know I suppose? How many of them are left?

It's in the bottom of the primary fluid bowl. Looks like a plug in the port.

Take the cap off, Take a flashlight. Look through the fluid. If you see it in there, take it out. Simple.


I told a kid the other day that he needed to turn something clockwise, not counter-clockwise. My mistake. They never saw an analog clock face, only digital.

[67 GT350]

Haha, thank you, I will check that, since I did not put the car together, I will have to check that. I bought it off a person who has, I think, a ton of experience, but since I got the car, I have had to tighten almost everything, including installing two helicoils so the carb would not pop off the car! Yes only held down by two bolts. So why would that not be forgotten also?....I will check that and post!

[6R07mi]

I have had this happen and found the front rubber brake hoses were the cause. They would not let the fluid flow back.

1+

This is common even on newer generation cars, usually with higher time & mileage, the inner wall of the rubber hose section separates from the fabric reinforcement/outer wall allowing fluid to pass into the cavity creating a temporary blockage to prevent fluid pressure release, holding the piston pressure for a period of time. Then the pressure bleeds off without the applied pressure in the line, the pistons relax and the brake frees up.

regards,

jim p

[67 GT350]

OK, pulled off the MC cover and I do not see any plastic part to take off, thus it must have been done correctly.
Next? I did order two new brake hoses. I guess that is next. Someone mentioned a adjustment to the MC itself?

[KR500]

67GT350
By the looks of your M/C photo someone has used DOT 5 brake fluid ( DOT 5 is identified by it's purple color ). Do not mix fluids! To be 100% sure take a small sample and see if it will mix with water. No = DOT 5, yes DOT 3 or 4.

[67350#1242]

The check valve mentioned actually is located underneath the tube seat(s) for the lines coming out of the MC,  you cannot see them by removing the bowl cover.
The disc brake MC is supposed to have a check valve in the line going to rear brake, while drum brake MC has check valves in both lines.
I really doubt your problem is there especially if they worked OK at one time.

[67 GT350]

Yes, I have DOT 5 in it.

[JWH]

A good friend in the local Shelby club had a '67 that would almost not move, the front brakes were so locked up. He finally discovered that the rod that sticks into the back of the Master Cylinder was adjusted just a tad too long, keeping the brakes engaged all the time. Before spending a bunch of $$ on parts, pull the Master Cylinder and shorten this rod just a bit, maybe an 1/8 inch or so. See if that helps. Your problem sure sounds a lot like his and this adjustment cured the problem and the brakes worked fantastic after that.

     If you do remove the Master Cylinder -- after adjusting the rod, re-install the MC, tighten the nuts to the booster and then re-install both brake lines. Tighten the brake line fittings until they are snug and then back off both fittings about 1/4 to 1/2 turn. Have a helper get in the car and S-L-O-W-L-Y push the brake pedal down while you have wrenches ready to tighten both brake line fittings under the hood. Brake fluid will seep from between the fittings and the MC as the pedal goes down. When the pedal is almost to the floor, have your assistant stop and hold the brake pedal steady. Do not let the pedal come up yet! Now tighten both fittings fully. This method should allow you to bleed out the very small amount of air between the brake line and the MC and you should not have to bleed the entire system. This has worked for me for many years and saves a ton of time and mess. Put paper towel or a cloth under the lines to catch the fluid as it seeps out. If your helper presses the pedal slowly, it will seep out and not spray all over. I hope this helps and solves the issue.
Jeff