Rock Hard Brake Pedal and Dragging Brakes on 1967

[Robert R.]

My Top Flite 1967 Roadster has an unusual problem, so I'm looking for ideas. It has stainless resleeved calipers all around and same in its master cylinder. (Non power brake system). It is loaded with silicon fluid, and everything was new a few years ago. After driving 3-5 miles, even with absolutely no use of the brakes, the brake pedal gets very hard, has no play at all, and then the brakes proceed to "drag", to the point where I need to downshift to keep up enough power to overcome the brake drag. Heat at all 4 corners seems about equal. Usually after allowing the car to overcome the badly dragging brakes by driving with extra power for several miles, it suddenly seems to return to normal. It will actually function perfectly for the next driven miles. The pedal play will return to normal, the dragging vanishes, and the brakes work flawlessly for up to several hundred miles just fine. But when the car is cooled down overnight, and the problem repeats itself.

Any ideas where I should start to look for solutions?? Strange problem. This happened daily on the NCRS Road Tour to Hershey last July, and only stupid pride and a "lead foot" allowed us to "drive through the problem". After 4-5 miles it "shook off the problem" and returned to normal for the rest of the day.

[Mike M.]

Re: Rock Hard Brake Pedal and Dragging Brakes on 1

Remove master cyl. disassemble clean, RUN THE SMALLEST WELDING TIP CLEANER THRU THE SMALL HOILES IN THE FLOOR OF THE RESIVIOU. GOOD LUCK, MIKE

[Wayne W.]

Re: Rock Hard Brake Pedal and Dragging Brakes on 1

Take a look at the pick up hole in the MC. Make sure that the piston is uncovering the hole. It sounds like the hole is just covered and the pressure builds with heat. There may be an adjustment on the push rod. You can see this by looking down into the reservoir and operating the brake pedal.

[Duke W.]

Re: Rock Hard Brake Pedal and Dragging Brakes on 1

The small hole that Mike and Wayne refer to is called the compensating port.
I think a very fine wire - on the order of .015" can be used to clear it.

Over time brake systems tend to develop debris in the system. On a system
that has never had a brake fluid change the bottom of the reservoir will often have a layer of sludge.

I believe the debris is some combination of mold release from the rubber parts and acutal wear particles from the rubber parts. Flushing out this debris
is important, which is why even systems equipped with silicone fluid need
to be flushed, but not as often as with glycol fluid.

A real easy way to determine if the system needs a good flushing is to look at the fluid in the reservoir. If the fluid is dark enough that you can't see the bottom of the reservoir, it's time to flush the system.

Duke

[John H.]

Re: Rock Hard Brake Pedal and Dragging Brakes on 1

The pedal free play adjustment also bears on this issue - if you don't have the clevis at the pedal adjusted to provide the specified free play, it can force the master cylinder pistons forward just enough to block the compensating ports; it only takes a few thousandths of piston travel to block the ports.