69 COPO brake problems

**Alss** · #1 06-05-2006, 01:42 AM

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Having some brake issues with my 69 COPO. All components are either new or rebuilt..calipers prop valve.. master. After a little drive time the front rotors and calipers heat up and get tight..brakes get jerky and the car will not roll ...brake pedal is high and hard. Once it cools off everything is OK. Either the calipers are hanging up... or could there is residual pressure in the system?. Anyone care to take a guess?? I'll probably start with the calipers as they are the easiest..what do you think??

Thanks

ALbert

VintageMusclecar · #2 06-05-2006, 01:53 AM

If the car pulls or "darts" to either side under braking, check the front caliper hoses. Sometimes they will deteriorate from inside out and cause the calipers to hang up even though they appear perfect on the outside.

Eric

**njsteve** · #3 06-05-2006, 03:17 AM

High and hard, huh? That's a punchline waiting for a joke. But seriously folks, it sounds like the master cylinder may have been rebuilt in drum brake configuration. I believe the four wheel drum cars have a check valve in the outlet port on both front and rear outlets of the master cyl but a front disc car will only have the check valve in the rear brake outlet. That check valve, if it's there, will hold the pressure in a disc brake caliper and wont let it release until the residual pressure bleeds off. If both of your calipers are sticking then it is most likely the master cylinder.

**Alss** · #4 06-05-2006, 06:09 AM

Thanks Steve..isn't the front disc check valve mounted inline under the master in 69?? There is residual pressure in the line..when I cracked the bleeder some brake fluid squirted out..is this normal? I have a spare..may swap them and seewhat happens. Thanks

ALbert

**WILMASBOYL78** · #5 06-05-2006, 06:29 AM

Albert, be careful with that brake fluid it can cause lots of damage to painted parts,etc. If you have silicone fluid in the system, then no sweat. Protect the areas around the work to keep things from getting damaged. Good luck..by the way it does sound like a MC problem.

wilma

**Lynn** · #6 06-05-2006, 07:02 AM

Actually, on the 69, I believe the check valve is underneath the brass flare nut mating surface.

Here is how to diagnose. Get the front brakes warm, then get the front wheels off the ground quickly. While an assistant tries to rotate one of the wheels, crack the line at the master cyl, being careful to catch any fluid. If the wheel suddenly rotates easily, then you found the problem.

To remove the check valve, you will need to take the line loose from the master cyl. You will see a pressed in fitting in the master cyl. Screw a sheet metal screw into the brass fitting about a full turn. Then pry the fitting out with a pair of dykes (yeah, now I know we have "high and hard" and a pair of dykes - oh well). The check valve is just plastic and can be removed now, as it is held in by the brass fitting. You can re use the fitting.

If I remember correctly (been 30 years, you know) the old rebuild kits come with the check valves, and the instructions say to discard for disc brake cars.

If the wheel doesn't rotate easily when you crack the line, then you probably have a piston caliper problem, which is very unusual on a GM car since the pistons are metal. Now, those damn fords, well this happens all the time because of the composite pistons which swell over time from, you guessed it, exposure to brake fluid.

Hope this helps.

HS PROFESSOR · #7 06-05-2006, 02:49 PM

I'm gonna go with the rod that attaches to the brake pedal is adjusted incorrectly.i've had this happen on my race car,and when everything heats up it is applying a small amount of brake pressure.just enough to cause a drag.if its severe enough.....brakes lock.when it cools......back to normal. just another idea??

bob

69 Code51 Z · #8 06-05-2006, 03:59 PM

Check you make sure you have the calipers on the correct side - made this mistake once when converting a drum car to disc and had a heck of a time figuring it out. Carl

**Alss** · #9 06-05-2006, 04:13 PM

Thanks everyone!!..I'll start checking all this stuff out. I'll post what I find.

Heres what I know:
Calipers are on correct sides..bleeders on top
Hoses are new
Master and prop valve have been rebuilt( Micky Hale )
Booster is a new repro..(looking for a nice original now)I am unsure about the rod length though..how do you adjust it? what parameters?

ALbert

**lowmile** · #10 06-05-2006, 05:33 PM

I would disconect the rod first and see if it realeased the pressure. If it does, just shorten the rod. I had this problem once. m