69 COPO brake problems

[Alss]

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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]

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]

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]

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]

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]

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]

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]

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]

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]

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

[YENKO DEUCE REGISTRY]

I would go with the rod issue, been there fought that!!

[Baldy]

I had this happen on my 69 Yenko. Incorrect rod adjustment. Drive the car untill this happens, take some tools with you,losen the master cyl. from the booster,if this helps adjust the rod. You should have about an inch or two free travel on the brake pedal

[Alss]

OK all fixed..just came back from a test drive http://www.yenko.net/ubbthreads/images/graemlins/naughty.gif. Master rod was too long!! you guys are the best!! http://www.yenko.net/ubbthreads/images/graemlins/biggthumpup.gif.had a nice 5 minute cruise around the neighborhood and they feel like they should..finished up with a nice 1st-2nd blast..5K or so..feels real good!! Thanks again.

ALbert

[mockingbird812]

Terrific! I love it when a plan comes together.

[njsteve]

Let that be a lesson to all those non-members: membership has its priveleges. If ALSS was a non-member he would have been charged the standard rate of $100 per question. Join today, operators are standing by, Mastercharge and Visa accepted, makes a great christmas gift...

[Alss]

http://www.yenko.net/ubbthreads/images/graemlins/haha.gif

[HS PROFESSOR]

Hey ALbert....those repop boosters will get ya every time!!! glad your all fixed up.Nicks LS-6 should be sportin some new green paint by the end of the week if all goes well.that car really needed a frame off. who ever heard of a "driver" LS-6 chevelle??? your copo vs his LS-6.what do say to a little friday nite grudge match???

bob

[Alss]

[ QUOTE ]
Hey ALbert....those repop boosters will get ya every time!!! glad your all fixed up.Nicks LS-6 should be sportin some new green paint by the end of the week if all goes well.that car really needed a frame off. who ever heard of a "driver" LS-6 chevelle??? your copo vs his LS-6.what do say to a little friday nite grudge match???

bob

[/ QUOTE ]

Bob the booster is actually a nice piece!..had the rod that attaches to the pedal too long and was not releasing the master!!..a 1/4 inch did the trick!..as for racing that crazy Bulgarian..no way!! he has more tricks up his sleeve than a magician http://www.yenko.net/ubbthreads/images/graemlins/grin.gif..and I like the idea of a "driver" LS-6..wish I had something I could drive and get dirty http://www.yenko.net/ubbthreads/images/graemlins/grin.gif Get that car done..been waiting to see it for over a year now..my spare 512 block is going in that car!!

ALbert