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Author Topic: Front Disc Brakes dragging...  (Read 5569 times)
Reeko
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« on: July 01, 2009, 01:37:54 PM »

Hi, new guy here...
Anyway, I have recently completed restoration on my 69 Camaro.
As pert of that, I added front disc brakes. Replaced the Master cylinder etc... New calipers...

Anyway, the brakes were working fine for a while (500 miles on it at least).
Recently however, the front brakes are dragging horribly.

I figure that if I had the wrong valves or Master cylinder, they would have had the problem from the start.
I know it is hydraluic because opining the bleeder on the brakes makes the wheels turn fine. But the next time I pump them up, they drag again.

Also, I don't think it is the brake pedle, as I pulled the pin on the pushrod and it still drags. Also note that it drags even if the car is not running.

Right now I suspect the Front Disc Holdoff valve (some call it a proportioning valve). I Believe the purpose of this valve is to prevent pressure from going to the discs until some set pressure is reached. Would my problems happen if that were stuck open?

I would think that if I had the wrong MC (with a check valve in the front) that I would have had this problem immediatly.

Any suggestions?
Thanks
Reeko
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Mark
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« Reply #1 on: July 01, 2009, 04:34:02 PM »

Did you swap the pivot point for the brake pedal?  There are two holes in the arm for the brake pedal, drum brakes use one, discs use the other?
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Mark C.
1969 Indy Pace Car
350/300HP RPO Z11
Reeko
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« Reply #2 on: July 01, 2009, 05:55:20 PM »

Yes,
In fact, I pulled the pin on the brake pedal so that the pushrod was disconnected and had complete slack. Still the brakes were dragging.
So not the pedal.

I am planning to replace the Metering (proportioning) valve on the front to see if it might be the problem. (The valve on the Driver Side below the MC that connects only to the Front Disc Lines.)
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Sauron327
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« Reply #3 on: July 01, 2009, 06:51:05 PM »

Loosen the MC from the PB and see if the brakes release. The MC piston needs to return to center to work correctly; make sure it is. You can also run a temp. replacement line in place of the prop. valve to isolate that if you want. Then you don't have to buy one to check it. If the fronts are working then it's opening but it would have to remain closed afterword to cause what you state. Remaining open all the time causes the nose to do a face plant when hitting the brakes. I'm assuming both front flex lines are new?
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Reeko
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« Reply #4 on: July 01, 2009, 07:03:27 PM »

OK,
Yes the lines are all new. The problem must be before the distribution block since both front brakes drag equally.

I will try loosening the MC off the PB.
How is that differnt from disconnecting the Brake Pedal, doesn't that ensure that there is slack in the linkage?
So, if loosening the MC causes the brakes to release, what does that indicate, Bad MC?

I suppose another check would be to release the pressure both sides of the Holdoff valve and see which side is the problem.
If the Holdoff is stuck closed and not releasing pressure, then opening the line between the MC and the Holdoff vavle will have no effect.
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Sauron327
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« Reply #5 on: July 01, 2009, 07:14:29 PM »

Just because you disconnected the pedal does not mean the piston is returning to center. 
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Reeko
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« Reply #6 on: July 01, 2009, 10:50:15 PM »

Ok,
If loosening the MC on the PB releases the pressure, what does that tell me?
Bad MC?
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Sauron327
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« Reply #7 on: July 02, 2009, 05:13:43 AM »

Incorrect pedal play or intermediate rod is wrong. But you stated the brakes were fine 500mi. ago. Both calipers and/or hoses would have to fail simultaneously or the MC has failed. Yes it's new but possible nonetheless. Question: Do the brakes drag immediately or slowly develop the condition? The slightest pressure will cause the system to tighten under increasing heat.
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Reeko
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« Reply #8 on: July 02, 2009, 05:23:52 AM »

Again, can't be pedal play since I disconnected the pedal and the drag did not go away.
I think the brakes were fine for the last 500 miles as I only noticed the drag recently. Could they have gotten progressively worse?
(I only noticed that burning smell and the earing grease only started to melt out the last time I drove).


They drag now even when cold. I can only spin the front tires about 3/4 turn by hand unless I release some pressure in which case they spin about 3 turns for the same effort.
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Sauron327
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« Reply #9 on: July 02, 2009, 05:34:36 AM »

Then the MC is holding pressure.
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JohnZ
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« Reply #10 on: July 02, 2009, 10:36:31 AM »

Ok,
If loosening the MC on the PB releases the pressure, what does that tell me?
Bad MC?

If that occurs, it says that the booster-to-master cylinder pushrod is too long, which places the piston seals forward of the compensating ports in the bottom of the reservoirs, holding pressure in the system.
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'69 Z/28
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Sauron327
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« Reply #11 on: July 02, 2009, 11:28:30 AM »

We just went through this similar situation in this thread: http://www.camaros.org/forum/index.php?topic=5521.0
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Reeko
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« Reply #12 on: July 02, 2009, 06:10:15 PM »

OK,
Losening the MC released the pressure.
So, I pulled off the MC (still left Hydraulic lines connected, and pulled out the pushrod from the PB.

(A little history). I had a good hotrod shop fix my brakes last year. They replaced almost everything but went with non original parts.
Anyway, the pushrod is adjustable on mine. Was set at about 4 in, but would shorten to about 3. So I set it as short as possible and put the MC back on.

No drag. Drove the car about 5 miles. Can still lockup the brakes, but they engage later in the brake travel. Was able to touch the bearing caps (before the bearings got soo hot the grease was melting out).
I might need to pull the MC again and measure how deep the pushrod needs to go in before it meets the plunger (or whatever it is called).

Since the brakes worked for a while, I wonder if something changed in the MC over the first few hundred miles?

Anyway, thanks for the help.
Reeko
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tom
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« Reply #13 on: July 02, 2009, 06:23:08 PM »

How does the rod adjust? Sounds like it went out of adjustment. When you get it adjusted right, try some loctite.
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69 X11 Z21 L14 glide
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Reeko
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« Reply #14 on: July 02, 2009, 06:30:56 PM »

It is a threaded tip on the end of the pushrod. Perhaps it shifted. Once I measure the depth and figure what length I need, I will locktite it.

BTW, Before I could barely turn the front tires about 1/2 turn with a hard push.
Now the passenger side does 2.5 turns, but the driver side about 1 turn.
How much drag is normal on disc brakes?
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