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WagonCrazy
12-03-2015, 07:12 PM
The Setup:
57 wagon with front discs/rear drums
CPP power front disc conversion kit (2 inch drop spindles,10 inch rotors with single piston calipers)
8 inch vacuum booster
CPP dual mastercylinder (front disc, rear drum)
CPP "auto" proportioning valve properly plumbed in.
New rubber brake lines installed. Still holding tight...no leaks.
New steel brake lines installed all the way around 8 years ago.

This brake system has been installed and working just fine for about 8 years now. Haven't had to mess with it.

The Symptom:
Brakes working fine for the first 15 minutes of driving (when cold).
Then about 2 weeks ago while running around town, hit the brakes and the fronts BOTH "skip". Rapidly. They lock up, release, lock up, release, etc. Very fast, as if I had antilock brakes. Let off the pedal, and brake again...same thing. Then they don't do it for 10 or more minutes afterwards. Intermittant!
No pull to one side or the other....both wheels seem to lock up and release quickly while "firmly on the pedal". Don't really feel it in the pedal at all (like you can with antilock brakes). Brake pedal is firm.
But after one of these events, I smell hot brake pad and the brakes feel like they "faded"...can feel it in the pedal.

First Diagnosis/Fix:
Removed and Disassembled the 2 front calipers, then cleaned up the pistons and inner surfaces. Nothing was scratched/marred/worn BUT there was a sort of hard shellac on portions of the piston surface, and what looked like a little rust shellac'd on them.
Reassembled, added brake fluid, bled the system (via wife inside on the pedal).
Brakes worked fine for about 10 to 20 minutes of city driving, then did the same thing.

Ive never drained the brake fluid since installing 8 years ago.
Ive never run the system out of fluid...always kept it topped off.
Dot 3 used.

Next up:
Thinking the Master Cylinder is sticking...caused by 8 years of crud, or some moisture, rust, lack of driving...sitting in the driveway, etc.

Gonna pull it, clean it, inspect it for leaking seals, etc. It's a cast iron corvette style MC that CPP sells with the clip on lid.
Gonna drain ALL fluid from the system, and bleed at all 4 corners after bench bleeding/installing the existing MC (after I clean it).

Should I screw around with fixing the existing MC, or replace it?
Would the proportioning valve malfunction to the point of causing intermittant fronts to lockup/release/lockup/release quickly?

chevynut
12-03-2015, 07:37 PM
Are you sure it's the front brakes acting up? What makes you suspect them and not the rear brakes?

WagonCrazy
12-04-2015, 07:13 AM
With the windows rolled down, I can hear it coming from the fronts.
What makes you think it might be the rears?

Either way, both are controlled by the push of a piston thru the mastercylinder, so my thinking is that if both fronts are locking up, then its not an individual wheel caliper causing it...it's something in either the master cylinder or proportioning valve components.

gonna pull it apart on Sunday morning this weekend. Will snap some pics and post after that.

Either way, the whole system is getting bled and new fluid put in.

Just curious if you guys ever experienced this, and what you found was the faulty component.

Bihili
12-04-2015, 07:59 AM
Sound like fluid getting past the seals in the MC.

rockytopper R.I.P 5-13-2017
12-04-2015, 10:24 AM
May not be related but several folks lately including my friends 55 had issue with brakes locking up and it was the booster causing it. Apparenently they have a defect that can cause them to apply brake pressure and not release. They say the ones that are chromed are worse because they get disassembled at chrome shop and not properly reassembled. Apparently there are only a hand full of manufactures making them so all the suppliers are having issues not just CPP.Might be worth looking into. It was so common last year that I bought Cnut 's bracket and went hydraboost to eliminate the booster altogether.
Rocky

Maddog
12-04-2015, 02:39 PM
That's a new one, never heard of those symptoms before. I would suspect booster or prop valve, probably would change booster first, they're cheap enough.

chevynut
12-04-2015, 02:53 PM
Paul, just because you think you're hearing it in the front brakes doesn't tell me that's where the problem really is. The front and rear brakes do interact inside the MC and the prop valve, if it's one that senses both front and rear pressure. I can't think of any defect that could cause what you're describing. If the booster was "locking up" it seems like you would have the brakes on all the time. I don't know what could make the brakes turn off and on like you're describing, but if it was me I'd isolate the problem by disabling the front or rear brakes to make absolutely sure where the problem is. Then I'd work on troubleshooting it from there.

I guess I can imagine drum brake shoes chattering in the drum before I could see disc brake pads chattering. That's what makes me think it might be in the rear.

Maddog
12-04-2015, 03:14 PM
Those Chicom CPP master/booster/prop valves are about $180 on fleabay. Just buy another entire unit, replace it and your problem will probably be gone, no need to try to play Sherlock Holmes.

chevynut
12-04-2015, 03:27 PM
Here's some stuff on brake vibration. Not seeing this in person is kinda hard to diagnose. If it's a vibration at high speed, it could be warped rotors. I had a vehicle that did that when the brakes got hot and you could feel it in the pedal. Do the rotors look like they're uniformly worn? Any burn spots? Does it go away after the brakes cool down?


What is Brake Vibration?

Brake vibration is where a shaking motion occurs when the brakes in a car or other vehicle are deployed. This can vary from a slight shaking to a quite severe shuddering, depending on the severity of the condition. It can also be known as rotor shimmying or brake pulsation.

What causes it?

If the brake rotors installed on the vehicle have more than .05mm of run out (where the brake rotor moves from side to side more than a minimal amount of .05mm), then brake vibration will occur through the steering. Usually, this is due to one of two different reasons. The face of the disc may have some rust or dirt on it, which is causing the run out figure to be incorrect. Such build up may occur during the lifetime of the rotor, and this can cause the run out to be up to five times the limit installed by the factory. If the problem is not due to this, it may be that a ‘thin spot’ has occurred on the rotor (where there has been intermittent pad contact instead of a constant motion). When the brake pedal is pressed this causes the brake vibration to occur. This is technically known as Disc Thickness Variation, or DTV for short.
As it is essential that your brakes run true, this must be sorted out as quickly as possible.

How to rectify the problem

The first thing to do is to determine whether it is the front or rear rotors that are causing the brake vibration. If the steering wheel itself is shaking, it is more likely to be the front, whereas if the whole car and bodywork shakes, it will probably be the rear. Additionally, it is not necessarily the pair of rotors that are the problem; it may only be one of them. Finding the location of the shaking is the first step to solving the problem, however.

rockytopper R.I.P 5-13-2017
12-05-2015, 06:02 AM
The folks that had booster problem had similar symptoms. After the car is driven for a short time the brakes lock up. The vaccum is apparently leaking and applies brake pressure or does not release after applying the brakes. The car can apparently set for a while and brakes work for a short time then lockup again.

chevynut
12-05-2015, 01:59 PM
So perhaps with the booster or MC causing the brakes to drag on the rotor the heat warps the rotor and causes the chattering/pulsating/"skipping"? Lockup is one thing, but locking uip, releasing, then locking up again doesn't sound like the same thing. My Bronco's brakes were usually pretty smooth but when they got hot they pulsated like crazy. It was a warped rotor (or two) that caused it. It does sound like the brakes are getting hot.


"The Symptom:
Brakes working fine for the first 15 minutes of driving (when cold).
Then about 2 weeks ago while running around town, hit the brakes and the fronts BOTH "skip". Rapidly. They lock up, release, lock up, release, etc. Very fast, as if I had antilock brakes. Let off the pedal, and brake again...same thing. Then they don't do it for 10 or more minutes afterwards. Intermittant!
No pull to one side or the other....both wheels seem to lock up and release quickly while "firmly on the pedal". Don't really feel it in the pedal at all (like you can with antilock brakes). Brake pedal is firm.
But after one of these events, I smell hot brake pad and the brakes feel like they "faded"...can feel it in the pedal."

WagonCrazy
12-06-2015, 05:08 PM
Update:
There never has been any shimmy in the disks when braking....hence I doubt warped rotors. I've had several newer cars do that (after excessive mountain pass braking) so I know what that feels like. Had none of those symptoms.

This morning, I removed the master cylinder and proportioning valve. Here's a pic just before the wrenches came out.
5293

When I removed it, I checked for fluid getting past the seals...None to be found. Dry...
5294

So then I drained and disassembled it. Other than some varnished looking stuff near the seals, it was fairly clean for being untouched for 8 years now.
5295

5296

5297

Cleaned it all up, inspected and everything seemed to look fine. So then I turned to disassembling the CPP proportioning valve. Same thing...not terribly dirty nor filled with evidence of gunk or water...
5299

5298

5300

5301

So I cleaned it up, and reassembled it. Then decided (since I had the MC off the booster) to do the "putty test" to make sure the booster pin was sitting tight to the MC pin.
A round dab of plumbers putty stuck on the booster pin, then hold the MC tight to it, then check the clearance.
5302

5303

Then reassembled the brake lines, filled the chambers (bench bled it before installing it) and used one of them Harbor Freight "one man" brake bleeding tools (with air hooked up to it) and bled at all 4 corners, starting with rear passenger, rear driver, front passenger, then front driver).
Hopped in an did a test drive for 1/2 hour around town and IT DIDN'T REPEAT THE SKIPPING from before.

So...I think I had dirty fluid, crud in an orifice somewhere that prevented adequate brake fluid flow when pressing and holding the pedal during normal braking. Seems to be gone now.

Before I did all this today, I had a friend tell me last night (experienced mechanic for a living) that he thought it may have been the booster going bad...allowing vacuum to slip out. He suggested pulling (and sealing off) the vacuum line from the engine, then driving it without the power brakes to see if it repeated the skipping again. That was good advice I think, but I went the route of looking into the MC and prop valve and flushing the whole system with new fluid.

Think it's fixed now...

Rick_L
12-06-2015, 07:14 PM
I've been reading this with interest.

I suppose that dirty fluid that has a lot of water in it could do this (the fluid must be boiling when the symptoms occur), but there must have been some other factor (like something making the brakes drag or stick) that added to the problem.

Anyway, good news that you apparently have corrected the problem.

Should be a word to the wise to change out the fluid every 3-4 years even if there's no problems/symptoms - as is recommended but few do. (Mental note to self, need to do that on my Nova.)

chevynut
12-06-2015, 07:44 PM
I have to say the proof is in the pudding, but I'm skeptical that the root cause of the problem is actually fixed. Time will tell, I guess. :) It seems like bleeding the brakes the first time should have flushed most if not all of the old fluid out of the system, but maybe not. Too bad we will never know what the real problem was since you cleaned everything up before testing it again. You did hit all the important things you needed to check.

Anyhow, glad it seems to be fixed. ;)

Rick_L
12-06-2015, 07:47 PM
If you bleed the brakes and quit when you see no bubbles, you are a long way from flushing and replacing all the fluid in the system.

WagonCrazy
12-07-2015, 06:55 AM
I bled more than a quart of fluid thru all 4 lines, till it was very clear and no bubbles. I'm sure I have all the old fluid out of the lines. They are only 1/8 inch lines...so not much volume.

I could have just started by bleeding the lines, but I think I would have ended up pulling and inspecting the MC and prop valve anyways, so I just chose to get it over with at the start.

chevynut
12-07-2015, 07:09 AM
Hope you solved it Paul. I'd just out of curiosity like to understand what the problem was and why the brakes were pulsing off and on. I'm having a hard time seeing how "bad" brake fluid could make that happen. ;)

WagonCrazy
12-07-2015, 09:32 PM
Well guys, today I went for the one aspect of the brake system I haven't looked into ...the rear brakes.
Bingo...

5320

5321

Lining of the shoe(s) was coming off. Yes...it started to squeel when driving it this morning. That was the final clue...

I installed these rear shoes 4 or so years ago, and don't remember where I got them, but they are CHEAP JUNK. They are "bonded only" to the metal shoe. So they let loose with less than 5000 miles on them.

New shoes installed are better quality with rivits holding the material to the metal shoe.

So I got a round trip accomplished all thru my brake system, only to find it in the last place I looked.

Didn't Laszlo ask me that question at the top of this post?????? :(

Dumbazz Paul. :mad: