2002 626-Brake Drag in afternoon

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Old 10-25-10, 04:57 PM
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2002 626-Brake Drag in afternoon

I posted earlier about an unusual brake problem:

http://forum.doityourself.com/automo...el-issues.html

In the morning brake work fine and if anything the pedal is soft, in PM as soon as you get in the car the brake pedal is tight and brakes drag. Can only drive a couple of miles until the rim is almost to hot to touch, front right appears worst, but also front left and at times the right rear and possibly the left rear.

Took it to the tire store they wanted to start replacing brakes, but didn't have a clue nor seamed interested in addressing the issue.

Took it home, purged and replaced brake fluid, no effect.

Now I have replaced rubber brake lines, inspected and cleaned calipers piston (no apparent issues). While doing the above replaced the pads and rotors. Took the old brakes to the auto store was told by (what appeared to be a knowledgeable person) that there was nothing adnormal about the wear. Some heat damage on the pads likely attributable to there thinness. Otherwise, even wear.

One poster on the earlier thread indicated that it should be relatively easy to push the caliper in by hand pressure, has this been others experience. These were not, and Im wondering if this is a problems

Before I put it back together, is there any other thing I should address. I'm told that the master cylinder would not likely cause this.

thanks in advance for your comments.
 
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Old 10-25-10, 06:09 PM
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well, i have done countless brake pads, and never ever managed to press piston back in by hand, or even leaning entire body weight on it via hammer. so.....

you said you purged brake fluid. ok, how? did you just replace it, or bled master cylinder same time?

i give you 2 guesses.
1. master cylinder got air inside. well, if pedal feels soft, and i know 626s, you have air in the system somewhere. wild guess is, it heats up under the hood towards the 2nd half of the day, fluid expends inside the system, and causes piston drag. brake fluid is, basically, castor oil with some additives, and does not have much of expansion ratio by itself.
2. why do i have that feeling that your brake booster has something to do with this? and brake booster is fed by suction from the engine, and that has a lot to do with how tight your engine is all around. check ur booster, will ya? i don't think you have electric booster on 02 model. check the hose that goes from valve cover to booster itself, also, google how to check brake booster.

you see, brake system is very simple and does not have many complicated parts to it. basically, it's master, booster, 2 cross brake lines, maybe a proportionate valve (if you have one, that might be a culprit either), caliper, and that's about it. very primitive and relaible mechano-hydraulic setup.
btw, jack rear wheels, chock front ones, make sure parking brake is completely released, and check for free rear wheels rotation. so that you know you do not have any parking brake drag.
 
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Old 10-25-10, 07:42 PM
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you said you purged brake fluid. ok, how?
via four bleeding valves on each caliper

did you just replace it, or bled master cylinder same time?

replaced it, I bled the system via the calipers, didn't know you bled the master cylinder, how.

i give you 2 guesses.
1. master cylinder got air inside. well, if pedal feels soft, and i know 626s, you have air in the system somewhere. wild guess is, it heats up under the hood towards the 2nd half of the day, fluid expends inside the system, and causes piston drag. brake fluid is, basically, castor oil with some additives, and does not have much of expansion ratio by itself.

That was what I originally thought, and no change after the intial purge and bleed.



2. why do i have that feeling that your brake booster has something to do with this? and brake booster is fed by suction from the engine, and that has a lot to do with how tight your engine is all around. check ur booster, will ya? i don't think you have electric booster on 02 model. check the hose that goes from valve cover to booster itself, also, google how to check brake booster.
I need to study more on this and check it out and get back.
 
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Old 10-26-10, 06:59 PM
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How to Bleed the Master Cylinder Without Removing it From a Car | eHow.com

Master Cylinder Bleeding - How To Bench Bleed Your Master Cylinder - Remove Air Bubbles

How To Bleed Master Cylinder and Brake System

instead of me trying to explain this all in my broken english.

something expends in your brake system towards the 2nd half of the day, causing caliper drag. i'd safely say, it is caused by engine heat. so, either a fluid is mixed with something that expands, or one of the parts that moves does this.
reason i have brake booster in mind is because they operate off air sucked via engine and press on a little push rod, that presses on master cylinder piston, increasing pressure you applied to the brake pedal. you see where i'm headed? air + heat = expansion = pressure.
i had bad experience with improperly calibrated booster pushrod, that caused brake drag, burning rotors and jamming them. found this AFTER i did what you did - had calipers and lines replaced. mucho dinero spent, all for nothing because of 3 mm too much sticking out push rod.

brake fluid by itself, when it overheats, becomes more compressible, and brakes loose their power. been there too. so, if it's sticky caliper, you should be losing your brakes due to overheating, not jamming them. jamming means - something is continuously/progressively applying pressure to the pistons. see what i mean?

btw, check your brake pedal for obstructions. esp where it goes through firewall.
 
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Old 10-26-10, 08:21 PM
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(Quote) In the morning brake work fine and if anything the pedal is soft, in PM as soon as you get in the car the brake pedal is tight and brakes drag.

Sounds like a brake booster issue to me. In the PM before you start the car try the following and post the results.

To check the vacuum booster, pump the brake pedal with the engine off until you've bled off the entire vacuum from the unit. Then hold the pedal down and start the engine. You should feel the pedal depress slightly as engine vacuum enters the booster and pulls on the diaphragm. No change? Then check the vacuum hose connection and engine vacuum. If okay, the problem is in the booster and the booster needs to be replaced.
 
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Old 11-14-10, 01:14 PM
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I ran the three test as described below and all appeared normal. With temperature change not sure that the problem will apppear until we have warmer days

1. Airtightness function check

Generating a power boost requires that the vacuum inside the brake booster be maintained, that the constant pressure chamber and variable pressure chamber be completely closed off by the vacuum valve, and that air must flow from the air valve. (1) Stop the engine after running it for 1 to 2 minutes. Vacuum will be allowed into the brake booster. (2) Depress the brake pedal several times. When doing this, if the pedal position is higher 2nd or 3rd time than it was the 1st time, the check valve or vacuum valve is closed, the air valve is open, and air is being let in. From this it can be determined that the airtightness of each valve is normal.

2. Operation check

If the engine is started while there is no vacuum in the brake booster, the vacuum valve is closed, and the air valve is open, vacuum will be allowed into the constant pressure chamber. The brake pedal condition at this time can be used to check the power boost operation.

(1) With the engine stopped, depress the brake pedal several times. Air will be allowed into the constant pressure chamber.

(2) Start the engine with the brake pedal depressed. Vacuum will be generated and a pressure difference will be generated between the constant pressure chamber and the variable pressure chamber. If the brake pedal sinks down a little bit at this time, it can be determined that a normal power boost has been generated. 3. Load airtightness function check

If the engine is turned OFF with the brake pedal depressed, the pedal condition can be used to check for vacuum leaks from the constant pressure chamber. (1) Depress the brake pedal while the engine is running. (2) Turn OFF the engine with the brake pedal depressed. In the hold state, the pressure difference between the constant pressure chamber and the variable pressure chamber will be held constant. Therefore, if there is no change in the brake pedal height while continuing to hold it for 30 sec, then it can be determined that the check valve and vacuum valve are closed normally and that there are no problems with the constant pressure chamber.
 
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Old 11-14-10, 02:05 PM
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(Quote) With temperature change not sure that the problem will apppear until we have warmer days

Is the above your way of saying that from the time the weather has become cooler, that the problem hasn't happened again?

If yes, or if it happens again:

Replace the steel brake lines (Front to Rear)
Install fresh new brake fluid
Power bleed the system
 
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Old 11-14-10, 08:23 PM
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if you have the plastic pistons in your calipers they most likely are sticking as they get warmer, and don't cool enough during the day to move freely. if they are the culprit replace them. if no plastic pistons check for dirt in the master cylinder, partially blocking the return hole for fluid, it is even possible that your brake pedal is not returning properly to the fully upright position you might try hooking your toe under it and checking for any upward movement before starting in the evenings.

Death leaves a heartache no one can heal, love leaves a memory no one can steal.
 
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Old 11-15-10, 01:52 PM
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(Speedwrench said) if you have the plastic pistons in your calipers they most likely are sticking as they get warmer, and don't cool enough during the day to move freely.

Hi Kenn,

Your car doesn’t have plastic, pvc, or neoprene, caliper pistons. Nor are the pistons constructed from any combination (or composite) of the mentioned three. If it did, it would be illegal and not meet the minimum safety requirements.


To keep it simple and without getting into legalities:

The car would be illegal….Not be allowed to be sold….And Mazda would be facing a major lawsuit for deliberately violating FEDERAL MOTOR VEHICLE SAFETY STANDARDS.

Busy right now. Check back in a few hours for more.
 
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Old 11-26-10, 04:43 AM
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I'm gonna stick my neck out here and advise calipers be replaced. The brake hoses certainly could cause this, but they have been replaced.
BTW ASE, Ford has used non-metallic caliper pistons in the past. Read ESCORTS.
 
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