Brakes come on randomly *solved (bad fluid)

[Horsehammerr]

Having an odd problem here. My brakes seem to apply them selves at random times. I can feel my '02 CC slow down at any time with no apparent reason. When on cruise the accelerator comes on to compensate and this braking happens uphill, downhill, straight flat road or curves. I know it's the brakes since I can touch the peddle and it is solid against the brakes. The only thing I can do to release them is punch the peddle down hard and the ABS seems to free them up. I went clear through all eight slider pins and they were all free but, cleaned and lubed them anyway. Worked fine for a couple of miles and bingo, on they came again. Any Ideas what to check next ?

[Horsehammerr]

Maybe I'm not saying this right. My brakes are coming on without pushing the brake peddle. I do mean all by them selves. What could make this happen ?

[HenryJ]

When was the last time that you changed the brake fluid? What is the condition of your wheel bearings?

[Horsehammerr]

Wheel bearings are solid and quiet. Have never changed brake fluid. Is there a proper way to do that?

[HenryJ]

Bleed the brakes until the fluid runs clear. It is helpful to replace as much as you can in the reservoir prior to bleeding the brakes.
I use an old Turkey baster to suck out as much as possible , then refill. Have a friend push on the pedal and open the bleed screw. Start with the farthest wheel and move to the closest. RR > LR > RF > LF. Close the screw when the pedal reaches the floor. Repeat as many times as it takes to get clear fluid. The first will take the longest.

Brake fluid is hygroscopic (an affinity for water) , with time it acquires enough moisture to alter is hydraulic properties. The fluid in the wheel cylinders never circulates in the system. Heat cooks it and alters its properties too. Changing just the fluid in the reservoir does not help the fluid in the wheel cylinders, therefore bleeding the brakes is the only answer.
I like to do this at least bi-annually. At a brake pad change is a good time too. If you live in a moist climate more frequently may be needed.
This is a good time to change top a high quality synthetic brake fluid. Unless you live in a very dry climate, stay with the recommended DOT3 fluid. I use DOT4 for my area, but we have single digit humidity much of the year. Moisture is not a problem. Do not use DOT5! It is silicone and not compatible.
Be aware that European specifications for fluids are different.

You should be able to find several ways to bleed brakes without help. There are several devices you can buy to do the job by yourself. A friend is the most cost effective most of the time depending upon his tastes in liquid refreshment, and appetite.

[Horsehammerr]

Thanks for the reply Brule. I'm trying to figure out how brake fluid or wheel bearings could make the brakes engage on their own. That is what's happening .

[HenryJ]

Wobbling rotors contact the pads. When they get heated up it gets worse. Almost like they are being applied.

Brake fluid will offer a picture of the system condition. Water expands more than brake fluid when heated. It also compresses more. Lots of water may indicate that a wheel cylinder is corroded internally and not releasing as it should. Same thing, once heated it feels like it is applying.

Throwing steps and ideas out there. It is tough to diagnose with no hands or, eyes on the problem. You have eliminated the slide pins which are usually the first suspect. Check those again. They can go bad very quickly. Never assume they are good.

[killian96ss]

Pull the ABS fuse and drive it around. This is safe to do, just remember that the ABS will not work at all. Does it still apply the brakes by itself? If the problem goes away get the ABS system checked out. I don't see how it could do it any other way since the brakes are a manual hydraulic system.

Steve

[green02crew]

Mine had an abs issue so if I touched the brakes the abs would come on. Pulled the fuse and bingo, no issues. Maybe not the same but similar to your problem.

[Horsehammerr]

Rotors are good. I'll do a fluid change and look for water. Should the ABS lines be drained also ? I just cleaned and lubed the sliders yesterday and they are good. This " brakes on " thing happened again after only a couple of miles after . I'll give the ABS disco a try and let you know on both checks.

[HenryJ]

I'll do a fluid change and look for water. Should the ABS lines be drained also ?

You will not likely see water. Brake fluid absorbs it. You may be able to calculate the amount by testing the specific gravity?
ABS system is part of the braking system and some of it will be bled with the rest. I don't think that you can cycle the ABS to get a 100% job. The really bad stuff is the fluid in the calipers. It it where it gets cooked.

[killian96ss]

Most GM dealerships cycle the ABS with a Tech II scan tool when bleeding the brakes, but they always want over $100 to do so! Speed bleeders are nice because you only need 1 person to bleed the brakes, just make sure you stay away from Russell Speed bleeders as they are known to collapse at the sealing point because they are made out of soft steel. Stainless steel bleeders are the best!

Steve

[roadrunner]

Have you checked your brake pedal free travel both running and shut off with the booster exhausted. Insufficient free travel can cause some weird problems with brakes too.

[ApproachMedium]

My brakes would do the same, they would get stuck on for long periods of times, or just slowly release. If you are in a quiet area, apply the brakes and release, can you hear any squeaking or creaking coming from the calipers? The CC has disc brakes all around usually and i found on mine I needed a fluid flush, had a bad caliper and the slide pins had ceased up. Id suggest if your capable checking out the calipers for travel etc and make sure everything is functioning. The slide pins on these trucks, esp the rears for whatever reason like to get ceased up.

What started it all was the bad slide pins, the caliper wouldnt release all the way then and it heated the rotor up, which fried up the fluid near the caliper, which destroyed the caliper, rotor, and pads. It went thru pads in a few months once then it went thru a set in just a few weeks, which is when i discovered all of these problems together.

[Horsehammerr]

Pull the ABS fuse and drive it around. This is safe to do, just remember that the ABS will not work at all. Does it still apply the brakes by itself? If the problem goes away get the ABS system checked out. I don't see how it could do it any other way since the brakes are a manual hydraulic system.

Steve

Well, I just did the fuse ABS disco and test drive. That had no effect and they came on by them selves again. I got on a gravel road and slammed the brakes on to see if they would release but , no dice. In fact this time , being on gravel , I discovered it's my front coming on, as this time on gravel the fronts stayed on and my rears simply spun and walked the rear around to the right. Hey at least I got to test my G80 works. So, I wonder why the fronts are coming on without touching the brake peddle ?? I will change fluid tomorrow, the saga continues .

[killian96ss]

If it's not the ABS then you must have stuck/seized slide pins or stuck calipers or maybe both.

Steve

[Horsehammerr]

If it's not the ABS then you must have stuck/seized slide pins or stuck calipers or maybe both.

Steve

I cleaned and lubed all eight slide pins two days ago. That is not the problem. If either the pins or the calipers were stuck/seized , how would they free up and then restick/ reseize without useing the brakes ?

[roadrunner]

And your pedal freeplay is how much?

[killian96ss]

I guess you have a ghost in the truck with you playing games! Brakes do not apply themselves!

Steve

[ApproachMedium]

If it's not the ABS then you must have stuck/seized slide pins or stuck calipers or maybe both.

Steve

I cleaned and lubed all eight slide pins two days ago. That is not the problem. If either the pins or the calipers were stuck/seized , how would they free up and then restick/ reseize without useing the brakes ?

Well, why did you have to relube your slide pins??? If the boots get wore out and any water gets in they can dry out faster than you think. Whats the brake fluid look like? Id suggest replacing it all possibly and the front calipers, you also could have a bad brake line thats collapsed internally. That happened with my suburban was NOT fun. Driver side wheel would slow down now and then.

When I did my brake work/mess clean up 2 months ago the driver side real caliper fluid came out like chocolate milk.

[Horsehammerr]

Pulled cap off master yesterday and was treated to an eye opening moment. The rubber seal in the lid was all puffed up and distorted. I did the #1 stupid. Power steering fluid in my brakes. I know this because I could not locate the brake fluid bottle, only PS fluid. So now I get to rebuild my complete brake system. Can anyone give a list of what actually needs to be replaced ?

[HenryJ]

Bleed the brakes and flush all the power steering fluid out. Something else may have attacked the lid seal?

[Horsehammerr]

OK !! This is what I did. First I sucked all the old C..p out that my snazy Turkey baster could suck. Then I filled 'er up with pure ethanol and pumped two quarts through the system with my handy dandy Dorman speed bleeders. When I finally saw good clear ethanol I then did the ole suck out the excess ethanol and filled 'er up with Prestone synthetic brake fluid and bled through RR, LR, RF, LF. Did this three complete rotations and used up a whole quart of fluid. I bled through an 1/8" clear fuel line and watched for clear fluid and zero bubbles. Works great again with no automatic brakes and ABS works perfect.

[HenryJ]

Glad you figured it out.

[killian96ss]

So, it sounds like the PS fluid was getting hot, expanding in the calipers and lines which forced the pistons to clamp down. Interesting! One thing I would caution here is that I personally would not use ethanol to flush the system since it is very corrosive and known to eat away rubber and plastic that is not designed for it. A better alternative would have been to flush a couple quarts of cheap brake fluid through and then finish off with a good quality fluid.

The funny thing to me is that I had a friend do the same thing over 10 years ago when he was drunk! So, never work on your vehicle when your drunk, and always double check what fluid you are using!

Steve

[roadrunner]

Glad you figured it out. If that fluid was in there for any length of time I'd still keep a sharp eye out for gremlins in your brake system. Hopefully you caught it in time but you can never be too careful when it comes to brakes. Lives depend on them.

[Horsehammerr]

Thanks for the concern. I DO NOT drink alcohol, and there is no possibility of drug related stupid mistakes. This was simply a head up a dark hole problem. Excuse Me ! I'm normally very conscientious when it comes to anything I do with my hands. Probably just to big of a hurry to get going when I put my new rear calipers on. Anyway, actually used denatured alcohol for the flush clean. I was told it's the same as ethanol but who knows. I was also told the main thing I have to watch for is seal break down due to the petroleum based power steering fluid. I guess that tends to attack the seal compound. I know it showed it's ugly face on my fluid reservoir cap seal. It was swollen up and a little sticky. Thats what made me question the fluid and then realize the screwup. Lesson learned !!

[killian96ss]

We all make mistakes, and I wasn't implying that you were drunk or anything. That reference was to a friend of mine. I once grabbed the top of an HEI distributor that was hooked up to an MSD ignition in order to adjust the timing, but failed to notice that I was standing in a puddle of water. Next thing I know I'm on the ground in pain wondering what happened. I'll never do that again! I'm glad you got the problem figured out. We all learn from stuff like this!

Steve

[Horsehammerr]