I lent my 2000 Chevy Silverado 4x4 to my girlfriend and, unfortunately, one of the rear brake lines in the back was rusty and let go when she was driving. In order to make it home, she got the idea of putting automatic transmission fluid into the rapidly draining brake fluid reservoir. I've since replaced the bad line, drained as much of the brake fluid as I could, and replaced with fresh fluid. However, the front brakes now stick when driving. I can't pick up a definite pattern, it seems random, and basically it slows the truck down enough that I usually have to press the tow/haul button to shift down so I can keep driving at normal speeds. I know it's the front brakes that are grabbing because I can pull over when the problem is happening, touch the rear rotors and they're fine but the front rotors are burning hot and pouring off heat. If I keep driving the truck when the brakes are sticking, it usually frees up after about 20 miles or so but, again, it's not consistent enough that I can see a clear pattern. Also, when I lift the hood and unscrew the cap to the brake fluid reservoir, the cap is often "stuck" and when I gently lift it up, I can see sticky, stringy fluid (about the same consistency as thick maple syrup). The fluid in the reservoir itself doesn't look too bad, it's just that layer of sticky fluid that sticks to the cap that I see. Any ideas or advice on how to remedy this issue would be greatly appreciated!

 

Stop driving the truck immediately. Take it to a certified mechanic and have them do a full system flush of the brake lines and clean any visable gunk up. You don't want anything contaminating the braking system.

 

Replace the master cylinder.

 

Thank you for the reply. I've already driven the truck for about month now. The problem doesn't happen all the time, it's about a 50/50 chance of having a normal ride or having to put up with the sticking front brakes. What would the process of flushing the brakes be? Is it something I can do at home? I'm familiar with working on vehicles. I only paid $4k for the vehicle used and can't afford to sink a lot of cash into maintaining it, which is why I'd prefer to fix it myself.

 

Would you mind elaborating on your answer? Why would replacing this one part fix the issue, in your opinion?

 

Both fluids are hydraulic fluids though they have different properties designed for different environments.. I would think several system flushes would clear the system.
You might be able to replace the rear brake cylinders and be fine (after flushing system) the sticking could be related or completely unrelated as rear breaks do 30% or less of the stopping.

 

But, it is the front pads that are sticking not the rear ones. It was the rear line that broke. His girlfriend poured ATF into the reservoir. He replaced the line and tried to bleed the system from the rear. Problem is the ATF got into the bore of the master cylinder and has swelled the seals. So when he hits the brake pedal the pistons move against the rotor but the swollen seals in the MC prevents the pistons from retracting because the seals doesnt move. It is an occasional thing but it always locks up the front brakes. Eventually it wont be a problem because he will start a fire in the wheel. But flushing the system is pointless to me because unless he is willing to rebuild the master cylinder, and replace the brake hoses there isnt an absolute certainty he will remove enough ATF(which is miscible with brake fluid). I d recommend new brake hoses all around with a new master cylinder and flush with mineral oil. These are the brakes, cant play around with this feature.

 

I would say to buy 4 or 5 bottles of brake fluid, then use at least 1 bottle to bleed through each brake caliper.
After a bottle has been bleed through all the brake calipers I would do a few last bleeds in each caliper to ensure
All of the burnt fluid is out and you have only clean freah fluid in your lines.

Oh, and your fluid is syrapy either because some kind of chemical reation has taken place in between the
ATF and brake fluid, or because your brake and transmission fluid in your line is burnt.
It is rated to operate stable below certain temperatures. After reaching a couple hundred degrees or whatever
Your fluid was rated for it starts to burn and deteriorate, same with oil.
Just spend some time giving the system a thorough flush and go from there.
Regardless, a shop would definitelly flush your system out anyway as a 1st fix attempt, so might as well try that yourself.

 

Find a new girlfriend??

I recommend flushing the entire brake system out VERY well. Then give it a go. Remember to start from the wheel end furthest from the master cyl. If it still sticks, I'd replace the master and/or calipers.

 

+1 on finding a new girlfriend.

Mine.... can't get her out of the camo gear, camo purse, camo seat covers, camo jacket, camo wallet, camo thong, camo hat, camo **** for god sakes.