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Any ideas why this happened.

2847 Views 28 Replies 11 Participants Last post by  geocougar
I notice a major drag on my left front rotor and checked the brake fluid and found the gasket on top of the cap enlarged. Thinking maybe contamination or heat. Heres a picture of a good cap and how i found mine . Thanks Sean for the picture and help .
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This is the good one.


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The brake fluid should be flushed every 2-3 years, that kind of damage looks like a petroleum product got in contact with the rubber.. in any case it's time to flush out the brake system.
You think that would only lock up one caliper.
Are you in a rust belt state? Corrosion would be a more likely cause to lock up a caliper. See if it moves freely on the sliders or if the piston is frozen (as in you can't squeeze the piston in at all)... Just something we don't see in Southern California, I don't have experience with "locked up" calipers of any kind here.

In any case it sounds like you need to replace that caliper and flush out the entire brake system.

I've refused to work on a few cars because of excessive corrosion, Sometimes the rust is just too much!
Mineral oil and rubber are compatible.

Brake fluid and rubber are compatible.

But let either one touch rubber that the other one has touched, and it screws up everything.

I wonder if some motor oil has found it's way into your brake system somehow. Or DOT 5.1 fluid, which is also incompatible.
The gasket on my brake master cylinder's cap looks like that as well (deformed). Appears to be a common occurrence when I searched the web.

And until your post, I didn't know you could buy just the gasket (diaphragm, reservoir cap seal).


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I know I am looking in the wrong corner of the picture, but I notice that the rubber of the top plate really needs to be changed
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I have a caliper on the way and planning to check the function tommorrow and flush some new fluid though that front caliper.
Caliper piston moved in freely. Greesed the slides,pump some new dot 3 fluid though all was good for 2 days than it started sticking again. Going to swap out caliper today. Guess just cause piston gos in doesnt mean its still good. These are not the type to move back in after releasing brake. What else would hold up the drag. Weird !
Greesed the slides,pump some new dot 3 fluid though all was good for 2 days than it started sticking again.
Did you use regular grease or high temperature brake grease?
The grease only gos on the slides and shouldnt recieve much heat sliding back forth. Thinking something else causing the sticking. Am on way to the base to swap out this caliper i got from member. But more i think it cant be the caliper if piston moving out. Leaning towards slides ill try high temp today on slides.
The grease only gos on the slides and shouldnt recieve much heat sliding back forth.
Actually it can get quite hot. It might not be the cause this time, but I know, because I once used regular grease on the caliper slides on my Insight. They WILL stop moving when the grease is baked into sludge. I pulled the calipers, cleaned up that old grease, and replaced it with the specialized brake system grease in August or September.

The calipers can develop rust inside the cylinders if the brake fluid is not replaced regularly as it absorbs moisture, and that will keep them from moving freely. Then there are the guides on which the brake pads slide. Don't ask me how I know these things either.
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On Volvos I’ve had the rubber brake hoses collapse internally with no outward signs of a problem. You could apply the brakes to stop, but they tended to stick and drag. Anyone seen this with Insights?
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I don't remember it ever being discussed as a problem. Perhaps use the search bar above and try a few hits.
"try a few hits".............of what? LOL
Lol..funny willie. I just put high temp brake grease on slides and flush a bunch fluid out and replaced the used caliper . Think your right about moisture and i suspect thats what caused the cap seal to go bad. The line showed good flow when unhooked from caliper but your right about possible failure there.
Some months ago I had cleaned my calipers, greased the slides, and still the brakes dragged on my CVT (front passenger side).

I watched this video
where he discussed (at 4:50) that the pistons should retract when pressure is released.

He also shows (at 6:20) how easily the brake pistons should move back into the cylinder. He said that if you have to use a clamp to move the brake pistons back in, then something is wrong.

My brake pistons would not retract without (using) a clamp. So I took the piston out and found that rust had formed on the sides of the piston. Sanding the rust off revealed deep marks, which would not do (they would eventually abrade the square seal). I bought new pistons, and sand papered the brake cylinder until I could push the pistons in easily like he showed in his video.

So far so good.

I do realize that in the video he is working on a motorcycle brake caliper, but the principle should be the same for cars.

And here's a tip for installing the rubber dust boot:

Good luck.

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Thank you. Very good info. Ill give it a try next time if it keeps sticking . Am going to rebuild the caliper i took off today as soon as the new seals come in . Stay tuned for update on condition of those pistons. Can you recall where u bought your pistons and seals.
You're welcome, glad to be of some help. I ordered all parts from Rockauto, the brake pistons were Carlson 7604, the brake repair kit was Carlson 15041. I also replaced the brake hoses for good measure (Centric 15040085 and 15040086). All for a 2006 CVT.

Here's a pic of my new (top) and old (bottom) brake pistons. The old (bottom) piston is after I'd already sandpapered it, but the marks left behind by the rust were etched deep and wouldn't come off. I also used Sil-Glyde when inserting the piston back into the cylinder.

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