So its been fridged outside and a bunch of things coming at me right and left, and coming home really late so i havent been able to do what i need to do with my car. For the last 2 weeks I've been grinding on my rear right brake. I finally got around to changing the pad yesterday. The piston was pushed all the way out...well, further than normal at least since there was no pad left. I pushed it in and changed the pad. Drove to the store, everything seemed fine. Stayed in the store about 30 min and started to drive home. No brakes (pressure)!!!....or little to none. If i drove another 1/4 mile there would be none. I coasted until I could make a turn into a parking lot. Got out to check things and the wheel I was working on was soaked. I know I didn't hit or pull the hose or nipple while I was working. So I'm assuming this is because I pushed the piston back in. The problem which I don't understand is I've ALWAYS pushed the piston in the way I did this time. It was however a little harder this time.

Here are my issues that im trying to confirm.

I asked the tow guy what he thought and he said because I allowed the piston to come so far out and I rode on it like I did, that when I pushed it back in, that's what caused the damage.

And the mechanic said that I may have even caused damage to the master cylinder and booster by pushing it in without opening the brake nipple or reservoir cover. This really doesn't make any sense to me because it's a closed system that simply keeps exchanging the same volume of pressure/liquid. Really trying to verify this before they try to jack me with repair costs.

I think more likely you have a bad caliper. The piston usually rides along a seal fitted in the caliper body. They are very hardy, but maybe something happened to it as you pushed it back as the piston could have been too far out. The seal could have been scratched/cut (not sure how easy it would be to roll it out of place, it's a square cut O-Ring).
Somehow the sealing interface is allowing fluid to leak out.


I do my service like you; pushing the piston back without opening anything. I think their claim for a damaged booster/master cyl is bogus. Only that one corner was affected, right?
I would be more inclined to just replace the caliper and call it good.

I agree. I thought it couldn't be anything more than a bad caliper that needed to be replaced. He just really bugged me out when he said that about the cylinder and brake booster. I'm just going to make sure I set up my roadsside assistance to tow my car home if he tries to say that on Monday, and change the caliper myself.

Brake fluid contamination is worst at the brake calipers, where heavy contaminants like metals, water & rust tend to accumulate since this is the lowest point of the brake system. It also is the place where the most thermal stress takes place on the fluid!
I was always taught that you should never push the contaminated fluid sitting in your caliper back through the lines towards the ABS valving & master cylinder.

I know a few people who are competent mechanics that I respect that tell me that brake bleeding is asking for trouble. Their argument is that by opening the system, one could possibly introduce air into the system that may be difficult to bleed out afterwards, especially if that air pocket gets up into the ABS valving, or the possibility of having to deal with sheared/broken/frozen bleeder screws.

To be fair, it is true certain manufactures over the years have included ABS cycling functions into their scanners to assist air purging of the brake system.
Some manufacturers use scanner functions to perform brake bleeds, but this does not mean ignoring brake fluid servicing just because one might not have the proper tools. Solution is to find a mechanic who does!

In your case, a possibility exist that the caliper piston may not have been resetting itself after brake applications, causing the pads to continuously ride the rotor. (piston was frozen into the bore).
Neglected fluid service could be a explanation as to cause of seizure of piston.

Bottom line is that if this was my car, I would want a competent mechanic to correctly flush out the old fluid from the entire brake system!

Turns out it was just the caliper. I'm mad because i could have changed that myself and saved $150 extra they charged me above what actual labor and what the calipers SHOULD cost smh...this is what happens when you are desperate and busy smh.

@steve_c what's the difference between flush and bleed? Is it just a matter of pressure pushing out all valves at the same time with flush?

TDot wrote: ↑

Tue Dec 25, 2018 7:24 am

@steve_c what's the difference between flush and bleed? Is it just a matter of pressure pushing out all valves at the same time with flush?

Bleeding usually means releasing fluid at the calipers to be sure no air is trapped, benificial because it removes the worst of your brake fluid. Flushing is similar, only you keep bleeding until you have removed & replaced 100% of your fluid. (from master cylinder to brake calipers).

My criteria is (others may have their own opinion):
I look at the master cylinder for fluid condition:
Fresh Fluid is clear
Fairly fresh/Mildly contaminated has yellowish tint
Moderate contamination has dark yellow/brownish tint (time to flush in my opinion)
Severe contamination is dark drown/black tint

What color is your brake fluid? (you can see it through the plastic reservoir)

Make sure you change the hoses to the calipers. These failed on my M35x rear and I replaced 2 sets of calipers before realizing that was the issue.