So, I haven't yet got around to doing this, and as a result at least one of my rotors is warped now. It's high time I get going on this.

I'm wondering if there is a way to test the pistons using this method without removing the calipers from the car. I'd rather not have to buy new caliper bolts if possible, is why I ask.

I was reading that you can remove the brake pads without taking the caliper off. Is it possible to remove the pads and then try to compress the pistons at that point? Or am I just asking for trouble doing it this way? Any help is appreciated.

 

Replacing the brake pads alone will not address your warped motor problem - it needs to be resurfaced or replaced.

That said, if you intend to just replace the brake pads (discarding the old pads), the best way to do it is to leave the old pad in place. Open the brake fluid reservoir cap. Insert a large blade screwdriver between the old brake pad and the rotor, and pry with a slow and steady motion. At first, the screwdriver can not be inserted very far in, but as the piston begins to retract, you should be able to insert the screwdriver progressively farther in. You're essentially using the old brake pad to push the piston back into its bore, sending brake fluid back into the reservoir. Be sure to pry with the screwdriver tip towards the old brake pad (this may damage the old pad, which we plan to discard). The front caliper has 2 opposing pistons fed by the same brake line, so while you pry to retract one piston, the other may get pushed back out by some amount. I believe the rear caliper has only one piston. Also, the pistons don't have to be retracted completely - just enough to fit the new and "meatier" pads.

You will not be able to fix the "stuck piston" without detaching the caliper - there is simply not enough room to get to the piston and its seals.

 

My rotors have never been turned. Pretty amazing as the car has almost 127k now. Previous owner was getting pads every 30k or so. I am at 20k miles and still have at least half the pad left. I am thinking the rotors will need to be turned before too long. Very slight movement in the peddle and a small lip on the rotor.

What causes our brakes to grunt? Mine grunts at very low speed breaking. Like at a drive through. As you are moving forward they kind of grunt as you are on and off the brake moving forward in line.

 

Appreciate the feedback. I think there has been a misunderstanding. I'm not hoping replacing my pads will fix the issue. Nor am I hoping that I can rebuild the caliper with it still attached to the car. Currently, I'm just interested in diagnosing which caliper is sticky at this point. I want to use the suggested diagnostic method of compressing pistons to feel which one is harder to push back than the others to determine which caliper is at issue. To do this myself it seems I'm presented with 2 options (hopefully):

1. pull each caliper off of the car (line still attached) and compress wtih brake pads still in place - this requires me to buy new caliper bolts though. At $20 per caliper from the local dealer or $20 per caliper shipped from Sewell, this adds up quick. Which leads me to number two:

2. leaving the calipers on the car, remove the brake pads and (somehow - not sure if possible) compress the pistons on each caliper to see which caliper puts up the biggest fight. The toughest one would in theory be the best candidate for a remaned caliper swap.

Hopefully that clears up what I'm trying to do. Is #2 possible? Thoughts?

 

You need a really strong c-clamp to push the pistons back in, and be careful not to damage them as they are aluminum.
I went through the same hassle 2 weeks ago. You just gotta use the right tool and everything will turn out fine.

I had to remove the caliper so I can correctly position the c-clamp with the maximum torque given out.
Easily and steadily I pushed each piston by itself.

After that, I had a lot of air in my system, and my break pedal was awfully mushy and full of air.
I could pump it a bit, but then it gets and becomes loose again.

Took it to Les Schwab and they performed a full brake fluid flush for me, and now it feels better than ever. .