Help: cannot retract one of the rear calipers piston (but the other did)

[jmarcos]

Model 3P 2019:
I was able to retract the rear driver-side caliper piston and install new pads; but I cannot do the same on the passenger side (I'm confused and tired after trying for two hours).
My procedure for both was:
-Remove caliper from bracket
-Set the towing service mode
-Unplug the electronic brake wiring just in case
-Remove pads
-Open the brake fluid cap
-Twist clockwise the piston with an adjustable tool that has two pins (I hate it because it's so adjustable it always comes off)
(do this for a while)
-Provisionally place the new pads to see if there's clearance vs. the rotor

This worked fine on the rear driver-side. But repeating the same on the passenger side I eventually start hearing that I'm turning some of the assembly inside (sounds like the motor/some gears). Even after a lot of fiddling I haven't increased the clearance, the old pads just barely fit on the rotor. I even put things back with the old pads, went out of the service mode, and re-did the sequence.
Only other note is that I have the MPP rear big-brake kit which needs more gap between the pads since the rotor is thicker. But then again I was able to do it on one side!
Any suggestions are welcome. Do I need to do the 9V battery trick to retract the electronic parking brake further?
I can always put back the old pad on the difficult side until I figure it out.

 

[Kimmi]

How many miles are on the car to be replacing brakes?

 

[jmarcos]

This car has been tracked, so that really throws any regular mileage out of the window.

 

[gearchruncher]

Brake retraction is now in the service mode for the last few software releases. You don't have to play with tow mode anymore. Have you tried this?

Service Mode

(congrats on tracking your Tesla!)

 

[jmarcos]

Thanks @gearchruncher regarding the service mode, it is really neat!
Even with the EPB mode, I was not able to retract the piston - I could hear the electric motor doing its winding, but the piston looks crooked.

Maybe it's the angle of the photo, but visually it didn't seem quite right.
I've rebuilt calipers once for another car and it's a major pain (anything with brake fluid is), so I might take it in to have it looked at. I did put the old brake pads for now. Thanks again for the help!

 

[Dangerous Fish]

I'm afraid you may have broken the epb worm gear. Although it's supposed to be possible to manually wind the piston in, you really need to do if with the motor either in service mode or with a battery connected to the terminals.

 

[gearchruncher]

You can easily take the EPB motor module off the back calipers too FYI. It's just two torx if I remember. Now you have a generic hydraulic caliper so you can see if you can retract it and get the pads on. You can also see if it appears broken.

I messed something up once and had to do this, and taking the EPB module off let me unwind it and get it put back on right and it's all fine now years later.

 

[jmarcos]

Thanks for the suggestions, I'll remove the EPB next weekend to see how it looks.

 

[Dangerous Fish]

You can easily take the EPB motor module off the back calipers too FYI. It's just two torx if I remember. Now you have a generic hydraulic caliper so you can see if you can retract it and get the pads on. You can also see if it appears broken.

I messed something up once and had to do this, and taking the EPB module off let me unwind it and get it put back on right and it's all fine now years later.

That's how I did a pad change the first time before I knew about the '9V battery to the terminals' trick.

 

[gearchruncher]

That's how I did a pad change the first time before I knew about the '9V battery to the terminals' trick.

You and me both good buddy!
Work harder, not smarter.

 

[jmarcos]

Follow-up: I removed the EPB after setting the service mode, and while I still could not wind the piston in, I saw that the piston would expand when slowly twisting the screw on the EPB side. The piston would still not change position when trying to wind-it (or unwind it) from the normal/pad side.
So I then tried a regular piston compressor and it easily compressed in... so I was able to get the clearance needed, not sure I can say nothing is wrong because it's not what I expected, but seemed to work!
Thanks all for the help.