Today I was in the process of replacing my rear disc brakes and was unable to recess the piston enough to install new pads.

On youtube I learned I was suppose to put truck in brake service mode to recess piston.

So when I went to do that I did not have pressure on the piston and it pushed all the way out and I cannot recess piston or put vehicle in service brake mode. I have an electronic parking brake.

Not sure what to do next?

couple pictures below

is this how you tried to put it into service mode

If the piston pushed all the way out you're going to be stuck buying new calipers.

Yes that is how I was trying to put in service mode. The piston has come all the way out. I only had passenger side removed..

BOHICA !!!

Could I recess the piston by removing the electric motor? The new calipers come without the electric motor.

Somehow I was able to get in maintenance mode. Still unable to recess piston.

The piston screws in not pressed with most electric e-brake vehicles

loosegoose is spot on. If the piston has left the bore , game over. There is very tight clearances there .001- .0005 . Once it has left the bore , it is almost impossible to get back in without rebuilding it.

The motor spins the piston to lock the brakes.

Interesting. I will give it a try.

Let me see the face of the piston. Does it have a couple notches in it? You probably need that special clamp that twists it while its applying pressure.

The first one I did had me scratching my head too.

This is just more of the same engineering so you have go to dealer for simple maintenance. GM trucks have similar problems if you do a brake job yourself, the truck will most likely go into limp mode.

I haven't tried twisting it in yet. Here is a picture of the face of piston.

Here I thought I was doing just some routine maintenance.

Yeah you need a special tool. It sucks the first time you do it. The trick I had was to remove the caliper, remove the cage thingy that holds the pads, use one of the bolts of the caliper back into the hole to hold the caliper for you, like I used the top one on the car so the bottom one of the caliper was above the rotor. Then its held b/c you need three hands to work this new clamp. Basically the shaft of the clamp is a threaded bolt and as you crank on the clamp the piston turns and as you back a nut off (thats also on the same threaded shaft of the clamp) it hits against the washer that is sandwiched in between the caliper so as it expands inside the caliper it pushes the piston in as it is also turning it. Let me find a video.

In dumb terms the twisting of the C clamp handle spins the rotor now and you back a nut up on the same shaft so that it hits the washer that hits the other side of the inside of the caliper which causes the force to push the piston in. It makes it be an expansion jack inside the caliper if that makes sense. So you are tightening the C clamp and backing a nut up the shaft of the c clamp at the same time.

This first link is where you can buy the kit on Amazon:
https://a.co/d/3gmR16R

These are videos on how it works:
https://www.youtube.com/watch?v=UOBcAWw8Mj4

https://www.youtube.com/watch?v=rd6Jr1mgsgs

So like this kit comes with all these disks and it looks like this one disk matches the face of your piston so that's the one you use kinda thing.

I believe some vehicles require a scan tool to disable the electronic rear brake before starting brake service.

Then scan tool back into service when completed.

Any of you mechanics know if that's 100% true?

or by disconnecting the cable and figuring out which lead makes it turn which direction and using a battery and some jumpers

if it didn't go back in during your switch to maintenance mode it may have disengaged from the gear that turns it as it is too far out


I would try taking the motor off , crack the bleeder and see if you can turn the piston back in , all you have to loose is time

you may well be buying a new caliper already but better understanding how it works shouldn't hurt

I think I will try this before I buy a new one. It seems as though I have screwed up and will need to replace caliper.

$25 dollar kit over nite from amazon. This brake job has gotten expensive. Should have just brought it to a shop.