I’m replacing the rear discs / pads on my L405 4.4 TDV8 and was not able to press the piston back into the caliper far enough to mount the caliper over the new rear discs / pads (I had put it into maintenance mode before starting the job).

On inspecting the parking brake actuator, I noticed the plastic casing was cracked around one of the mounting bolts and water has obviously been entering the inner workings for some time. I unbolted & removed the actuator & manually adjusted the parking brake back which allowed the piston to press back further & the caliper to clear the new pads.

New parking brake actuators are available on eBay for about £40, which isn’t too bad.

My question is how to correctly adjust the parking brake back to the correct position before then refitting the actuator and is any calibration needed or does it self adjust as part of taking it out of maintenance mode?

As always seems to be the way, a simple discs/pads change has grown arms & legs!

If its anything like my Evoque, BMW 5 and 6 series and my old man’s Scirocco, I generally wind out the parking brake to its full extent, then push back the piston using the actuator side ever so slightly so that its not hitting against its limit, the put the actuator back on.

Then I just fit it all back. Yes it’ll be be loose initially. When you take the brake out of service mode, the motors will push the pistons all the way back till they bite, then they’ll back off the necessary amount.

As I understand it, the system self adjusts by measuring the current needed to drive the pistons home. When they bite tight, the motor stalls and the current spikes … the system senses the high current and uses that point as the correct adjust point.

I think it then just backs off the piston a set number of motor turns, rather than a measuring an actual linear distance of the piston’s travel. V8 or else ...

That's pretty much it. I've never known a vehicle with on-caliper EPB to need any calibration.

I had assumed maintenance mode would wind the parking brake actuator back far enough to accommodate the extra width of the new disc / pads but perhaps mine was out of adjustment in some way - although it all seemed to work ok beforehand despite the cracked actuator casing and water ingress.

In any case, appreciate the advice and that all makes sense so I’ll give it a go

Maintenance mode is essentially the opposite of service mode, it drives the piston fully off until the motor stalls, if there is something blocking it, the stall will happen earlier, leaving the piston too far out, which is what it sounds like is what has happened in your case.

When the motor winds back, it only winds back the inner rod that pushes on the inside back of the caliper piston. This relieves the force on the piston and pads to allow you to take the caliper and pads off the disc.

However, whilst the rod retracts, it doesn’t actually ‘pull’ back the caliper piston with it. . With the rod retracted, you can then push back the piston in the normal manner.

That might explain what you had to do. V8 or else ...