SLK 32 AMG. Brake pedal not returning fully

[sailorP]

This is a 2002 R170 SLK32 AMG.

I've just put her back on the road this afternoon after nearly six months on a SORN and I had a bit of an issue with the brakes.
When first started and moved on the driveway, slow speed manoeuvring felt a bit odd, the car was reluctant to move without a prod on the throttle.
Then noticed that brake lights were on while stationary, in Park, without handbrake on.
Hmm.
Next noticed that brake pedal was not in fully up "off" position. I could lift it with my left foot an inch or so, back to it's proper "off" position. When lifted, the brake lights were extinguished.
When re-applying the brakes fully again and then releasing the pedal, the pedal again didn't quite fully release, and brake lights stayed on. The pedal could be lifted with left foot, so I set off on a short run to see what else was wrong.
Nothing else found. Brakes operated fine, brought car to a halt very effectively, but the pedal had to be lifted with left foot after every application, to bring the pedal fully up and release the brakes fully.

Has anyone any previous experience with this issue, or a possible diagnosis and fix?

And, yes, I know, I shouldn't really run with brakes even remotely dodgy, but it was a short run to attempt to diagnose the problem and see if it self-cleared (it didn't). Apart from a sticky hood (solution for which is on another thread) that's the only issue.

She's booked into Gerry Dovermans Hereford for B service plus spark plugs, filters and MOT in a couple of weeks. I won't be putting her on the road again until then. But I'd like some advice on this brake issue so I can sound semi-proficient when I discuss the problem with them.

I'll be reading this thread every evening, no rush for solution.
Thanks Phil

 

[television]

Not easy when a car has been standing, best to drive it a bit and see. the caliper pistons could be stuck on, this could cause a lower brake pedal, I would suspect that the caliper pistons have rusted while standing. Can you pump the pedal up, if you can does it stay up, or slowly sink again.

Another thing is the seals on the master cylinder could have failed, this would cause a very low pedal when pressed.

 

[Uncle Benz]

The pedal pivot pin is plastic, believe it or not! It's common for the pedal to seize to the pin when they've been laid up for a while. It'll need the unit removing and in the past I've had to drill out the plastic pin, clean up the bits and then fit a new one from Mercedes.

 

[television]

Be nice if it is that Uncle, never heard of this one.

 

[Uncle Benz]

Be nice if it is that Uncle, never heard of this one.

Not hugely common, but I've seen two or three with this fault.

 

[sailorP]

Thanks for the suggestions.
I won't be trying to fix this myself, but your comments will help me talk semi-knowledgeably with the garage.
I'll post what it was when they have fixed it.
Rgds

 

[sailorP]

Fixed

Part of the service was change brake fluid, with bleed of brake system, of course.
That, and rotating the caliper pistons through 180 degrees, as a precaution, has cleared the brake issue.
Car has been fine since, apart from a mystery power loss just after the service, which has been cured by replacing the new fuel filter that was fitted during the service...looks like the first new fuel filter (genuine MB part) was dodgy.
This car is still such fun to own...P