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Discussion Starter #1
Hi All,
I love my SLC top down and top up! My first proper automatic though so trying to get my head round the options. My SLC auto has two parking brakes. One is a parking lock activated by pressing the ‘P’ button next to the ‘R-N-D’ selector. This seems to hold the car using the normal hydraulics system on all 4 wheels. I assume this operates in the same way as the ‘Hill Hold’ when stopped on a gradient to allow you to move your foot from brake to throttle without slipping backwards.
The parking brake on the other hand is a separate push/pull button low down on the dash which seems to operate like a conventional handbrake except its electronic I can’t see any cable going to the rear wheels or any separate calipers on the rear discs so my questions are, (and I apologise in advance if these appear dumb questions!):

1. If stopped at the lights in ‘Drive’ mode I presume I should use the parking lock function as opposed to just keeping my foot on the brake and dazzling the guy behind with my brake lights. The parking lock automatically disengages when I press the throttle.

2. Does anyone put their car in neutral and use the parking brake at the lights?

3. Apart from the above under what circumstances would you use the parking lock as oppose to the parking brake?

4. Is the parking lock some kind of separate servo operated piston that exerts pressure on the hydraulic braking system?

5. How does the parking brake operate, is it on just the rear wheels, is it hydraulic or cable.

6. Presume if the car was left for a long time with the parking brake on and the battery went flat the car would role away if on a gradient so would need chocking?
 

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DAS/STAR Registered Owner
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4,018 Posts
The P in an auto box is normally a Pawl that locks one of the shafts in the auto box .. on the 171 it's a physical thing and will lock the gearbox (or try to) even if you select P when moving .. guessing the 172/slc is the same, just with electrical operation as opposed to a physical lever.

Probably the same with the electronic handbrake .. electrical operation the physical mechanism in the rear discs...
 

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Premium Member 2013 SLK250
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2,339 Posts
Pyecrust; 1. If stopped at the lights in ‘Drive’ mode I presume I should use the parking lock function as opposed to just keeping my foot on the brake and dazzling the guy behind with my brake lights. The parking lock automatically disengages when I press the throttle. 2. Does anyone put their car in neutral and use the parking brake at the lights? [/QUOTE said:
Can not speak to the SLC but have a GLA.
1. If the 'parking lock' is the same as 'Hold' when you use it the brake lights will still be on the same as foot on brake pedal.

2. If you have Stop/Go the engine will shut off when stopped at lights. Does not matter if foot on pedal or you use the HOLD feature.

3. Use the HOLD when driving and stop and go traffic. When you put the car in PARK the parking brake will engage while trans is in park unless you disengage it.

4&5 Can not speak to them.

6. My GLA has been parked a over two weeks and found no drain on battery. When taken out of park and put in drive and start to move can feel the brakes release.

Maybe other will confirm that the SLC is the same.
 

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Registered
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500 Posts
Hi All,
I love my SLC top down and top up! My first proper automatic though so trying to get my head round the options. My SLC auto has two parking brakes. One is a parking lock activated by pressing the ‘P’ button next to the ‘R-N-D’ selector. This seems to hold the car using the normal hydraulics system on all 4 wheels. I assume this operates in the same way as the ‘Hill Hold’ when stopped on a gradient to allow you to move your foot from brake to throttle without slipping backwards.
The parking brake on the other hand is a separate push/pull button low down on the dash which seems to operate like a conventional handbrake except its electronic I can’t see any cable going to the rear wheels or any separate calipers on the rear discs so my questions are, (and I apologise in advance if these appear dumb questions!):

1. If stopped at the lights in ‘Drive’ mode I presume I should use the parking lock function as opposed to just keeping my foot on the brake and dazzling the guy behind with my brake lights. The parking lock automatically disengages when I press the throttle.

2. Does anyone put their car in neutral and use the parking brake at the lights?

3. Apart from the above under what circumstances would you use the parking lock as oppose to the parking brake?

4. Is the parking lock some kind of separate servo operated piston that exerts pressure on the hydraulic braking system?

5. How does the parking brake operate, is it on just the rear wheels, is it hydraulic or cable.

6. Presume if the car was left for a long time with the parking brake on and the battery went flat the car would role away if on a gradient so would need chocking?
Hi @Pyecrust, I had a SLK R172 250d, the automatic selector mechanisms are slightly different to the SLC but basically they work in a similar fashion... however, yours is even more intelligent!

The online SLC manual is you friend here, this is the relevant section.

1 & 3. The P button by the gear selector puts the transmission in park, it isn't connected with the brakes at all. I don't think putting it in park is the intended thing to do when stopped at the lights, surely you'll be having to select drive before you move off?

either hold the car on the footbrake, apply the parking brake under the dash, or alternatively the car should have the "HOLD" function... when you brake to a complete standstill pushing the footbrake pedal a bit harder will cause the brakes to turn on the "HOLD" function and the light on the dash to illuminate (provided certain criteria are met, like having stop start switched on). Stop start will kick in and you can then take you foot off the brake and sit there as long as you like without touching anything..magic!

Then, when the lights change, just press the accelerator to move off. On an A*** this brilliant "HOLD" function is a £90 option but you've got it for free! :grin:

2. not usually, I think you may be trying to drive it a bit too much like you would a manual transmission, just leave it in drive and do one of the above.

3. When you are actually parked, rather than just temporarily stopped. Quote from the manual:-

Park position
This safeguards the vehicle against rolling away when stopped.
Only shift the transmission into position more when the vehicle is stationary. The parking lock should not be used as a brake when parking. In order to secure the vehicle, always apply the electric parking brake in addition to the parking lock.
If the key is removed from the ignition lock, the transmission is locked.
The automatic transmission shifts to automatically:
when the key is removed from the ignition lock
when the engine is switched off with the transmission in position or and one of the doors is opened
In the event of a malfunction of the vehicle's electronics, the transmission may lock in position . Have the vehicle electronics checked immediately at a qualified specialist workshop.


4 & 5. The parking brake switch under the dash applies the parking brake, which electronically clamps the the pads on tight to the rear disks (you can hear the servos operating the brake pistons if you listen carefully), no old fashioned bowden cables here! As I understand it, it doesn't use hydraulic pressure at all. I think the "Hold" function does use the ABS system to apply hydraulic pressure and clamp the pads though. All this means that replacing the rear pads is a different procedure from a cable operated handbrake (there's a thread about it on here somewhere if you want to know more)

6. I don't think it will just release if the battery gets low but putting the transmission in P is a failsafe in any case. The manual says it may fail to APPLY the parking brake if the battery is low :-
The function of the electric parking brake is dependent on the on-board voltage. If the on-board voltage is low or the system is malfunctioning, it may not be possible to apply the released parking brake.
If this is the case, park the vehicle only on level ground and secure it to prevent it from rolling away.
- Vehicles with automatic transmission: shift the transmission to position .
- Vehicles with manual transmission: engage first gear.
It may not be possible to release an applied parking brake if the on-board voltage is low or if there is a malfunction in the system. Contact a qualified specialist workshop.
The electric parking brake carries out a function check at regular intervals when the engine is switched off. Noises that occur are normal.


Sorry for the long post, but I hope it helps :smile:
 

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Premium Member
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Discussion Starter #6
Thanks bastivock for the comprehensive reply that's very helpful indeed.
Made things much clearer.
 

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500 Posts
I may be driving a TT Coupe now but I don't harf envy you on nice sunny days like today... really hope you're enjoying your new SLC, I know I would have if I could've got my hands on one in a sensible timeframe. I still think SLK/C s are drop dead cool 😎
 
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