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Car Forum / Mercedes-Benz Cars / June 2006Parking brake design
I note that my 2004 CLK 240 Auto exhibits a bit of a lurch after setting the parking brake - especially if I am on a slope. Sequence of events would be: stop car with right foot on footbrake - shift Auto stick into Park - tread left foot on parking brake - remove right foot from footbrake - lurch. Can anyone advise me what wheels the parking brake operates on, and why there is a slight 'backlash' in the system. Anyway, it seems safe enough. David I am not sure what you meant by lurch... a slight roll perhaps? The reason for that is the tranny has a cam and cog for parking... so there is a wide gap in cog to make sure you can park without excessive roll. So the car will roll a bit until the cam and cog meet each other. Parking brake are not a strong brake... they are only tiny brake shoes... so car will roll if not tighened up properly... which bring us to your case... you need to have your parking brake shoes adjusted a tad tighter. > I am not sure what you meant by lurch... a slight roll perhaps? The > reason for that is the tranny has a cam and cog for parking... so > there is a wide gap in cog to make sure you can park without exces- > sive roll. So the car will roll a bit until the cam and cog meet > each other. Speaking of a slight roll, all three of my W123 and W124 cars have had the opposite characteristic: a certain amount of slop in the driveline that's noticeable when Drive is engaged. There's a slight hesitation and then a bump when I press the accelerator as driveline lash is taken up, before the gears engage and the car begins moving forward. It's particularly noticeable in the morning, when the transmission is cold. This driveline lash is also noticeable when descending a grade while running on cruise control. The cruise control will "hunt" back and forth as it struggles to maintain a constant speed, causing the car to jerk back and forth slightly. It's mildly annoying, but pressing on the accelerator smooths it out. Since all three of my 5-cylinder models have done that, I gather it's normal. (My SDL doesn't display this behavior for some reason.) > Parking brake are not a strong brake... they are only tiny brake > shoes... so car will roll if not tighened up properly... which > bring us to your you need to have your parking brake shoes adjusted > a tad tighter. It occurs to me that perhaps the OP simply isn't pressing on the parking brake pedal hard enough. The parking brakes on my W124 take a lot of pressure on the pedal to set them properly, and the pedal has more travel than it seems like it should -- significantly more than was the case with my W123s. It goes most of the way to the floor before I can press it no farther and the car stops rolling. I brought this to the attention of my mechanic, but he swore up and down that the parking brakes were adjusted to spec. I had occasion to drive his personal W124, and its parking brakes were adjusted the same way. Maybe this is a characteristic of the more recent Benzes in general, not just W124s. Geoff  Signature"Admittedly, conservatives give as good as they get. The difference between us and [leftists] is that we can argue as well as inveigh. They can only hurl invectives." -- Don Feder The lash is usually bad mounts... maybe your tranny mounts are bad... or the flex-disc are worn. Also the engine mounts... they do affect the driveline as I had that happened to my W126. >I am not sure what you meant by lurch... a slight roll perhaps? Yes, the car definitely seems to move just a little... >The reason >for that is the tranny has a cam and cog for parking... so there is a wide >gap in cog to make sure you can park without excessive roll. So the car will >roll a bit until the cam and cog meet each other. But shouldn't the brakes operate such that even though there is a bit of movement around the tranny park cog, the wheels will be jammed from further movement by the parking brake, if it is the last thing applied? Otherwise, what is the point of these brakes? >Parking brake are not a strong brake... they are only tiny brake shoes... >so car will roll if not tighened up properly... which bring us to your >case... you need to have your parking brake shoes adjusted a tad tighter. It may be that I have to apply this brake more firmly. It cannot be worn, or even need adjusting - the car has only done 3500 miles, and has just had an A service. (it was a Embassy car, mainly garaged for 2 years. I've rescued it....) David >>I am not sure what you meant by lurch... a slight roll perhaps? > [quoted text clipped - 12 lines] > >David Just to wrap this up... I was in my local Mercedes main dealership today, and raised this parking brake issue of mine. The guy in the Service Dept said that: 1. The parking brakes operate on the rear wheels only. 2. They are separate pads that grab the regular brake discs. 3. There is a tendency for all current MB car to 'settle' after they are applied, especially on a slope. I'm assured that the road wheels are not moving - it just seems that they might be. David >>> I am not sure what you meant by lurch... a slight roll perhaps? >> Yes, the car definitely seems to move just a little... [quoted text clipped - 25 lines] > > David From my experience any vehicle that has disk brakes MUST have expandable shoes used for the emergency brake, and there has to be a little movement or they couldn't expand. That's why many cheaper cars were so late in installing them for production. The only exception I can think of is for a 1956 Dodge that tried to be innovative by using circular shoes around the drive shaft. They discarded that design before years end! :-P
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