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2005 SLK55 AMG
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Discussion Starter · #1 ·
I have just of fitted new, Rear, OEM M-B Discs to my 2005 55 AMG. While doing this I met a problem with the Hand brake system and as well as describing my Disc change process I thought I would share how I did the job with the SLK Members. I hope it proves useful to those who, like me, enjoy doing their own Maintenance on these great cars.

I did lots of Searches on the Forum before beginning this job and some of the info I found is included in this Post. I’m sorry I didn’t make a note of the Members whose info helped me so cannot name them individually, but would like to express my thanks to all of you.

I have started with the right hand side. (Forgive me if I use this opportunity to vent my frustration with the use, on this Forum, of the terms Off and Near side As this is an International Forum it means that the first time I read a post which uses one of those phrases, I have to check to see which Country, and therefore side of the road they drive on. If only it was as easy as looking for the information about the member in the box to the left of their post. Often no Country is mentioned, just a town or City or, for our American Cousins, what may be just the initials of their State, so I have to waste time trying to figure out where in the World they live. Rant over. Back to the Post)

Removing the Disc Brake Caliper was relatively easy.

Having first disconnected the Pad wear indicator I used a light hammer and round punch to drift out the two disc pins, this enabled me to remove the Pads and their spring tensioner but I had to buy an E14xE16 extra long, flat ring spanner to remove the Torxs bolts which hold the Brake Calliper to the Upright, There was insufficient space to get my Torx socket and Bar onto the head of the bolts. This was because the plastic Link Rod, that goes to the Anti-Roll/Sway Bar, was in the way. It would have been possible to remove the Link but that would have complicated the job and it wasn’t necessary with the Torx Ring spanner.

It needed to be a long spanner as those bolts are tight and are also Threadlocked in place. If anyone is interested I bought the spanner on ebay from Tools 2 U Direct. It is 320 mm long and cost £9-95 inc P&P. The head size of the Bolts was E14.

To prevent the hydraulic brake cable being put under tension I laid it under the car raised up on a block of wood. After removing the small countersunk screw, located next to the wheel bolt holes, the next job was to remove the Disc. If you are lucky it will lift off but it is more than likely it will snag on the Hand Brake shoes. Since the Hand brake works from two small shoes, approx 160mm diameter, which press on the interior of the Disc, these will needed to be backed off.

To do this it is necessary to screw either the small countersunk screw or one of the wheel nuts back on. The disc can then be manually turned until one of the wheel bolt holes is at the 10 o’clock position Doing this enabled me to see. with the aid of a small torch, shone through the hole, the 15 pointed Star screw which is used to adjust the Hand brake set point.

However to rotate the disc the Car must be in Neutral. Unless the car was left in N before you started work, mine wasn’t, this will entail starting the car up and the brake pedal being pressed.

IMPORTANT: THE CALLIPER PISTONS MUST FIRST BE CHOCKED.

I put the pads back in and packed the remaining space between them with a piece of wood. If this is not done, and it all too easy to forget to do it, the pistons can be ejected from their bores.

It is such an automatic process to jump in the car and start the Engine, that it is all too easy to forget that you have no brakes. The natural reaction when selecting N is to push the pedal. When you feel no reaction you carry on pushing. If you stop doing that quickly enough you may get away with it. If not when you get of the car you could be met with one or more Brake Pistons pushed out, a pool of brake fluid and a lot of extra work. Hands up all those who have suffered that?. I haven’t done that one myself but can think of too many other silly car related mistakes I have made over the years.

Once the Engine was running and Neutral selected I switched off and returned to the task.

I was surprised to find that the Star screw was still at its minimum i.e. there were no threads showing. To double check I used a suitable screwdriver to rotate the screw to take up the play between the shoes and surface of the Brake Disc. As it is a Right Hand thread this meant levering the points of the Star upwards. I then backed it off again. Since this is an 11 year old Car, with over 110K miles on it, I had expected to find it had been screwed out over the years to take up brake shoe wear. The Hand brake has always worked well so maybe the shoes had been replaced previously, although there is no mention of that in the Service records. That meant I couldn’t back the shoes off to allow for the inevitable wear ridges in the Disc surface.

It was a real struggle to get the Disc off. It kept trying to drag the lower of the two shoes with it. When I finally got it off I discovered that the small spring that held the shoe to the Back Plate had come away and had hooked itself onto the upper spring, The reason for this turned out to be due to corrosion of the Back Plate.

The two pictures I have, hopefully, included show the difference between the upper and lower spring locations on the Back plate. As can be seen, once I had wire brushed most of the rust off the Plate, and cleared the lower location of the remaining, wafer thin metal, I was left with a large hole.

My first response was to remove the Back Plate to repair or replace it, but reading some further research I would have had to remove the Axle Shaft, Wheel Flange and Bearing Carrier to get the Back plate off. As I didn’t have either the Tools or all the information to do this procedure and wanted to get the Car back on the road this will have to wait until I take the car off the road this winter

I am also not happy with Mercs way of securing the Shoe Springs. It may have been easy to clip them into place in the Factory when it was a sub assembly but it is another matter to do it on an assembled rear suspension. For me to have to compress the spring through the slot in the brake shoe, find a blind slot in the back plate, rotate the spring, under tension, 90 degrees and try to find the small location hole, as I release the spring, would be a difficult and frustrating process. When, eventually, the Spring hooks onto some part of the Back Plate there will be no guarantee that the Spring hook is in its locating hole.

I practiced clipping the Spring into the undamaged upper hole and even with just the bare Back plate, and being able to see what I was doing, it still wasn’t easy to get that hook into its hole.

I decided to use a different method, one used on a lot of older English cars. I bought a set of Girling Springs and pins, part No. SP 1006 (ebay again). The advantage of this Kit is that the locating pin for the spring protrudes through the slot in the brake shoe. It is then an easy job to slip the spring and cup over it, compress the spring so that the locating pin passes through the slot in the cup, rotate the cup 90 degrees and release the spring so that the tab on the pin sits in its locked position in the cup.

Fitting the upper brake shoe pin to the back plate was a simple matter.

As the diameter of the pins shaft is very slightly larger than the width of the slot in the back plate, the width of the centre of the slot was first eased, not drilled, out. The pin was then inserted from the rear of the back plate and through the brake shoe slot. The spring was slipped over it, and with the cap held in the end of the jaws of a pair of pliers, and with its slot in the cap lined up with the tab at the end of the pin it was placed onto the spring. Using the pliers, the spring was then compressed, the pliers, and therefore cap, rotated 90 degrees and the cap released into its locked position.

There were two problems to overcome before this sequence could be repeated for the lower brake shoe:

Firstly it wasn’t possible to insert the pin from the rear of the back plate. this was due to part of the Suspension Upright blocking its entry. However there was approx. 10mm of clearance.

Secondly I needed to retain the pin in the large hole in the Back Plate.

To solve these problems I cut out a small piece of sheet metal, small enough for me to be able to slip it through the front of the hole in the back plate but large enough so that, when in place, it would be held in place by overlapping the upper and lower sides of the hole.

A hole was made in the middle of this piece of sheet metal so that I could insert the pin in it. The 10mm clearance behind the back plate allowed me to feed the assembly from the front, through the hole. Once in place the lower brake shoe was fitted over the pin, and the spring and cap fitted as mentioned above

The new Disc and countersunk screw were then fitted. With the hand brake released, the Star screw was adjusted to take up the play to the inside of the Disc and then backed off, approx. 5 clicks, which gave a free turning disc.

The Calliper, with new Pads and pins fitted, was reinstalled. Wheel fitted and, by spinning the Wheel by hand, Hand brake operation checked again . I wasn’t happy with the amount of Hand brake movement so removed the wheel again and readjusted the Star nut slightly.

I am glad to say that the replacement of the Right hand side Disc went without any problems. Both the upper and lower springs, that hold the Brake shoes to the Back plate, were in place and the old Disc came away easily.
 

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*DAS/STAR Premium Member
2005 SLK55 AMG
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4,038 Posts
Great write up

FYI, there is no need to start the car up to put it in N - under the shift lever gaiter there is the shift lock over ride (the yellow flap at the front of the shifter)
Pressing this allows you to move the gear lever without the engine running ...
 

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Discussion Starter · #3 ·
Sean

Thank you for your generous comment, and also for the telling me about the Transmission Override switch. I wasn't aware of it. I guess that is used when all else fails. I hope I never need it :|

Tom
 
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