Mercedes Benz W108 rear callipers

Before this technical ‘off-topic’ post begins I need to do a big shout out to a few people.

Yesterday, here in Cork, we had one of the biggest races/fun-runs in the region.  The Ladies Mini-Marathon.

This race doesn’t attract the regular ‘I’d piss in a ditch’ type of female runners but is aimed more at people who run once a year.

I have to admire these people because I think that it is a substantial commitment to run 4 miles from a base of 0 miles.

Anyway – big congratulations to:

Finola O’Rioridan (Mrs. Beirut Taxi)

Pia Cronin (8 years old!)

Shola O’Riordan (Cousin to Pia)

Kathy O’Riordan (mother to Shola)

Hillary Doonan (Mrs. Brisighella)

Anita Thoma (Chef/owner of Il Primo – Dublin)

Pamela Brice (CEO of Brendan)

Laura McGonigle  – raising €1,000.00 for Marymount Hospice


How to change the rear callipers on a 1971 Mercedes Benz W108 3.5l V8.

this will be of no interest to the runners who read this blog but to those googling the Mrec W108 I hope yo get something from this post.

The rear brakes on this car are disk brakes (as are the front). the original car came with either bosch callipers or ATE callipers. Before you attempt this (pretty straight forward piece of maintenance )you’ll need to gather you tools and spares.

The W108

The car comes with all the equipment you’ll need for this job but you might want to get a few extra bits in for this one.

The car service kit is pretty comprehensive and the car is very standardised. The same spanner that does the oil sump does the safety belts and does the wheel lug nuts – a car designed by Paul Bracq but built by engineers!

Spares that make me look organised

As a basic, in order to remove the callipers you’ll need:

A jack (the mercedes blisten one is the best for this) and a tyre wrench for taking off the wheel.

A 19 spanner/wrench for the calliper bolts

An 11 spanner/wrench for the brake line

A basin for the brake fluid.

In reality you’ll also need a tin of WD40, a can of brake clutch cleaner, a lump hammer (to persuade the calliper bolts), A small screwdriver and lighter hammer (to open the calliper bolts anti-slip device), some knee pads (if you’re a keen runner), a boiler suit, some latex gloves (something I didn’t have but wished I did), a kettle for some tea and a needle nose pliers.

OK, this will be a tale of three parts. This post will be the one where, apart from a few scuffed knuckles everything goes swimmingly. The second part is the bleeding of the brake system and the third part is the  fuck up (still not finished).

To start, park the car on level ground and put it in park (if it is an automatic) or in gear (if a manual) and apply the handbrake.

Unless you chock the two front wheels you shouldn’t jack up both rears at the same time (the handbrake and the drive are both back wheel).

Loosen the wheel nuts and remove the jacking point cover. then just jack it up and remove the wheel. If you are of the nervous type you can stick an axle stand in under the car and shove the tyre under the wheel. This gives you belt and braces if you don’t like/trust the main jack.

The offending calliper and the belt and braces

The calliper is a fairly basic affair. Held in place by 2x19mm bolts around the back. If you’ve gotten this far it’s time to pop on the kettle and make a cup of tea. You’ll need to spray the calliper bolts with a fair bit of WD40 (or something similar – you’ll see in the photos that I’m using a tin of 3-in-1. Hundreds of uses) and let it soak in.

The photographs from here on in are not the best as all the action is around the back (sounds like a double entendre)  so from here on it you’ll have to go out and look at your car as you read this.

Once you have the bolts all sprayed your tactics will be to loosen everything and then, once the brake line is disconnected, remove he calliper.

Before you go at the bolts you’ll notice that the calliper bolts have an anit-slip device attached. It’s hard to describe but if you try and get the spanner over the bolt you’ll see what I’m talking about.

It’s easy enough to get off – just un-prise it with a few taps from a small screwdriver and a hammer and then opening it up with a small needle nose pliers.

Start by loosening the calliper bolts (you’ll need to tap the spanner with a lump hammer – nothing serious – just a few sharp taps).

A few taps with a lump hammer and you're away!

Don’t take off these bolts as otherwise you’ll have the whole lump hanging by the brake line.

Next, tale an 11mm spanner and loosen the brake line bolt.

don't use a lump hammer on this one

Before you loosen this one totally, get the basin (did I mention that you should have a basin handy?).

You’ll need to catch the draining brake fluid so you don’t cause any ‘environmental’ damage or piss your wife off by pouring car body fluids all over the drive.

Once you have the brake line disconnected and the fluid is caught go ahead and take off the calliper bolts. In order to get the calliper off you’ll need to ‘persuade’ them off with a few taps of a hammer. Again, nothing spectacular, just a few taps.

Now, if you’re lucky, the calliper is off and you’re still in possession of 10 fingers.

39 years of service versus the new boy

If you scoot back to the top of this post you’ll notice that I mentioned that the brakes are either ATE or Bosch. This is important to know because the callipers are not made any more so you’ll need to hand back you old callipers for re-conditioning. Before you do any of this you should have had your chassis number (the whole thing) to hand as you’d have had to be down your local Mercedes specialist to  order the replacement callipers. This is important as you’ll feel like a tool if you have the wrong callipers in your hand now.

the pads inside in the old callipers are only a couple of thousand miles old – this was to be very important in the next stage.

You can see from the next photo that the pistons at the back of the old callipers were totally perished (for the non-mechanical this means that they look like the arse of a wino’s trousers – shit).

callipers and bits

In the left of this photograph you can see 2 bolts. One has a connector hanging off of it. this is the anti-slip device I was trying to describe earlier. You can also see the  in this photograph the existing and new brake pads. A gold star to anyone who has spotted that the new pads look bigger than the old pads.

Before you commit to anything (in terms of fully installing new pads and callipers) you need to test everything out. This is a real case of measure twice, cut once.  So my advice is to temporarily set up the new pads and callipers without tapping home the new holding pin fully. By doing this I discovered that my new brake pads were the wrong size. No problem as the old ones were in good condition but if you reached this point and the old pads were crocked you’d be sitting at home for another week waiting for the right pads to come into stock.

old versus new pads

Anyway, I recycled the old pads (the re-conditioned callipers came with a little tube of grease for the backs of the pads). My only advice about mounting pads is that it is easier to take them apart than to mount them in the callipers.

Once the pads are in the re-mounting of the callipers takes minutes (as opposed to the hours the removal will have taken!)

Next post is the bleeding of the brakes.

Next, we'll be inserting the tube and squeezing.......

On the running front I had a ‘nice’ 24 miler yesterday morning at ‘Thomas O’Clock’ . Skipping the run the previous day made this long run pretty easy in 3:22. That said, my left knee is killing me today (that would be a technical/running term for being sore).


4 responses to “Mercedes Benz W108 rear callipers

  1. I admit I skipped the car repair thingy after about 2 words, but I like the “Thomas o’clock” phrase. Sounds better than thus usually worded “stupid o’clock”, though I have it on good authority that the two words are entirely interchangeable anyway.

  2. Thanks for the post! I’m trying to replace the rear pads on mine and was wondering if the process is the same (i.e take callipers apart to replace pads) or is it simpler. ***sitting in garage scratching my head***

    • Hi Sam,

      I don’t think you have to take the callipers off the car to replace the pads. Above anything else this would be a waste of time for a commerical garage so I expect Mercedes worked that out very early on. If I remember (from almost 18 months ago) there is a pair little pins that holds the pads and their spacer in place – click on the photograph title old versus new pads and you can see the shiny new pins and spacer.

      You’ll need some sort of nail or punch to tap these pins out as they have a deforming head that locks them in place. This should sort out how to get the pads out. Your new pads should have come with a new set of pins and a new spacer. (spacer is a word I just made up but you get the idea).

      • I figured that out after taking half the caliper off!…but its ok, an opportunity to learn. I saw the pins and its actually pretty simple to perform a pad change…I did notice that one of my calipers looks like…how did you put it..”a wino’s bee-hind”, so I’m going to get a brake caliper repair kit.

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