How to change rear struts on B-Class W245

This will be a short one. Easy job, anyone could do it!

Almost forgot to mention: There is a CATCH, that might get you stuck! Better read on then.

Preparation

Get some new struts. Prepare your tools. You should have a hammer and a couple of drive punches also in addition to the normal socket tools and a set of spanners. This job is fairly easy and anyone who can change their own wheels are able to do this job if you are prepared.

Procedure

Start by taking the rear wheels off. I recommend putting the rear on jack stands while you work on the rear end. There will probably be a lot of banging with the hammer, but you will probably no be moving under the rear end. Now you can locate the lower bolts, spray them with rust penetration so it will be easier to loosen the bolts. They are probably a bit crusty from rust. It is also a good time to inspect other suspension components such as the rear sway bar bushings and the brakes. Make note of worn components and order them for a fix later.

Wheel removed, rear end supported with jack stands.
Lower strut bolt w245
Locate lower strut bolt and spray with rust penetration fluid

While the rust penetration fluid is working, start by locating the upper damper mounts in the rear trunk. The left side is located below the first aid kit area. Open the lid, remove the first aid kit and the warning triangle, then locate the foam and remove it to find the upper strut mount.

Fist aid kit area in trunk
Left side strut is located behind this area
First aid kit in w245
Remove first aid kit and warning triangle
Upper strut mount w245
Remove foam to locate the upper strut mount

Make note of how the bushings and supporting plates are mounted. Support the lower control arm with a jack, because the spring will push out the arm once the damper is loosened. When the strut mount is found. Use a spanner along with an adjustable wrench to keep the shaft from spinning when loosening the upper nut.

Loosening top strut nut
Loosen the top strut nut with an adjustable wrench and a spanner

Now that the top of the strut is loose. You can move to the lower bolt. This is a bit more tricky if it is stuck. Use two sockets or a socket in combination with spanner. You might need some force to loosen this nut because of rust.

Loosening lower strut nut
Loosen the lower strut nut with two sockets.

When the nut is removed, the tricky part starts. You will need to drive out the lower strut bolt. Is is probably rusted and needs a good pounding with your hammer. Hammertime!

Hammertime

No pictures of that process here since I got so frustrated I forgot to take any. Anyhow when the strut is out you can mount in the new strut. If you completely break the bolt you will need to get a new one, since most of the dampers do not come with new lower bolt and nut. Be sure it has enough strength and do not simply get one from the hardware store without checking the steel rating. The nut used must have self locking threads, otherwise you will need to use a locking washer with the nut. Tighten the nut until you feel it is tight.

You might need to use the jack down or up in order to move the control arm in the height so you can get the strut in properly.

New rear strut fitted
New rear strut fitted

Now move up and fit the upper strut bushings and nut. Place the bushing first, then the plate. The new strut can either come with 1 self locking nut or two separate nuts. When tightening the nut you have to make sure the shaft is not turning. Turning the shaft excessively can damage the inner seals of the strut and it might start leaking. Start tightening the nut until you reach the bushing. The rest of the tightening must be done while the car is fully weighted on its suspension.

Upper strut bushing
Place upper strut bushing first
Upper strut support plate
Then place the support plate
Upper strut nut
Start tightening the upper strut nut. Final tightening Is done while the car’s full wight is on the suspension.

The same procedure is obviously for the right side. It is located behind the right side compartment, and behind the plastic cover which can be removed.

Location of Right side strut nut
Location of right side upper strut nut

When tightening the upper strut nut, tighten so the ribber bushing is a bit squeezed and you feel a resistance. This is usually enough. If the new strut has two nuts, use the upper one to secure the lower nut. This is not necessary if the damper comes with a self locking nut. Do not reuse the self locking nut front he old strut.

Hope the car will feel a bit more responsive in the rear end!

Robs Out!