Top Suspension Arms/Wishbone Replacement

         The Quick and Easier Way

This is one of the items on the list that is a commom on all the 300C's with front end noise problems. Unless I can see the problem (a worn bush or excessive play in a ball joint) I start at the cheapest part to fix and work up as the 300C front end can be hard to diagnose.

The top wishbones are about half way up the list so its not that bad of a job

The failure of the arms is always at the balljoint, I have never come across the rear bushes failing yet. So unless you are sure that this is your problem and go out and buy your new parts, it maybe an idea to check the balljoint for excessive play first

To do this you need to release the ball joint from the strut

          without damaging the the nut or the threads, so you can put it back together either because its ok or to use the car while you order the parts. So to do this I undo the nut of the ball joint but leave it on the end of the shaft to protect the threads while I use a ball joint spiltter,. On releasing the joint I can then check the ball joint for ecessive play



So having decided that your arms do need replacing, I have come up with a quicker and easier way of doing the job without having to remove the whole susension strut. Doing the job "by the book" you need to remove the strut to get at the two bolts that hold the wishbone to the inner wing of the car.My way you don't need to do this, saving time and quite a bit of struggling, especially if you are doing the job on your own

But you will need a set of basic spring compressors ( I have included instructions for the "by the book" method but If you will be working on your own please see the Side Note at the end

So lets get started

Jack up the car and remove the front wheels, before placing the car safely on axle stands.

Now remove the nut from the ball joint shaft and either using a ball joint splitter like the onepictured above or a pickle fork type spiltter separate the joint  (be ready to catch the suspension upright)

Secure the upright to stop it pulling on the flexible brake pipe (I use a bungee cord)


Now to my short cut......Use pair of spring compressors to compress the spring until you can turn it. You will now be able to remove the two bolts by just turning the spring

Now the hard part......getting to those two top bolts

On the nearside you need remove the air box and move the power steering and coolant header tanks out of the way. Do do this first remove the air box top by poping the clips and disconnecting it from the hose. Then remove the bolts and pull the sucker out!! Next remove the self tapping bolts that hold the coolant tanks and lift then in one unit till you can get at the suspension arm nut


Now the rear nut !!!!!

You will be lucky to even see it !


Best way I have found is to remove the electrical connector from the cross brace then use a ratchet spanner on the nut, you just have to feel your way down to it

Take your time and DON'T drop the spanner!!!


Remove this connector.....every little bit helps

On the other side that back nut doesn't get any easier,but at least access to the front one is a little better. All you have to do is unclip the fuse box and move it up out of the way (its hinged)

The other thing you must do is to remove the headlight leveling sensor arm from the suspension arm and of course refit it to the new arm


Fuse box hinged forward and proped with a pry bar

If you don't have any spring compressors or perfer to do it by the book, you will now have to remove the strut by undoing the bottom bolt releasing the anti roll bar link bar and removing the top three top nut for the inner wing (You will need the use of a pry bar to free it AND..... Check out the SIDE NOTE on page two

Special Notice...... Make sure when buying new arms that the offside arm has the bracket cast into it for the headlight leveling sensor. All UK cars that are fitted with HID headlights MUST have this bracket

The front suspension of the 300C is its achilles heel, causing all sorts of complants of knocks rattles and bangs. I think this stems from the suspension layout being based on  components derived from the W211 Mercedes-Benz E-Class but made from heavy cast steel rather than the light alloy Mercedes use. I have found it difficult to diagnose these faults and indeed so have many MOT inspectors, judging by the number of failed components I have found just after cars have passed their MOT. I therefore tend to start by replacing the cheapest and easiest component first (unless the failure is obvious) when tying to cure a noisy front end

The order I change components is;   1st Anti Roll Bar Bushes    2nd Drop Links (or Anti Roll Bar Link Bars)    3rd Tension Struts,     4th Top Wishbones( or Upper Control Arm)     5th Lower Control Arm  and    6th  Lower Ball Joint.