R170 upper control arm replacement - Mercedes Benz SLK Forum

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#1 Old 04-20-2014
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R170 upper control arm replacement

Replacing the upper control arms is not rocket science, however it needs to be done right. I found another write-up about this job, but it lists wrong tools (a 15 mm wrench instead of 16 mm for the axle nut).
What started as a routine and simple job actually transformed itself into a lifesaving and major repair.
In order to be able to remove the right side axle, you need to remove the battery to gain access to the axle nut with a 16 mm wrench. You will have to rotate from the bold end with a 15 mm wrench because the space at the nut end is to narrow.
Removing the battery, the battery tray will most likely unveil some rust built up from acid which was released from the battery. This is not unexpected and also not something to worry about, however if rust shows on the inner fender, that is something you might want to address and prevent from a possible disaster, namely ending up with a destroyed inner fender. I am very happy to report that I caught the beginning of depreciation in time and was able to save the body. I removed the battery tray and gained access to the part which showed the inception of corrosion. I also found that that specific body part is factory treated different than in places not exposed to battery acids. I power brushed the entire zone and carefully wiped it with paint prep fluid. Then I applied a layer of rust prevention and stabilization “POR 15”, with a brush. This layer needs to sit for four hours in order to assure a perfect reaction and setting. After that I sprayed the car specific paint to cover the black layer. In the main while I did the same with the battery tray, which was left with the black finish.
The next thing I noticed was the loose hose feeding the headlight wash system (not used because of facelift without the system). This hose was detached from the pump and if operated by the button, it would empty the windshield fluid. I attached a rubber cap and fastened it with a ring. I also removed the power cable feeding the pump and insulated the contacts and fastened it with a plastic strap for eventually retrofit.
The main reason for this write up is to inform the valued audience of the fact that the control arm needs to be lubed before installing it. I didn’t do so and had to get back after driving the car because of rubber squeaking noise generated by the bushings. Also the axle needs to be tightened with a torque wrench at 24 Nm which might feel loose, but over tightening will bend the inner fender. You will have to use blue thread lock medium strength on the thread.
Replacing the upper control arms solved the following problems:
- Steering vibrations between 50 -64 mi/h (with perfect balanced tires)
- Uneven braking (with new rotors and pads)
- Clonking noise (With new tie rod and lower control arm ball joints)
One of the photos will show the professional rust prevention product.
Job specific tools:
15, 16, 17 mm wrenches, ball joint extracting tool + according wrench + low torque capable torque wrench.
Thanks for reading and good luck with your projects!

I was not able to upload photos due to an error in the process (I informed the admin)
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