107 steering coupling

[ctaylor738]

I just finished putting a new steering coupler in a 1977 450SL. I'm not sure if the differences I encountered are due to the 380 vs the 450, but I want to post what it took to replace the coupler in a 450.

Disconnect battery ground (mainly to keep door buzzer from going off)
Raise car (I used ramps)
Remove small heat shield (3 screws)
Spray coupler clamp bolts liberally with PB Blaster
Get wheels absolutely straight
Remove steering wheel
Note or mark position of steering shaft for straight ahead
Put steering wheel on shaft, and turn until head of clamp screw on coupler points straight down
Unscrew lower clamp bolt using cut-off 6mm hex bit, 6mm socket, ratchet and extensions as needed.
Unbolt steering boot from firewall (4 bolts 10 mm head), remove clamping screw, and slide boot up steering cover as far as possible
Working by touch, unscrew upper coupling clamping bolt.
Return wheels to straight-ahead position
Re-remove steering wheel
Remove combo switch (2 screws) and disconnect horn leads
Remove steering wheel hub bolts (4 - 5mm hex bit)
Turn key to ACC
Pull steering shaft up about 2"
Remove old coupler - it may have stayed with the steering gear or the shaft.
Tricky part - slide the new coupler on to the steering shaft, working by feel from the inside of the car.
Be sure that the steering shaft is still pointed straight ahead, and slide the shaft down so that the coupler engages the splined shaft on the steering box.
Check the staight-ahead alignment carefully, correct position of coupler on splined shaft if needed
Insert and loosely tighten the clamp nut on the shaft side of the coupler.
Stick the steering wheel back on and turn wheel so that lower clamp bolt hole is pointing down
Tricky part - prise the coupler toward the steering box, observing with a good light, until the groove in the splined shaft lines up with the holes for the clamp screw.
Insert and tighten the lower clamp bolt
Install heat shield
Tighten the upper clamp bolt
Re-install steering shaft boot
Install the 4 bolts holding the steering shaft to the jacket
Intsall the combo switch
Install steering wheel
Re-connect battery
Road test car, check turn signals for correct cancelling.

[jdhill]

It still blows my mind the jobs people will undertake on these forums without first springing the $50.00 for a service manual. You can lower your anxiety level and the actual time it takes by 70%. They'll even tell you what tools you need. Oh well, I guess it depends on what you think your time is worth.

[ctaylor738]

I'm not sure what "service manual" you have in mind. I have the Haynes and MB manuals for the 107, and the instructions are not all that detailed or accurate for the coupler replacement. That's why I posted my experience in some detail.

[Richard Wooldridge]

I did this job on my '79 last year, and it took around 2.5 hrs from start to finish, not rushing anything. I used basically Chuck Taylor's description above when I did the job, except I didn't use the ramps, just a floor jack when I needed to get under the car to remove the shield and bolt on the steering gear side of the coupler. An easy job.

[jdhill]

Sorry if I gave the impression my post was a criticism of Mr. Taylors instructions. It was not. It was meant as a general observation. When undertaking any project without a manual for instance, how do you know about all the fasteners and parts that the manual declares "DO NOT RE-USE" or "ALWAYS REPLACE", or "RELACE AS A UNIT", how would you know the torque values? Going back to my original point, my manual has more than once convinced me that with all the specialized tools required I was much better off taking the part to be re-built to my local Merc mechanic. Again I apologize for any misconceptions.

[Tom McMenamin]

What were the symptoms on the car that led you to do this replacement?

[Richard Wooldridge]

The big symptom in my case was about 4" of slop in the steering. I could also look at the coupler and see that it was totally worn out, and the slop was coming from it.

[ctaylor738]

Same symptoms. The rubber bushings in my coupler were completely gone, so the coupler's steering wheel side had to move about a quarter inch or so for the steering box side to move. But when you multiply this up to the circumference of the steering wheel, it meant the wheel had 3-4" of slop in it.