[W126 Coupe] Diff repairs

[marcus Johnson]

Hello all,

I am having some diff problems in my 380 SEC.

I have had a subtle whine and vibration at around 90km for a long  
time and my mechanic has attempted to rectify this.

We have had the car out on the road extensively as well as up on the  
hoist and listened carefully while it runs. The conclusion is that is  
definitely the diff.

First step was to do the pinion (?) bearings and reset all the  
clearances. Didn't fix it.

He has taken the diff out and tried a couple of second hand units,  
but they were also noisy. Given that most of the diffs now available  
at the wrecking yard would have around 200,000 km on them, this is  
not surprising.

After trying to swap in a used item, he sent the diff out to a local  
guy and had another go, making sure the backlash was set up properly.  
Still didn't fix it. In fact, all it did was change the vibration and  
noise to 70km/h instead of 90.

Other items have been checked and repaired previously and have helped  
but not fixed the problem.

The tailshaft has been rebalanced and had new bearings / uni's. The  
centre support bearing and rubber has been replaced. The motor mounts  
are good. The flex discs have been done. The rubber diff mount has  
been done. The tyres are new and the wheels have been balanced.

If it's under there, it's been replaced or checked.

His conclusion, supported by the diff specialist is that the crown  
wheel and pinion need to be replaced. Of course, you can't buy these  
items in Australia or ex-Germany. The dealership says they have no  
more supplies.

However, I also contacted another local mechanic for their opinion  
and they were surprised at the diagnosis. Their experience says that  
the crown wheel and pinion rarely give trouble.

Before I lay claim to the world's most expensive 380 SEC by refitting  
the internals at huge expense, does anyone have any advice?


marcus johnson
1985 380 SEC
Melbourne, Australai