M104 Idler bearing
 

On the M104 engines (in my 1993 300E2.8), is it possible to replace the idler bearing without pulling the radiator and only removing the fan and shroud?

If so, what tools would I need? My bearing is making a horrible noise right now, driving the car is almost an embarrassment.

Yes, it's possible. I saw my mechanic do it, but I can't tell you what tools to use.

When the idler bearing went out on my 1993 300E 3.2, it was making such a terribly loud noise, people would cover their ears when I drove through a supermarket parking lot.

I pretend that it's the Chevy/Ford/GMC truck in front of me that almost everyone where I live seems to drive.

ok, so it's possible (I thought it might be, just wanted to check) - how about tools, anyone?

I might have a similar problem as yours.

Just wondering does the noise change depending on your engine speed (RPM)? Higher pitched? or does it stay constant?

Mine went up and down with engine rpm.

The bearing on the air pump also went out at a different time, and made the same horrible screeching noise.

yup, same problem here - I believe it's possible to replace just the bearing, not the entire air pump (I hope so, as remanufactured air pumps are $600+)... can that be done with the radiator in place too? I believe it's in a fairly akward place tucked in close to the exhaust manifold...

Yep, the dealer sells an air pump rebuild kit, which is basically the bearing assembly, and it costs about $200-ish, plus labor to install.

The air pump is removed from the car, the bearing is replaced on the bench, and its reinstalled in the car.

I tested this last night - the noise stays the same, but the drumming sounds increase in frequency as the rpm's rise.

Removing the radiator on my 94 E320 was the easiest thing I've done on that car.

The noise on my car suddenly got a lot louder over the past few days, and it turned out to be the fan bearing that was failing and the fan blades were hitting the belt tensioner.

I was going to order a new bearing and fan blade early next week, but what do I do about the special tool required to remove the fan and viscous clutch? Is there something I can buy or rent that will do the job?

It can be done with a belt wrench on the pulley.

For the belt tensioner, I believe I have to remove the plastic cover and slacken the nut 1/4 to 1/2 of a turn before I release the tension on the belt.

I couldn't get mine to move, and I thought I read somewhere that one of these two is reverse-threaded - which way does this turn?

To remove the fan clutch in my 94, I use a 1+ foot-long 4mm rod bent about 75 degrees the last half inch. Stick it down between the tstat and the block; it fits in a hole on the backside of the flange the fan clutch pulley bolts onto. Now use a long ?8mm allen ($20 set was well worth it--a hex socket is a pain--too long) and a cheater pipe. For the tensioner, it takes a larger hex key--?10mm. I use a 3/8 hex socket and a long breaker bar. It is torqued to a seemingly very high 75 Nm--about 55 ft-lbs as I recall. The job is waaaay easier with radiator removed. The extra inch of room is so nice. I don't recall either bolt being LH thread.

A few questions...
 

Do I need to drain the crankcase before removing the heating water return line that's obstructing the final bolt of the fan bearing bracket?

For the same water return line, the manual says to 'replace seal (27a)' - can I reuse the existing seal if I pull that water line out? If I need a new one, is it a generic one that can be purchased anywhere?

The manual also says for the 124 model that I should 'replace seal (97) in timing case cover' - I didn't see a seal where it's pointing to in the diagram, do I need to worry about anything?

When attaching the idler pulley to the fan bearing bracket, what torque should I have my wrench set to?

Someone must know at least some of the answers - I want to get this car finished and running again today!

My knowledge is for a 94 3.2 engine, but I'm guessing if you don't drain coolant from the crankcase you will get some drainage when you pull off the steel pipe.
The pipe seal is a fattish o-ring--I don't know the answer.
I don't have my manuals with me to answer the last two, sorry.

I'm pleased to say that my car is back on the road again, thanks to this website... some of my notes might make this job easier for other people:

An allen key can be used as a lock for the fan bearing, but make sure you don't lose it behind one of the pulleys should it fall out of place.

Removing the radiator isn't necessary, but makes the job waayyyy easier. It took me longer to drain the radiator than it did to pull it out. Plus it gives you the chance to clean the front of the radiator too (I found three big dead bugs on the inside of mine)

Removing the water return pipe doesn't seem to be necessary either. I removed the bolt holding the pipe to the fan bearing bracket and then backed off the nut holding the pipe onto the water pump a little to slide the pipe out just a bit, and was able to move the pipe up enough to get a socket underneath and then the bolt in and out.

The bolts on the bracket are not all the same size - the top-left one (looking from the front of the car towards the back) is much bigger than the others, but the rest are all similar in length (but not the same). As you're removing the old bracket, drop the bolts into the same holes on the new bracket so you don't forget which is which.

Those are all the big issues I had... hopefully someone will be able this thread to make their replacement go easier!