Hi all --- thought I'd write up my experience on this repair. Last week I recieved the dreaded call from my wife.... "my car is making this horrible noise when I drive it". Sure enough, I put a long screwdriver against the air injection pump (car has 90k miles on the od) with the engine running and quickly determined it was a faulty bearing. After some quick research on this site, I contacted Ben at mbpumps.com and ordered a replacment/rebuild (MA13) for $215! In two working days, I had the pump in hand -- the quality of the pump is top notch. Ben said these pumps typically last around 80k and have a bearing in the front clutch and one in the rear of the pump. I felt it would be cheaper and simpler for me to just buy his reworked "full" pump, rather than just the front clutch --- as I only wanted to make this repair once.

Anyway, the repair was very straightforward and I wanted to share how I did it.

1) remove the splash pan from underneath the engine
2) loosen the serpentine belt and slide it off the A.I.R. pump pulley/alternator pulley - almost easier to do from underneath. You might consider also loosening the fan shroud, as you may need to move it toward the air filter housing to get access to the serpentine tensioner bolt
3) remove the molded rubber hose from the rear of the A.I.R. pump - I used a large pair of vice grips. This is kind of tricky, but what worked best was when I completely compressed one of the clamps. I think there are three. You only need to remove one of these connections.
4) remove the air filter housing. This is very simple. First, pull the cover to the housing and the filter. Next, pull the "cover" that is right in front of the air filter housing. I'll call it the air filter housing "air intake". It will allow you to pull the air filter housing up and out. This cover just snaps on. Next, remove the single nut from the left side of the air filter housing. It holds down a rubber "wedge" and hold down clamp that helps keep the air box in place. Once this is removed, you can remove the air fillter housing. Just pull up the left side, and then the right. There are two rubber nipples at the bottom of the housing that hold it in place. The air filter housing will just pop out.
5) get a catch pan for your coolant and remove the connection to the heater core. (I think! this is to the heater core) -- anyway, the coolant crossever tube that runs right in front of the engine, the one that bolts up to the thermostat housing, the rubber hose on the A.I.R. pump side will be in your way. Just pull the rubber hose from the hard line and pull it out of your way. Now the A.I.R. pump will come right out.
6) remove the electrical connector to the A.I.R. pump. You'll need to pull the black cover that snaps over the front top of the engine (just in front of the valve cover) to access this connector. Just trace the A.I.R. pump electrical wire routing to this connector. I think the wiring loom from the A.I.R. pump is less than 1' long.
7) now you're ready to pull the pump -- two bolts (13 mm I believe). The top bolt is very long. The bottom, short.

That's it. Really simple. Hope this helps.

One word of caution. Be very careful when loosening and increasing the tension on the serpentine belt tensioner. I've had more trouble!!! with this thing than I'd care to admit, as the tensioner rod breaks very easily. And when that happens, the repair involves a lot of steps that I'd rather not write out . So, just be careful when adjusting the tensioner rod.

Nice writeup, should be helpful to the folks out there in MB-land.

Ironically, I just replaced the tensioner rod on my '93 two days ago. They do break too often, and too easily. It's more tedious than difficult to replace them.

Air pump is still fine on that car, with 107K on the clock. The fan bearing, on the other hand, is starting to concern me. Not looking forward to that repair.

On the coolant pipe running across the front of the engine, isn't there a seal where it attaches to the thermostat housing? Aren't you supposed to replace that seal anytime it's disassembled?

- JimY

If that's the heating water return line, then there's a small o-ring on the end of the pipe that goes into the thermostat housing. The manual (20-3140) does say "replace seal".

I need to do this same thing on my car - this write-up is just what I'm looking for.

Glad I could help! I really appreciate finding posts like this one when it comes time for me to make a certain repair. So I like to return the favor whenever I can.

Hey Jim. Thanks for the note. Yes, the coolant pipe has an O-ring that you should replace. I didn't, as I replaced it with a water pump job last year. It still seemed good.

Did you see my writeup on the door panel repair? I did a followup message on it. Let me go dig it up. (found it ----- '95 E320 W124 driver's door panel pull / center door pull is loose - suggestions?)

No, I hadn't seen that writeup. Sounds like you did a good repair. Be interesting to hear whether the glued/melted rear hook holds. I suppose there's not that much stress placed on it when closing the door - the front hook takes most of the load? Perhaps it will last a long time.

- JimY

Hey Guys,

Another really effective solution for broken hooks on the back of door panels is Oatey Heavy Duty Clear PVC Cement. Comes in a green 8 oz can at Home Depot/Lowes. Normally used to join plastic plumbing pipe together - it kind of melts, then welds the plastic together. It is the only really effective means I have found of joining broken plastic parts that are subject to some stress. Worked decemtly omn my door hooks, now trying it on broken sun visor piece.

Kermit