This internet thingy is kinda neat. My air injection pump ('90 300SEL) started rumbling, so I removed it and took it apart today. Very obvious that the clutch bearing was beginning to seize. I'm not sure of all the different models, but a lot of them appear to use a design with a proprietary INA bearing that costs around $200. No biggee.....I'll just go to the shopforum and find out how to repair and parts and.........WHAT? No references?

I googled for air injection info and what did I find? A link to this shopforum thread: 300E no reverse which shows this has been a saga for several others.

After searching, searching, linking, and more searching, it appears there is an exact replacement available from several sources. If you need a replacement bearing, this one ($19) should work: http://bearingsdirect.com/products/index.php?action=item&id=5114&prevaction=category&previd=56&prevstart=0

Thanks forum!

Last night, I finished the rebuild of the pump and installed back on the car. Works great, no noise, and ready for another 250k miles.

There are a total of six bearings in the air pump:

Pulley/clutch bearing (1)
Air vane carrier rear cover bearing (1)
Air vane bearings (4)

Generally, it's the pulley housing bearing that causes the problem because it spins 100% of the time, and the rest of the bearings spin only when the clutch is engaged during engine warmup. I replaced the pulley bearing and the vane carrier rear cover bearing because it was fairly easy to service. The four small bearings on the air vanes (two bearings/vane) can be replaced, but great care must be used. Mine seemed perfectly serviceable, so I cleaned and greased them and left in situ.

Here are the product numbers for the bearings:

PULLEY BEARING
32BG05S18G-2DS (see weblinks earlier in thread for vendors)

VANE CARRIER REAR COVER BEARING
B188 (Timken 1 1/8" X 1 3/8" X 1/2" needle bearing)

That's cool! I am going to try that as well. My car runs without pump at the moment but if there is a cheap and good way to put it back to reduce startup emissions, why not?
Thanks, Bruno

90mbenz:

Thanks for taking time to post your findings.

For whatever reason(probably $$$$$), the air pump on your vehicle is priced off-the-scale. What companies charge for this part is nothing short of rape.

__________________
Mike Murrell
1991 300-SEL - Model 126
M103 - SOHC
"Fräulein"

Bruno and Mike - you're welcome. The board has been very helpful for me, so it's a pleasure to actually contribute for a change.

Bruno:

IMO, air injection may exist as an emissions mandate, but it serves a purpose. Bypassing air injection can have long term effects (performance and longevity) of other components, especially the catalytic converter(s).

If you go ahead with your rebuild, post your questions and we will work through them.

Mike:

I was amazed at the prices these pumps command. It made the decision to attempt my own repair pretty easy. As I already wrote, others trod this path before me, and it was obvious that sourcing the pulley bearing was the biggest problem. That problem should go away for anyone else wishing to do their own rebuild. I should have posted that my total investment (both bearings and shipping) was just under $50 - and I paid a premium for the pulley bearing. I wanted to give my business to a bearing supplier who went the extra mile talking with me by identifying the correct Timken bearing for the carrier cover.

Ok, I ordered the bearings. The clutch seized and is off center. I tried to remove it but did not have the best tools at home to do so. I'll try again whit access to a vise etc.
Do I need special pullers to remove the old bearings? Any other special tools that you would advise to get before I start?
Many thanks, Bruno

__________________
_
1992 300TE 160 kmiles

I got my 1981 380SLC airpump rebuilt for $145 + shipping and tax at Express Parts Exchange, Inc. (Rebuilding Factory: Your Part, Rebuilt, Fast!) Now that did not include the front bearing on the clutch, which I will find on my own. That is a lot cheaper than other links here and it appears they did a good job.