Hello All,

I am curious if rebuilding the Air Pump is possible for the home mechanic? If so, what special tools will I need and what are the costs(roughly)?

I just rebuilt the Power Steering pump last week, so I am wondering if this is do-able or not.

TIA

Greetings TIA,

Yes, you can rebuild your vacuum pump I did. You didn't mention what car it was, so I can't give a price or parts that you may need. Mine was done on a 300D engine and required only a new diaphragm to get it back up and running. The cost was $8.34 for the rubber from Fastlane and 30 minutes of work. What is the problem to suspect the vac. pump?


Charles

Are you sure its the pump? You could have a broken or detached vacume line or a corroded electrical connector. Can you hear the pump operate when you operate the locks?

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Earl



1993 190E 2.3
2000 Toyota 4x4 Tundra

Even though air pumps and vacuum pumps pump air, they are not the same thing. A.I.R. pumps actually stood for air injection reaction and are emissions devices and in all the belt driven models necessary to carry the belt (mainly). On newer versions and Ca. versions the check engine light is lit during pumping faults.

The clutch can be purchased from MB and can save some money, but the pump internals are not generally available. I have only heard of rebuilders doing this task internally.

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Steve Brotherton
Continental Imports
Gainesville FL
Bosch Master, ASE Master, L1
33 years MB technician

By the way Steve ... thanks for the info about the connectors in the central locking system. I found the red with white stripe wires under the carpet, inside the channel and wrapped inside the wiring harness. I had to cut the harness open to find them. They were crimped together and corroded to powder. I had pulled out the front passenger seat in the process.

The car looked like a tornado hit it while all the doors were open. I had it entirely pulled apart.... posts, doors, flooring.. everything.

Smiles.

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Earl



1993 190E 2.3
2000 Toyota 4x4 Tundra

I am unsure if the Air Pump is the correct terminology, its the pump that is run off the accessory belt on the uppermost right side of the engine bay. Upon startup it is engaged and is getting rather noisey, I believe that a bearing is starting to fail because as soon as it disengages after about a minute, the noise ceases.

I have a feeling its only a matter of time before a replacement/rebuild is in store. Its a 92 500E BTW.

Thanks In Advance (TIA)

Ross,

I am much more experienced with M103 air pump operation and repair than I would like to admit, but I'm not sure if they're the same pump on a 500E. If they aren't they should be similar. The vanes in the pump are carbon, IIRC. MB will not supply any parts to the overall component. The individual vendors who supplied the parts to MB will not supply them to anyone in the US.

My first Air Pump died at around 150k miles. All that really died was the bearing on the pulley. I pulled the pump, pressed the bearing out of the pulley, and thought the hard part was over. There is an MB p/n on the bearing. MB won't sell it and it doesn't show on the dealer stock system. MB (and all of the other mfrs) sign agreements with EPA in the US that they won't sell any parts below the component level for emissions control equipment. That's why the pumps are so freaking expensive. The rebuilders reverse engineer the parts they need and that's possible because they're rebuilding hundreds or thousands of pumps. If you try to reverse engineer a single bearing on the pump, it's cheaper to buy a new pump. Others on the list have suggested machining the pump or the pulley to accept a standard size bearing. This is fine except for the day you finally eat your custom sized bearing pully and now you can't get a core charge back on the pump when you go for a rebuild. That plus the fact they usually live about 150k miles anyway and you see the point.

FWIW, I hear that on a 1991 model 300TE you can disconnect the Air Pump electrically and it doesn't cause the check engine light to come on. Maybe you can do the same on a 500E. They really don't help do anything except warm up the cats quicker so the emissions are lower quicker. Since most US tests are on warmed up cars anyway, what's the point? Since MB won't tell you how long the serp belt should be if you take the Air Pump out of the loop, you either play the game and replace them or disconnect them and run a $400 idler pulley in the loop.

Not that I'm recommending anything that the Democrats in Congress wouldn't espouse, but MBs run pretty clean anyway, don't you think?

Thank You Mike,

Your reply makes perfect sense. If anyone could email me with further details I would most appreciate it.

ThanksInAdvance,
Ross
roas@altavista.com

[Edited by roas on 06-01-2001 at 03:30 AM]

Roas

How difficult was the PS pump rebuild? My 500E has had 5 in its history before I purchased the car. It does not leak now, but there does appear to be a fair amount of end play on the shaft. At some point, I realize that I may attempt that adventure.

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dwight

Heh,
My Air pump is making quite a racket on start up too. I unplugged a connector but it didn't seem to do anything. So I'm assuming it requires power to disengage the clutch? What is the purpose of the clutch? Does it disengage when the engine is warm? If someone could tell me that 12volts will disengage the clutch, it would really help me diagnose this noise. Thanks.
Darryl
'91 190

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'91 190E

when the engine is warm. It is possible just to replace the clutch and not the complete unit.
Jim
'85 300D
'95 E320
'97 CRV

Dwight, sorry I did not respond to your question sooner. I just got back from my short week long vacation in Guam and am slowly covering ground in the forum.

Actually it was not that hard at all, after calling around and getting quotes that are currently not on the "Do-able list", I decided what the hell. I have to use all those tools I have been collecting all these years!

I looked at the CD procedure and figured half the day. After reviewing Benzmac's tip, I decided that was the way to go, removing the front half of the pump and most of the guts while leaving the back half in the car. If you knew how to do his method already, it you take you 1/2 hour to remove the pump, then another hour to rebuild it. Without knowing how to do it, triple the time.

I actually got 95% of the job done before dropping a little bolt down the power steering hose (bottom of P/S reserviour) and into the pump! Damn did that make me feel stupid! I had to complelely remove the pump with mounting bracket and tear the pump apart, this time replacing one larger O-ring I had not done prior. I can now do the job pretty fast if I had to.

Best of all, not a single drop of P/S fluid leaks! Now I have the Air Pump to consider.

If you need the whole run down, let me know, I will try and give a blow by blow recall so you avoid any setbacks. All in all, I thought it would me much more difficult, just plan having the car out of commission for extra days if you need additional parts or run into setbacks.

To Daryl,

If the air pump is screeching when electrically disconnected, the problem is either the clutch or the idler bearing on the front. The clutch engages when power is supplied. The front idler bearing is a double row, sealed ball bearing unit made from virgin, billet unobtanium. The manufacturer won't sell them in the US and MB won't either. I have the id and od dimensions but they are useless if you can't find replacements. I even had a friend who is a nuclear grade procurement specialist try to find an equivalent in the commercial market and he couldn't. You'll know the bearing is shot if, when you remove the serp belt, the pulley flops around with fore and aft movement on the shaft. Good luck with the rebuild. If you just need a clutch, you should be ok, but anything deeper and you're probably screwed.

BTW, remember that the normal life of these pumps is about 150k miles, so think about that before putting more than $100 into any work on it.

Hi Ross: I think the AIR pump is one of those few but common problems that the 500E/E500 has, such as leaking power steering boxes. Like yours and others, mine makes an annoyingly loud clicking noise for the first 5 minutes of operation until the clutch disengages

It's a pollution-control device but not actually needed for reliable engine operation, so my mechanic pulled the plug and disconnected the darn thing. Noise went away but after several thousand miles the "check engine" light came on. Re-setting that is a minor annoyance because a special tool is needed and the battery must be disconnected. After going through that a couple of times I am now willing to put up with the tick tick tick noise.

Up here in Canada, you are only required to maintain pollution-control equipment for four years, which coincidentally is the length of Mercedes-Benz's warranty on the item.

Let us know if you find a cure that doesn't involve buying a new pump.

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Dean Albrecht
"Lead, follow, or better yet, get out of the way!"E500 owners motto

Dean,
I have not tried it yet, but I think you may be
able to fool the check engine circuit by using a
12v lamp to complete the disconnected clutch.
I also used a BB in the switch-over valve becase that
still will work when the clutch wires are energized.
I am going to try it and let you know.
Arthur