I need to replace the p/s pump in my 300E, and I don't really want to drop the $250 for a new one. I found some online from the 90+ 300E's, but wasn't sure if they will drop into my 87. Are the pumps in the 1987 300E's the same as in the 90+ 300E's? (sorry if I sound like a dumbass, but I searched already and wasn't able to find out).

They all use the same pump from at least '86 to '92. You can also buy a rebuild kit containing all the o-rings and main shaft seal for under $10 from Fast Lane.

As far as the rebuild kit goes, my mechanic (the guy I had check out the car before I bought it because I'm unfamiliar w/ merc) said that the leaky part of the p/s pump was a "pitman arm seal" and that in his experience it means that a rebuild will just end up being another pump. Is this guy lying to me just to get me to have him do the job?

Also, if I do take the pump off, is tension automatically put on the belt or do I need to add tension myself?

Thanks for your help thus far.

I don't believe there's a pitman arm seal on the PS pump.

Are you sure he's talking about the pump?

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2012 E350
2006 Callaway SC560

There is no pitman arm on the power steering pump. The pitman arm is on the power steering gearbox. The seal is a common failure - are you sure he said the pitman arm seal was on the pump? If your pump is leaking, just buy the rebuild kit and be done with it - it is a very easy job and will save you a couple hundred bucks.

After removing/replacing the pump, you will need to readjust the tensioner. Forget using the little gauge, and go by feel instead. Don't go too tight.

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08 W251 R350
97 W210 E320
91 W124 300E
86 W126 560SEL
85 W126 380SE Silver
85 W126 380SE Cranberry
79 W123 250
78 W123 280E
75 W114 280

Thats what he said, and wrote down on the list of things wrong w/ the car - "P/S Inop - No Fluid - pitman arm seal". Perhaps he's wrong, who knows, or maybe trying to take me for a ride. I remember him saying it was at the bottom of the pump where the leak was.

This doesn't sound deceptive to me. It says the power steering is inop due to no fluid, and it pinpoints the pitman arm seal as the culprit. That is a common cause of fluid leak, and it is on the bottom of the p/s gearbox. Now the above doesn't rule out a leak at the bottom of the pump; you could easily have a leak at both locations. More than anything I think there may be a communication issue between you and your mechanic.

The pitman arm seal can be replaced without removing the gearbox, but it's best to have it removed and get all the seals done at once, otherwise plugging one leak may cause it to leak at another weaker seal (ask me how I know). As for the pump, like I said earlier, the rebuild is simple if you want to do it yourself.

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08 W251 R350
97 W210 E320
91 W124 300E
86 W126 560SEL
85 W126 380SE Silver
85 W126 380SE Cranberry
79 W123 250
78 W123 280E
75 W114 280

Just spoke w/ him, there was some miscommunication - it is the power steering gear box, not the pump. I just looked over the step by step to reseal the gearbox, but it doesn't cover how to remove it from the car. Does that involve taking the belts off, or can I circumvent that whole process?

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87 300E
202k on the clock

Removal from the car is very easy. It just bolts to the fender wall, 2 or 3 bolts. Then disconnect it from the steering input shaft (a collar with a bolt through it most likely), and pull the pitman arm with a puller. Be certain to center everything before starting.

I have never done this on a W124, but recently did my W126. I replaced all the seals except the steering input shaft seal (since it was bone dry) and - guess what - that one started leaking a couple weeks later. So I will have to pull my gearbox again just to change that seal! Take a lesson from me and replace them ALL at one time, and you won't be sorry.

Oh yeah, when replacing the gearbox be sure to use blue loctite on the 3 fender bolts and the pitman shaft nut.

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08 W251 R350
97 W210 E320
91 W124 300E
86 W126 560SEL
85 W126 380SE Silver
85 W126 380SE Cranberry
79 W123 250
78 W123 280E
75 W114 280