1990 300E. Did this job today. Had a leak of the front seal and the seal under the reservoir. New seal kit was in the $6 range.

I like to put the car on ramps; it makes it easier on the back not to have to bend over so far.

Remove the air filter and snorkel. Loosen the belt. Remove radiator shroud. Drain about a gallon of coolant into a clean container. Remove top radiator hose. Loosen belt AFTER you loosen the three pulley bolts on the PS Pump pulley. Don't forget to loosen the 19mm bolt on the tensioner first. Remove belt from pulley. Remove pulley.

Place a plastic cup under the return fitting. Loosen the return line and drain the reservoir into the cup. It's easier than sucking it out with a syringe like the manual says. Place a pan under the pump. Remove pressure line and let the remaining fluid drain into the pan. There won't be much. Hang the pressure fitting on the coil wire so it won't keep dripping. Remove the filter from the reservoir. My pump had a tie-wrap holding a couple of electrical lines on the back. Just cut it; don't try to remove the bracket.

There are FOUR bolts attaching the pump. They are all different. One bolt goes in from the back of the pump and also there's a long bolt with a nut in the back. There is just enough room to get your hand down in there. Loosening the back bolt can be tricky, though. A ratchet barely fits. Don't drop the bolt or the nut back there.

Remove the pump and clean it up. Remove the three 10mm bolts holding the reservoir and set it aside. Remove the four 13mm bolts holding the front on the pump and ease the guts out by holding the shaft. Mine was stuck together inside at this point but the back piece will break loose and pull off. Then you will see the clip that holds the impeller on the shaft and you will see all the little vanes. Remove the clip. Slide the shaft out. Now the impeller is sitting loose in the housing. Ease it out. Forget about trying to keep the vanes from falling out; ain't gonna happen. It's like herding cats. Remove the housing that fits around the impeller. Keep up with which way these housing parts are turned, just in case it matters. Now, you have the front housing with the seal in the nose. Pry the seal out. Lube the new one and tap it in with a block of wood or a socket. Don't go too deep with it. About level with the nose is correct.

Keep things clean with carb cleaner.

Lube the shaft and ease it through the new seal. Replace the housing that surrounds the impeller. Slide the impeller over the shaft and replace the clip. Now then, slip all the vanes back into the slots. The inside edges are square, the outside edge is slightly rounded. It's not hard. Replace the back of the front housing - the part that covers the impeller. Replace the two o-rings in the back half of the rear housing. Slide the new big o-ring down into the groove on the front housing and replace the little o-ring to the outside of the big o-ring. BTW, all the old o-rings are hard and flat. Pick them out by working a straight pin into them.

With the nose of the front housing pointed down (you don't want all your hard work to fall off the back), ease the rear housing onto the front housing. Replace the four bolts. Install the new reservoir o-ring and reinstall the reservoir. Replace the filter and rod. Put the lid on.

Don't put the pulley back on until the pump is secured on the engine or you won't be able to access all the bolts.

Installation is the reverse of the removal steps.

Don't forget to replace the coolant. Pour in some PS fluid, maybe half way up the plastic guide. It will bubble awhile as it fills the pump below. Recheck the level. BTW, my Factory MB manuals say ATF is fine. Suit yourself. I used PS fluid because I happened to have some. I also replaced the serpentine belt while I was there.

I started the car and backed off the ramps. The PS was working fine right off the bat and seemed to have no air in the system to bleed out.

Not too tough a job, just nasty if your pump has been leaking like mine was. The fluid was slinging off the pulley and leaving a stripe because of the front seal and that seal was as hard as a rock. During removal it just broke up.

Again, keep the inside of that pump clean. I used carb cleaner spray as I reassembled it.

Have fun!

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2012 E350
2006 Callaway SC560

brewtoo, nice description of replacing seals on a power steering pump. I'll keep it in mind if I ever have to do same.

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Fred Hoelzle

The directions here were very helpful, but there are a few things that will be helpful for others who follow the instructions above. There are also some differences between models and years.

WARNING: My pump broke off! I am lucky it didn't happen under difficult driving conditions. I found another used one with cracked mounts. My mechanic says this happens. If you see cracks on the mounting points of your pump don't put it back in!

1. Crack-loose the bolts that hold the PS pump pulley on before removing the belt.

2. On the 1991 350SD it is not necessary to drain any radiator fluid or remove the air cleaner.

3. When the belt tensioner and belt is loosened remove the pulley from the shaft of the PS pump.

4. The pump on the 350SD has a small steel bracket attached to it in the back with two star-drive bolts. These bolts do not need to be removed to get the pump out, and it would be too difficult anyway. Instead loosen, but do not remove, the aluminum bracket that attaches the steel bracket to the engine with the two 13mm bolts, then remove the two long bolts that hold the pump on from the front. On mine the lower bolt was another one of those star-drives.

5. The belt can be removed and replaced by loosening the fan shroud with the clips at the top. The directions showing the order for replacing the belt are in the owner's manual.

6. Make sure that you remember how the pump comes apart so you can put it back together the same way.

7. The clip that holds the rotor on the shaft is tough. I used two small screw drivers to open it up a bit and then stuck one of them in on one side to pull the clip over the end of the shaft. It had to be bent back into shape before re-installation.

8. When rebuilding the pump use one of those fat rubber bands to hold the vanes of the pump together so they don't fall out. Unless you need to clean it up I think it is best to let the vanes have their original homes.

9. Make sure you use a new filter and seals.

10. The pump goes back in the same way it came out. A little WD40 on the steel bracket at the back of the pump makes it slip into the slot easier.

11. Clean oil and grease off the long bolts and the nut on the top one, put them in and partially tighten them.

12. Re-tighten the 13mm bolts that hold the aluminum bracket to the engine block.

13. Tighten all the bolts up.

14. Put the pulley back on.

15. Be very careful not to cross-thread the fittings to the pump. The pump is aluminum and it would be easy to do.

16. Don't use automatic transmission fluid to refill. Order Beilstein PS fluid because it will prevent the seals from drying out.

17. Run the car for a minute, turn the steering wheel both directions, and refill the fluid to the max fill mark.

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1991 350SD (updated rods)
Biodiesel B100 when I can find it.
Dino when really cold outside

Some time ago I rebuilt the tandem pump on a 350 sdl, up to a point.
I was unable to get the drive shaft out so I sent the unit to a shop to remove
the drive shaft (the part that goes throught the vanes). While they were doing
this work to install the front seal, they discovered that the front bearing was also worn out of tolerance. That part of the rebuilding cost me about $ 150.
The front of the shaft is threaded for using an extractor or puller.

For future use can anyone describe the procedure in removing that drive shaft?

Regards,
Constantine

The only thing I would like to add is to reinstall the parts exactly as they come out you can rotate the halfs and then its maddening.

I have a 1991 350 SD with a minor leak in the power steering pump but the problem is that the pump also connected to the traction control system. I'm told this is rare in diesel models. Do you know of a place that replaces the seals etc. that I can send my pump off for repair. The leaking mist has caused the unibelt to disentregate three times.

Thanks for the write up guys.

Here's some tips for a 92 300D - 602.962 engine and a LUK 61 pump.

There are only 2 bolts on the front on the left that hold the pump on the engine. Take those of the front (13mm) and the metal bracket holding wires on the back, and the 2 hoses off (17mm 19mm) and the pump comes out.

When taking the pump apart, line up the pieces in order, and orientation as you go. The thing that holds the vanes can go in either way - the beveled center should face up so the circlip thing can recess into it.

My main seal was screwed - dried out so bad I had to take it out in little pieces, being careful not to scar the aluminium body of the pump of course.
Apart from that it's a relatively easy job. Just be methodical.

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1983 240D Silver/Blue "Sadie", unknown miles. 100k miles on WVO single tank, converted to 2 tank about 10k miles ago, FPHE, Injector Heaters, Aux Fuel pump. Alcohol/Water injection. Frantz oil bypass filter
1992 300D 2.5 Turbo Green/Tan "Jade" 267K miles Stock.
1992 300D 2.5 tan/tan "Rocky" on 2 tank WVO. Pressure actuated Turbo "rat's nest" surgery completed. 197k miles

Is the pressure valve easily removable once the lower pressure line is removed? I would like to try to modify it for a bit more boost.

I have mine apart right now, we got the main shaft pulled out and replaced the front seal. Now we can't get the shaft back in because of the off center cam (the brass pei e). The bushing it fits into is held in the center position by 4 springs which are held in place by 4 caps. How do we put this shaft back in place?

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1987 300TD named Klause
1987 300TD named Spouse
1987 300D named Seabiscuit
1980 300TD names Chloie (now sadly gone)

Well, the vanes fell out of mine and I've lost 3 of them. Having trouble finding replacements.
John

I know it’s been a while since anyone posted here. I resealed my pump with directions above. Replaced and refilled. My steering wheel will barely turn only under very hard effort. I assume the pump is not pumping. Could this be due to a part no put back correctly or my hoses? I put all the items back in correct order but if the spine housing was backwards, does that make a difference?

do you see any turbulence at all in the power steering fluid? - if not then you have a "short circuit leak" in the vane assembly. Fluid is blowing past pressure to suction side.

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2012 BMW X5 (Beef + Granite suspension model)

1995 E300D - The original humming machine (consumed by Flood 2017)
2000 E320 - The evolution (consumed by flood 2017)