How can I tell, with the PS Pump still in place, whether I have a Vickers or ZF. I need to order another pump to replace the one I have. It makes a groaning/whining noise around between 15 and 40 mph and it's getting worse. I tried flushing the old ATF (PO had used ATF) out and putting clean, fresh, M-B PS fluid in and it didn't change a thing, still groaning. I pulled the accessory belt and checked the idler pulley, it seems okay. Am I missing something? Could it be the steering gear and not the pump. You can, if you pay very close attention, feel a slight pulsing or vibration, sorta a "buzzing" feel, in the steering wheel when the noise occurs. The noise is intermittent, not continuous. I haven't tried to replicate the noise in the garage due to lack of someone to operate the accelerator (and we all know what happens when you grab the accelerator cable from inside the engine compartment...)!

Look at the face plate on the pump itself. It will say ZF like this one that I pulled off my 1993 400E. You may need some brake parts cleaner to clean the grease off the plate to read it.

FWIW, I once ran out of MB power steering fluid after changing the reservoir and resorted to Ford ATF instead. I noticed that it was making the same type of noise you describe in your post.

Attached Files

93400EpsPump.pdf (249.5 KB, 142 views)

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1993 400E, 256,000 miles (totaled)
1994 E420, 200,000+ miles
1995 E420, 201,000 miles

last year I had the same problem. took out my pump and used the rebuild kit and replaced the hose going from the reservoir to the pump. After I did all that and replaced the fluid with new fluid the sound went away. I think the rebuild kit cost me around $30. The hose was expensive due to the fact that I had to buy a meter of it. I think I have some hose left if you want to buy some.

Good idea, Team Adidas.

Also, if neither the supply line nor return line is leaking, you may just want to check for obstructions in the lines at the banjo bolts where they connect to the steering gear. If something happened to get in the supply line, say at the reservoir, it could get lodged at the banjo bolt and would cause an obstruction. In my case--and at the risk of highlighting a stupid mistake I once made--it was a tiny, protective rubber plug on the supply port that the pump rebuilder inserted to look like it was part of the pump. The plug worked its way under pressure from the pump all the way through the supply line to the gear box where the line bolts on. I found it melted into the hole in the banjo bolt there.

When I pulled the front of the pump off to investigate, it was apparent that the system was overheating due to no flow, because the plastic retaining seal on the cam cover had actually melted. The pump also made a groaning noise while operating. It took me about 20 hours of troubleshooting to finally figure that one out.


I changed my supply line last week because it was leaking. It was fairly easy to get to because it is the closest to the bottom at the steering gear. The return line banjo bolt is up a few inches higher and you will need either an 18 mm or 19 mm (I can't remember) open-end wrench to get it loose (an offset open-end wrench would have probably been even better). I couldn't fit a socket on it.

The supply line was a no-brainer to replace because it wasn't mounted to anything or routed through an inaccessible area. The return line runs all the way to the back of the reservoir, but I suspect the rubber portion is accessible without removing the reservoir itself. Maybe Team Adidas can confirm this.

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1993 400E, 256,000 miles (totaled)
1994 E420, 200,000+ miles
1995 E420, 201,000 miles