Catastrophe-o-the-day - siezed PS pump on freeway
 

So I'm headed to the junkyard today to get some trivial W140 parts for my car and about half way there the alternator light comes on.

Thinking that it was just an old belt I texted a friend and arranged to have him come pick me up since the replacement belt was at home (unfortunately). At any rate he calls and says he's stopping to get a belt on the way and surprisingly he finds one.

He gets there and I get the belt installed and buttoned up and the car starts no problem. it seems to be idling fine so I go to take off and notice a significant lack of power and a new squeal so I pulled off the freeway into a filling station and pop the hood.

At idle the squeal wasn't there but applying the throttle brought the squeal back. After I decided that the PS pump was the source of the noise I got in the car and found that the wheel was very hard to turn.

At any rate it was not a good day and tomorrow will be busy rounding up a PS pump and getting the car brought home.

steve a

Does your car have ASD?

-J

Well at least you can say your Thread is different than most.

After it is off see if you can find out why it seezed.

No ASD, no SLS, nothing but PS, so the S320 pump at the junkyard should be a direct swap even though EPC says different part numbers.

Steve A

How was the fluid level?

fluid level was fine, in fact it was just two weeks ago I changed the filter and replaced a leaking return hose.

This isn't the first pump on this car either, I dug through the maintenance history and found that the pump was replaced once before.

steve a

That is highly unusual....a few of our MB's are running original P/S pumps with over 300k on them and no issues. Mine leaks, but its because I used synthetic fluid in it for a while.....none have ever had bearing issues.

Perhaps the belt tension is set too tight?

There's no belt tension to set, 603s use a multi rib belt with an automatic tensioner.

Oddly enough my 350SDL had a PS pump replaced in the past. I wonder if there was a bad run around 1990?

-J

Well I suppose it could be but since it uses a serpentine belt and a non-adjustable tensioner I'm not sure that it's a tension issue TBH.

Tomorrow on my way to the salvage yard I'm going to stop and check the stiffness of the PS drive pulley, but it sure sounded like that's where the noise was coming from, and I checked all other belt drive components and they all spun freely, the PS pump was the only thing that I don't really recall whether I checked it when I installed the new belt, but it certainly would explain why the belt disintegrated...it was more work getting the remnants of the belt out of there, and there's still some wedged between the fan clutch and the pulley that I couldn't get out.

The stupid part of it was that I had a new Continental belt at home that would have sufficed, but since I was stuck out there with my house key no one could swing by and pick it up, so instead the friend swung by Napa to see if they had one....it was spendy, more than double what I paid for the one at the house!

Steve A

Even the automatic tensioners have a "set" tension when you adjust the tensioner....

There's no adjustment. I suppose if you somehow fitted the wrong spring onto it?

Tensioner has never been messed with. It was in for service just before I bought it, the MB indy replaced the fan clutch and reinstalled the serp belt, never did anything with the tensioner at that time. As far as I know it's the original spring tensioner.

steve a

I have a 3L 603 pump if you need it, I have no use and do not want much for it. Drop me a line if you need it.

Thanks, if I can't get one locally I'll drop you a note.

I looked in the repair history and the existing PS pump was installed (new) by MB in 2005, now that's a pretty short life for something like a PS pump.

steve a

Ok, so I stopped at the car on the way to the salvage yard and sure enough, the pump would turn but it would apparently start binding after a few rotations. At the time though I just assumed that the problem was in the pump and not elsewhere.

I fetched the new PS pump at the salvage yard and before I removed it I checked to see whether it would spin without binding and it did. I was therefore confident that it would suffice.

Once installed however, the new pump took on the characteristics of the old pump (D'oh!) and binds after a few rotations, which tells me that the problem is likely upstream from the pump, on the pressure side, since the reservoir isn't being drained I find it hard to believe that there's a restriction in the return flow that would cause this.

Any insight now would be great, the only thing I can think of would be if there's a check valve at the gearbox itself that's a problem or perhaps the gearbox just crapped out.

MB says the steering box on the 95 S320 (closest parts donor to me) is not the same although I've checked 15 different part numbers on my 300SD gearbox and they are the same as the 95 S320 so who knows. There is a VIN cutoff for this part that I haven't been able to rationalize yet...who knows.

lets here some suggestions...

Thanks
Steve A