603 Serpentine Belt Problems - PeachParts Mercedes-Benz Forum

stephenson · #1 11-25-2006, 07:06 PM

350 SDL ... 190K miles

Started noticing noise on start up ... sort of a "rrrr ... rrrr ... rrrr ... rrrr" synced with the engine speed - goes away above 1000-1200 rpm. Kept looking for the noise - thought might have been the vacuum pump ...

Noise changes when I engage the a/c compressor - but, doesn't go away.

Today I carefully examined the belt while the engine was stopped - noticed the belt was beginning to shred along the inside edge (closest to the engine side) - the edge was damaged with a sliver missing from the inside edge along an area about 12 inches in length ...

I had noticed this same damage on a previous belt - since then I have replaced the belt, the tensioner, tensioner pulley, and shock absorber. In fact, I have replaced the portions of the tensioner four separate times over the last seven years.

I then carefully examined the tensioner assembly - I don't note any of the excessive movements that were characteristic of previous issues with the tensioner.

So, ruling out the tensioner itself (admittedly a simple, but poorly designed mechanism on this engine), what could be causing this - and, is the belt damage likely related to the noise?

I examined the alternator, a/c compressor, belt routing, etc ... just can't see anything that looks like something is incorrectly installed, mounted off center, or unaligned, not square with belt, etc ...

Anyone have any suggestions? I can continue to replace the belt, but it seems like this is indicative of other issues ...

Brian Carlton · #2 11-25-2006, 07:16 PM

Does the belt track in the center of the tensioner pulley?

I've noticed that the belt on the '86 sits about 1/8" forward of center and there is a distinguishing line along the belt where it stick forward of the pulley edge. I'm convinced that the tensioner is causing the issue, but, it hasn't presented any annoying noises and it hasn't become any worse over the last 10K.

Viesel · #3 11-25-2006, 07:30 PM

I have the same problem and I just chewed up another belt today being the 3rd belt in 9 months. I have also changed the pully, snubber, and spring a few months back. I have noticed that the tension pully rides off to the side some and would assume that the entire tension mechanism might need replacing to keep it centered. If you think this is a fix let us know as I will repair mine ASAP.

speedy300Dturbo · #4 11-25-2006, 07:35 PM

A "rrr rrrr rrr" noise at idle that goes away above 1000rpm or so is ALMOST always a faulty belt shock. While the engine is idling, press on the belt shock with a screwdriver and see if the noise goes away.

stephenson · #5 11-25-2006, 07:46 PM

You guys are saying exactly same thing I would say to someone who presented with the symptoms I noted ...

The belt tracks dead center of the tensioner pulley ...

The tensioner shock appears to be working normally - I used to diagnose my faulty shocks with a large screwdriver pushed down on the tensioner base, too ... shock is only about 6 months old and appears to be functioning properly ... I will check, again, though ...

Viesel · #6 11-25-2006, 09:29 PM

I think this is what needs to be replaced.... what do you guys think? If this is worn it will cause the belt to ride to the side of the pulley and also the rrr rrr rrrr noise would be the play in the center bearing
http://replacement.***********************/parts/autopartswarehouse/quote.jsp?year=1991&product=G6002-32871&application=000230034&part=Acc.%20Belt%20Tension%20Adj.&dp=false

stephenson · #7 11-25-2006, 09:34 PM

I replaced this part, as well, about six months ago ... seems to be operating properly, but I'll check it, again ...

Thanks - anyone with any other ideas? I will pull belt and check operation of the shock, level arm, and pulley tomorrow ...

Viesel · #8 11-25-2006, 09:46 PM

When I replaced the snubber (shock thingy) a few months ago, it helped to keep the belt from flopping around a lot and also quieten it down a lot but mine still makes the rrr rrr rrr noise a little too, but on my way home from the beach today it shredded a belt to spaghetti like pieces and left me stranded. That makes the 3rd one in like 9 months. I am going to repalce the belt tensioner listed above on Monday.

Viesel · #9 11-25-2006, 09:56 PM

I also find somthing else interesting about these belt pulleys. I have another 350 sdl engine sitting in the corner of my garage and it has an additional pulley that is mounted above the top most portion of the belt that rides on the complete top of the belt and adds a little tension by pushing down on the upper portion of the belt. (did that make since?) Mine does not have this pulley and I have looked at several other sdls and they dont seem to have it either. Does anyone else have this pulley? Maybe it was an upgrade?
Maybe I will try and post a pic of this

sixto · #10 11-25-2006, 10:05 PM

93 SD has the extra pulley, 87 SDL doesn't.

With the spring and shock upper mounts detatched, does the tensioner arm pivot about any other axis than the big bolt through the bearing? Is the big bolt still torqued to spec?

Sixto
93 300SD

redassag00 · #11 11-25-2006, 10:26 PM

I just changed my Belt "shock" today on the W124 when I put the new compressor in. The Hammering/knocking noise went away.

stephenson · #12 11-25-2006, 10:36 PM

The lever is most probable cause in my case - I think ... will remove belt and see it it is square with the plane of the belt and that it rotates normally ... how loose should it be following torqueing to spec?

I reviewed the shop manual CD - seems like I recall mine having a washer between the level bolt and the engine, but the flared area on the bolt would not seem like it would receive a washer, right?

Part number 362 in the manual on the exploded view (13-345) appears to be the bearing, right? It isn't anything else in between?

Thanks ....

Viesel · #13 11-25-2006, 10:41 PM

Here is a pic of that extra pulley. I wonder if it puts a little more support to the belt and help with the rrr rrr rrr noise.
http://s102.photobucket.com/albums/m115/Viesel/?action=view&current=DSCN3440.jpg

stephenson · #14 11-25-2006, 10:46 PM

So, your 350 SDL has this pulley on it? Is it the original engine or one from later model 603 engined S class?

I wonder if it solves the common issue we are all talking about and what parts are needed - or, even if they will fit? Clearly would need a longer belt ...

Viesel · #15 11-25-2006, 10:50 PM

No it fits perfectly in 3 screw holes that are not used on most sdls. You use the same belt as it just slightly put a little pressure on the top of the belt so that the long portion of the belt has something to ride along between the pulleys. Keeps it stable and from floppinig around so much.
I am thinking of taking it off the spare engine and put it on mine after I change that tensioner on Monday. I can get the part number if you guys want it.