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 01-04-2007, 02:26 PM

Just shredded another belt!!!! Aarrrrrgh ....

Have replaced components multiple times ... wanted to propose we all toss in what we know to see if there is a single issue or multiple issue that continues to cause repeated failures - and, whether it is .970, .960, etc.

Two interesting posts from above:
1. Viesel noted he has another 3.5L with an additional pulley mounted high that may have been a later model change to alleviate the problem - cost to retrofit with new parts looks to be about $200 or so ... tough to swallow for me.
2. Constantine noted he has carefully checked the alignment of the various driven pumps, etc and has found some significant eccentricity that may be contributing.
3. Sixto and all of us determined that some of the spring level assemblies have a washer behind them and others don't ...

So, could you let us all know your year/model and experiences re this painful replacement cycle? Please specify whether your car has one or two pulleys (most appear to have only the lower pulley - it tensions, the upper on some models appear to just align and eliminate some belot movement).

If anyone has an extra pulley and bolts etc, I would be glad to pay shipping to try it (have to go to a longer belt) and see if it resolves the issue - if so, we can develop a long term fix for this!

Thanks!

Hit Man X · #8 01-04-2007, 03:39 PM

Not sure of your issues, but I have no slippage with my '87 603.

stephenson · #9 01-04-2007, 04:01 PM

Hi Hitman ... not a slippage issue - issue is continuing failure of the damper and lots of folks reporting shredded belts ...

Hit Man X · #10 01-04-2007, 04:15 PM

You mean you have the shock failing? Shredding belt would point to a misalignment of the pulleys to me.

sixto · #11 01-04-2007, 04:17 PM

There is a related thread at allpar.com with Mitsu 3.0 V6s shredding belts. Goodyear offers a replacement tensioner that's a documented cure. Given that, the problem with the 603 might be with the spring. Some allpar-ists say switching to a Goodyear Gatorback belt (ribs are interrupted rather than continuous) solves the shredding

The bracket and pulley are $100 list based on the Sept 01 EPC. The pulley is shared with the early 300E so there's our resident boneyard hunters can probably find a good used one for cheap. Is the -14- head tapped for the additional pulley?

When you say eccentric pulleys, do you mean the pulleys are out of round or they wobble? I would think wobble rather than out-of-round-ness would shred belts. Out-of-round-ness would wear the damper. I suppose cycling the belts through length changes is not a good thing. I can see where interrupted ribs would stand up better than continuous ribs in either case.

Sixto
93 300SD

Hit Man X · #12 01-04-2007, 04:20 PM

Now I do have a Goodyear belt on the SDL now, but it had an OLD Conti belt when I picked it up.

Also, the bearing was failing on my idler pulley that's part of the tensioner, so I replaced that this summer. But, I could swear it was 60x not 103 part.

sixto · #13 01-05-2007, 09:46 PM

While fitting a new tensioner on the 3.0 block going in the SD I noticed that there is indeed a ~2.5mm thick washer between the tensioner arm and the front cover. There's a washer in the 3.0 block and in the 3.5 engine that came with the car.

Sixto
93 300SD

sixto · #14 01-06-2007, 02:24 PM

Nice write-up!

Might be easier to loosen the water pump pulley bolts while the belt is in tension.

Alternatively you can put a long screwdriver shaft across two bolt heads and loosen the other bolt/s. Move the screwdriver shaft among bolt head pairs to loosen the remaining bolts.

The tensioner arm hole goes through to the timing chain cavity so be careful how you clean the threads.

The tensioner arm bolt torque spec is 100Nm/73 lbft... into the aluminum front cover

Sixto
93 300SD