603 Idler Pully Replacement - Fan Belt - PeachParts Mercedes-Benz Forum

Ken300D · #1 10-10-2004, 12:20 PM

I can hear a low rumbling under the hood and took a look. I think the idler pully for the one-does-all fan belt is causing the problem. It is bouncing a lot. Rumbling is worse with the increased load of the A/C compressor.

Did a quick search - know this has been discussed before - but can't find it.

So, I'm now looking for tips on belt removal and idler arm pully replacement.

Records show it was replaced about 50K miles ago. Apparently not a long life thing.

It could be another device, but this pully would be the first suspect. It is running straight, not sideways, so maybe not critical at this point.

Ken300D

sixto · #2 10-10-2004, 08:08 PM

To remove the belt:

- remove the 13mm head nut in front of the plastic hinge that holds the upper end of the spring

- put a tire iron in the big hole on top of the plastic hinge and pivot the hinge so you can pull back on the 13mm head bolt that goes through the head and hinge

- swing the hinge the other way and pull the spring off the hinge

- pull the belt off the idler and check the idler for smoothness

- check also the tensioner on which the idler pivots for smoothness

The idler shouldn't wobble on the tensioner, the tensioner shouldn't wobble on the timing chain cover, and the tensioner shouldn't click when swung through it's range. You already mentioned that you checked that the idler is parallel to the other pulleys.

If you have to get to the tensioner, the bolt that goes through the tensioner pivot takes an 8 or 10mm hex bit. The bolt goes into an oil passage so don't be surprised to see oil. If you're lucky you can replace the tensioner without removing the fan or other pulleys. I think you can replace the idler by popping the cap and undoing the bolt.

Sixto
95 S420
87 300SDL

OhioSDL · #3 10-10-2004, 08:16 PM

I had to replace the idler pully this past spring but have no records of when it was last replaced. My guess is much longer than 50k ago. i was amazed that when my pully let go the front berings were released and the whole outside assembly was leaning to the passenger side. but it held the belt for another 10 miles. changing it out was a snap. the clearence was tight but i took a 6mm allen head socket to remove the center bolt.
if you have a bouncing problem the tensioning spring or the pnumatic shock my have weakend. remove tension from the spring side, slide the belt clear and check to see if your pnumatic shock has gone wimpy on you. as i understand it the springs also have a lifespan too.

little tip. the stock lug nut tire iron fits quite nicely into the hole on the top side of the upper spring tensioner mount. use the tire iron to release tension while you remove the upper long bolt that comes out by injector #1. and again use the tire iron to pull the spring back up when you are done.

Ken300D · #4 10-13-2004, 05:40 PM

Well, I just had a chance to investigate this - and thanks for the input. Certainly better than the manual.

I knew the belt was getting old because the inside ribs show cracking, and I've had a replacement on-hand for some time now. So its good to learn how to do this. Actually pretty easy relative to how it looks complicated at first glance.

I can't really find anything in bad shape. The pully runs smoothly, there is only the slightest looseness to it along the axis of the shaft its mounted on. The pivot operates smoothly and with no looseness. The shock absorber is a lot more tight on compression than extension, so I may go ahead and replace it. The spring looks to be possibly original equipment, so that will get replaced too.

All the other device pullies are smooth and easy to turn, except of course the crank.

So, I think I'll go with a new shock, spring and belt and see how it goes. Those are the easiest things to replace too.

Thanks,
Ken300D

sixto · #5 10-13-2004, 10:13 PM

Just to be clear, pulleys should turn smoothly and NOT make noise. New pulleys feel smooth and heavy. Pulleys on their way out feel smooth, light and make a whirring noise. What's a light whir when spun by hand is a growl when spun by a loaded belt.

Sixto
95 S420
87 300SDL

psfred · #6 10-13-2004, 10:53 PM

Do yourself a favor and take the fan off -- piece of coat hanger wire, an 8mm allen, and it's off. Takes less time to R&R the fan than to fish the damn..d belt around the bottom of the engine.

I suspect your belt is the problem -- when they are cracked like that, the pulley is riding on the bottom of the grooves in places and it's grabbing.

Peter

#7 10-14-2004, 01:00 AM

I have a '91 350SD and have had that pulley replaced. I keep wearing out engine shocks though. When mine idles, the grumble that I hear is a vibrating shock. When the shock is replaced it is as quiet as can be.

I have had 2 shocks in 2 years. Any ideas?

sixto · #8 10-14-2004, 02:40 AM

Are you wearing the engine shocks by the engine mounts or the shock of the belt tensioner? If it's the shock of the belt tensioner, maybe your tensioner is shot and the shock is doing all the work. If it's the shocks by the engine mounts, maybe the engine mounts are worn or broken. Maybe it's rods. Just kidding

Sixto
95 S420
87 300SDL

#9 10-14-2004, 10:13 AM

Funny guy!!! It is the shock on the belt tensioner. The belt tensioner has been replaced....the shock still wears.....

Ken300D · #10 10-20-2004, 09:00 PM

I completed the repair and can report on the results now. I ordered a new tensioner spring, shock absorber and idler pulley just to have everything I would (most) likely need on-hand.

Starting the job, I intended to replace the shock absorber, the spring and the belt. Really the shock was not in bad shape, as I found the new part had the same characteristics as the one on the car. Hard to compress but easier to release. Looking at the shock on the car, hmmmm, that takes some work to replace - I'll just do the belt and the spring.

So, after the new belt and spring were installed its all smooth again. Although two components were replaced, I'm pretty sure it was the belt. On inspection, not only were all the interior ribs all cracked up, there was a small notch missing out of one side. I suspect this was contributing to the vibration as it passed some pulley.

The manual says to push up a loop of the belt between the crank pully and the water pump / fan pully to hook around the idler pully. (They tell you to turn the fan pulley anti-clockwise to assist.) No way are you going to push a loop up between these two pulleys - not enough clearance. You have to make the loop, push it up well past the gap between the crank and fan pulleys - then push the belt into place on these pulleys. That is, you push the loop through while in FRONT of the pulleys, then slide it into place. At that point you can immediately complete the loop over the idler pulley and continue routing the belt elsewhere.

Overall, not as hard as it looks. I did have to refer back to the manual to get the belt routing correct. If you don't have a manual showing this - please draw all the pulleys and the belt routing first before taking off the belt.

Ken300D

sixto · #11 10-20-2004, 09:39 PM

In my limited experience with belt shocks (1 603, 1 103), it's not the shock itself that fails rather it's the bushings in the Heim ends that get loose and cause all sorts of noise. I suppose the shock could lose pressure but it hasn't happened to me.

Sixto
95 S420
87 300SDL

OhioSDL · #12 10-21-2004, 12:30 PM

when re-installing the belt the loop method works well. one note would to be once you have the loop made infront of the water pump/crank pullies drop the bottom half down onto the crank shaft groove and run it around the idler pully and come back and slide the belt under the water pump pully. this frees up just a bit of clearance as opposed to trying to get the double thickness of the belt through that small clearance.

Ken300D · #13 10-29-2004, 08:38 PM

Well, I've had to start over on this job because the rumbling noise and vibration came back after the car had been run on the highway.

Now it seems to me that the shock is pretty loose where it spends most of its time traveling. The idler pully itself is fairly tight, but the pivot arm (tension lever) is a little loose side-to-side.

So, now I'm going to replace the rest of these parts and hopefully be done with it for awhile. Already have the shock and the pully. Yep - have to order the tension lever and have the car parked until it arrives.

Ken300D

Ken300D · #14 11-10-2004, 06:53 PM

Well, this went very well and then very badly.

Replaced all the tensioner components, and in the process replaced the water pump (it seemed a little grindy in turning) and the vacuum pump. Started up and everything was smooth as glass. No shaking or bouncing and no noise.

I don't really know what happened. I was on the first test drive out about five miles and back. It sounded and felt just like I ran over a rock, but I saw nothing in the road. Then the belt started flapping around a little bit, then worse. I pulled over and popped the hood - belt was gone, tensioner was sitting sideways somewhat, and the belt had snagged the lower transmission fluid cooler hose and snapped it in two. Jumped in and got another 1/10 mile to a service station and then got towed home.

I really thought maybe the tensioner lever bolt had come out. I used a sealant on it and torqued it properly. Unfortunately the bolt was fine, but the timing cover has broken where the tensioner is mounted.

So I gave up for today, maybe I'll see what caused all this tomorrow. It was really smooth and running great. I suppose the earlier bouncing around stressed the timing cover and cracked it - but that seems a bit of a stretch.

Have a feeling the cover will be quite expensive.

Ken300D

TimFreeh · #15 11-10-2004, 07:10 PM

Oh boy....Sorry to hear the latest news. I never liked the way the mounted the lever to the front timing case cover.

If I had to bet at this point I'd bet the threads in the aluminum case got damaged when you removed the old lever.

Let us know what you find in your post-mortum inspection.