Belt chirp -- How to replace? - PeachParts Mercedes-Benz Forum

renaissanceman · #1 01-07-2015, 03:56 PM

On my 700 mile drive from CA to OR my '87 300D developed a mild belt chirp. The belt is somewhat old and hard and I'm assuming stretched. It still has decent tension, but I'm thinking it's getting close to the maximum travel of the tensioner. The sound goes away above about 1000 RPM.

Can the belt be easily replaced without complete removal of the fan/shroud/etc/etc? On my front drive cars, the serpentine belt is a 5 minute job -- I'm hoping this is the same?

Fulcrum525 · #2 01-07-2015, 04:07 PM

This thread will walk you through the procedure to replace the entire tensioner. However if you are just replacing the belt most of the procedures remain the same. It's a very straightforward job.

DIY - 1987 300D serpentine belt tensioner replacement

With that being said it is possible to replace the belt without taking anything out. It's a bit of a pain but you can pass the belt over the cooling fan and onto the pulleys. I can't explain how it's done but i've done it before. Now that I have the pulley holder i'd much rather just take the fan off.

renaissanceman · #3 01-07-2015, 04:15 PM

I was thinking this might be the case. I need to get in there to put in a new vacuum pump anyway, so I may as well just wait until I'm ready to tear into the whole accessory drive.

What's the best way to check the tensioner/damper, or should I just assume it's getting to the end of its lifespan at 145k miles and replace it?

Thanks!

Dan Stokes · #4 01-07-2015, 04:48 PM

Actually, that chirp is no longer available NLA) and is rare. If you no longer need or want it you might try selling it on Ebay. I'm pretty sure they were installed at the factory.

(Resident local smart alec)

Dan

renaissanceman · #5 01-07-2015, 04:59 PM

Haha, Thanks Dan.

I think I'll just kick it to the curb.

Zacharias · #6 01-07-2015, 05:10 PM

I just fixed what I could have sworn was a belt chirp by swapping out a completely drained battery outside in the dark at -4 F on December 30, followed by buying a new alternator on January 2.

Beware, a dying alternator *can* make a very similar sound, and in my case it went away off idle as well....

Just sayin....

renaissanceman · #7 01-07-2015, 05:58 PM

That's a bit more unnerving, as this is my "long trip" car (since it's sooo quiet, comfortable and powerful through the mountains). I'll grab a video next time I'm working on the Benz for your input.

engatwork · #8 01-07-2015, 07:40 PM

Before you remove the belt look closely at the tensioner pulley where the belt makes contact. If the belt is not centered on it then you need to replace the worn parts of the tensioner. Also, with the belt off spin the idler and tensioner pulleys. If any of the pulleys spin REAL easy (or real hard) replace em. Typically, these items on MB's can run out to 200k miles before needing to be replaced but it is a good preventive maintenance type measure. Also, see if the ps pump, alternator or a/c pulley are "harder to spin" that you think it should. That could be root cause of squeek if the squeek just recently came up.

As already stated, the belt can be changed out but is somewhat of a pia without removing anything other than slacking off tensioner.

renaissanceman · #9 01-09-2015, 07:43 PM

I got a chance to at least take a look at the belt today. The tension appears ok to me, but I made a video of pressing on it: https://www.youtube.com/watch?v=YrzZugxrNyQ

The belt is about flush with the front of the tensioner pulley and maybe a mm or so from the back edge:

Front

Back

Thoughts on either? Is this tensioner toast (and if so, what needs to be replaced?)

Sorry for all the ignorant questions -- I'm trying to learn the quirks of this beast.

engatwork · #10 01-09-2015, 08:32 PM

There is a bushing in the pivot point of the tensioner that wears and causes the misalignment that you see. I have seen em run till you get about a mm of the belt overhanging the front of the pulley so it is up to you whether to replace at this time or not. Make sure, when you remove the belt, you check the pulleys. The pulley on the tensioner can be changed independently of the tensioner itself. Belt looks good so I would doubt if the belt is the root cause of the noise. Noise is probably being caused by misalignment, alternator, power steering pump, compressor, water pump or one of the pulley bearings getting to the end of their life.

renaissanceman · #11 03-07-2015, 05:54 PM

I got it all apart (still need to get the tensioner off -- I didn't have a 12mm hex key socket on hand) and the tensioner arm bushing has a lot of play in it.

Since it was such a PITA to get the fan/shroud/etc/etc off, I'm thinking I'll replace the damper since it's apart now. It still feels 100% good, but I don't want to repeat this exercise for another 150k. Is the Stabilus from Pelican a good choice?

97 SL320 · #12 03-07-2015, 06:24 PM

Belt noise also occurs as the back of belt rides over smooth pulleys. When the belt / pulley becomes polished, it slides across the pulley making noise.

Sanding the pulley with 80 grit works wonders. Sometimes a new belt will make noise if it has a smooth part number sticker, light sanding fixes that too.

sixto · #13 03-07-2015, 07:39 PM

It's difficult to determine serpentine belt condition by eye unless there's physical damage. For a while, Gates gave away simple gauges -

I'm sure some parts stores give them away or sell them for change.

And because we live in this age, it shouldn't surprise you that there's a smartphone app to determine serpentine belt health - PIC Gauge Belt Wear Diagnosis App | Gates Corporation

Sixto
MB-less

renaissanceman · #14 03-07-2015, 08:08 PM

The flat side of my old one is very smooth and has no rubber feel to it, just braided fabric. The grooved side is all cracked up.

toomany MBZ · #15 03-08-2015, 07:57 AM

Cracks indicate it's time for a new belt.