Mercedes E320CDI Serpentine Belt Shredded

[Windy Miller]

Evening All!

I have a scruffy old E series Merc Estate with a 3.2 straight 6 TD. Nothing at all to look at, but a lovely car to drive, and (compared with my L200) fairly economical to run. It's very comfy, surprisingly fast, and has loads of room. A while ago, it developed a problem though.

Driving it late one evening, I heard a noise which sounded suspiciously like a belt flapping about. Sure enough the serpentine belt had shredded. One of those poly vee things with grooves that run all round the belt.

A few hundred miles earlier, I had changed the belt, the generator pulley (one with a clutch), the tensioner and both idler pulleys. So I'm wondering why the belt went so soon.

Pulley alignment was pretty good, with about 1mm runout, and everything that the belt drives all rotate nicely with no nasty bearings. Bottom pulley sound, water pump and power steering pump pulleys all good. Everything seems good, apart from the air con pump pulley, which had some belt debris embedded deep into the grooves.

I'm wondering if maybe somehow the pump seized and the belt slipped around the pulley for a short while before it broke? The pulley rotates freely now though, as does the centre shaft so if it was seized it's not now. To be honest, I'm a clutching at straws here, as I'm a bit stumped as to why the belt broke, and the seized A/C pump is all I could think of. The belt was a Gates one, so I doubt it's just a dodgy one.

Andy ideas?

 

[ford34/2]

Half tempted to just stay stick another belt on, if you are very happy all pulleys rotate freely, possibly once things warm up one of them may become tight. I had problems with the Golf a while back similar setup clutch pully etc, it was the pully. Power steering was groaning and squeeling, at low revs you think the car was labouring and in the wrong gear. Was super pleased the pully on the alternator was the culprit--mind you a new one only lasted a few weeks -same again, this current one been on a couple of years now.
Stan

 

[rikrobson]

the A/C pump could be seized. They have a clutch on them that engages to drive the pump. with the clutch out it may turn freely, but if the pump itselft is seized the pulley is gonna wanna stop when the clutch engages. I think it should have a 12 feed to engage it. its worth checking if so before you wreck another belt.
you could check the haynes or online for the non A/C version which will have a shorter belt, not going round the pulley. if you are lucky it may aviod the pulley but if not the pulley will be on the way.

 

[Windy Miller]

I'll have a play with a 12v feed and see what happens to the air con clutch. Pretty sure that it's ok though, as the centre shaft turns easily enough. Deffo worth a try though!

Stan, did your dodgy pulley have a one way clutch on it?

 

[Bill Edwards]

If you switch the air con on then it should engage the clutch. You'll then be able to establish whether it is seized or not.

If the unit is seized then there isn't any reason why it wouldn't run fine with the air con off but then be destroyed if the air con was switched on - do you know whether the air con was on or not?

 

[the snooper]

the only thing I will add is if there is a seized or partially seized pulley you should be hearing the belt squealing quite loudly, I would examine the belt for damage over its length

 

[Windy Miller]

If you switch the air con on then it should engage the clutch. You'll then be able to establish whether it is seized or not.

If the unit is seized then there isn't any reason why it wouldn't run fine with the air con off but then be destroyed if the air con was switched on - do you know whether the air con was on or not?

Erm I can't be 100% sure, but I very much doubt it was turned on. It was about midnight just before last December, so it's more likely the the heater was on.

the only thing I will add is if there is a seized or partially seized pulley you should be hearing the belt squealing quite loudly, I would examine the belt for damage over its length

That's a very good point - I'll have a good look at the belt along its length. No squealing though, so I think that probably rules out my air con pump theory.

So it's looking like my original idea is a non starter, but I'm still left wondering why the belt should have broken like that.

Any other ideas?

 

[mike os]

I have had similar and it was the ac pump, no belt squeal or just enough to think... belts slipping I need to check when I get home

As said the ac pump has an electric clutch and freewheels when off. If you turn ignition on and turn on ac the pulley will engage and you can try to turn it ( don't start the engine tho

 

[CompoSimmonite]

My recently acquired 300TDi Discovery had belt that was shredded on one side. Turned out to be very slightly worn idler / tensioner pulley bearings

 

[ford34/2]

Stan, did your dodgy pulley have a one way clutch on it?

Yes it did, allows the alternator to keep spinning during deacceleration from high engine revs. Easily checked with the belt off and hand spinning the pully/shaft on the alternator

Stan

 

[colnerov]

Hi, the belt drives the A/C pulley and the clutch connects the pulley to the compressor shaft. As stated the clutch engages with 12v when the A/C is turned on, BUT only if the A/C system has sufficient gas in under pressure. I have to say it sounds like the compressor has seized at some point and the shaft has sheared off inside somewhere.

Colin

 

[Cal]

I've got a sprinter, so I am used to merc serpentine belts, I would check the AC comp and the power steering pump.

 

[Windy Miller]

Yes it did, allows the alternator to keep spinning during deacceleration from high engine revs. Easily checked with the belt off and hand spinning the pully/shaft on the alternator

Stan

Yeah that's what the Merc has got. A completely unnecessary complication as far as I can see!

Well you have given me some pointers to check on.

If I apply 12v to the A/C clutch, I should be able to bypass the gas pressure sensor switch and that should tell me if the clutch still works. I'd still have no idea about the broken A/C pump shaft though. I'd like to think that I'd feel something when I try to rotate the shaft, but it feels pretty smooth, and with enough drag to suggest that there's something happening inside - a little bit like stirring heavy oil.

I'll have another look and I'll look carefully at the power steering pump and the water pump bearings. Maybe I'll try to spin them up with the drill to see if they sound OK whilst they're 'running'.

Thanks for all the comments so far - keep them coming!

 

[ford34/2]

Yes it did, allows the alternator to keep spinning during deacceleration from high engine revs. Easily checked with the belt off and hand spinning the pully/shaft on the alternator

Stan

if you do check it out, it will turn the altenator in one direction only, so when you hand spin it the alternator clutch will engage and spin the alternator, trying it other direction it wont spin it up, similar to a centrifugal clutch-but only working in one direction
Stan

 

[the snooper]

this could be as simple as you didnt get the belt on one of the pulleys correctly and upon starting the engine it moved the belt accross on all pulleys and just wore out very quickly

 

[Windy Miller]

if you do check it out, it will turn the altenator in one direction only, so when you hand spin it the alternator clutch will engage and spin the alternator, trying it other direction it wont spin it up, similar to a centrifugal clutch-but only working in one direction
Stan

The one way clutch is definitely working ok - it's brand new anyway, but I have checked and double checked it.

this could be as simple as you didnt get the belt on one of the pulleys correctly and upon starting the engine it moved the belt accross on all pulleys and just wore out very quickly

Yeah I guess that is a possibility, but I'm usually pretty careful with that type of thing. That isn't to say I didn't screw up this time though!