Help: 2003 540 Serpentine belt keeps shredding

[lesguy]

124,000 miles. bosh remanufactured alternator and Graf waterpump installed 11/2016 at about 119k. No issues until last week, low rpms in traffic. Alternator light on, Power Steering out. Pulled over, belt shredded like spaghetti wrapped around clutch fan bolt. Prior to this, zero squealing from belts, no odd noises at all.

Towed home, removed all of the belt material. No pulleys were wobbling and all spun smoothly. No unusual noises. Tensioner assembly had mild side to side play, but the pulleys still spun freely. Regardless, went ahead and replaced the tensioner assembly (which includes new idler and tensioner pulleys already installed). Also new conti belt (again). Parts from FCP Euro. Motor mounts are about 2 years old, and appear to be fine. (no drips/leaks)

Started engine and she ran perfectly. Put about 60 miles (mixed city/highway) over the weekend and then yesterday, again, low rpm in parking lot, alt light on. Shut engine off immediately and same thing..belt shredded.

Cant figure out whats wrong. Power Steering housing/bracket appears intact, and all other pulleys are spinning fine. Visually, appears all pulleys line up fine/are all on same plane. (See video for evidence).

Below is Link to videos clips of pulleys being tested, and of engine operation right after the install last week. Clip of the tensioner assembly being wiggled, is the old assembly. Thats the one I replaced last week. Last two clips are vid clips of right after I replaced the belt and with new tensioner assembly.
https://************/yd4s8buy


Thoughts? This is driving me nuts.

Thanks

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Not sure why the asterisks keep appearing. Its a tiny url link

[cfries3]

I had a similar problem but on my AC belt. Replacing the drive pulley solved it. It was apparently bent enough to let the belt ride out of it's grooves and shred lengthwise until it came apart. It was a royal pain getting the strands of belt unwound from the pulleys and tensioner.

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[edjack]

Drive pulley =?= crankshaft pulley

[WBAD530i]

I remember reading something about this specifically for the M62. Are your mounting points for the power steering pump intact? IIRC the mounting ear can fracture and allow the pump to wobble around resulting in the belts shredding.

[lesguy]

I remember reading something about this specifically for the M62. Are your mounting points for the power steering pump intact? IIRC the mounting ear can fracture and allow the pump to wobble around resulting in the belts shredding.

correct. I've read those posts as well. Im almost positive the power steering pump is intact. Once I get the car back home/in the garage, I'll need to triple check again. But from what i've read, thats a pretty obvious break/tear in the bracket. as shown in the vid clips from last Thursday(if you replace the asterisks with tiny url (no space), you can see the video clips). , all of the pulleys were aligned properly/belt turning perfectly smoothly. No run out/no play. Cant figure out whats causing the shredding.

[WBAD530i]

You did mention it occurred at low rpm when the power steering pump would be doing more work. Such as rolling through a parking lot to park the car. You won't see any stress on it at idle because you aren't turning the wheel. This is just speculation of course. Maybe have someone turn the wheel full lock left/right a few times while you are looking under the hood with a fresh belt on?

Or even just get inside your engine bay with the hood up and have someone drive the car slowly and make sharp turns. Yes, this is the best idea. LOL, jk.

[lesguy]

You did mention it occurred at low rpm when the power steering pump would be doing more work. Such as rolling through a parking lot to park the car. You won't see any stress on it at idle because you aren't turning the wheel. This is just speculation of course. Maybe have someone turn the wheel full lock left/right a few times while you are looking under the hood with a fresh belt on?

Or even just get inside your engine bay with the hood up and have someone drive the car slowly and make sharp turns. Yes, this is the best idea. LOL, jk.

LOL. Sounds like a sure fire way to end up on an episode of Ridiculousness!

I actually thought about that (power steering pump only locking up at random times, slowly causing tears in the belt until it fully lets go eventually). Once i get it home and in the air I'll do that..examine that pulley pump while someone sits inside and turns the wheel at idle.

[edjack]

In any event, always a bad practice to turn the steering wheel full against the stops, as this places MUCH load on the pump.

[lesguy]

Agreed. That's something I always avoid doing

[geargrinder]

The PS pump does have that weird rear adjuster bolt , maybe it's way off? Hows the fan clutch?

[lesguy]

Thanks for all the tips/input guys.

Fan clutch about two years old and tests out fine. Fan itself fine as well. Will check the PS pump fully this weekend but as seen in the video clips belt appears to be traveling in perfect plane/alignment. No runout, no pulley wobble.

Will have someone rev engine a bit while turning steering wheel as I view the belts this weekend

[Mach540]

In any event, always a bad practice to turn the steering wheel full against the stops, as this places MUCH load on the pump.

I just noticed on my 540 when doing a U-turn, that the steering box seems to reach its physical limit before the wheels reach their limits. This does not put any extra stress on the PS pump like pretty much every other vehicle I've owned. It just stops turning.

Just an observation.

[geargrinder]

yeah it does seem like the PS doesn't 'over-drive' at the ends of the travel on these cars.

[lesguy]

reporting back..after diving into this extremely carefully, checking everything. Final result? Loosening the tension on the (new) Conti belt, is what has gotten things back to normal. Coincidence? Maybe. but seems that it is possible to have too much tension on a brand new belt on the M62Tu. Have put about 500 miles on her and so far, all well. Made no other changes. I didnt think you could have the belt too tight with this hydraulic tensioner, but Im not going to argue with results on my car thus far

[JimLev]

Maybe the bearing in one of the idler pulleys is wobbling so with lower tension it is working OK??? Just a guess.
I don't set my tension to the max limit either. After my alternator seized and broke the PS pump brackets off I decided to tension the belt 1/2 way just in case the alt seized again, hoping the belt will just start slipping and spare the PS pump.

[lesguy]

Thanks Jim. But took at least two hours fully and carefully inspecting every single pulley. Alignment, spin, debris..you name it. Even had a BMW mechanic come over and eyeball from underneath he car, from up top/under the hood. In the end, using two people to carefully adjust tension (one tightening the tensioner nut while the other held the tensioner just so) to just a bit beyond squeal territory, seems to be doing the trick. Maybe this issue is more common with a brand newish belt that's put on too tightly? But either way, glad it's resolved.