[MountainsRcalling]

About the truck
2006 4runner Sport, V6, 203300 miles, new OEM serpentine belt change two years ago.

About me
Off-roading taught me a long time ago to do as much of my own work as I can. The more I know, the better I can trail fix and or diagnose as needed. I rent a garage bay with a lift that is supervised by a master mechanic who looks over my shoulder and keeps me from doing stupid stuff!

The Drama
So 280 miles into a 600 mile road trip without any warning, my dash lit up like a Christmas tree. I immediately pulled over the side of the highway in the middle of nowhere between NW Texas and NE New Mexico and realized I had no power steering or aircon.

Popped the hood to see a mess of shredded belt, oil and what I assumed was coolant over everything. Belt did not break and had not slipped off, but was almost completely gone. ODB reader showed code P0117, no surprise there as it was 97degrees out and I had been driving at highway speeds for two hours.

Pulled out chunks of belt while waiting for the tow truck. Got the truck into the shop and up on a lift. Spent an hour cleaning up the engine enough to determine I had a power steering leak from the pump. Replaced the pump, threaded on the new serpentine belt, checked pulleys and idlers without identifying any issues, refilled power steering fluid, topped off the coolant and cleared codes (P0117). Test drive home went well, no codes and no leaks over night. Normal driving around town for two days with out issues.

Back in to the garage with the intent to replace/upgrade the suspension (still on stock XREAS at 200K without issues!). As soon as I pulled into the bay, oil starts raining down. More engine compartment cleaning to find a fine mist spraying out from the crank shaft. Pulled off the crank shaft front seal and replaced. Back of the crank shaft pulley was wrapped with more of the shredded belt which I assume damaged the front seal. Cleaned oil off of things as best I could, carefully put the belt back on and had the master mechanic verify the belt was threaded correctly. Changed out my differential and transfer case fluids (it was time) so the day wasn't a complete waste and drove her home. No leaks the following morning.

Yesterday I headed BACK to the garage and started the process of replacing and upgrading the suspension. While removing the sway bar up front I noticed that the new belt is now starting to fray very slightly on the engine side, just like the first belt. The good news is that I caught it very early on.

Reading the forums, my plan on Tuesday will be as follows

1) Recheck all of the pulleys and idlers a second time
2) Check the tensioner
3) Replace the thermostat as it may have been damaged with the initial overheating
4) Recheck the torque on the power steering pump and the crank shaft

Questions:
1) Is it worth pulling off the idlers and anything else relatively accessible to rule out more pieces of shredded belt being behind them?
2) What else should I check or consider?

Thoughts and help appreciated!

Images attached show the dash lights, the shredded belt, the fan, old PS pump, old Crankshaft seal, new crankshaft seal. I have not figured out how to label the images.

[Brian3676]

Check that the balancer is not separating. There is a rubber type insulator in the middle of it. On some engines the rubber will break down causing the pulley to wobble. I have seen this take out belts and cause the front crank seal to leak/need replacing.

[gm350reratliff]

Good to see another NM member on here!

As for your belt issue, I would inspect all the pulleys and verify that none of them are walking or have vertical play, causing the belt to jump. I would also inspect the belt tensioner. It should keep tension on the belt but still move some. I replaced a worn belt tensioner on a coworker’s suburban a while back that would allow the belt to slack for just a second, causing the belt to jump every now and then. If you have never replaced the idler pulleys, might be a good time to do that now.

[Atlanta_man]

I remember a tiny wobble in a pulley (that I could not see, but my mechanic could).
It caused the inner belt from my '71 Corvette to come off and take the other 3 belts with it.
After several of these events I went to my mechanic.

A misbehaving serpentine belt must have something bad wrong given the wide area of grab. Or something it is driving is locking up.

[MountainsRcalling]

Awesome advice thank you, I will check it tomorrow and let you know what I find

[waypoint]

In your second picture, the belt is riding about 2mm rearward of the pre-existing travel path as shown by the paint wear on the idler pulley surface. This may have happened after the belt began failing, but with the new belt in place I'd check the same witness marks to see if the belt is riding the normal pathway or it's being shifted rearward again.

[TechWrench]

The most common cause for a serpentine belt to shred in the manner you describe is the belt is being forced to ride up on the raised edge of one or more of the pulleys. This raise edge will cut into the belt fairly quickly and cause it to 'blow' up. The most common causes for a belt to wander up the edge of a pulley is a worn bearing on a pulley causing the belt to track off, an improperly installed pulley/device what is not inline with the rest of the pulleys, or a worn belt tensioner that is allowing too much slack in the belt.

[kgbagent]

Originally Posted by TechWrench

The most common cause for a serpentine belt to shred in the manner you describe is the belt is being forced to ride up on the raised edge of one or more of the pulleys. This raise edge will cut into the belt fairly quickly and cause it to 'blow' up. The most common causes for a belt to wander up the edge of a pulley is a worn bearing on a pulley causing the belt to track off, an improperly installed pulley/device what is not inline with the rest of the pulleys, or a worn belt tensioner that is allowing too much slack in the belt.

And be aware that if you replace the idlers Toyota has superceded the parts diagram and introduced spacers on the front and back of them. If you do not have the proper spacer washers you risk running a misaligned belt.

[MountainsRcalling]

So after spending longer than I wanted to on the new suspension (thank you East Coast Loctite...aka rust), today I was able to get back into belt shredding trouble shooting. I took my time and examined everything I could think of, but no smoking gun. No sharp edges, damaged/bent pulley's or a separating balancer.

I replaced the idlers, the tensioner (PITA), and the alternator (simply because it was off and easy to do). The water pump pulley had more of the old belt fragments behind it, so I cleaned those off and took the opportunity to clean as much oil as I could from what ever I could reach. I ran out of time and have to wait for tomorrow to reinstall a new belt, the fan and shroud and test drive her. Logic tells me that the problem SHOULD be solved, but I would have liked to find that smoking gun!

Appreciate all of the advice from the forums. I will post a final result once I have it.

[Tunky]

Reviving an old thread.. I have an 04' T4R 4.7L V8. The serpentine belt keeps riding off the tensioner and alternator. I have replaced the power steering pump and alternator including throwing on a new pulley on the tensioner. The tensioner doesn't seem to be bad. (I do have a new tensioner which I plan to install tomorrow.) All pulleys spin freely and all seem to be in alignment with no damage. I can't quite figure out what's going on with it. I'm now leaning towards tensioner because I have replaced everything else on that side of the motor that could be the culprit. I have used a straight edge on all the pulleys and all seem to be straight and aligned. Does anyone have any ideas?

[daprotege5]

recently went through this as my mother borrowed the truck, and the belt shredded. upon taking it out and putting a new belt on i realized it was still leaking oil. so continued to diagnose by taking the pulley off and low and behold the belt had shredded the crankshaft seal with it as well. some of the belt was also still wrapped around the pulley as well.

i knew something was wrong though because the belt showed deteriorating signs after 500 miles. since i've had it always had an issue with one of the tensioners not riding the belt all the way, which hopefully ends up being the issue, as i had the alternator tensioner and the bottom tensioner in the wrong locations. swapped them and so far so good.