What did I do? Differential damage? 4 WH test and now yuck sound...

Is this sarcasm?

What happens when you're on rough terrain (sand/mud/snow/etc) while going up or down a mountain for example?

I'm not trying to be a d#$%. It's an honest question. I've never done any serious off roading, but from seeing others do it, are they really shifting back into 2WD every time they come up on a turn, and then switching back into 4WD until the next turn?

ETA: To put it another way - surely if you're driving down switchbacks next to a drop off then damaging your differentials probably isn't your biggest worry, but I would think 4WD Toyotas (and other brands) had to have been engineered with that in mind.

Or in other words, off road trails (whether in sand, mud, snow, gravel, etc) are most likely not going to be perfectly straight roads.

 

Pretty sure he meant on pavement you can run in 4H but should avoid sharp turns

 

Like other wise folks have said, the dealership isn’t your friend, even if ur friend works at the dealership lol. Don’t lie, but don’t tell them everything if you haven’t already over the phone, don’t give them too much info cuz they’ll stick you with it - 100% they’re already going to sell you more than you need. It’s possible it’s no as bad as you fear. I swear if you tell these people you blew your diff, they’ll quote you a diff

 

You’re correct, you can do whatever you want with it off the pavement. I’m sure the post was about street use since that is what the OP was talking about in terms of causing the issue.

I have a 4th Gen and IIRC, their system is different. I have no qualms about driving in 4HI on pavement and have done so many times in the 10 years and 170K miles I’ve had the truck. Not just to do it, but as part of the monthly 10-mile “exercise” recommended to keep the system happy.

 

Well, spoke too soon, still making a decent amount of concerning noise

 

There is a service bulletin for the front diff, you might get lucky. The humming / whirring / vibration you hear at the 35-45mph is the bearing in the drivers side of the front diff. You might get lucky, some people are getting the whole front diff replaced due to this service bulletin. Somebody post the front diff cycling humming TSB please.

 

I suspect if the dealer mechanic cross-threaded the bolts holding the skids on he/she wouldn’t say shit. Take that as you choose.

 

Hey, I think we are all guilty. Some just admit it sooner than others.

Cheers,

Sean

 

That's right, none of that woke 2WD shit

 

IGNORANCE!!!

 

When you put the vehicle in 4WD you are forcing the front wheels to rotate in sync with the rear wheels...they are locked together. When you turn the steering wheel, say in a left turn, the outside (right) wheel has to rotate faster than the inside (left) wheel because it has more ground to cover, but it can't because it is locked to the rears so you are putting binding/stress into your driveline. You must have noticed that the steering was difficult when parallel parking in 4WD on pavement because that's about the worst thing you can do (sharp corner). That's why your owner's manual tells you only to use 4WD on slick surfaces where the front wheels can slip. You still have a lot of traction on rain-covered pavement so it's not a good place to use 4WD.

But the 4Runner driveline is strong. Almost every owner has felt the binding in their steering when they use 4WD when they shouldn't, but I think it's rare for it to cause a problem. I know that even when parking on grass I feel some binding if I turn sharply, so I'll sometimes take it out of 4WD to eliminate the binding but even if I stayed in 4WD I'd be shocked if damage occurred.

So in your case there is no doubt that you did something wrong, but given that there is also a Technical Service Bulletin about defective front differentials there could be some doubt about whether your problem was caused by you or the vehicle. Google "4Runner front differential TSB" to see the TSB.

Regarding what to tell the dealer I agree about being honest. Biggest question in my mind is whether you tell them that you tried 4WD briefly in the rain (in which case most 4R owners would not expect any problem) or whether you also tell them about parallel parking on pavement in 4WD since that might be considered abuse.

 

I know people are mentioning that the front diff might be making the noise, because there is a known issue with all front diff needle bearings. Some/many can make noise in 2wd at around 30 to 45mph. The noise goes away when you shift it into 4wd, in fact, putting it in 4wd is a sure fire way of diagnosing a loud needle bearing. If it goes away, it’s your needle bearing.

That said, I don’t think there is reason to suspect differential damage over other possibilities. Turning sharply in 4wd on a paved surface is also straining the transfer case and driveshafts.

That’s worth keeping in mind when you state your problem at the mechanic. I’d take the approach of stating your problem (it’s making a noise), let them ask you questions, and let them sort through the process of diagnosis. If you give them info that makes them favor an explanation, they may not be as careful looking for the cause, which can lead to replacing expensive parts that don’t fix the problem.