1997 eddie bauer explorer 4.0L Vibration HELP

[kylerebbe]

My explorer is making a humming noise/vibration starting at 60mph and gets worse the faster I go. The only thing I noticed that changes this is if I put the truck in 4x4 High instead of 4x4 AUTO at this speed. The noise/vibration goes away almost immediately.

First I want to start out by saying I am new to explorers, I got this off my sister for free but it was broken at the time.

I guess I will give a little history of everything I have done to it to get it going.
When I got the truck it had a shot rear end, very loud slipping/clunking noises coming from the rear end.

Replaced rear end with one from junk yard

We then replaced the rack and pinion because the power steering was completely shot. Got front end alignment

Replaced the failing ball joints.

New Hubs

Truck already had 2 new tires on the back, still had the blue dye on the tires. I bought 2 more new ones for the front but they are different brand. Also, found the rear rims to be bent, so I bought 2 more rims from the junk yard. Balanced all tires with Road Force Balance and they all pass.

All u-joints look good.

The noise seems to be coming from the transfer case area, definately not the rear end at least. Maybe rear drive shaft. I noticed I can push the rear drive shaft up 1/8 inch about I was wondering if that is normal? Maybe this is where the vibration is coming from.


Possibilities that I can see that are causing the vibration/noise
2 front tires are 7/8" circumference larger than the back tires - ( I am unsure how the auto4wd works in these cars, if someone can tell me if the front and rear drive shafts are always engaged maybe this could be my problem? )
rear drive shaft out of balance
Transfer case bearing for rear drive shaft shot?
Bent Axle ( I took it into a shop and they said my left side rear axle was bent, they put it on hoist and spun the wheels. I really think they were just trying to charge me money because it doesn't feel like a bent axle, there is no hopping or noise coming from the rear of the car and when I slow down it doesnt bump around at all )

 

[McSlug]

Don't know about your issue's but my father is adamant that all 4 tires must be the same size and tread pattern when driving in 4x4 or binding will occur.

The amount of work and type of parts you have replaced tells me the truck has been treated fairly harshly and it could be anything.

It may be trying to auto select 4x4 intermittently with the different size in tires. Do a search for "the brown wire mod" this will eliminate it as an issue or fix it.
In saying that I have driven 200klm's with a spare that was completely different in size and tread with no effect on driving what so ever.

Sorry I can't be of more help.

 

[joe doe]

you should never drive in 4by4 mode on dry pavement/roads.binding can and will occur.plus you can damage the drivetrain.

 

[McSlug]

I drove my vehicle with the odd tire in 2wd.
But I have experienced binding issues when in low 4 Whilst bogged in soft beach sand with the front wheel free spinning.