Four Wheel Drive engaging its self

ggarner · #1 (**permalink**) 07-01-2009, 03:07 PM

My truck recently started vibrating pretty vilolently right around 50-55 mph so i took it to my mechanic and he said that on a road test that they seem to think that the four wheel drive is auto engaging at this speed. I am just wondering if any one else has ever heard of this??? There is no vibration except a small amount from the tires then BAM @ 50-55 everything starts vibrating like crazy and a super loud whirring sound that is loud enough to hurt your ears.

He pulled the hubs off and took them apart and apparently a C-clip in one of them had fallen off and was still sitting in the enclosure of the hub.

Apparently the left front wheel bearing is also going out because it is making quite a bit of noise when the wheel is spun by hand and you can feel it vibrating the A-arm.

Anyway he is replacing that wheel bearing etc and hopefully thats whats causing the vibration but if not does anyone have any ideas?

The other strange thing is that i had my tires rotated about 3 months ago and the fron left is worn down really unevenly. I have 32" BFG mud terrains on it and the lugs are worn unevenly from front to back. I have seen this happen before when i went too long between rotations but its only been ~2000 miles and the front right tire is not worn down in a similar fashion. I am wondering if this could also be caused by the 4x4 kicking on @ freeway speeds on dry concrete.

Info on truck
98 ranger XLT 4x4 extended cab
3.0L engine
97,000 miles
32x10.5x15 tires

Thanks!

Rockledge · #2 (**permalink**) 07-02-2009, 11:22 AM

I suppose it's possible that a broken hublock could cause only one front wheel to occasionally engage. The '98-'00 "pulse vacuum hublock" (PVH) system is prone to failures which have caused unwanted engagement (or lack of proper engagement) and your problem would not be inconsistent with that. If indeed one of your front hubs is engaging while the other one is not, that could also cause uneven wear on the tire.

ggarner · #3 (**permalink**) 07-02-2009, 04:42 PM

Well its fixed.

After the right front wheel bearing was replaced and the hubs were greased up well and repacked it no longer vibrates. So I am not really sure what the culprit was or if it was just a combo of the 2.

Thanks for the help Rockledge!