Need help with grinding, grumbling, whatever the heck the vibration is.

["J Staub" <jstaub@domain.elided>]

Hello Binders;

My 79 Scout II has just this week developed a strange intermittent grinding.
It is very hard to describe- I can feel a very light high speed rumble
through the driver's floor. It feels to me to be in the front driveshaft but
it is too light to tell. It feels like either a bearing that is rusty or a
dragging of a knurled surface. The closest way I can describe it is when you
drive on a road that has just been scraped by the road crew. It has that
very high speed but low amplitude feel to it. It will happen four or five
times on my 25 mile drive to work, and will happen 'out of the blue' but
most ly when I hit a large bump. It occurs all through the speed range.

I just changed the fluid in the engine, auto transmission, and transfer
case. All were up to the correct level and did not contain any alarming
shavings. I have noticed a larger than usual puddle of a reddish brown fluid
under the transmission area that coincides with the same time frame.
Tomorrow I will put in fluorescent dye to see where it is escaping.

I checked the driveshaft u-joints and changed the back ones because they had
play. It drives smoother but the problem still exists.

I also pulled all four tires and checked the rotation to make sure nothing
was binding. All brake pads were good and the surfaces smooth and clear. I
couldn't feel anything unusual when I turned tham (but since it is
intermittent, I guess it could have been an 'off' period).

If I shift into Neutral while it is happening it will continue to occur.

Finally, I could swear that when I put it in 4 hi with the front lockers
disengaged, it is barely noticeable if there at all.

So, can anyone recommend a course of action? Something else I should check?
If it happened full time I would suspect the front bearings. I've never seen
one that went in and out like this.

Also, I bought two bottles of fluorescent dyes at the local NAPA. One is for
transmissions and the other for oil. unfortunately neither said how much to
put in so it can be seen with a black light. Has anyone used this fluid?

Thanks for your help,
John