This is my first post here, so please be gentle.

My 16 yr old son and I have spent the last year working on an 87 4Runner we picked up for 1K bucks. We've rebuilt, replaced and repaired more things than I have space to mention, but overall it has been a great father/son project. Figured he'd learn a lot and also have a lot more appreciation (read "won't tear it up so fast") if he had a lot of his own sweat and blood invested in it. Major things we've done are complete engine overhaul and body repair/paint (ourselves), plus a bunch of little things. It's on the road now and looks and runs great. (I'd post a pic if I knew how)

Finally, here's my really simple question:
I'm hearing a slight rumble coming from the rear, and am suspecting rear axle bearings. Are the outer bearings bathed in the rear differential oil, or are they separated from it by the seal?

 

Welcome to Yotatech.

Slight rumbling from the rear? Sure it isn't your u-joints?

http://www.4x4wire.com/toyota/mainte...wheel_bearing/

http://www.wabfab.org/products/rearaxle/rearaxle.htm

 

Well, with 240K miles, it could be a lot of things. And u-joints have crossed my mind. It sat for a few years before we bought it, which got me to wondering about those outer bearings. If they don't run in oil, they might be pretty doggone dry.

 

Sealed bearings a little on the expensive side

seems there is a inner and outer seal With seals I have around $180.00 maybe more for both sides.

Does it make the noise all the time.

 

I'd say it does do it all the time, but at high speeds with the tire and wind noise, it's harder to isolate. At slower speeds, it develops a sort of harmonic "wave" of rumble. Kind of a rough, kind of slow "wump wump wump", which to me means driveshaft (spline shaft portion) and/or u-joints are still possible causes. I yanked around on the driveshaft, and couldn't find any slack that I felt was excessive.

 

check the u joints just for assurance, drop the drive shaft to check them. Thats the mistake i made, i though mine were fine because they didnt have any play, well they didnt have any play because they were seized lol.

 

Could always drop the rear driveshaft off and lock the front hubs and use 4H in the transfer case (assuming working front drive components) and give it a test drive. If the noise remains it could be the bearings. The noise should vary in turns, getting louder when the bad bearing is on the outside wheel in the turn.