My 1967 amazon wagon required a new transmission. I nearly lost the remaining gears on the return trip and had to tow it the last 150 miles home. I put it up on jacks pulled the old gearbox and dropped a replacement M40 in with fresh gear oil. After gettign everything bolted back up I took it for a drive. While the gears worked fine, I heard a "runk-runk" noise I had not heard on the drive home. I was concerend that I had installed something wrong, so I checked the driveshaft to gearbox bolts and discovered that they were a little loose. I tightened those back up and took it for another drive. The "runking" noise stopped, but noise continued to come from the rear-end. I first thought it sounded a bit like brakes scraping, but the rear pads were just fine when I pulled the drums off (didn't need to use a gear puller - lucky me!).

I put the rear en up on jacks and ran in in place for a while. There is definitely a noise comeing from the rear...someplace, I can't quite get it pinned down due to engine noise. The sound only occurs when the car is on motion. No noise when stopped. Shifting into neutral or other gears makes no difference in the tempo or type of sound.

My guess is that it's coming from the driveshaft or the differential, maybe the axles. I have been running some heavy degreaser under the car to get the leaked-out gearbox oil off everything and I wonder if I may have degreased something I shouldn't have. Any thoughts on diagnosis?

If it was me, I'd ignore the differential until I'd made sure that it wasn't something less disheartening. I'd carefully check all 3 U-joints (actually if I were keeping this car I'd replace them). I'd also get me a new rubber doughnut center bearing support and replace the bearing (about $8). Also check your motor mount and transmission mount rubbers.
Only after I'd done this would I turn to the rear end (axle bearings?)

Is there a lot of 90 wt slung onto the body right around the pinion flange? replace that seal. Have you removed the filler plug in the dif and stuck your finger in to see how far down the 90 wt is? Might be very informative to spring for a dif cover gasket and pull the cover and see what kind of goop is in the bottom of the dif.

I drove over 800 miles ot get this car, I am keeping it, so my u-joint will get replaced. I'd just like to get the noise traced first.

there was quite a bit of oil on the underside of the car, but I'm not sure it got onto the pinion flange (that's the flange where the driveshaft bolts to the differential, correct?) It was the worst in the drive tunnel when the drain tubes had dumped water onto an oily gearbox creating that greyish sludge we often see when a head-gasket blows. I've been hitting it pretty heavy with engine degreaser then some purple degreaser from Carquest.

Motor and transmission mounts are good, I had to loosen them all to get the dang gearbox out of the car. The transmission one will need to be replaced eventually, but it's still solid now.

The rubber center bearing sounds like a candidate, as well as the U-joints. Come to think of it, the sound may be u-joint related. I don't know all that much about u-joints, but could hitting them with degreaser have mucked them up?

I have not opened the differential or checked it's oil. Like a gearbox, it should be full to the plug, right?

It is also possible that whatever happened, happened while the car was on the tow dolly. The car was towed front first on a u-haul tow dolly. I didn't drive it more than 50 feet once it was home and it was making a lot of gear noise. Could it have damaged that way? and if so, what may have been damaged?

the rubber center bearing sounds like a candidate, as well as the U-joints. Come to think of it, the sound may be u-joint related. I don't know all that much about u-joints, but could hitting them with degreaser have mucked them up?

Better U-joints have grease fittings. Makes them a little more difficult to replace, as the yokes are cast in such a way as allow the grease fitting to be directed in only one direction, otherwise it's snapped off.
I do mine, but the first time was no fun - actually it's never been fun. Sounds like your cheap (thrifty, I should say) like the rest of us and will do it yourself. If your's is a 67, it should have a rubber doughnut surrounding the carrier bearing (earlier version has the carrier supported on 2 pins and bushings)

I have not opened the differential or checked it's oil. Like a gearbox, it should be full to the plug, right?

Yes.

Thanks for the info. One reason I wanted a 67 was because I wanted a car I could service myself. I plan on rebuilding the engine myself (if it does actually need it) or the spare B18 that I got freee with the car.

I have a spare rubber doughnut-thing in my parts collection as well as a spare brace for it. How do I tell if it's still good?

It should look good, be fairly firm and fit snugly into the carrier and the bearing should fit snugly into it.

Bearing should be quiet, smooth and turn reasonably easily.

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Mike!