<VV> Whump, whump, whump

[NicolCS at aol.com]

So far we have: ring gear, pinion shaft, and tire.  I believe that the  noise 
is something turning at axle-shaft speeds - this might rule-out the pinion  
shaft theory.
 
Here's a list of things that turn at axle shaft speeds:
Ring and pinion
Differential side bearings
U-joints
Wheel bearings
Tires
 
Since the noise occurs only under power, not while coasting, that reduces  
the possibility of the tires being the source of the problem but then it only  
takes a few minutes to swap with the front tires to check that out.  No one  
has mentioned U-joints, but if you had one that was bad enough to go "whump",  
you should be able to spot the bad one with a visual inspection.  While the  
car is up for that inspection, it's easy enough to wiggle the wheels and look  
for a loose wheel bearing and to spin the wheel with the drum off and check  
for roughness.  Once you have eliminated those external possibilities you  might 
as well plan on pulling the differential for inspection.  I have seen  many 
ring gears where the top side (out of the lube oil) was rusty after a long  
period of rest.  I have never had or heard of any side bearing failures,  but I'm 
sure there are others on the list who have and know what to look for  there.  
Check the external stuff first.  I had a wheel bearing fail in  my '62 wagon 
(Eric E. are you listening?) and the whump-whump was so loud I  thought the 
axle was going to grind itself in two!
Good hunting!
Craig Nicol