Hello all, back from the shadows. I finally got the ol' 72 Dart back on the road, and after fixing what 6 years of sitting can do, I can say that I've missed driving it.
Now while it was sitting, I found a great deal on a 8 3/4 Sure-Grip to bolt in place of my sickly 7 1/4. I haven't driven the car with the new axle assy until this weekend. I expected cruising to be hindered with 3.91 gears (was 2.76), but it sounds like the title describes. At 60 it doesn't matter if the windows are up or down; you can't hear thunder for the axle noise! I pulled the chunk, gears look fine, I adjusted the lash to spec, and put it all back together. Better below 20 mph, same wailing any higher. From what I've gathered, the gears were probably not setup right (aka before I got em) and have "lapped" wrong. Sound about right? Any tips on rebuilding? I know some pros are here.? Oh, and I went
from 22 to 13 mpg with just the axle swap. No further adjustment to carb or timing yet. Around 3000 @ 55. But I can bounce the headlights with the go pedal at that same speed.

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225 Cubic Inches of Iron-Head American Muscle

225 bored .040 /.100 off block, Schneider Cam 224@.050~ .480 lift - Stock valves, blended bowls, Offenhauser intake with 500 Edelbrock carb

You mentioned lash, but did not mention your "picture", that is, the actual meshing of the gears in terms of how high the pinion is riding on the ring. Did you check that?

Sort of like never shifting out of second gear.



I have 3.55 gears in an 8 3/4 Suregrip, and on a trip that constant 3000 rpm at 60 mph becomes a bit too buzzy. I do get 18.5 mph with it though.

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67' Dart GT Convertible; the old Chrysler Corp.
82' LeBaron Convertible; the new Chrysler Corp
07' 300 C AWD; Now by Fiat, the old new Chrysler LLC

Go find another center section to swap-in, while you spend some time re-setting the 3.91s ( sounds like it has the wrong pinion depth spacer)
Look for a 3.23 or a 2.94 ratio
DD