Ring and pinion set up

I recently installed a 3:54 in my '40. I've noticed a slight knocking sound when going over bumps. I confirmed that the sound comes from slight axial runout (side-to-side) movement. How do I correct this condition? I'm thinking I need to add or subtract housing gaskets, but not sure. Always appreciate the advice.
 
Five-O, Maybe you have too much clearance between axle and the inner differential case? Like the spider gears have too much clearance to the axle gear? Maybe a shim between the axle and diff housing under the inside gear.
 
My guess is the axle has too much end play not the center section of the rearend, but who knows. Grab the axle on the end and move in and out while trying not to move the carrier. Early Ford rearends don't have all the room to see what's going on in there like a modern rearends do. I've rebuilt a lot of rearends at work over 30-years but never an Early Ford. Maybe you can take out an axle housing bolt out and a dial indicator in the hole so it's just measuring the side play of the carrier and not the axle. The axle could be worn where the spider side gear rides against the housing or the spider gears are worn out, or like you said there is too much backlash in the pinion gear. I've never completely rebuilt an Early Ford rearend, but I have about 20 of them in the garage. Years and years ago I had one that had too much side play, just like yours. I took it apart just to see what lived inside and the axle carrier and spiders looked okay, I couldn't see any wear in the parts, but something had to be obviously off on the axle side play. I shimmed the axle's side gear to get rid of the excess play. A shim should be locked in place and not be able to spin. So, I used red Loctite on the shim to the axle housing so the side gear could ride against it without the shim spinning and eating the axle housing. Not exactly the best setup but it got my end play of the axle back inline.
 
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Finally got the rear end set up with the new gears,
As on the old one ,it needed .020 to get the pinion depth as per the etching on the pinion (4.375), then another.020 to get the pattern as per the run in mark on the new gears, then backlash set at .005,
I ended up with a very nice pattern and good backlash,
to do the second gears was way quicker as I knew what to do and how.
the test drive turned out to be really quite and smooth, did about 20ks on it today and are really happy
My take from this exercise ,take note of the pinion depth etching on the new repo gears, and start from that,
I will do an article for our club mag on this later.
Lawrie
 
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