I have been spending some time setting the lash on my pinion/ring gear. My original axle housing was cracked and I replaced the halves. So the original shims don't mean a lot. I set up to measure on the pinion.
With no ring gear shims at all, I measure more than 0.025" lash.
With a 0.010" shim the lash is 0.018"
With a 0.015" shim the lash is 0.014"
With a 0.025" shim the lash measured 0.010"/0.012"/0.013" --- 2 to 3 thou of run out.
With a 0.030" shim the lash measured 0.003"/0.005"/0.006"
Then with the 0.030" shim I measured the lash on each tooth. Actually only 3 teeth have the 0.003" the rest are either 0.005" or 0.006".
I checked for burrs on the ring gear and differential surface. Didn't fell any and I ran a flat stone over and nothing shines up.
Thought that maybe tomorrow I'd rotate the shims and see if it stays the same.
Question is --- is the 0.003" too tight? I'm thinking that I'll just use the 0.025" shims and call it a day.
I have a 1926 Tudor which I drive maybe 3000 miles a year. The pinion and ring gear are a 'MARK' and are about 4 years old. The wear pattern is very good.
Thanks for the help
Personally, I'd use the .015 shim setting the lash at 14 thou. Its really impressive than your run out is only 2 to 3 thou. Done a lot of rear ends and learned that more clearance is better. The quietest rear end had 15 thou lash.
Use whatever shims make the gears run smoothly with each other, with reasonably full contact. Roll them together by hand and when you feel no discernable engagement/disengagement of teeth you've got it. At that point the final shim thickness is not important, only that you have a smooth mesh.
I agree with Richard. Use the .015 shim. I mistakenly set the gears tighter ans ended up with drivetrain noise .
Changed to about the same .014 lash and had a quiet running gear set.
I set mine up like it says in the Ford Service book. They don't use shims or dial calipers! Never had a problem!