I just finished my rebuild of my dead 12 bolt. Installed 3.73 gears new strange center section. My question the pinion spacer needed to be .043 to get a good patern with .008 backlash. does this sound out of line?
I have never had a 12 bolt that needed a .043 pinion shim. Most are .034-.028. What does the pattern look like?
Are you trying to use the original side shims?
Have you tried a thinner pinion shim with different side shims? The pinion shim comes first. Get it right (based on pattern or a depth gauge) and worry about the side shims last.
Not trying to panic you but .043 seems like a bit too much.
You said you have a Strange center section. Is this a complete Strange housing? Is it a 12 bolt center section for a 9 inch Ford housing? If you have a different housing than GM disregard my comment about the shims.
Ok lets start with the pinion shims. original was .030 removed 3.42 ratio changed to 4.56. Used synthetic oil Factory diff started acting strange. Decided to change to 3.73 and a new differential. Got a strange diff and 3.73 gears from Summit. .030 was what worked in the first change ( 4.56) So i started there. Worked up to .043 thats were im at.