Swapped my 4.56 gears this weekend to 3.73.
Took out spool and put in a TrueTrac, new axles, etc.
Pattern looked good but I have a bad gear noise on Decel.
I have done several gear swaps and never had this. I did'nt have tools to check pinion depth but I have jus ordered one. Backlash was .009" Motive gears. Could my noise just be from incorrect pinion depth? I reused the shim from the original setup b4 the 4,56's and they were also quiet.
Thanks, Brian

It probably is from incorrect pinion depth. That is the most common cause of noise like this. Setting the pinion depth does not require a tool. I had one and didn't keep it because it was not accurate. The most accurate way to check for proper pinion depth is by reading the contact pattern. Pinion shim changes of .002 inch can be easily seen by reading the contact pattern when you know what to look for.

Another question, solid pinion spacers, good, or bad idea? Also now I see that my pinion seal is leaking. Only thing I did different than any other diff I have setup is use a solid pinion spacer. Everything seemed fine, but the pinion seal is leaking excessively now too. Why me ?!?!?!? I guess I will pull it apart, recheck gear pattern and install another new seal, and double check everything again. Thanks for any info, Brian ............. $1400 later and more headaches.

Did you get the pinion bearing preload set right? Something that I have found on the 12 bolt is that the pinion seal will cause problems with the bearing preload and will also fail quickly. The seal that is being sold for the 12 bolt now is not the correct seal. If you drive it in all the way it may contact the outer pinion bearing, which will give you a false preload reading, and also cause the seal to go bad quickly. I usually leave the seal out about 1/8 inch so that it doesn't contact the bearing. Check it out and see if you have this problem.

Thanks for the help again BGH
Preload was set at 28inlbs, without a seal in place. Maybe the seal is hitting the bearing??? Looked same as old one which was not leaking, but I put that together about 7 yrs ago so the seal may have been a little different. Well I got a new seal this morning and will be taking it back aparrt tonight and we'll see what I find. Man I have never had these problems B4. I guess all the other ones I got lucky!! Just always reused the original pinion shim and had quiet gears. Even richmonds that people claim to be noisy. Now I figure I'm gonna do everything right, get the mini spool out, put in true trac, 33 spline axles, solid pinion spacer, new 3.73's, etc., etc. and all I have is a big friggin headache. Just seems strange that I have the noise AND the seal is leaking. and its not just a little drip. The yoke is the only thing I reused and it did not leak before. It is only a couple months old, because I upgraded driveshaft and joints to 1350 joints. So there is no wear grooves. What really irritates me is I probably have done over 50 customer diffs as I am a Auto Tech and never ever did I have these problems!!!!
Brian

Well the pinion leak was the seal being to deep and running on the bevel of the yoke near the outer bearing. The new one is now left out about an 1/8" and seems fine. I ended up adding .009 to the pinion for a total of .044. Which pretty much looks like a text book pattern. The factory 3.08 gears had a .035 shim. Which is what I used on the 4.56's and was ok. But I rechecked pattern a few times and realized how high it was on the ring gear. So I start adding pinion depth. I am now at a good pattern, with .008 backlash. Went for a drive, the noise is better, however far from gone. Have I done irreversible damage to the gears??? Will the noise get any better, worse, same,? Thanks again, Brian

It doesn't take long to damage a gear. You should see what happened to a gear that I replaced 2 weeks ago. Someone installed a 4.10 in a truck 12 bolt and after 10 miles the pinion teeth were sharp enough to cut you. There was a pile of metal in the bottom of the housing. You may have to live with this noise, or replace the gears again. One thing I would suggest, 28 inch pounds is a little too much bearing preload. You might want to try for 19 to 22 next time.

Thanks for the help, I guess I'll run it for a while and see what happens.