I just got my rear rebuilt, went from a 4:11 Open diff to a 3:42 True-Trac, I wanted to find out what the proper break-in procedure for the new rear end is, how many miles on what type of driving and recommended oil. Thanks a lot.

manufactures recommend a few short trips -20 miles or enough to get to operating temp,a 30 minute cool down and repeat -before putting a heavy load on gears,racing or towing.Don't know if it really affects gear life or not.I have installed numerous sets in customers tow rigs that I know hit the road with a trailer the next day with no problems .Maybe they traded truck before problems surfaced.Bottom line ,it won't hurt to follow the recommended procedures and change the oil at first 1000 miles if you have the time.If it was mine ,I would drive it like I stole it and not worry........

I like that answer harold. kind of makes sense. giving the gear mesh time to develop before subjecting it to any serious loading.

I use the lakewood gold colored $12 a bottle gear oil in my 12 bolt sans any additives...no problems or chatter....