I have about 200 miles on my new 5.13's. Up until yesterday there hasn't been a single notable noise. At 55mph I can hear a very slight sort of rattle noise. I've read of a lot of people mentioning a whine, but I can't find any experiences of a rattle. It is very minor and doesn't do it at all until the higher speed. Anyone have any ideas?

 

I don't have an answer for you, but I'm also in about 200 miles on my new 4.88 gears. Fortunately, no noises at this point, but I was advised to stay below 50 mph for the break-in period. Have you been exceeding that, and if so, for how long? I believe the danger is when the fluid that's used for the break-in gets overheated, although I wouldn't think that's much of an issue with higher speeds if it's not for long distances, and definitely don't want to do any towing during the break-in. Anyway, hope you get it figured out and good luck. Curious to hear what you find out.

 

I was advised to stay below 55 and I've done that. Heat treatments are all finished. I did 12 cycles of 30 minutes of driving and 40 minutes of cool time.

 

Sure sounds like you've taken all the precautions. Hopefully the rattling is unrelated to the gears and is easily fixed. I'm like you, I've heard about new gears that whine, but not about a rattling sound.

 

Could be driveshaft. Ripping it out now

 

This was going to be my recomendation. Also check for play in the pinion yoke/flange. A rattle/vibe above 55 could be loss of pinion preload.

 

There's a small amount of play in the pinion yoke. Very minor. Should there be zero play once the driveshaft is gone?

 

What type of play?

Up and down?
In and out?
Rotational (backlash)?

 

Agreed, define the play.

In and out/up and down, bad news.... Rotational is ok (as long as backlash was set properly).

 

Up and down, very minor in/out. I checked the pinion nut and it's not loose. No noise driving home without the driveshaft.