Questions about 9"diff break in

[bosephus 10]

I've just completed a rebuild of the differential in my car. I used 3.70 gears and added a tru-trac while I was there. Pattern was good,preloaded carrier bearings,pinion was on the tight side (29 inch pounds of preload) but within spec.New balanced driveshaft was installed along with a t-5 transmission. Problem is at @ 60 mph it gets a vibration/ buzz . Acceleration sometimes quiets it down while coasting seems to make it just a bit worse.The rear probably has less than 50 miles on it and seems to not bother me as much with each cruise. Does this sound like a "break -in " thing or should I be concerned. I don't want to trash that tru-trac,that thing was expensive. Tell me what you think! Thanks,Bo

[barnett468 418]

check your drive shaft angles, especially if you lowered the trans to get the t5 in.

[RPM 1,190]

Yep, angles. There's a plethora of internet Mustang posts of vibrations with the t5 because of the changed angle due to fitting the bigger t5.

[bosephus 10]

Will check the angles with the tremec tool app. The new crossmember came from modern driveline and went in without a fight so I thought I was good. I should have gotten the angles before I took it apart. Thanks,Bo

[fvike 173]

TruTrac diffs are sensitive about oil too. I had Mobil1 oil in my (also 3.70) TruTrac, and it had a little noise to it. I changed to RedLine, and it was quiet. I read somewhere sometime that the TruTrac diffs was developed on Valvoline oil.

Edit: I had no vibration, just a little bit noise.