Grinding noise in 8 3/4

[msbaugh]

I got my new center chunk in! A bran spanken new 489 unit, crush sleeve eliminator, 3.55 ring and pinion and a eaton/Detroit true trac limited slip sure grip giving power to both wheels. I got the thrust button in and both axles slid in fairly easily. I torqued the axle retainer nuts and got everything ready to go so they have to be in right! I greased the bearings and filled it with 80-90 weight gear oil. Unfortunately I haven't ran it yet because I need to wait for a 7140\7160 conversion u joint to come in. With the driveshaft not attached to the yoke and both wheels off the ground it's making a sort of grinding noise. Ill grab one axle and turn it and the yoke will turn for a little bit until it feels like it "slips".. I assume that it is just normal operation of the truetrac but it's making a puzzling grinding noise when I turn it an axle. I imagine its just slipping because of the truetrac? Does anyone know if this is normal? It makes me nervous because that rear cost a pretty little penny! It said somewhere online that the truetrac need a little bit of resistance from the tires in order to function properly. Someone calm my nerves please!

[74challenger03]

you can ask Dr Diff    http://www.doctordiff.com/   I emailed him and he wrote right back.

[72cudamaan]

Something doesn't sound right. Grinding is never good with any bearing surfaces. Are
you sure it's grinding and not just rubbing? Maybe rotate the diff a few times to get it covered with oil.
I definitely wouldn't put any power to it until you're satisfied that nothing is wrong.

[brads70]

Did you add the limited slip additive ? My tru-trac said to add it?

[GranCuda1970]

I added a sure-grip additive to mine as well. No noise.

[Jamiez]

Royal Purple (and probably some others) make gear oil with it already added in.  That's what I used when I did the fluid swap on mine.

[msbaugh]

Everything in the manual I've got says that no sure grip additive is necessary. The oil is a limited slip oil though... It's strange whenever I spin the yoke it doesn't do it, it's only when I try to spin one if the axles (no driveshaft connected) the axles are bolted in all the way so how could it not be seated in good? I need to call dr diff I guess and see. Something is making me nervous about it. I had to torque the nuts to get it seated all the way but it felt like the axles slid in very well. It's just making some sort of noise. Can someone go over the steps with me for re-seating the axles so I can double check?

[Chryco Psycho]

The True Trac is a great design , it will not allow any slippage when driven from the driveshaft yolk but unlocks and allow easy rotation when rotated at the axles so it sounds normal But you still should not have grinding

[msbaugh]

The axles went in smoothly until the last inch or so. I was able to get them on the studs and torque the retainer nuts down till they sat flush. Is it possible that the noise I'm hearing is the end of the axles rubbing on the thrust button? With the true trac came a thrust button that's just simply a neatly cylinder. If its to big or my axles are to long maybe they're just rubbing the thrust button? That would explain why I had to torque it to get them fully in there right?

[Changin Gears]

Did the axles slide all the way in, or did you have to pull them in with the retainer nuts?

[msbaugh]

They slid all the way in except for the last 1/2" or so then I used the nuts. Even then though it wasn't difficult to get in, I just couldn't do it by pushing

[msbaugh]

Got it put back together and got my 7260/7290 conversion u-joint.  No grinding or anything! 
It runs great and is very quiet.. I haven't gotten a chance to get on it yet since I'm now having brake problems lol  but after I fix that and run some break in procedures I'll be ready! Hopefully Ill be able to eventually get the bigger drive shaft custom made.  Can the output transmission yoke be changed to the bigger 7290 style very easily with out messing with the transmission?

[HP_Cuda]

Is that orange sealer I see where the gasket goes on the chunk installation?

[msbaugh]

yeah its copper RTV. I was too lazy to go get blue or black or whatever so I just used it because i already had it.  It had orange sealant on it 4 years ago when I bought it and it never leaked so i stayed with it lol

[HP_Cuda]

Hmm I was going to just use my felpro gasket. I've had bad luck with just using sealant before and at some point or another a weakness is shown but then again this isn't a pressure point in the car.