Just to clarify a few thinks the 9.75 use the same axles from a 10.25 that are available in the 97-03 7700's. The newer 9.75 from 04 up will not be a direct bolt in as they have 3" leafs and dual location pins. I no my truck isnt lifted yet but i run 4.30's on 34's.....

 

Well i noticed my truck was bouncing around a little today in the rear. Then i started hearing the chattering coming from the back.. So much for the Auburn differential being so much tougher.. lasted 3.5 months with a 220 hp 4.6 with gears basically, stock differential lasted longer than that!!!

 

it may just need a fluid change and friction modifier

 

It just ahd new gear oil and friction modifier when it was installed 3.5mo ago.

 

Yeah, but was it enough? Did you put one bottle of friction modifier in or two initially. Depending on the gear oil used (some are more "slippery" than others), it sometimes takes a little extra, so don't be afraid to add more, a half bottle at a time until the chattering stops. Drive it around a while before adding more, or go into a parking lot and do some figure 8s. If you let it chatter very much or very long you could damage the unit.

My Auburn's been in for two years and hasn't made a peep... and I regularly tow VERY heavy loads. Mine's a 10.25, which holds a little more oil than yours, and it took two bottles.

 

I wish i could get away with friction modifier. It looks like i chipped a couple teeth off the ring gear. Thats bad, but not nearly as bad as a broken differential imo. Regearing the rear for the third time now.

 

As tey say... bummer dude. What cause the ring gear to lose teeth? Too many burnouts (;< )?

 

Well.. the wear patterns look good.. yeah, i believe that last one did me in. I know when i did it, it caught traction SO hard. Im selling the truck so i migh just put the cheapest gear set i can get in it. Or i might just put motive back in it. They aren't too bad expensive as far as gears go.

 

That sucks man!!! Sorry to hear that.

 

What different gear brands have you used?

 

Just Motive. The first time it was the diff that messed everything up. This time it was the gears.

 

The pinion nut had backed off!! In just a few months. It couldn't have been tightened down to spec in the first place! Or they used the old nut and it backed off, shouldn't ahve happened in 4mo though. The guy who did the install is a total being a total a hole. Won't take any responsibility. There is a ton of pinion slop, they wanted 1100 dollars to regear the rear. He was like, "if i would have found that once we got in there, i wouldn't have charged you." BS. This is why you should do your own work if you can! I told him he could shove that 1100 bucks btw.. would neve pay that!