489 THIRD MEMBER CASE CLEARANCE?

[JARRETT LYNCH]

Hey everyone, I have 69 superbee with 489 third member case with 3.23 open gears and I'm installing 3.91 gears with posi unit all parts from DR. diff. I have been busy so I gave the job to a local diff guy and he is telling me he has to clearance the 489 case in order for the posi to fit. This doesnt sound right to me?????

 

[R413]

Contact dr Diff and ask him if it will fit without grinding. Never know on aftermarket parts.

If so then go pickup your parts.

 

[davek]

Does not sound right to me. I have a 489 case with 410 in it. Came out of my 70 Bee.

 

[PurpleBeeper]

Doesn’t sound right

 

[1 Wild R/T]

I've built 489 case 8.75 chucks with 4.56, 4.30, 4.10, 3.91, 3.73, 3.55, 3.23, 2.94 & 2.76 gears.... Never had to clearance any of them...

 

[Chargerjase]

I wonder if he forgot to install the outer bearing before the pinion seal.
See video from Dead Dodge Garage. Important part is at 22:25

 

[JARRETT LYNCH]

Update, turns out he didn’t have to do any clearancing. He said he thought I had the smaller 8 1/4 and said he has had to clearance. Anyways, got the third member in with Amzoil 80/90 non synthetic gear oil and a bottle of motorcraft additive from DR diff. I notice when I turn slowly right or left it makes clunking sound like the posi is grabbing too much. Is this normal? Do I just need to drive it more to break in?

 

[dadsbee]

Go and do figure 8's in a parking lot, tighter and tighter for 15 minutes or so and see if it settles down. If not it might need a second bottle of additive (after you take 4 ounces of fluid back out).

 

[1 Wild R/T]

Anymore I go straight to two bottles... Stuff doesn't seem as effective as it once was..