JD 450D Differential

What would a "broken differential" involve in a 450D six way blade machine? One for sale near me. Everything runs and it looks pretty good. It's open to offers and the fellow said it had a broken diff. From the pictures it still looks all together so I don't really know how he made the diagnosis. Any thoughts would be appreciated. Is this common and are parts costly and available?....Thanks....Ron

There isn't any "differential" in a 450D. I suppose he means the trans turns and the tracks do not. I have seen a few 450s sheer the rivets off the ring gear and stop moving. I think the person is confusing the word "differential" with "ring and pinion." Two very different things but in cars and trucks - found together in the same place. Not on most crawlers though. Only ones I can think of with differentials are those with Clark Corp. transaxles (Oliver-Cletrac, Case 310/350, Terratrac).

There are 2 shafts each driving the final drives.. I wonder if it snapped the inner [ much thinner ] shaft off.. Does it drive at all ?? one side or neither ?? If you need to pull the ring and pinion out.. Start at the front and work your way to the rear of the machine.. When you have the center rear section out, there will be nothing standing in the machine but the engine main frame rails...I wonder if something happened to the pump circuit causing a no drive situation.. One way to tell what's happening is to install a gauge into the HLR pressure port and run the machine to see if it actually makes any oil pressure [ 155-185 lbs].. If it has pressures in all ranges, block the front of the tracks , jack up the rear and block under the sprocket/track, remove the PTO shaft or if not equipped with PTO , pull the cover off and have someone try to operate the machine.. With a flashlight in hand look in there for movement..If the ring gear turns, but nothing drives the final drives.. Either the inner shafts are broke or the steering clutches are slipping/not driving.. The transmission and the steering clutches both operate off the same transmission pressure..

Thanks Roy and jd for your input. Service manuals are great but they will never replace experience and hands-on knowhow. Thank you for taking the time to help so many people out. As for the 450D, maybe after cropping. Saw it for sale on Kigigi . Looks like another "project" but have lots on the go now and we're not getting any younger.....Ron