glang Posted June 14, 2017 Share Posted June 14, 2017 Hi,Ive just bought a second hand 3.89 diff but its quite notchy to turn. Ive looked inside and all appears to be good but the pinion which is the crush spacer type seems to be too tight. If I slacken off the front nut a little (having marked where it was originally) it rotates much more freely. I know the bearings have to be preloaded but just how smooth should it be as its not as nice as some others Ive tried?Thanks Quote Link to comment Share on other sites More sharing options...
Nick Jones Posted June 14, 2017 Share Posted June 14, 2017 The pinion bearing on a used diff should not have any significant pre-load and should certainly not be tight.Suspect someone may have renewed the seal and over-tightened the nut on reassembly and over-crushed the crush spacer.You need a new crush spacer or solid spacer plus shims and then to reset it. Trick is..... what to. The bearing has already bedded in and you don't want to return to the factory new pre-load figures. I'd suggest tightening to the point where all detectable free play has gone (even with some reasonable leverage) and leaving it at that.Nick Quote Link to comment Share on other sites More sharing options...
glang Posted June 16, 2017 Author Share Posted June 16, 2017 Thanks Nick, Ive always thought the preload was for thermal expansion so that when the assembly expands as it reaches its working temperature theres no play produced but of course as you say bedding in sounds more likely. I'll get another crush spacer and install it as youve suggested. Quote Link to comment Share on other sites More sharing options...
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