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small differential rebuild


johny
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Im having a look over a couple of used spare small chassis diffs Ive got and found both have very little preload on the pinion bearings. According to the WSM they should be set to 12 - 16 lb.in so the pinion (with crown wheel removed) should need this not inconsiderable torque to start turning. Looking online at why preload is used on taper roller bearings it seems theres quite a few benefits of which one is noise reduction both in the bearing itself and gear meshing if used for that purpose. Its needed whether the bearings are new or old and of course tends to reduce as they wear so Im wondering if the lack of preload could explain the whine that some diffs develop. Unfortunately Ive never run these diffs so dont know if theyre noisy but it could be something to try for anyone who does have that problem. On the later collapsible sleeve type its just a case of tightening the pinion nut (obviously difficult to measure the actual setting) while the earlier shimmed arrangement would need stripping down.

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I would worry about changing the mesh pattern on the CWP if tightening up a collapsible spacer. 

Besides, having fitted a couple of reconditioned diffs, although they are tight when rebuilt, they very quickly slacken off as they bed in, so just tightening up to "freshly built" spec may not be wise. A better figure would be for a diff that has done just a few thousand miles and settled down nicely.

 

Saying all that, I leave diff building to others, all a bit of a black art! I have played with Subaru diffs, swapping carriers etc and been successful, but their tolerances are rather better and I have been able to just swap the shims keeping everything as a set.

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Thanks Clive and its true the pinion will move but it should only be fractions of a thou as the preload is shared between the two bearings and the difference between a free running bearing and one with 12lb.in is achieved by only a small movement of the nut.

If the diff is noisy anyway I think its worth trying this, especially on a collapsible type, before exchanging it for an expensive overhauled unit...

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you can only upset the mesh if you change the taper bearings and the shiming behind the thrust race , if the mounting distance is as it should be then lost pre load

would affect overun as the spacer is not on the thrust side of the bearing races ,  adding a little more nip on a colapsible or removing a small shim from a fixed will increase the pre load without affecting the mounting distance of CW and pinion that remains as is .

Pete

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if you measure the  crownwheel   backlash ( normall etched on the edge of the gear) of around  0.004/0.006"you must position the dial indicator at right angles to the tooth flank or you dont measure what your are looking for if the stylus slips up and down a tooth while you rotate the gear clearance you get a false reading

dont get backlash mixed up with planet gear free play which can give up to a good 1/8 turn of the coupling

Pete

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Do you think its a good idea then Pete to, if possible, ensure a good preload is always maintained on the pinion (in neither of my diffs did I find the same issue in the carrier bearings)? Online it even says correct preload extends the life of the bearings because even under movement due to flexing or thermal expansion theres guaranteed contact over the full roller surface rather than possibly just part of it...

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well pre load in diff bearings is essential , any end float means things are moving about , there all the drive torque thro the diff it needs all to be stable and not shift mesh due to float

there is no real spec for a 'used' pr load   i dont see a extra nip on a collapsible or a removal of a 0.002 shim being detrimental 

if you dont have a meter to measure lb ins  a wind of string round the coupling and a spring balance to measure the pull calculate the  torque will give a clue 

 

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