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Gearbox query


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After little bro drove middle bro's Ninety across a roundabout there was a bang and no drive. In gear when the clutch is lifted there's a crunching banging sound and no drive. With the centre diff locked, it drives fine. I expected a halfshaft or diff, but he pulled the rear axle bits out, all is confirmed ok and needs no dental work. Excellent, but also bad. Further diagnosis shows neither propshaft is turning when the diff is unlocked and the banging noise is summoned. When the diff is locked, both props turn.

What's broken and how do I fix it? I guess centre diff, but is it rebuildable? I have a spare T-box which is full of swarf.

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I'd go for broken spider gears and or cross shafts inside the centre diff. It may be rebuildable if the internal hemisphere surface where the 4 pinion gears seat is ok. In Australia Mc Namara Differentials remachine damaged hemispheres and fit double thickness thrust washers to the 4 pinion gears. Anyone in the UK do the same ? Ashcrofts perhaps?

Bill.

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I'd go for broken spider gears and or cross shafts inside the centre diff. It may be rebuildable if the internal hemisphere surface where the 4 pinion gears seat is ok. In Australia Mc Namara Differentials remachine damaged hemispheres and fit double thickness thrust washers to the 4 pinion gears. Anyone in the UK do the same ? Ashcrofts perhaps?

Bill.

I've repaired mine before now by removing any burrs and polishing the surface - it just depends how bad the damage is. AFAIK Ashcrofts don't offer this survice although they do sell a solid cross shaft for the diff to help improve strength.

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I've repaired mine before now by removing any burrs and polishing the surface - it just depends how bad the damage is. AFAIK Ashcrofts don't offer this survice although they do sell a solid cross shaft for the diff to help improve strength.

A friend of mine does the centre diff machining at Mc Namaras, and tells me he has learned that in the majority of cases the standard hemispherical surface is not concentric with the bores that locate the side gears. What that means is that instead of the loads and wear being evenly distibuted over the 4 pinion gears, only one or two gears are doing the work, until their thrust washers wear a bit or wear away and gradually the other gears come into play. Usually by the time this happens the centre diff is getting a bit sloppy or breaks due to uneven loading, so a correctly remachined carrier if you can get it done can prove to be longer lasting and stronger than original.

Bill.

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A friend of mine does the centre diff machining at Mc Namaras, and tells me he has learned that in the majority of cases the standard hemispherical surface is not concentric with the bores that locate the side gears. What that means is that instead of the loads and wear being evenly distibuted over the 4 pinion gears, only one or two gears are doing the work, until their thrust washers wear a bit or wear away and gradually the other gears come into play. Usually by the time this happens the centre diff is getting a bit sloppy or breaks due to uneven loading, so a correctly remachined carrier if you can get it done can prove to be longer lasting and stronger than original.

Bill.

Interesting.... it would explain why when my centre diff went one of the gears was in 8 peices, one was in 3, one had a tooth missing and one was still complete (all be it welded to the cross shaft).

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