Non Standard 9:31 Crown Wheel and Pinion

[David FaulknerParticipant]

A couple of weeks ago I had a differential pinion shed a couple of teeth when pulling away at a roundabout and felt it worth sharing what was found that appears to be the cause of the failure. Fortunately the broken teeth fell into the bottom of the bell housing and didn’t jam anything up cracking the casing but the car was undriveable and required recovery.

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Basically the gearbox had been rebuilt in the distant past using a pinion shaft that had been made with an oil way (to feed a bush presumably) which is where cracks started, eventually spreading to the point where the adjacent teeth sheared off under load.

Now it may have been a manufacturing issue during the case hardening process or excessive stress from a road wheel incident (hitting a pothole etc.) sometime in the past before we got the car, but if anyone is rebuilding a gearbox it’s worth paying particular attention to the pinion to see if it has such an oilway in it and if so check carefully for any sign of cracking.

The replacement that was fitted from Jose Fransen doesn’t have that modification (and was 138 euro cheaper than Der Franzose for the same ‘Made In Germany’ Crown Wheel and Pinion set)

[Author]

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