S2000 diffs: Why they break, and how to stop it from happening (again) – Part 2

We received a customer’s broken S2000 diff last week.

This is the worst one we’d seen so far; clean snapped the centre section of the bearing cap on the crown wheel side off. The usual chewed pinion was the result.

By our reasoning here at Neat Gearboxes, this is the sequence of events that causes this failure:

  1. Hard acceleration is applied by the driver
  2. Heavy load is applied to the crown wheel and pinion (CWP) as the Torsen limited slip differential (LSD) does its job and sends torque to both axles with sticky tyres on the ends.
  3. As load increases, the hypoid gears (CWP) force each other in opposite directions (pinion perpendicular from crown wheel)
  4. This increased side thrust forces the crown wheel and its carrier hard up against the side thrust adjuster screw closest to the crown wheel (see picture)

    the side adjuster screw was forced into the side of the aluminium rear housing

    the side adjuster screw was forced into the side of the aluminium rear housing

  5. The bearing cap is forced outwards and the carrier bearing comes out of alignment
  6. The high grade 12.9 bolts stay put and the cast iron caps eventually give way (see pic)

    the cap closest to the crown wheel snapped clean in two places

    the cap closest to the crown wheel snapped clean in two places

  7. The crown wheel eats the pinion (see pic)

    The result: a destroyed final drive gear set.

    The result: a destroyed final drive gear set.

It seems that locating dowels on the bearing caps won’t be enough to stop this from happening as the load seems to be between the bolts. We have attempted to machine dowels into the housing but alignment is an issue when trying to centralise over a threaded hole, so we’ve had to have a rethink.

We found this interesting: the little bolt that holds the tag that stops the side adjuster screw from undoing itself was completely sheared off and the side adjuster screw was a full turn out (see pics).

The bolt that holds the tag that prevents the side adjustment screw was sheared off

The bolt that holds the tag that prevents the side adjustment screw was sheared off

The side adjustment screw had unwound itself a full turn

The side adjustment screw had unwound itself a full turn

We have had a rethink and are presently making a prototype “assembly” that prevents the bearing caps from flexing apart – can;t give too much away, but stay tuned, more to come.

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