RE: Rear End Twitch

[Mike Wattam <MikeWattam@domain.elided>]

Hi John

If you look at the rear suspension, the trailing arms are mounted on the
rubbers at an angle to the body.  This means that as the suspension goes up
and down, the wheel moves in an arc - not just up and down, but
horizontally also causing rear axle steer.  As the axis of the wheel arc
does not coincide with the half-shaft length, the splines are moving in and
out all the time with suspension movement.

So what happens with rear end twitch is that dry splines tend to lock under
load and thus stress the rubber mounts on suspension movement.  When the
power is released, they go back to their natural position, causing the
'twitch'.  This effect is at its worst on a fast power-on bend, where it
can be lethal to suddenly power-off.  CV joint grease stops this terrible
behaviour.

Fitting new (harder) rubber/poly mounts should reduce the extent of the
'twitch' but are second-best to eliminating the cause.

A rear anti-roll bar is NOT recommended on an unmodified rear end as this
reduces/prevents rear toe-in and gives the car a lot of understeer.

IMHO - Mike Wattam
Chairman - Triumph Stag Register