[alfa] Axle bump stop

["Bain, Bill" <Bill.Bain@xxxxxxxxxxxx>]

Mike B asks about the rear axle bump stop.  The bump stop is designed to
cushion the axle(s)' vertical motion when the car bottoms out.  IT
wouldn't affect the forward/rearward motion of the axle under
acceleration.

The rear axle is attached to the car by the trailing arms, and the ends
of the reaction triangle that attaches to the top of the differential.
The rear shocks don't really count as attachment points.  The trailing
arms should locate the movement fore and aft of the axle.  So, IF the
axle is moving fore and aft under acceleration, it's usually that the
bushings are worn out and their worn-out slightly ovoid shape allows the
axle for move forward on the driver's (left) side of the car under
acceleration.  The engine torque is taken up by that forward bushing on
the trailing arm and it usually fails first.  Now, that's not a whole
bunch of movement, but it's enough to sort of "rear wheel steer" the car
since the passenger side (right) bushing is usually not as worn out.
This is a pretty common issue with 105/115 cars and the replacement of
these bushings is commonly discussed.  I'll not get into the whole
rubber vs. urethane debate, but after the old ones are pressed out, the
urethane ones are a whole lot easier to install .

Bill Bain 
AROC Atlanta 
'83 Spider (back on the road as soon as I change the oil!  Woo hoo!) 
'87 Milano (I have to take apart a parts car for the pieces to fix the
damage from that ^&*$# BMW driver). 
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