[alfa] Re: Polyurethane vs. OEM Rubber Bushings?

[Johnson David-QA2282 <David.R.Johnson@xxxxxxxxxxxx>]

Dio Genio asked about the wisdom of using polyurethane bushings in his Super and Spider:

"However, a local, reputible Alfa mechanic has advised me to stay far away from non-OEM bushes on these cars.  His reasoning is that these "red things" are "squishy" and cause the rear end of the car to act in an uncontrolled manner.  He went so far as to say that others have experienced the rear end "hopping" or abruptly jumping position under accelleration or hard cornering!"

It is possible that your mechanic has misunderstood a potential problem with using poly bushings on certain suspension geometries.  Poly bushings should be harder and less compliant than stock rubber:- that is the whole point.  But some suspension designs rely on the compliance to work properly, allowing flexibility in a certain axis which would not be there if the joints were not somewhat squishy.  If the required compliance is removed by installing harder bushings, then the suspension can bind or jump unpredictably.  If this happens during a critical manouever, then the results can be very dangerous since the car may do something unexpected at just the wrong moment.

I am not intimately familiar with 105 rear suspension, but in general live rear axles with training arms can be subject to this problem.  For example, the live rear setup on the 4th generation Chevy Camaro can suffer from this.  Despite this harder bushings (generally sold as part of uprated trailing arms) are available, but the better solution is to replace the critical bushings with spherical bearings.  I have done this on my Chevy, and also replaced the torque arm (which the Alfa doesn't have) with a version including a sliding joint and two spherical bearings.  The result is a rear suspension with complete freedom of motion in all intended directions, but devoid of the mushy responses inherent in rubber bushings.  It works extremely well on the track, but does result in a significant increase in road noise on the street!

Also, something else I have heard about polyurethane - it can wear out relatively quickly.  Most of the poly parts in my Camaro have grease fittings and have to be lubricated regularly.  At least one performance suspension vendor I spoke to was pushing a new more durable bushing material with the trade name "Delalum" or something similar.  Maybe this is less of an issue on lighter cars like Alfas though?

Not certain that this is your situation, but it's something to be aware of.  Perhaps someone with 105/115 suspension experience can comment as to whether this is an issue on these cars?

Dave J.
1964 2600 Sprint (with squishy bushings)
1987 Milano Verde (with proper rear suspension ;-)
1994 Chevy Camaro Z28 (modified...)
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