Suspension Notice for S/SS by NHRA

[Mark Madison]

Originally Posted by Bill Harris

Polyurethane does flex a little, surely not as much as the OEM rubber, especially a 40 year old rubber bushing, but they have a little give. However, a spherical bearing like the Calvert for the FoMoCo cars absolutely positively does not flex at all. So please explain why it is inadvisable to use a poly bushing while arguing to use a solid bushing instead?

The OEM strut rods were not designed to take the beatings they see when a 3500 lb car comes down from a 3+ foot wheelstand. Nor were they designed to maintain perfect alignment when someone stands on the brakes at 120+ MPH.

As you can see in that picture, the Ford strut rods are necked down and threaded and the break is at the threads which are almost certainly cut and not rolled, making them weak (stress risers galore). Coming down from a wheelstand puts those rods in tension and if there is no compliance from the bushing the rods are going to be prone to breaking at the threads. The break in the picture has nothing to do with over-tightening the bushing as the portion of the rod that is being subjected to tightening tension is between the two nuts.

I have the Calvert spherical bearing on a SS/GT 69 Mustang and I am seriously considering taking them off and replacing them with new OEM rubber. I don't think a solid bushing should be used with an OEM strut rod, especially 40+ year old units. Rather, aftermarket or custom made strut rods should be used that has enough safety factor designed in to make sure it can stand up to this sort of abuse.

If this is about safety, then the last thing you want is a solid bushing.

It it not tension that is the issue. Trying to flex the strut in the stiff urethane bushing is what could lead to fatigue of the strut rod . The spherical rod end allows the needed range of motion without bind or aft movement of the A- arm. Calvert explains this best, if in doubt I would call him first.


Mark Madison
7995