Quote:
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.
|
Yes you are correct. The polyurethane does flex some. I think the difference between the poly and the spherical bearing is the poly doesn't let the strut rod pivot up and down therefor breaking it at the end of the threads in a shear type break as where the spherical bearing might be solid in the before and aft travel it will freely pivot up and down causing no shearing effect therefor only tensile loads are applied. I've not seen or heard of any negative issues with the spherical bearing. I agree that these strut rods where not designed to keep control when coming down off a wheelie or stabbing the breaks at 120 which would support the request for aftermarket strut rods so you can replace a 45 year old part. All of this also supports the fact that all the information on this subject has not come to light and therefor NHRA should keep investigating this issue.