Suspension Notice for S/SS by NHRA

[Bobby DiDomenico]

Originally Posted by Tom Nolan

Broken strut rod photo!

Do you think this happened because the stiffer bushing didn't compress like the factory rubber one and caused the shaft to flex there? We had a car where the rubber one had cracked and moved which then was allowing the retaining washer to hit upon braking but never had a rod go like that.

[69Cobra]

Originally Posted by Bobby DiDomenico

Do you think this happened because the stiffer bushing didn't compress like the factory rubber one and caused the shaft to flex there? We had a car where the rubber one had cracked and moved which then was allowing the retaining washer to hit upon braking but never had a rod go like that.

Yes! Exactly the polyurethane bushings do not flex at all and are probably the worse thing to use.

Originally Posted by Tom Nolan

Almost 30,000 views, poll, major safety issues and NHRA tech dept still ignores the stake holders! WTF?

Its appears they don't care how the stake holders feel.

[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.

[Mark Yacavone]

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.

Bill, I don't know where you're coming from on this. I don't have an engineering background and it sounds like maybe you do..
So, are you saying the break in the picture was caused by stretching, rather than flexing?

Thanks

[69Cobra]

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.

[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

[BBF67]

Since the strut rod swings in an arc as the suspension goes through its full travel from extended to compressed, would a solid fixture such as a heim or ball type bushing on one end of the strut rod cause the cars alignment to change throughout the swing of the lower control arm?

[Jeff Lee]

Originally Posted by BBF67

Since the strut rod swings in an arc as the suspension goes through its full travel from extended to compressed, would a solid fixture such as a heim or ball type bushing on one end of the strut rod cause the cars alignment to change throughout the swing of the lower control arm?

No.

[Bill Harris]

I think I would want to see a metallurgical study of that fracture before I assumed that it was a shear and not tensile break. I don't want to be the one that finds out when one lets go. The poly bushings are much more resistant to vertical motion than either the rubber or spherical, but I have used them (Prothane) in the past on my '71 Mustang and have been able to pull the strut into position on the lower arm with one hand so they aren't that bad. I have a hard time seeing that the bushing could exert enough bending force to shear a strut rod even though there is more side loading than with the alternatives. Has anyone had one just bend without breaking?

I don't know of any aftermarket strut rods that are advertised as being tougher than the OEM and are direct replacements. Opentracker has a unit that looks fairly stout that might ease my mind, for one...

http://www.opentrackerracingproducts.com/strutrod/