Suspension Notice for S/SS by NHRA

[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/

[Paul Precht]

Are the B and E body Chrysler cars suffering the same issues as the Fords.

[Peter Ash]

Originally Posted by 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/

X2 on the metalurgy.

Parts can have minute fractures for long periods of time before a "Montreal " size pothole causes total failure.

Dye-checking strut rods may be in the future for those requiring their own and others safety.

[MLP]

This is the NHRA at it's worst! I would really like to see some response from them as to why this was done.

They allow aftermarket disc brakes that are a performance advantage over factory drums due to weight savings because they are much safer. I understand why they allow them and nobody disputes the importance of having adequate braking at high speeds with heavy cars. What's more important than high speed steering and braking in a race car?

So considering that the strut rods and their bushings directly affect high speed steering/handling and braking, shouldn't they be held in the highest regard in terms of safety and the implementation of new rules? Especially when the modifications in question offer no performance advantages?

My Belvedere at 3500 pounds going 130 mph (hoping) in A/S doesn't have the same safety concerns as a SS/J car? Just admit you dropped the ball NHRA and fix this before someone in a real fast heavy stocker gets hurt for absolutely no good reason at all.

[Tom Nolan]

I was told that if wheel stands are a problem, with safely controlling the movement with stock OEM rubber bushings & strut rods, wheelie bars are legal in stock....use 'em! Well anyone that has tried to hook a heavy high powered stocker on a 9" tire knows if the wheelie bars touch the ground the car's tire will unload. I can get away with riding the wheelie bars for 30' on my super stocker because it has a big fat tire.... 2 different animal's. If the majority here {poll results} are OK with aftermarket strut rods who is advising NHRA tech to not legalize after market strut rods in stock? After all it's OK to have after market strut rods on a SS/MA car and not for a A/SA ???? Where is the common sense?

[69Cobra]

Exactly! I'm curious after looking at the entry list for Pomona and seeing all the brake strut rod cars that are pre entered, if they all are going to show up with rubber bushings, especially Calvert.