Adjustable Strut Rods - What's their function??

[bigmanjbmopar]

So we have fixed strut rods from the factory, several vendors mostly PST sell the adjustable strut rod. What is the advantages if any over stock? Should you use them with a stock suspension as an improvement feature or do you need to get all the other stuff like tubular upper a arms and LCA stiffening plates etc? Also what exactly is the adjustment you can do on these and has anyone here used these and can speak to these?

Description from PST -

Dramatically improve the cornering performance, traction, and steering response of your muscle car with PST's new Adjustable Strut Rods! Designed to positively locate the lower arm, these strut rods improve responsiveness and driver control. The adjustable design features 5/8" high articulation rod ends, CNC bent brackets, and lightweight TIG welded 7/8" tubing. Finished in a lustrous nickel-plated finish, these strut rods even look great standing still and push your performance to new levels.


Description from RMS -

Our tubular strut rods use a special pivot point to eliminate the flexing and bind of traditional bushings.The result is friction-free motion vertically, and no fore/aft flexing of the lower control arm, which causes hard to control dynamic alignment changes. These alignment changes cause the "wandering feeling" that's so common in older cars. Freeing up vertical motion allows faster weight transfer on the strip and a smoother ride on the street.

 

[WileE]

I'll offer a basic, condensed idea on it. On any conventional suspension, you have the spring load on either the upper control arm ( think Ford), or lower arm as in these Mopars. In addition to the spring load, the lower arm must locate the suspension. These only have the single point on the frame, unlike others that have 2 locating points at the end of the arm on the frame. Thus, the strut rod. The factory rubber bushing offers a softer ride, at the expense of precise arm location. The fore-aft movement at the wheel end of the arm affects the caster, and any aft movement is a detriment to any positive caster. A more firm strut rod & bushing aids the position of the lower arm. The kit that boxes the factory arm also aids to reduce the flex of the lower arm.

 

[426Hemiman]

I'll offer a basic, condensed idea on it. On any conventional suspension, you have the spring load on either the upper control arm ( think Ford), or lower arm as in these Mopars. In addition to the spring load, the lower arm must locate the suspension. These only have the single point on the frame, unlike others that have 2 locating points at the end of the arm on the frame. Thus, the strut rod. The factory rubber bushing offers a softer ride, at the expense of precise arm location. The fore-aft movement at the wheel end of the arm affects the caster, and any aft movement is a detriment to any positive caster. A more firm strut rod & bushing aids the position of the lower arm. The kit that boxes the factory arm also aids to reduce the flex of the lower arm.

Plus 1 on the above.

I would like to add:

The front suspension components are not blueprinted from the factory so there are deviations in the attachment points for the control arms. Also over the life of a car it will incur flexing and movement within the components of the suspension, frame and steering components. Thus the need for alignments over the life of a vehicle. The adjustability will allow you to ensure that the lower control arm to pivot bushing/pin is positioned at a 90 degree angle thus ensuring that there is no binding of this pivot point or undue stress/load placed upon it that would lead to premature failure.

 

[WileE]

Excellent point. The adjustable strut rod allows more precise compensation for all those variables.

 

[Kern Dog]

I like the idea but I think the main "selling point" is the ability to increase the caster angle. If the strut rod is adjusted to pull the outer edge of the control arm forward it has the same effect as tilting the top of the spindle/knuckle rearward. The wheelbase is stretched a slight amount by doing this.
I am concerned though that by cranking the adjustment too far, it will distort the lower control arm bushing, leading to early failure.

 

[Derwud]

I like the idea but I think the main "selling point" is the ability to increase the caster angle. If the strut rod is adjusted to pull the outer edge of the control arm forward it has the same effect as tilting the top of the spindle/knuckle rearward. The wheelbase is stretched a slight amount by doing this.
I am concerned though that by cranking the adjustment too far, it will distort the lower control arm bushing, leading to early failure.

I would not use them to make alignment corrections. I would say, they are adjustable to make up for factory tolerances and modifications. My secondary concern would be noise or vibration.

 

[MarPar]

 

[WileE]

I like the idea but I think the main "selling point" is the ability to increase the caster angle. If the strut rod is adjusted to pull the outer edge of the control arm forward it has the same effect as tilting the top of the spindle/knuckle rearward. The wheelbase is stretched a slight amount by doing this.
I am concerned though that by cranking the adjustment too far, it will distort the lower control arm bushing, leading to early failure.

Absolutely not. It is meant for reasons already stated.You DO NOT use this to "pull" the lower arm.

 

[bigmanjbmopar]

Ok got it from the horse's mouth, Thank you James even though you don't even know what you did lmao anyway here is the explination thanks to James at P-S-T


https://youtu.be/h41-9Uvgcsg

 

[Derwud]

James does Chevies, I don't trust him...

 

[Yatzee]

Lets be honest here. Unless your using non-compressable urethane bushings or solid aluminum bushings on the ends of the rods, the rubber bushings will compress with tension. It'll probably be the forward bushing that compresses first as you tighten the rod adjuster and it's length decreases. To me this seems self defeating unless the right bushings are used Did PST have a recommendation reguarding bushings?

 

[bigmanjbmopar]

I have no idea, was hoping some of you experts can get this clarified

 

[Kern Dog]

Absolutely not. It is meant for reasons already stated.You DO NOT use this to "pull" the lower arm.

By your tone, it seems that you are blaming me here. I am not at fault for anything so take your opinions elsewhere.

 

[WileE]

By your tone, it seems that you are blaming me here. I am not at fault for anything so take your opinions elsewhere.

What are you talking about ? Blaming ? For What ? I merely stated the incorrect way to get caster. But... you're right... I will take my opinions elsewhere.

 

[Cranky]

Well, the factory setup was for sure not by the blue print once the cars hit the assembly line. So how much deflection does the lower arm create when hitting bumps and during hard braking? A bunch! And 'pulling' the lower arm a bit forward for more caster is a very old trick and has been done for years, even with poly bushings. Exactly how much is ok depends a lot on the type of inner bushing used. Does a Polyurethane bushing compress? Sure it does but it depends on it's rating and there are many. What's the rate that's used for cars? You probably would have to contact the manufacturer for that one. Wanna know how much you can compress one? Throw it in a press and go at it. How much it compresses might surprise you . As for pulling the lower arm forward, 1/16th" probably won't do a thing to a poly bushing. Heck, 1/8th probably won't do anything either. Let's use a rubber one. Wanna get more roll out on the lights at the drag strip? Pull one side forward 1/4" and push the other side back 1/4". Some might feel a difference in how the car drives down a track with some dips and rises but most won't. Lower the air pressure some and you might even be able to leave on the 2nd bulb Not saying doing stuff like this is correct or good for long term driving, but.....I've had front end bushings wear out pretty fast just using stock factory parts and settings and had front ends last for a very long time using my own settings which were not even close to the factory numbers. I guess what I'm saying is whatever way you get your car to do what you want and it lasts isn't really the incorrect way so long as things are done with safety in mind. Our cars ain't rockets ships and the tolerance is pretty wide and what the factory prints for alignment specs doesn't always work so good on all the 66-67 Belvederes or 68-70 roadrunners that came off the assembly line. Keep in mind too what kind of tires were produced for these cars 40-50 years ago.

 

[WileE]

Just because something is done, or can be done, doesn't mean it's the right way. And we're talking street, not track. Back when these cars were barely used then, lazy mechanics would crank the struts to get caster.... And we would replace the premature worn bushings. YES, there's deflection engineered into the system, you don't remove it by compressing the bushings. There's a HUGE difference in load forces; once the shock of the load force has been absorbed, the geometry returns to its static position. Example, just a few years ago I was doing a k frame on someone's car, I noticed that the inside of the strut bushing was cupped, why ? Probably, there was not enough deflection in a compressed bushing, so when it hit a bump/ pothole the load force transmitted into the k frame, because there was no deflection remaining inside the strut bushing. I saw this 45 years ago, and again recently. I'll just keep my experience and opinions to myself. I apologize if I ruffled anyone's feathers.

 

[SureGrip]

Probably, there was not enough deflection in a compressed bushing, so when it hit a bump/ pothole the load force transmitted into the k frame, because there was no deflection remaining inside the strut bushing. I saw this 45 years ago, and again recently. I'll just keep my experience and opinions to myself. I apologize if I ruffled anyone's feathers.

I see no need for removing your opinion from this discussion. This has always been my take on it. The strut rod 'locates' the LCA. The factory LCA have a lot of flex in them. This can be resolved with stiffening plates, or stiffer bushings, but the main function of the strut rods is to absorb the beating the LCAs take. I suppose you can 'dial in' the LCA with the adjustable ones, but unless it's for track use, I don't see the use.

 

[Derwud]

The strut rod is there keep the lower arm straight, but in order to keep it compliant and reduce NVH they use bushings, great for 60's and 70's. If you want your Mopar to handle, compliance is not your friend.. Adjustable cause they have to be achieve a neutral set up for range of motion based on ride height...