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5/01/2014 3:09 PM  #1


Question about strut rods

I just bought some adjustable strut rods for my 66 convertible.  After looking at them I've gotten myself really confused by the information I have seen in the past and how it may apply to these new units.  So, I came here seeking enlightenment.

In the past, many people (on many boards) have stated not to use poly bushings with the strut rods because it causes the strut rod to break.  I had always assumed that this was because the rubber bushings reduced the shock load on the strut rod by increasing the time over which the shock load was imparted to the strut rod whereas the poly bushings more directly and immediately transferred the load to the strut rod, causing it to reach it's fracture point.

The strut rods I just bought have no bushings at all between the car frame and the strut assembly.  Further, they came with grade 5 bolts to attach the rod to the frame, the heim joint to the box that attaches to the frame, and to the lower control arm.  

Obviously, I want to avoid breakage.  I'm having trouble seeing how these adjustable units are any better, at least as far as breakage is concerned, than having an OEM strut rod attached by a poly bushing.  

If anyone can offer an explanation I'd love to be enlightened.  Math is OK too.

TIA


Founding Member of the Perpetually Bewildered Society
 

5/01/2014 4:15 PM  #2


Re: Question about strut rods

I like to use extreme examples to make an illustration: pretend that the bushings in the original struts were not rubber or poly, but steel.  Do you think the strut rod would move up and down if the rod and bushings were torqued to spec? Imagine the stress put on the strut rod as the suspension attempted to move up and down.  Rubber bushings deflect allowing the strut rod to move more or less freely in an up and down arc, and put a small amount of stress on the rod.   Poly bushings also allow some movement, but are stiffer and put more stress on the strut rod than rubber.

Now heim joints on the other hand offer essentially zero resistance to the up and down movement of the strut rod.  Remember, it's not the fore and aft movement that damages the strut rod, but the up and down.  A heim equipped strut rod can be bolted directly to the support, and offer essentially zero fore and aft movement (no rubber or poly to compress), and virtually no resistance up and down.

John

Last edited by John (5/01/2014 4:16 PM)

 

5/01/2014 4:38 PM  #3


Re: Question about strut rods

Now I'm a bit confused too.

John, are you saying that the heim joint units CAUSE breakage, or prevent it?

Seems to me that the vertical travel of the heim joint, with the horizontal flex being eliminated would make for a stronger, more durable unit; you're not stressing the strut rod by flexing it any more with that setup, right?

(as opposed to the regular connector, which requires rubber or plastic to 'slop around' and take up the flexing)

Or have I got this wrong too?  Vertical travel should ONLY be a problem with the 'normal' setup - not with the heim joint unit?


"Whatever you are, be a good one." - Abraham Lincoln
 

5/01/2014 4:47 PM  #4


Re: Question about strut rods

Technomancer wrote:

Now I'm a bit confused too.

John, are you saying that the heim joint units CAUSE breakage, or prevent it?

Seems to me that the vertical travel of the heim joint, with the horizontal flex being eliminated would make for a stronger, more durable unit; you're not stressing the strut rod by flexing it any more with that setup, right?

(as opposed to the regular connector, which requires rubber or plastic to 'slop around' and take up the flexing)

Or have I got this wrong too?  Vertical travel should ONLY be a problem with the 'normal' setup - not with the heim joint unit?

Simply Put... Heim Joint = GOOD  http://cdn.boardhost.com/emoticons/grin.png

 


"The OLDER I Get....The FASTER I Was..."
 

5/01/2014 5:21 PM  #5


Re: Question about strut rods

Captian Obvious here...I believe those stock strut rod bushings do more than just help adjust for the up an down motion that is incurrend by the wheel moving up and down, hence the lower control arm moving up and down, hence making the strut rod need to move up and down, and provide some flex for that to happen....

Those bushings have an affect on acceleration and braking, which I must assume is the reason they are on both sides of the frame.  Durng acceleration the front strut rod bushing compresses to help limit the rearward motion of the lower control arm.  During braking, the the rear strut rod bushing compresses to help limit the forward movement of the lower control arm.   With this being said,   a heim joint is creating a pivot point to allow free up and down travel with no resistance, yes.  But i think it has a  huge down side,  in that all the forces of acceleration and braking now are all on that single pivot point heim joint.  So I vote no on the heim joint,  and yes to a new pair of stock rubber strut rod bushings.

Last edited by MarkinSC (5/01/2014 5:23 PM)


GET HER DONE BULLETBOB!!! ..
 

5/01/2014 5:28 PM  #6


Re: Question about strut rods

With the 'fore and back' play that the rubber joints allow, that's going to change toe during hard braking, bumps, all sorts of things though too.

Seems to me that the heim joint unit would offer more precision, but also transmit more vibration.  

So maybe the heim joint setup is better for racing apps, versus the rubber stuff for daily drivers?


"Whatever you are, be a good one." - Abraham Lincoln
 

5/01/2014 6:19 PM  #7


Re: Question about strut rods

A whole lotta folks have switched to the rod end style of strut rods. Most rave about the difference in the ride. I have not read of anyone switching back to the oem rubber.


Bob. 69 Mach 1, 393W, SMOD Toploader, Armstrong  steering.
 

5/01/2014 6:57 PM  #8


Re: Question about strut rods

rpm wrote:

A whole lotta folks have switched to the rod end style of strut rods. Most rave about the difference in the ride. I have not read of anyone switching back to the oem rubber.

I have strut rods with a solid connection and a ball for movement (TCP).  Handling is much improved.  However ride is much rougher as now there is no fore & aft movement when hitting a bump.  now all that bump energy is transferred directly to the chassis along with more noise and feel to all parts of my body.  BTW: pebbles are bumps too.  You will feel all of them.  Not just pot holes.

Want better handling?  There is a price. 

I am getting along in years and the old bum likes some softness, so I am thinking about reinstalling my original, stock, strut rods for the smoother ride.
 


Original owner - 351w,T-5, 4whl disks, power R&P
 

5/02/2014 5:19 AM  #9


Re: Question about strut rods

Technomancer wrote:

John, are you saying that the heim joint units CAUSE breakage, or prevent it?

Prevent! 

I used the extreme example of a steel bushing to demonstrate how more stress is put on the rod the stiffer the bushing is.

Picture four strut rods bolted solidly to a wall.  One having stock rubber, one having poly bushings, one having steel bushings (extreme example to prove a point) and the last with a heim joint.  Now  imagine grabbing the end of each and pushing them up and down.  The rubber bushed rod would move up and down with a fair amount of resistance, the poly one would also move but with more resistance than the rubber.  The steel bushed one of course wouldn't move at all and would snap if at it's weakest point if forced to move.

The heim jointed rod would actually be hanging downward off the wall because it's a spherical bearing offering insignificant friction.  Moving it by hand could be done with a finger.  So heim joints allow full unrestricted up and down movement of the strut rod.  And because there's no rubber or poly bushing, heim joint equipped rods also won't contribute the fore and aft flex under accel and braking that rubber or poly parts do.  Win-win..

Properly built for strength, there is no down side to heim equipped strut rods except for some anecdotal stories of harshness because the NVH isolation properties of the rubber is lost, but others say there is no downside from a ride perspective.

John

 

5/02/2014 6:06 AM  #10


Re: Question about strut rods

John wrote:

Technomancer wrote:

John, are you saying that the heim joint units CAUSE breakage, or prevent it?

Prevent! 

I used the extreme example of a steel bushing to demonstrate how more stress is put on the rod the stiffer the bushing is.

Picture four strut rods bolted solidly to a wall.  One having stock rubber, one having poly bushings, one having steel bushings (extreme example to prove a point) and the last with a heim joint.  Now  imagine grabbing the end of each and pushing them up and down.  The rubber bushed rod would move up and down with a fair amount of resistance, the poly one would also move but with more resistance than the rubber.  The steel bushed one of course wouldn't move at all and would snap if at it's weakest point if forced to move.

The heim jointed rod would actually be hanging downward off the wall because it's a spherical bearing offering insignificant friction.  Moving it by hand could be done with a finger.  So heim joints allow full unrestricted up and down movement of the strut rod.  And because there's no rubber or poly bushing, heim joint equipped rods also won't contribute the fore and aft flex under accel and braking that rubber or poly parts do.  Win-win..

Properly built for strength, there is no down side to heim equipped strut rods except for some anecdotal stories of harshness because the NVH isolation properties of the rubber is lost, but others say there is no downside from a ride perspective.

John

 
John,  you say " heim joints allow full up and down movement of the strut rod".  IS that what is really desired?    The lower control arm bushing and the strut rod are supposed to work together to allow the lower control arm to move up and down, BUT, not to allow it to freely go up and down without any resistance, and also to create a "center" or "resting" position for the lower control arm, and to also help with the fore and aft movement of the lower control arm by limiting this movement, while at the same time allowing it at a very slow rate using rubber bushings to absorb the movement and using the rubber bushings to absorb the shocking motion.

The lower control arm is supposed to go up and down with the wheel..yes,  but not supposed to allow it travel a huge distance up or down, and definetly not supposed to allow the lower control arm to go up and down freely without any resistance. There is a lower bushing in the lower control arm. You tighten that bolt with the weight of the car on the lower control arm to create a "center" or "resting" position of the lower control arm.  The bushings  have rubber surrounding the sleeve to PREVENT the control arm from moving up and down freely without resistance, and also prevent the control arm from moving too far up and too far down. The rubber flexes and twists and is supposed to help "center" or "return" the lower control arm to its original level position while at the same time slowly allowing it to  go up and down when the rubber within the bushing stretches in either direction.  The rubber is not supposed to stretch too far either or it won't stop the lower control arm from traveling too far UP or too far down.   So if the lower control arm and the strut rod are supposed to work together to perform that functionality, WHY would you want the strut rod to move up and down freely with no resistance?  The strut rod is supposed to help the lower control arm bushings with that function.  Now you are putting that lower control arm bushing under stress, and will probably rip the rubber in those bushings alot sooner. 

to me the lower control arm bushing and the strut rod bushings work together to also do another thing,  which is to also help with the fore and aft movement of the lower control arm during acceleration and braking.    YOU said,  that a solid steel bushing would snap the strut rod becaus it wouldn't allow it to move at all.  So it makes sense that it is SUPPOSED to flex forward and rearward in a very small amount, and its supposed to do it SLOWLY and not RAPIDLY. Thats where the rubber comes in on the strut rod bushings.

Last edited by MarkinSC (5/02/2014 6:09 AM)


GET HER DONE BULLETBOB!!! ..
 

5/02/2014 6:21 AM  #11


Re: Question about strut rods

Ford had the solution in 1928.  Those of us familiar with the Model A will recall that the front wishbone...a "V" shaped, one-piece trailing rod that located both sides of the beam axle...pivoted from a mount under the transmission.  This formed a triangle with the axle that alowed the axle to move up and down easily at each, or both, wheels but eliminated fore and aft movement.
The rear point of the triangle...the point of the "V"... had a ball about 1 1/2 inch in diameter that had a replaceable hollow rubber ball, with 1/8" thick skin, covering it.  This mounted in a two-piece socket and absorbed the extreme element of harshness from the road shock but allowed necessary movement.

For what its worth, the same system was used on all Ford passenger cars throuth 1948 so it mush have worked a little.

Hmmmm, may have to do a little codgetating here.  I hate Heim joints in street suspension but I really want to have adjustable trailing arms (strut rods).  A ball and rubber socket might give the best of both worlds by eliminated most, but not all, of the allowable compression of the stock bushing while allowing fore and aft adjustment.

'Nuther machine project...while I am at it.

BB

Last edited by Bullet Bob (5/02/2014 6:26 AM)


"you get what you pay for, good work isn't cheap, and there are NO free lunches...PERIOD!"
 

5/02/2014 6:49 AM  #12


Re: Question about strut rods

John wrote:

I like to use extreme examples to make an illustration: pretend that the bushings in the original struts were not rubber or poly, but steel.  Do you think the strut rod would move up and down if the rod and bushings were torqued to spec? Imagine the stress put on the strut rod as the suspension attempted to move up and down.  Rubber bushings deflect allowing the strut rod to move more or less freely in an up and down arc, and put a small amount of stress on the rod.   Poly bushings also allow some movement, but are stiffer and put more stress on the strut rod than rubber.
John

Interesting - so you're saying that the breakage due to poly bushings is caused by bending forces, not tension forces (tension forces would be caused by, for example, a tire hitting a pothole or other obstruction that causes the wheel, tire and suspension to "stop" briefly while the rest of the car continues on it's way).  I'd not thought of that.  The photos I've seen of broken strut rods did not appear to have any bending to the broken ends - they were just separated as one would expect to see if the steel failed due to being stretched too far too quickly by a large tension load.  That's why I was concerned about not having the rubber bushing where the new units attach to the car, since it seems like the rubber bushings would cushion and absorb some of the impact to the strut rod, much as an airbag cushions and absorbs the impact of a person riding in a car that suddenly stops due to a collision.  Guess I should have explained that better.

The type of links used in the past as described by Bullet Bob would put those links in compression if a tire hit a large obstruction, which would tend to bend the link rather that causing a large stretching force that could break it.  So for the Mustang I am still concerned about the tension type of load, the way the adjustable unit is attached to the frame of the car and breakage due to a large tension load on the assembly.

As always, I'm learning.   Thanks again!

Last edited by John Ha (5/02/2014 7:57 AM)


Founding Member of the Perpetually Bewildered Society
     Thread Starter
 

5/02/2014 7:59 AM  #13


Re: Question about strut rods

http://i652.photobucket.com/albums/uu247/FYIFORD/Mach1_Ron/snapped_strut.jpg


From one manufacturers web...

Strut rods (technically called brake reaction strut rods) attach to the lower control arm and control the tire motion fore and aft in the fender well. Standard bushings deflect during acceleration and braking allowing the tire to no longer remain consistent in the fender well. This movement slightly changes the wheelbase; front-end alignment is directly affected and the cars stability suffers. Stiffer strut rod bushings are one way of reducing the fore and aft movement, however to stiff a bushing can cause the strut rod to break.
Their unit comes with a clevis, a spherical rod end, adjuster, and attachment rod to the lower arm. The stock rubber bushing and strut rod is eliminated.
 

Last edited by Mach1_Ron (5/02/2014 8:02 AM)


"The OLDER I Get....The FASTER I Was..."
 

5/02/2014 9:12 AM  #14


Re: Question about strut rods

Mach1_Ron wrote:

Their unit comes with a clevis, a spherical rod end, adjuster, and attachment rod to the lower arm. The stock rubber bushing and strut rod is eliminated.
 

Right, that's what mine has too.  My concern is the bolt that attaches the clevis to the frame of the car, and the other "stuff" downstreem (the spherical end, adjuster, link to the LCA.  

Mach1_Ron wrote:

... however to stiff a bushing can cause the strut rod to break. 

If too stiff a bushing is bad, isn't no bushing at all much, much worse?   With no bushing the loads are going to be imposed on the bolt that attaches the clevis to the frame, the clevis, etc. directly with no cushioning effect of a bushing.  This, in my mind, leaves those components much more susceptible to breakage.

What if one were to use a longer bolt to attach the clevis to the frame, install a rubber bushing and cupped washer on the front side of the frame, then install the nut?  It seems to me that would let the bushing protect the bolt, clevis, etc. from large loads that would otherwise break them, but still allow the freedom of motion that the spherical joint provides.

Thoughts?

Last edited by John Ha (5/02/2014 9:19 AM)


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     Thread Starter
 

5/02/2014 10:04 AM  #15


Re: Question about strut rods

The difference is the spherical bushing can MOVE.  The poly bushings cannot move, and will not allow the strut rod to move, hence the breakage.

You also must consider the strut rod bushing also acts as the front lower control arm bushing.  The strut rod and lca are bolted together and form a rigid assembly that both have to picot in the same plane.  Every move the LCA bushing makes, the front strut rod bushing must also make.  Spherical rod ends work fine for this, but you must keep an eye on them for wear and be sure they stay torqued down.  They can be installed incorrectly, and that would put them in a bind as the LCA pivots.  You must be sure they are clocked just right so they cannot get in a bind.  If they do, they will snap just like a strut rod with a poly bushing.

Another consideration, and this goes contrary to what the racer guys want to have, is a rubber donut type bushing will also dampen any oscillation of the LCA, kind of acting as a mini shock absorber trying to keep the lca in a static position.

Bottom line is it is not just a fore-aft type connection for braking and accelerating.  It is also the front pivot bushing for the entire lower control arm. 

I have the rod ends on my car and they did make a difference in how the car stops and corners, holding the wheel in position without undesired changes in caster as the LCA pivots.


Money you enjoy wasting is NOT wasted money... unless your wife finds out.
 

5/02/2014 10:15 AM  #16


Re: Question about strut rods

Rubber bushings only work if they accept loads in both directions.  Having a bushing on only one side still hard mounts the strut to the body.  I think there seems to be confusion between axial loads (compression and tension) on the strut rod versus bending moments.  The compression and tension loads imposed by braking and positioning of the lower control arm during turns primarily are well within the design of a heim joint or spherical joint system.  The heim joint keeps the lower control arm in position in the fore-aft direction and more easily permits lower control are rotation for up and down movement of the spindle.  The ride height ideally is determined by the springs and not any bushings so bushings are not intended to be used to maintain ride height and in many cases the bushings need to be tightened only after ride height is established so that there are no static loads on the bushings themselves.  The bushings provide isolation from the shock loads into the frame but they do not prevent the suspension components from sensing the shock loads. When you hit a pot hole the axle senses this.  The bushings lower the shock that reaches the body.  When you change out an entire suspension including springs and shocks the rough ride may be attributed to the heim joint strut rods but in fact any of the other changes may be responsible for teeth-knocking response.  The best test would be to evaluate a stock suspension and only change to the adjustable heim joint strut rods and then evaluate how bad it gets.  The biggest reason that I built my own adjustable strut rods is for adjustment.  I want to get some additional camber to work with the Borgesson steering - it likes more caster in many cases to get improved return-to-center performance.

Another improvement from the heim joint strut rods in in bending or moment loads.  As stated above, when the spindle moves up and down a moment is applied to the strut rod at the bushings.  The bushings provide some resistance to this bending moment and this in racing applications diminishes the performance and response of the suspension.  The poly bushings provide improved tension and compression performance but have even greater resistance to the bending moments.  The picture of the broken strut rod above has been shown in many forums and it is difficult to know how many cases have actually occured.  One picture on the internet makes it true but we don't know if the strut rod was compromised (cracked or a stress riser from corrosion) well before the poly bushings were installed - I suspect failure was imminent either way.

If I wanted a smooth ride and was happy with my current alignment I would stick to good rubber bushings.  In practice, the rubber bushings probably need to be replaced every five years due to deterioration of the rubber.  The fact that many are now manufactured overseas where controls on the elastomers are not so great the replacement interval should probably be shorter.  If you have 50 year old bushings in your car you may say hogwash but if you take them out and compare them to new you will probably find them to be compressed and hard and probably not much weaker than a poly bushing.  People have been satisifed with the rubber bushings for years.  I personnaly would avoid poly as I don't think they offer any improvement versus the higher bending loads on the strut rods.

If you need additional adjustment and/or a more responsive suspension then the adjustable units will work for you and will not produce higher stresses because they infact will lower due to their essentially zero stiffness in the bending moment at the frame attachment point.

Sorry for the long-winded response but I hope it makes sense.  It all boils down to what you want to do.

 

5/02/2014 11:12 AM  #17


Re: Question about strut rods

Just for reference... The day I intalled my rod ends, I did not change anything else.  Hard to believe it, but the car actually felt smoother.  It did not appear to have any clang-bang type action going on at all, and I put it through every type of scenario I could think of to punish the strut rods.  I was very surprised.

I did NOT find that the case when I installed roller bearing coil spring perches.  I did not notice any dofference at all with those.


Money you enjoy wasting is NOT wasted money... unless your wife finds out.
 

5/02/2014 11:19 AM  #18


Re: Question about strut rods

Thanks GPatrick!

I hoped to increase my caster just a bit to improve the driving quality.  But after I got the units I started thinking about what the bushings do, what others have said stiff bushings do, and probably over-thought it to the point that I was overly worried about an increased risk of loss or damage to myself and/or my car because there were no bushings.  

Some of that feeling was promoted by the "I've sold XXX of these and none have failed" response when I asked the vendor about this.  That suggested to me that there was not any real design work (involving loads analysis, materials and construction method choices based on the results of those analyses, etc.) done when these were designed.  That, in turn left it to me to do "due dilligence" to be reasonably confident that I was not doing something really dumb by installing them.

I guess I'm more comfortable now - at least your response provided some technical facts that help me understand how things work a little better (I was a spacecraft systems integration engineer in a former life but don't have a good grasp of all the nitty gritty stuff that a structural or loads engineer does - obviously). 

Thanks all!

Last edited by John Ha (5/02/2014 11:24 AM)


Founding Member of the Perpetually Bewildered Society
     Thread Starter
 

5/02/2014 11:58 AM  #19


Re: Question about strut rods

 

John,  you say " heim joints allow full up and down movement of the strut rod".  IS that what is really desired?    The lower control arm bushing and the strut rod are supposed to work together to allow the lower control arm to move up and down, BUT, not to allow it to freely go up and down without any resistance...

From what I understand, the purpose of the strut rod is only to locate the lower control arm and prevent forward and aft movement of the LCA during braking, accel, and during wheel impacts.  Unfortunately, strut rods must move up and down because the suspension does.  Having them resist the up and down movement does nothing to help ride or handling.  The less resistance they offer to the movement of the suspension, the better.  Let the springs and shocks determine the resistance and damping of the suspension.  In a perfect world, there'd be no friction in a suspension system.


The lower control arm is supposed to go up and down with the wheel..yes,  but not supposed to allow it travel a huge distance up or down, and definetly not supposed to allow the lower control arm to go up and down freely without any resistance. There is a lower bushing in the lower control arm. You tighten that bolt with the weight of the car on the lower control arm to create a "center" or "resting" position of the lower control arm. 

The center or resting place of the LCA is not determined by the strut rod, but by the weight of the car and the rate of the coil spring.  You can unbolt the LCA, bounce the car up and down, and it will act pretty much like it did with the strut rod, other than the reduction in resistance offered by the strut rod bushings as they're forced to deflect.  Of course, without the strut rod in place, the LCA will be flopping fore and aft if the car is accellerated or braked. 

Also, the rubber bushed strut rod will offer little resistance to movement right at it's natural center.  The resistance it offers grows exponentially as the bushings are forced to deform when the rod is forced to follow the LCA.  I believe that the point of failure occurs when the rod is at the extreme ends of it's travel when bending forces are at their highest.

Rubber bushings are a comprimise.  They locate the strut rod solidly to the support, but must also give as the rod is forced to follow the LCA.  A heim joint will solidly locate the rod to the support to limit fore and aft movement, but not interfere with the natural up and down movement of the suspension.


John
 

Last edited by John (5/02/2014 12:25 PM)

 

5/02/2014 12:13 PM  #20


Re: Question about strut rods

John Ha wrote:

Interesting - so you're saying that the breakage due to poly bushings is caused by bending forces, not tension forces (tension forces would be caused by, for example, a tire hitting a pothole or other obstruction that causes the wheel, tire and suspension to "stop" briefly while the rest of the car continues on it's way).  

I guess we'd have to do some computer modelling to find out exactly what exactly happens, but it seems that there would be a lot more force in the bending moment than tension (I guess we can eliminate compression) if the strut rod bushing is too stiff or restrictive.  Unless a wheel hits the queen mother of all potholes, it seems that most of the energy of the impact not actually absorbed by the tire is transmitted upward through the control arms and into the spring and shock, not pulling on the strut rod.

John
 

 

5/02/2014 1:24 PM  #21


Re: Question about strut rods

John wrote:

 

John,  you say " heim joints allow full up and down movement of the strut rod".  IS that what is really desired?    The lower control arm bushing and the strut rod are supposed to work together to allow the lower control arm to move up and down, BUT, not to allow it to freely go up and down without any resistance...

From what I understand, the purpose of the strut rod is only to locate the lower control arm and prevent forward and aft movement of the LCA during braking, accel, and during wheel impacts.  Unfortunately, strut rods must move up and down because the suspension does.  Having them resist the up and down movement does nothing to help ride or handling.  The less resistance they offer to the movement of the suspension, the better.  Let the springs and shocks determine the resistance and damping of the suspension.  In a perfect world, there'd be no friction in a suspension system.

The strut rods are bolted to the lower control arm like MS says, so the strut rod needs to go up and down with the lower control arm. It has no choice but to go along for the ride.  Its primary purpose is the fore and aft movement of the lower control arm, so there wil be forces on the strut rod to go forward and backward,  as well as up and down since its bolted to the lower control arm.  Its a suspension system, and all the components are designed to work together.  If the strut rod BUSHINGS are no longer helping to create some resistance to the up and down movement, then more of that job is falling onto the other components such as the lower control arm bushing, springs and shocks. 

The lower control arm is supposed to go up and down with the wheel..yes,  but not supposed to allow it travel a huge distance up or down, and definetly not supposed to allow the lower control arm to go up and down freely without any resistance. There is a lower bushing in the lower control arm. You tighten that bolt with the weight of the car on the lower control arm to create a "center" or "resting" position of the lower control arm. 

The center or resting place of the LCA is not determined by the strut rod, but by the weight of the car and the rate of the coil spring.  You can unbolt the LCA, bounce the car up and down, and it will act pretty much like it did with the strut rod, other than the reduction in resistance offered by the strut rod bushings as they're forced to deflect.  Of course, without the strut rod in place, the LCA will be flopping fore and aft if the car is accellerated or braked. 

I never said that the center or resting place of the LCA was determined by the strut rod. I  said that its determined by the Lower control arm bushing being tightened with the weight of the car on it.  If you don't beleive me, jack the car up in the air, and tighten the lower control arm bushing bolts while the lower control arms are dangling down due to gravity.  then put the car back on the ground.  You will see that the lower control arm is not in its proper center or resting place.    The springs will affect the height of the car.  ( lowering springs,etc.)  The springs will also affect the rate of suspension travel.  Shocks dampen the movement of the springs.  

Also, the rubber bushed strut rod will offer little resistance to movement right at it's natural center.  The resistance it offers grows exponentially as the bushings are forced to deform when the rod is forced to follow the LCA.  I believe that the point of failure occurs when the rod is at the extreme ends of it's travel when bending forces are at their highest.

Rubber bushings are a comprimise.  They locate the strut rod solidly to the support, but must also give as the rod is forced to follow the LCA.  A heim joint will solidly locate the rod to the support to limit fore and aft movement, but not interfere with the natural up and down movement of the suspension.




John
 

 


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5/02/2014 2:55 PM  #22


Re: Question about strut rods

MarkinSC wrote:

If the strut rod BUSHINGS are no longer helping to create some resistance to the up and down movement, then more of that job is falling onto the other components such as the lower control arm bushing, springs and shocks. 

It's not the bushing's job to add resistance, control, or damping to the suspension.  Unfortunately, they do have an effect, but it's by and large unintended and a function of the cost versus performance decision that bean counters must make. 

I never said that the center or resting place of the LCA was determined by the strut rod. I  said that its determined by the Lower control arm bushing being tightened with the weight of the car on it.





Oops, missed that.  Read your reply too quickly.  Sorry.


If you don't beleive me, jack the car up in the air, and tighten the lower control arm bushing bolts while the lower control arms are dangling down due to gravity.  then put the car back on the ground.  You will see that the lower control arm is not in its proper center or resting place.  

Sure, but that's just another unintended consequence of using rubber bushings instead of bearings, and is really a demonstration of the limitations of the original design (and actually exposes the Mustang's economy car roots).   In addition to putting heim joint strut rods on my car, I'm also doing a spherical bearing in my LCA because I don't want any drag/resistance/friction in my suspension when I can easily eliminate it, plus the spherical bearing will allow the LCA to be moved forward with the strut rod adustment for increasing caster without causing LCA binding.  The spherical bearing in the LCA will completely eliminate any deleterious effects the original style bushing will have on the suspension (and the LCA can be torqued down even when it's hanging down unloaded).

John

Last edited by John (5/02/2014 3:01 PM)

 

5/02/2014 3:57 PM  #23


Re: Question about strut rods

When is someone going to come up with roller sway bar bearings, and heim joint rods to connect the sway bar to the control arm?  http://cdn.boardhost.com/emoticons/confused.png
http://cdn.boardhost.com/emoticons/confused.png
http://cdn.boardhost.com/emoticons/confused.png


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5/02/2014 4:16 PM  #24


Re: Question about strut rods

John wrote:

MarkinSC wrote:

 
 

  I'm also doing a spherical bearing in my LCA because I don't want any drag/resistance/friction in my suspension when I can easily eliminate it, plus the spherical bearing will allow the LCA to be moved forward with the strut rod adustment for increasing caster without causing LCA binding.  The spherical bearing in the LCA will completely eliminate any deleterious effects the original style bushing will have on the suspension (and the LCA can be torqued down even when it's hanging down unloaded).

John

Where are these spherical bearings and how hard is it to install them?! Sounds like a great solution for more caster adjustment.
6s6

Last edited by 6sally6 (5/02/2014 4:17 PM)


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5/02/2014 4:34 PM  #25


Re: Question about strut rods

Opentracker is one source.  The install is fairly straight forward but - you have to remove the old bushings and use a holesaw to increase the diameter for the revised bearing housing.  Welding is tricky to keep it round but from there on out it installs like a stocker.  Mine did not end up round by the way.  A brake hone was required to clean up my mess.   I started wtih aftermarket LCA's from Raybestos and I think the bearing kit install actually works a little better with these because they are thicker and wider than stock units at the bushing.  http://www.opentrackerracingproducts.com/diylowerarm/

 

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