Building adjustable strut rods for your early Mustang is easier than you might think

"The step by step process of fabricating heim type adjustable strut rods for an early classic Mustang"

What is the benefit of adjustable strut rods?
Through the course of my restoration project, I have done extensive research into Mustang suspension and ways to improve it.  Through this research, I have learned that adjustable strut rods are an obvious choice as a means to improve suspension and handling. To understand why they are so effective, you must first comprehend the function of the strut rod in a classic Mustang.  The strut rod is there to stabilize the lower control arm in a fixed position that  prevents its movement forward and aft, but still alows it to travel vertically with suspension compression and decompression. The stock system is designed so that, during regular driving, the rubber bushing gives, allowing vertical travel as the lower control arm moves up and down.  The give in the bushings, unfortunately, has a negative side effect of unwanted movement, they compress and stretch during braking and acceleration. The result of the compression and stretching of the rubber bushings is an increase and decrease in the length of the strut rod. As the strut rod increases and decreases in length, the lower control arm is not held fixed and can move forward and aft a small amount, which puts the alignment in a constant state of change during driving. One option to remove the compression and stretching of the stock rubber bushings is to replace them with polyurethane bushings. The polyurethane reduces the movement of the strut rod, 
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which eleviates the issue of compression and stretching, however, it has the unfortunate consequence in that it increases the effort required for normal strut rod  movement during suspension travel and puts far more strain on the strut rod than it was ever designed to handle.  I have seen many times where people have bent or broken their stock strut rods by replacing the rubber bushings with polyurethane.

With negative side effects from both rubber and polyurethane, the challenge is to have a joint that freely moves vertically so as to not overtask and damage the strut rod, but is also fixed in such a way that it cannot shift forward or aft. This can be easily accomplished by using a heim joint at the bushing end of the strut rod.  An added benefit of a heim joint system is that by having two threaded ends with opposite thread directions, one on the heim joint and one at the base of the strut rod, you can use a threaded connecting tube and make the strut rods adjustable for an easier and more fine tuned alignment.

10/09/12 The original web site I created describing in detail how to make these adjustable strut rods used a cast steel part at the frame.  However the company that sold the cast steel parts has switched to a cast iron part which I do not feel is up to the task of strut rods.  I am working on making another part work and will repost the info on this page once I have updated it.  consiquently I do not recomend using the cast clevice.

Adjustable strut rods are such  a popular and effective way to improve Mustang suspension and handling that there are many aftermarket performance part manufactures producing them  and they are selling for prices of  $300.00 a pair or more.  I found this cost to be quite high, especially when very few fabrication skills and tools are required to make a set at home.  The following is the process I used to build a set of adjustable strut rods for my 1964 & 1/2 Ford Mustang.  The process will work for later year Mustangs, as well as Falcons and Cougars but measurements will be required to account for changes made in various models and years, but  the process and basic concept is the same for all vehicles utilizing this style of strut rod in the suspension. 

At first, building a set of adjustable strut rods at home seemed relatively straight forward.  The only obstical that needed to be overcome in building  them was the frame mounting point.  In the aftermarket and in home garages, there have been many solutions to the mounting issue, These solutions have included drilling mounting holes through the side walls of the frame and running a bolt directly through it with spacer sleeves on either side of the heim to center it,  fabricating a welded together bracket that mounts to the original bushing holes and attaches to the heim, and milling out or casting a solid one piece unit.  These are all fine options with their own pros and cons.  I, personally, am not fond of the idea of drilling holes through the supporting rails.  The main issue I see with this option is that it would be very difficult to get a good straight hole drilled through the rail while it is still under the car.  For me, the welded bracket seemed like a much better way to go, but I had reservations doing the welding myself, being that  I wanted to make sure that the piece would  handle the stress that would be placed upon it.  All these factors forced me to put my adjustable strut rod project on hold, with the intent to eventually have a set of brackets fabricated at a local machine shop.  The project was revived  when I was informed of a company that had a clevis that would be perfect for my application.  This company sold a cast steel threaded rod clevis that has a load capicity of 4250 LBS. (part # RC-05) Its dimentions are such that once a bolt has been run through it and a nut placed on the bolt and torqued down, the assembly fits perfectly up between the rails at the strut rod mounting point.  The distance between the eyes on this clevis is 3/4", which is perfect for a 5/8" heim joint by itself and, with a little modification ,the opening can be widened to accomodate the heim with two rod end seals, one on each side.  Finding this piece gave me everything I needed to finish the project.  The following is the process I used  to fabricate adjustable strut rods at home.  NOTE: 12/12/11 I recently received an email from some one who had one of these rod ends shear.  It was most likely a bad casting but just something I figured I would pass on. The strut rods on my car have been there for over 7 years with out issue.

Parts needed: Quantity
Source Part #
Sum Total
stock strut rods pair
your car
could purchase new $0
5/8" left hand thread heim joints 2
Speedway Motors
1750706
$25.90
1/2” I.D. and 5/8” O.D. bronze bushings 2
Hardware Store
1" long
$4.50
10" long 5/8" swegded tubes 2
Speedway Motors 91034258-10
$13.90
5/8" rod end seals
4
Speedway Motors 91001504
$11.95
1/2" grade 5 bolts
2
Hardware Store 3" long $2.20
1/2" locking nuts 2
Hardware Store all metal $2.40
spacer rings cut from steel pipe 2
Hardware Store scrap or nipple
$0
washers with a 1.125" I.D. and 2.5" O.D 2
Hardware Store grade 5
$1.90
washers with a 7/16" I.D. and 2.5" O.D. 2
Hardware Store or fabricate
$0
7/16" grade 5 bolts 
2
Hardware Store 1&1/4" long $1.00
7/16" locking washers 2
Hardware Store grade 8
$.16
5/8" jam nuts with  right hand thread
2
Speedway Motors 1756046-RH
$3.45
5/8" jam nuts with  left hand thread 2
Speedway Motors 1756046-LH $3.45
Spacer washers
2
Hardware Store custom fit
$.18



Total Cost
$107.17

Tools required for the project:
Metal cutting saw, grinder, die grinder with cut off wheel and small conical grinding stone, angle grinder, calipers, 5/8" fine thread die, flat file, and a rat tail file.


Threaded rod clevis, the part that makes it all possible.

Stock strut rod with rubber bushings  on one end.

Stock strut rod being cut at 8.5" so that it can be thread
Process:
The first step is to begin by modifing the stock strut rods.  As with any modification to a stock used part, it is extremely important that you are beginning with a sound componant with no obvious wear or major defect.  In the case of strut rods, you want to look for extreme bending or cracks.  Once you have determined that your strut rods are a solid platform from which to build a modified part, you can begin by cutting them.  In the case of my application, I cut them to a length of 8.5”, measured from the lower control arm end.  I recommend taking your own measurements and determining where you want to cut the strut rod, based on the length of the swegded tube you chose to use. I am running an aftermarket 1” sway bar and was concerned about clearance issues, so I chose to use a 10” swegded tube so as to maximize clearance and locate my jam nuts as far away from the sway bar as possible.  After the strut rod has been shortened, about 2 & 1/2" of the rod needs to be turned down to 5/8” and threaded.  The reason that the strut rod is not left at the 3⁄4” thickness and simply threaded at that size is that, by doing so, there becomes clearance issues with the larger 3/4" swegded tube and corresponding larger heim joint.  There is no real concern about removing metal from the strut rod.  The heim joint frees up the strut rod's movement and reduces pressure on the rod.   5/8” is large enough considering the new freedom of motion. There are two ways to get the strut rod to the required 5/8” size.  The first is to use a lathe.  If you have your own or access to one, you can turn it down to the correct size.  If you do not have access to a lathe, you can take it to a local machine shop and have them turn it down and thread it for you.  Option two, and what I did, is to use an angle grinder and cut an octagon shape into the rod.  This is a tedious process that takes lots of double-checking and patience, but is very effective and only costs your time.  Start by placing the strut rod on the floor or bench with one of the flat sides down.  Hold the rod firmly against the floor or bench and use an angle grinder to flatten the up side until the flat stripe measures 3/8” wide.  You then flip the strut rod over and do the same thing on the other side.  Once both sides have been cut, take a thickness measurement between the two flat sides.  If the thickness is greater than 5/8”, continue taking a small amount of metal from both sides until the thickness is slightly greater than 5/8”.  You can then turn the strut rod on its side and repeat the earlier steps so that you are left with a 5/8” square rod.  The same technique is then used to cut the 4 corners of the rod, so that you now have a 5/8” thick piece of octagon rod.  A flap disc can then be used on the angle grinder to round off the 8 corners of the octagon to convert it to a round 5/8” rod.  The strut rod is now cut to size and can be threaded to 5/8" fine thread.  CAUTION; as you are grinding do not let the rod overheat!! You want to retain its original temper.  Also, it is very important to take small amounts of metal off at a time and measure often so that you do not remove too much metal.  I cut mine down to .65” and used the threading die to remove the remaining width as it cut in the threads.  When cutting threads it is important to use a quality die, lots of cutting oil, and to take about 1/16 of a turn forward and then a half turn backward to constantly clean the new threads.  If you do not take small bites and constant back turns, you will break the tips of the threads off as you are making them. Now that the strut rod has been sufficiently modified, we can turn our attention to the other end of the assembly and modify the heim joint.

Please note: not all heim joints are created equally, some are of high quality and some are not.  Strut rods absorb lots of stress and strain, so this is not a place to cut corners and go with a poor quality part just to save a few bucks. A heim joint can be purchased with a 5/8” shank and a 1/2” hole, however, it is cheaper and just as effective to buy a 5/8” 5/8” heim and press a 1/2” I.D. and 5/8” O.D. bronze bushing into the heim’s eye.  In the case of my strut rods, I chose to use rod end seals on either side of the heim to keep out contaminates and, thus, prolong the life of the joint.  The seals add .05” to each side of the heim, making it .1” thicker.  With this in mind, I wanted the bronze bushing to protrude out of the heim a small amount on both sides to hold the seals in place.  It is important that the bronze bushing does not protrude past the rod end seals so I measured the thickness of my heim .75” and added .075” to account for most, but not all of the rod end seals thicknesses. Using a cut off wheel, I cut the bronze bushing to  .825”.  I then used a file and cleaned up the end I had just cut.  The bushing is now ready to be pressed into the heim. I did this in a vise.  The process is relatively straight forward.  Simply start the bushing in the heim, place them both in the vise, and close the vise to press the bushing in.  It is important that you make sure the bushing is seated squarely in the heim before you begin to press it in.  Also, once the bushing is most of the way in, you will need to remove the heim from the vise and place a washer with a 5/8” hole in it behind the heim and place them in the vice to finish pressing the bushing in.  This allows the bushing to move slightly past the leading edge of the heim without bottoming out in the jaws of the vise.  The heim is now ready to be used on the strut rods. Our attention can now be turned to the key component in the homemade adjustable strut rod, and that is the threaded rod clevis. The beauty of this part is that it is a solid one-piece unit, with a 4250 pound load capacity, and it takes very little modification for it to be used in this application.

The first thing that needs to be addresed on the clevis is that the opening between the eyes of the clevis is a perfect fit for the 5/8” heim joint by itself, but will require enlarging to use rod end seals.  The advantage of using the seals is that the life of the heim joint will be prolonged by protecting it from dirt, water and other road contaminants.  The disadvantage is that some of the metal on the clevis needs to be removed to accommodate the .05” thickness of a seal on both sides of the heim. This will require some machining that will slightly weaken the clevis, but not significantly enough to be of concern.  I chose to use the rod end seals. In my mind, the advantages far out weigh the disadvantages.  Any machine shop can mill the clevis opening to the correct size, however, as before with the modification of the strut rod, there is a relatively simple way to modify the clevis at home with a simple bench grinder.  There again, the only cost is time, but also, as before, the process can be tedious and require repeated measurements to ensure that the correct amount of metal is removed.  To enlarge the opening, simply slide the clevis over a grinding wheel and use the flat side of the grinding stone to grind away metal on the inside of both eyes.   Frequently, remove the clevis from the grinder to ensure that the surface is still square and to prevent the clevis from overheating.  The key to doing this accurately is to be patient and take lots of measurements. Once the opening has been enlarged, our attention can be turned to the clearance between the clevis and the heim joint.  Place the heim with a seal on each side in the clevis and insert the 1/2” bolt.  Most likely, the heim will bottom out at the base of the clevis in the middle.  A rat tail file or a die grinder can be used to round out the inside of the clevis so that the heim has 1/16” to 3/32” clearance between it and the clevis during its full range of motion.  It is important to have adequate clearance so that the heim joint doesn’t bind up, but it is equally as important to minimize the amount of metal that is removed from the clevis to maintain the part's strength and integrity.  Now that the clevis has been fitted for the application, the aft retaining washer needs to be modified to fit over the clevis, a spacer ring needs to be fabricated to center the clevis in the mounting hole, and the forward retaining washer needs to be aquired or fabricated.

My local hardware store had oversized washers that measured a 2.5” O.D. and a 1.125” I.D.  I placed the base of the clevis over the washer hole and marked each of the hexagon points.  I then used a rat tail file to remove a small amount of metal at all six marked locations.  This made it possible for the washer to fit easily over the hexagon base of the clevis, and made a nice flat surface for the mounting ring to rest against.  I could not find a washer to be used as the forward retaining point so I decided to fabricate one.  I took a piece of 3/32” plate steel and cut it into a 2.5” by 2.5” square.  I then used the straight edge from corner to corner and an awl to scribe two perpendicular diagonal lines to mark the center so that a 7/16” hole could be drilled out.  Then, with the aid of a cutting wheel and bench grinder, I transformed the square into an “almost” round piece.  To put finishing touches to the washers, I bolted a 7/16” bolt through my newly fabricated washer, mounted the bolt in my drill, and used the flap disc on my angle grinder to round out the washer by lightly grinding it while I spun the piece at a low speed in my drill. These processes left me with a wonderful mounting surface that would press firmly against the mounting plate and sandwich the required spacer ring. 

When I was first contemplating how to best create a spacer ring, I took careful measurements of the mounting hole in my Mustang, grabbed my clevis and my calipers and headed to the hardware store.  I was pleasantly surprised to find that 1 & 1/4” steel pipe had a 1” I.D. and an O.D. that was just slightly larger than 1.25”.  These dimensions made it a perfect fit for the mounting holes in my Mustang.  The next step was to determine the thickness of my ring.  I took many measurements of the mounting plate where the strut rods pass through it and found the thickness of the metal there varied in thickness from .368” to .372”. It is important that the ring not be thicker than the mounting plate because, if the retaining washer bottoms out on the ring, then there will be a gap between the washer and the plate and this will cause play and movement in the mount.  It is equally important that the ring not be too small because without metal on metal contact, many of the advantages of torking down the mounting bolt are lost.  Keeping this balance in mind, I decided that my finished rings needed to be .365” thick.  For me, it made sense to error on the side of not thick enough and three to seven one-thousands of an inch is a minimal amount of slack that will easily be taken out simply by the retaining washers bending slightly during torking. I cut two rings that were slightly thicker than .365" so that I would have some metal to work with as I squared and cleaned-up their cut surfaces .  Even after the ends were clean and square, I left them at a thickness slightly greater than .365”.  I then used the same technique as before with the washer and marked and filed the hex pattern into the ring.  With the ring, however, I removed small amounts of metal and checked fitment often.  My spacer rings are a tight fit that need to be tapped on with a dead blow hammer or pressed on by applying the forward retaining washer and tightening down the retaining bolt.  Once I pressed the ring on and tightened down the bolt, I took measurements of the gap between the two washers on all sides and removed metal on the ring in the places where the measurement exceeded .365”.  Many times, I removed the ring and made minor adjustments by moving it across a file or 80 grit sand paper laid out on a flat piece of metal.  After each modification of the ring, I reinstalled it on the clevis, tightened everything down and checked to see what the measurement was between the two retaining washers.   The finished result was a solid front  mounting point that is equal in form and function to our modified strut rod end.  There are now only a few small details to address and the adjustable strut rod project can be completed and ready for installation.

There is an issue you need to be aware of with buying a bolt that is just long enough to fit through the clevis and have enough room for a nut on the end, and that is that bolts of that length are threaded down too far and some of the threads end up inside the heim and through one of the clevis eyes.  The problem with that is that the diameter of the threaded part is just slightly less than 1/2” and that will create some play in the mount. For best results, the 1/2” bolt that goes through the clevis and the heim joint needs to be longer than required and then cut to length.  I found a bolt that the base of the threads was about 1/4” inside the outer edge of the clevis eye, that way, once the nut was torqued down, it would not bottom out at the base of the threads.  It is also important that the bolt be grade 5.  Grade 8 is stronger but more brittle and I would rather have the bolt that was going bend in extreme situations rather than break.  After taking careful measurements, I cut the bolt so that when it was passed through the clevis it was one thread longer than what was required to fit through the all metal locking nut.  There is very little clearance in the mounting rail so any extra threads, other than one, will create clearance issues.  The 7/16” clevis mounting bolt will also need to be purchased long and cut to length. For the same reasons as stated above, it also needs to be grade 5 rather than grade 8. It is important to have it long enough to utilize all the threads in the clevis, however, due to a small amount of give in the retaining washers, I recommend cutting the bolt 1/16” shorter than is required to utilize all the threads, that way if when torqueing there is give in the washers, the bolt doesn’t bottom out against the heim.  The last detail to address is that a spacer washer needs to be placed inside the spacer ring between the clevis and the forward retaining washer.  I found that the clevis base was not quite long enough the fill the spacer ring, and if you do not put a washer in to fill that gap, you will warp the retaining washers when you torque down the 7/16” bolt.  As with the thickness of the spacer ring, it is better to have a washer that is slightly thinner than what is required to fill the gap rather than thicker.  I was able to find a washer that was the correct thickness and width to be a perfect fit. 

All the parts have now been fabricated and the only thing left to do is assemble the strut rods and install them in the car.  When putting it all together, I recommend using lots of anti-seize oil on the heim joint threads, strut rod threads, swegded tube threads and corresponding jam nuts.  I torqued down the 1/2” locking nuts onto the 1/2” bolt that goes through the clevis and heim to 60 foot pounds.  The 7/16” mounting bolt was also torqued down to 60 foot pounds and, when I installed it, I used lots of lock tite on its threads to ensure that it would not come loose.   There are those of you who may be wondering why I did not do any welding to attach the mounting washer and spacer ring to the clevis or to fill in the gap between the clevis and the end of the spacer ring.  The answer is that a cast steel part like the clevis I used has lots of internal tension that is formed during the casting process.  When you weld on a piece like that you mess with those tensions and inevitably weaken the piece.  Also, different steel alloys require different types of welding rod so without knowing exactly what type of steel the clevis is made of, you are far better off not welding on it.

Cut, turned and threaded rod end.

5/8" O.D. 1/2" I.D. bronze bushing being pressed
into a 5/8" heim joint.

Heim joint ready to install with a less than .05" lip of the bronze bushing sticking through on either sides.

Inside edges of the clevis being ground down to make room for the rod end seals.

Base of clevis being ground to allow clearance between the heim and clevis.

The clearance is being checked and, as you can see, there is about 3/32" gap between the heim and clevis.

Spacer ring being cut from a 1 & 1/4" piece of steel pipe.

The hex points on the clevis need to be marked on the ring so that it can be shaped to fit.

  A rat tail file works well to cut the hex shape into the ring.

As you can see, there is a clear hexagon pattern inside the ring.

The same hex pattern needs to be filed into the backing washer.

The washer is a perfect fit on the clevis.


My spacer rings are a tight fit over the clevis end. Notice the gap that will need to be filled with a spacer washer between the end of the clevis and the ring.

Complete frontal mounting assembly.

A gap needs to be established that is slightly less than the mounting flange on your car.  The spacer ring was machined to create a .365" gap.


This is an exploded view of the mounting assembly.  Not pictured but very important is the spacer washer that goes inside the spacer ring.

Clevis assembly mounted in the car to the mounting plate.  Notice the tight clearance between the assembly and mounting rails.

Here we have it, a completed adjustable strut rod in my car.  All the car  needs now is a high quality performance alignment.

Other Things To Consider:
Concerns have been expressed that a 7/16” bolt is insufficient to deal with the stress and pressure that this application will subject it to, especially since the aftermarket uses 1/2” mounting hardware.  My response to this is simple:  force applied to the bolt is in compression and tension, not side to side shearing force.  The free movement of the heim joint eliminates any shearing force that would be applied to the 7/16” bolt.  Secondly, a 1/2” fine thread bolt and a 7/16” fine thread bolt have the same number of teeth per inch at the same tooth depth.  That means that the only decrease in holding power is related to the loss in surface per tooth area, due to a 7/16” bolt having a smaller diameter than a 1/2” bolt.  The number of threads in the clevis compensates for the difference in area.  On aftermarket systems, they use a 1/2” bolt and everything is held in place with a single 1/2” retaining nut.  A 1/2” nut has 8 threads inside it where as the clevis has 12.  If you do the math, the square area of a 7/16” circle is .151”.  The square area of a 1/2” circle is .197".  If you multiply that area times the number of teeth, you get 1.812” for the 7/16” bolt threaded into the 12 threads of the clevis, as opposed to only 1.574” for the 1/2” bolt threaded into the 8 threads of a 1/2” nut.  As you can see, with more teeth being used in the clevis, and thus more surface area, the 7/16” bolt has 15% more holding power than a 1/2” bolt with just a nut.  Lastly, the clevis comes from the factory with a 4250-pound rating and that rating is going to include the 7/16” mounting hole, as long as high quality hardware is used in it.

For those of you who would rather buy than fabricate :
Rosehill Performance Parts sells high quality adjustable strut rods at a much lower price than the other aftermarket  options.



They are available for years 1964&1/2-1966 and 1968-1970.  These are quality race proven units and they utilize high quality 5/8" heim joints.  They mount directly to the vehicle with solid professionally fabricated mounting brackets. Purchasing information for these strut rods can be found at this web page http://www.rosehillperformanceparts.com




Disclaimer on Daze Tech Tips
      I am not an expert in this field. I have performed these modifications myself with very good results. I am passing along restoration and performance tips for the purpose of education.  If you are concerned about reliability or safety issues, I do not recommend that you or any other individual perform these changes or attempt to modify your cars from stock configuration except under your own volition.  I do not assume nor accept any liability for the use of this information or how it is applied.

















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