Torque Arm Link Construction

With the link made, it was time to get the connections done.  I managed to do the entire project with parts that were leftover from previous endeavors.

The chassis side pivot point for the link was made from a universal shock mount that was part of one of the many failed attempts at mounting either the front or rear shocks.  I think front, as it is painted red, but I cannot be sure.  And yes, that is the old, too short, link that is replaced in the entry shown at the top of this page.  The torque arm has two mounting holes in it, so no work was needed there.

There is the torque arm attached to the axle.  While it wasn’t in exactly the right spot at the time, it was close enough to make some cuts and locate where the link would go.

Unfortunately, the nut plate you see to the left of the cut is for the factory seatbelt latch, which is now unusable.  This plate also made cutting harder because it is (quite thankfully for those ever in a wreck) much thicker steel than the surrounding sheetmetal.  The view from the inside confirmed that I had made the cuts where needed.

The silver bar visible through the hole is the torque arm, and clearly visible is the mounting hole.  The black bar in the foreground is the seat mount.  I considered using that to mount the pivot, but decided against it because I didn’t want anything to compromise my ability to mount the seat safely.  I also, I don’t want any forces from the axle transmitted to the bar if I am in a crash.  Both the torque link and aluminum arm will be failure points before the seat mount, but better safe that sorry.

I’ll show how the link pivot gets attached to the chassis.  It is still in progress to some extent, so I don’t know when that will be exactly!

Part 1
Part 2

Next up in the hierarchy of axle positioning was setting the lateral location.  This is determined by the panhard bar.  This is the easiest of all the rear suspension positioning  steps since it requires adjustment of just one suspension member and changes are linear as long as the panhard bar is level to the ground.

The bar attaches to the axle on the driver side.

And to the chassis on the passenger side.

Thus, shortening the bar moves the axle towards the passenger side.  The only possibility for a mistake comes from not having the bar level.  Since my chassis mount is on a slider and the axle mount is bolt on, allowing it be loosened and rotated around the tube to change the height at the other end, this is easily accomplished.

Yes, another circle track part.  It is a Howe Racing cast mount was bought used for less than $20 and does everything I need.

A level panhard bar is important because it minimizes side-to-side movement.  As the axle moves vertically, the panhard bar scribes an arc.  Any bar with one end fixed and one end moving will do this.  The longer the bar is, the less lateral movement there will be.

While length is a design criteria, angle is a setting.  If we take the arc of travel and continue it, we will end up with a circle.  At 90° from the plane of the axle, motion will be almost all lateral and very little vertical.  Conversely, the motion when the bar is level to the axle is mostly vertical.  I have tried to illustrate this below.

Hopefully you can see that an angled bar results in much greater lateral motion.  The astute amongst you will also have noticed that the angled setup also yields less lateral motion than the level bar when the axle moves downward.  If you know that your axle will only move one way, such as on a circle track car, you can use this to your advantage.

Also note that with a level panhard bar the axle moves to the right (passenger side when looking from the rear) in both compression (upward movement) and extension (downward movement).  This means that if the axle is centered in the car when the bar is level, all movement will put it off-center.  A compromise is to set the neutral position slightly to the driver side.  This cause the axle to move towards center at first, and then proceed more to the passenger side.

How much static offset is the right amount?  That requires trigonometry and my memories of that particular subject are strangely dominated by images of the rather well developed blond who I was fortunate enough to sit next to in class, and very little math.  So I guessed and set it at just under ¼”.

Next up, pinion angle.

The first step in positioning the rear axle is done – fore aft location.

The wheel is still slightly towards the rear of the wheel arch at neutral position.  This is because at neutral position, the rear trailing arm is level.  Any travel will cause the axle to travel on an arc that brings it closer to the front edge of the fender.  I tried to compensate for this by leaving the axle a little towards the rear.

I had to slightly shorten the rear trailing arms to reach this position.  Since they are aluminum hex tap tubes, it was easy to do.

Now that everything is in place for the rear suspension, it is time to position it accurately.  This means that it must be at ride height, positioned longitudinally, and located laterally.  I will call this neutral position.  There are a number of reasons that this must be done.

1. I cannot truly check clearances if the axle isn’t at neutral position.  Checking clearances will require me to move it from neutral position, but I have to use that as a starting point.
2. At neutral position, I want all adjustments to be in the middle of their range so that changes can be made in either direction.
3. Neutral position will allow me to take measurements for fender flares.
4. I can finalize everything involving the rear suspension, a major morale booster.

First order of business is longitudinal positioning, aka fore-aft location.  Here is the problem:

Pretty obvious by comparing the curvature of the tire to the fender arch that the axle is much too far towards the rear.

Next post, the solution.

In a previous blog, I wrote about the design of the link that connects the torque arm to the chassis.  Now I will detail how I made it.

I am using aluminum hex tap-tubing, bored to accommodate a ¾” tap, that I bought from Speedway Motors.  This is what I made the rear trailing arms and front strut rod out of too.  As with those items, I will be using a 5/8″ bore QA1 XM series rod end.  These rod ends get solid reviews in online forums and cost about $30 each.  While that isn’t cheap, they are the cheapest units that get good reviews.  Also, they are American made and widely available.

5/8″ bore was chosen because the original Mazda holes were 14mm, so 5/8″ is minimal work to fit.  The 3/4″ shank ups the load capacity from 17,955 lbs to 31,680 lbs.  That is higher than the capacity of the 3/4″ bore 3/4″ shank also.

In this case, I started out with a link made from a scrap of hex tubing.

Unfortunately, once the mount was placed, I found out it was too short.  Cutting the tube is easily done since it is aluminum.  I used my table saw with an abrasive wheel fitted because it is easier to make a square cut than with my band saw.  After cutting, chamfer (bevel) the inner edges.

You can see the stone I used to produce the chamfer.  A stone like that is to some extent self centering, so it is easier than doing it with a smaller stone or a file.  The chanfer doesn’t have to be big, but it makes getting the tap straight so much easier.

Above are the taps and cutting fluid I used.  All the rod ends I have ever seen use fine thread, in this case ¾”-16 UNF.  Big taps like this aren’t cheap, so take care of them.  Store them in the sleeves they are shipped in and apply a light coat of oil to avert rust.  Note, you will need a left hand and a right hand tap if you want to adjust the length of the link without disassembly.  If the threads on each end are the same direction, loosening one simply tightens the other, resulting in no change in length.  Obviously, you will need to purchase rod ends threaded accordingly as well.  If you go with the QA1 units like mine, the part numbers are XML10-12 and XMR10-12.

Here you can see how the chamfer helps engage the tap.   Always use cutting fluid when tapping and if the tap begins to bind, do not force it.  Back it out, clean off the tap and the hole, re-lubricate and proceed.  Tapping aluminum is easy compared to steel, so you shouldn’t have a problem.  Just be careful if you remove the tap that you reinsert it precisely.  It is easy to cut new threads over your old ones thus ending up with a mess that has reduced thread engagement.  If this happens, throw the piece of tube in the scrap pile and start over.

Here is what you will have when you are done with the taps.

I like to run the tap in deep enough so that the rod end can bottom without issue.  Remember that the tap has some lead-in threads that don’t cut fully, so take that into account in your depth calculations.  Make sure you clean out the threads and lubricate them with anti-seize before use.

I like to label my links and rod ends so I know which ones are left hand thread.

Since aluminum threads are easy to strip, I think it is a worthwhile precaution.  I use the red paint pen you can see in the image below to make my marks.

That is the finished product.  It is surprisingly easy to make your own custom suspension arms, as long as they are straight.  If you have any questions, feel free to ask them by using the comment box below.

Since the SA22C rear suspension was originally a four link design, there is no accommodation for a torque arm mount in the factory structure.  While it would seem that the first step in running a torque arm suspension would be to add such a mount, I didn’t do it that way.

Beyond the design of the mounting point, the way in which the torque connects to the chassis is important.  The height and position on the wheelbase determine anti-squat and the system needs to not bind.  The torque arm represents a different swing arm length than the rear trailing arms, so it has to be able to plunge (change length)  in order to avoid binding.  Factory torque arm setups, like the GM F-body, use a bushing to accomplish this.  While this can work well, a bushing can still bind and is not always easy to find in the proper dimensions.  There are, unfortunately, very few universal bushing designed for adapting to one-off project like mine.

I decided that the best way to make a torque arm link would be to make an extra strength sway bar end link.  I have experience with them, they are designed to transmit force without binding, they are compact and easy to make.  A single rod end mount will not work.  It doesn’t have the capacity to handle plunge.

That is Stephen and Shane putting together the rear axle.  The large, flat, silver piece of metal is the torque arm.  As you can see, on the end, there are two holes.  Each is 5/8″, making it very convenient since all the rod ends on the car except for the panhard bar are 5/8″ hole, 3/4″ shank.  The link could be made from parts I already own.

The major complication would be the driveshaft.  The torque arm and the driveshaft run quite close together, and I would have to make sure that there was no chance of contact.  To do so would require getting a driveshaft, and I will post abotut that process soon.

Today marks a major milestone in the V8Mongrel project – the rear suspension is complete!  Everything fits, nothing binds and it is all in the car.  Big thanks to Brad Thompson for coming over yesterday and helping with the muscle work to get things where they need to be.  Moving a quick-change axle is not a one man job and without Brad’s help, this part of the project would not be as far along as it is now.

I will have pictures and details to share soon, but after six plus hours of cutting, grinding, fitting, welding, painting, refitting, measuring and adjusting on a day that came close to 100°, my motivation is focused on the shower and the couch at this point.

While complete, the rear suspension is not truly done.  It could be if I wanted, however I want my starting settings to be in the middle of all adjustments ranges, so I have to make a longer link for the torque arm and shorten the trailing arms slightly in order for that to be true.  Aluminum tap tube is easy to work with, and that won’t take too long.

But it will be another day and making those changes with give me the opportunity to take some pictures I didn’t today.

Mounting the rear shocks has been more of a pain that I had originally imagined.  Universal dampers with rod ends on each ends should be easy to mount.  After all, they are designed to be adapted to as many configurations as possible, so ease of mounting is something the manufacturers try to incorporate.

The problem was, like many other things, I am trying to adapt the parts and methods from a 108″ wheelbase stock car to a sportscar with a 96″ wheelbase.  Add into the fact that not only do I have a whole foot less between the wheels, bot a lot less overhang as well, and I often feel like I am stuff sardines in a can.

The main issue I was facing was trying to minimize compromises.  At first, I was wanting to keep the dampers upright.  An angled damper is less effective, and since I will be running coilovers, that would hold true for the springs.  The best way to accomplish this would be to mount the shocks inside the frame rails.  There is almost nothing there, so the dampers could be almost perfectly upright.

Then I was reading Circle Track magazine and learned about the important of spring base.  The spring base is the distance between the springs and like the old Pontiac slogan, wider is better.  The farther from the wheels the spring is mounted, the less effective it is.  It is a lever arm working against you.  While the spring rate can be increased to compensate, the problem is that in a live axle suspension the entire rear suspension moves vertically, so without the lever arm in effect.

The bottom line of all this is that a narrow spring base requires a higher spring rate to control roll and that higher spring rate makes the car tend to ride very roughly and even hop over bumps.  A wide spring base became a high priority.

I was having trouble working things out, so one evening Mike Westerfield came over to help out and we went through all the possible options.  The bottom mount was relatively easy, but the top mount seemed like every possibility created more problems than it solved.  We finally decided on a radical solution – use the stock mounts!

The only hurdle in that plan was the difference between mount styles.  The new shocks use a rod end while the factory units have a pin mount.  A pin mount is a simple threaded end that is an extension of the shock shaft.  It mounts to the body via a split bushing that allows for some misalignment.  Overcoming a vertical body mount and a horizontal shock mount was actually quite easy.

I took a universal shock mount, cut it down, drilled a hole in the top and pressed a wheel stud into the hole.  The stud was tack welded into place for security and the head partially ground down to allow for 100 percent shock articulation without bind.

The mount is a tight fit in the factory shock tower, but it seems to work just fine.  Part of the reason I used a wheel stud was because the factory hole is metric and it was one of the few metric fasteners I could find.  Also, it allowed to use a wheel nut on the other end.  A 19mm head M12 wheel nut cone taper fits very nicely into the hole of a 5/8″ washer.  The washer helps distribute the load and the interference should help keep everything tight through hard use.

The bottom mount was the easy part.  I had to use some tapered spacers for clearance, but beyond that, it was a simple bolt-in.

A long time ago, I posted about the factory Watts linkage used to locate the rear axle.  At that time, I wasn’t sure what I was going to do, and while at this point I have already done it, I figured I would do a quick blog about how I came to my decision.  No pictures, just thoughts.

The factory Watts linkage is known for binding, but changing it over to spherical bearings solves the issue.  It is relatively easy to buy some rod ends, some tap tubing, and make the links yourself.  In fact, this is how I made the trailing arms for the rear suspension.  However, even with the bind removed, the Watts linkage has one major disadvantage that I could not see a way around – lack of adjustability.

The weakness of the Watts linkage is in the axle mount.  It needs to be as centrally located as possible in order to keep the arms long and even.  If they are short, they can bind, and if they are uneven, the axle will move laterally.  Of course, the big problem is that in the center of every axle is the differential.  Space is hard to find, especially for something like pivot point and bellcrank.

The axle mount is also difficult to make adjustable.  While any pivot point should be easy to adjust, the central location and the fact that the outer pivots need to be kept within a certain relative height range as well quickly complicates things.

Now, there are some solutions.  The best I have seen is from a company called Fays2.  They mount the pivot to the frame and the links to axle.  The pivot point is then easily adjusted.  Really a nice solution.

However, I decided to go with the panhard bar.  It is simple, readily available, and most importantly, easily adjustable.  I am under illusion that I will get the suspension setup right the first time, so I am building in at every possible opportunity the ability to make changes quickly and easily.

Simple – one chassis mounting point and one on the axle.

Readily available – it used by every full body circle track racer so parts are easy to find.

Easily adjustable – lower the chassis mount to lower the roll center.  As long as the two ends are close to the same height, that is all that needs to be done.

So the panhard bar not because it was the better system on paper, but because it would allow me to do everything I want more easily.  It isn’t often that I take the easy way out, but it does happen.

It seems that a lot of my fellow car guys believe that a live axle is a useless relic of a bygone era that should be relegated to museums. Perhaps there are right, but since I am running a pushrod engine and a carburettor, their opinions on modernity obviously mean nothing to me, so the old technology live axle is here to stay. The SA22C came from the factory with a live axle (detailed in previous posts) and converting to an independent rear suspension (IRS) is a project I am not willing to undertake at this time.

Note that I am not saying that IRS isn’t superior to the live axle. A top level IRS is better than the best live axle; that much has been proven hundreds of times by those with the resources to do so. Yet, getting an IRS right is not very easy. While it is possible that I could duplicate much of what I have done with the front suspension, there are other variables to consider that would complicate things. Furthermore, my models when undertaking large changes have been NASCAR and other circle track race class cars. It is no coincidence that I am running an SLA front suspension like they do, and therefore, following what they do in the rear, I believe, is a good way to go.

Of course, there is the element of cost. A live axle, especially given good access to used parts from circle track racers, is much cheaper than an independent suspension. I have seen a Miata IRS adapted to a first generation RX-7, but I am wary of using production pieces from a four cylinder car to transmit the power of a V8. Other solutions, such as a Corvette based system, are very expensive.

With the live axle here to stay, the question then becomes, what type of suspension system should be used with it? To say that there are a number of choices is an understatement. Some were immediately thrown out.

• Truck arm – The system that is mandated in the highest levels of NASCAR, the truck arm is simply too large and too difficult to fabricate or adjust for me to use. I cannot use a NASCAR takeoff truck arm as their cars have a 14″ longer wheelbase than I do, so they just won’t fit.
• Any system with leaf springs – I have neither the room nor the desire to run leaf springs. They are expensive, large and difficult to source, unlike more common and compact coil springs that can be found used for as little as $5 each.
• Angled four links – This is what the SA22C comes with from the factory. This style has been popular with OE manufacturers for years, most notoriously in the Fox-body Mustang. Everyone ditches these systems at the first opportunity, so I will too.

With those out of the way, what is left? Well a lot. If you want to get the goods, I suggest reading the Herb Adams book, Chassis Engineering. It has the most complete treatment of all the major live axle suspension designs I have seen. Here are the ones that made my cut.

• Three link – Two links near the wheels, under the axles and one close to the center on top. Offers almost no chance of bind, significant adjustability, and light weight. The system is very popular in a number of circle track classes and can be made to do almost anything with the addition of pull-bar style third links that cushion the application of power to the wheels.
• Four link – All four links mounted close to the wheels, parallel to the centerline of the car (or very close to it), two above the axle, two below. The four link system has a dizzying variety of configurations ranging from simple trailing links to the Z bar with floating birdcages that are popular on the dirt ovals.
• Torque arm – Simple trailing links near the wheels with a single, long arm mounted rigidly to the center of the axle to a pivot point on the chassis near the transmission. Used in the GM F-body with great success, the torque arm has also been a popular choice of Mustang tuners for about a decade. Best known for delivering excellent traction through high anti-squat values.

The more I read, talked to people and learned, the more I realized that a properly executed example of any of the three system detailed above would be fine. Technically, they each have their strengths and weaknesses, so I would have to find another way to make the determination.

On a cost level, the three link has an advantage if kept simple. It requires two simple outboard brackets and one in the middle. With the purchase of the quick change, all could be bolted on. The three link was therefore the early leader. However, the more I looked, the more I realized why the three link has seen limited use by vehicle OE manufacturers – packaging. In order to have the proper geometry, the third link would likely project into the passenger compartment a large amount. Since drilling into the rollcage is a no-no, this could present a problem.

The four link is more difficult to do cheaply because all the readily available units are floating birdcages. The point of a birdcage is to allow the axle to rotate within the mounts to minimize bind by not being attached rigidly. The lack of cheap, used four link parts really put a damper on the idea of running one. Thinking about it more as I write this, I also realize that the the packaging of the four link could be a real challenge as well.

As you might have guessed, the winner was the torque arm. With the huge amount of Mustang aftermarket and Camaro/Firebird OE information available, it really is a good choice. However, cost was always the issue. Some custom torque arms can cost $400 or more. Thankfully, eBay to the rescue. I found a torque arm designed to bolt to the quick change for just $15. Yes, that is right, $15. Even if this doesn’t work, chances are I will learn something, and for $15, it will be a cheap lesson.

I will have pictures to share when the part arrives, but in the mean time, I have to wait to assemble the axle because the torque arm needs to use many of the same fasteners. Not the first delay and likely not the last. Still plenty to do, so really no worries.