Torque arm/coilover question

[jaybee]

Assume here the coilover lower mounts are on the axle tubes rather than on the trailing arms. Can the coilovers be mounted in a fore/aft staggered fashion, as shock absorbers often are in a leaf spring suspension?

[dontlifttoshift]

Why? The shocks are staggered on leaf springs to help overcome leaf spring design deficiencies. You don't have any of those with a torque arm.

[jaybee]

Why? Packaging. Sometimes it's more convenient to leave things roughly where they started out.

[SPG]

Why? Packaging. Sometimes it's more convenient to leave things roughly where they started out.

If your intention is to use the stock shock mounts the leaf springs used, don't. The stock mounts are not able to hold the weight of the car. You'll cause yourself more problems instead of doing it properly.

[marolf101x]

Also, if performance is your intended goal you want each side to react the same for consistency and easier tuning.
Having the shocks staggered can make them perform differently side-to-side.
Ideally you want the sides to mirror each other.

What vehicle is this being installed into?
What is the intended use?
Any pictures?

[Rod]

the shocks mounted fore and aft on a leaf spring car is to control axle wrap and its just a shock it doesn't contribute to the suspension geometry in any way.... the torque arm controls axle wrap with the center torque tube, horizontal axle location with the outer bars and vertical axle location with coilovers and lateral axle location control with a pan hard or watts link .... factory shock locations usually are to weak to support a coilover

[jaybee]

Right, good point that factory shock mounts aren't strong enough for coilovers. A whole lot of trunk floors were ruined by air shocks back in the day, and they didn't even fully replace the springs.



My main question is this: with a torque arm, does the spring in front of the axle provide a different effective spring rate from a spring behind the axle? Angles being equal and opposite, distance from the axle flange being equal, and so forth. The Panhard bar, Watts link, or whatever handles axle control side to side. The trailing arms handle thrust and braking loads in the fore/aft direction. The torque arm does exactly what the name implies, it controls axle rotation. Does that adequately divorce the various functions sufficiently as to provide an equal wheel rate side to side? Or does one of the other links, most likely the torque arm, impact the wheel rate?

I acknowledge the best coilover position in a torque arm is going to be vertical in side and rear view, and the car isn't in my possession yet, but I'm trying to think through how to do it in stages, with minimum possible downtime at any point. That means building things ahead to bolt in and a minimum of needing to rebuild things like trunk floors and exhaust. Something like the RRS bolt in torque arm system for Falcon-chassis Fords. Please don't say "so buy the RRS package." It misses the point of my question, which is to understand how the suspension works. It also costs something like 4600 Australian dollars, which I'm sure they earn, but again not the point. I have a preference for things that are garage-built.

[marolf101x]

does the spring in front of the axle provide a different effective spring rate from a spring behind the axle?
Yes. It's just motion ratio.
Though it is a small amount, it's still different.

[jaybee]

Thank you. I suspected as much, even though one of the points of the torque arm is to divide the functions of lateral location, fore/aft thrust, axle rotation control, and spring/damping more completely.

[marolf101x]

Well, yes, but so do most “non leaf spring” suspension designs.

Lateral location is controlled by the lateral locating link (panhard bar, watts link, etc.)
Shock/spring effective rate is controlled by motion ratio.

Fore/aft “thrust” is a matter of suspension link geometry (instant centers) and how they relate to the rest of the car (roll centers, roll axis, center of gravity, moment arm, etc.). It’s relatively easy to see where the forces go when the car is static, but another thing when it’s pitching and rolling.

Which rear suspension you choose really depends on everything (your goals for the car, what car is it? What’s it weigh?, what’s the weight split, what’s the front geometry doing?, on what kind of surface will it compete if it is competing?, is the suspension philosophy high travel, low roll; low travel, low roll, etc?)
It’s all a compromise and you pick what you feel is the best compromise for your goals and situation.

Give us some info and we can hopefully provide enough information/education for you to feel comfortable about your choice.

[jaybee]

OK, thanks for asking. I'm still looking for the right car, but the intent is to find something in the Falcon/Fairlane/Torino/Maverick family. A Mustang at the right price would work, but those are harder and harder to find, even in a notchback. The vision for the car is to have it drive well by modern standards even when pushed a little. None of this "handle like a new Corvette" nonsense, but I should be able to throw it into a cloverleaf, blow through a roundabout, or work the pedals on a twisty road enough to get my heart rate up without scaring me half to death. Or killing me to death. I had a 1968 Cougar and a 1969 Cougar. LOVED the '69, but I never had any illusions of what it could do. No 700hp, no Coyote swap, no mini tubs, no radical body mods, no bespoke chassis. Engine limited to a 351W or 347 with enough work so there's no question it's warmed up but not so much as to make it a temperamental beast. As much of the work as possible should be in stages. I love the magazine quality builds on the Projects page, but I don't have that kind of money. Besides, there's a secret hidden in that part of the forum, and a lot of others. How many threads start with big plans, get some parts bought, big chunks of the car cutaway, and then they go dead? Cars should be on the road as much as possible, within reason.

About those stages, which of course will vary based on the principle that Job One is to make sure it's safe and reliable. First, Monte Carlo bar and Export Brace, maybe some other details like Boss 302-style belly bar or some of the other shock tower reinforcements that were used on various 1st gen Mustangs. Rollerized spring saddles. Shelby/Arning drop. Sway bars. My preference is for a soft spring/stiff(ish) bar setup. I don't like the movement that can come from the stock strut rod bushings, but I'm also no fan of heim joints or other unsealed, metal on metal joints on the street. That stuff is for race cars, which get checked, cleaned lubed, and replaced constantly. Opentracker has Delrin monoball bushings which look like a good option. They're not metal on metal and the concave washers may do a good job of wiping dirt out of the bits. Dial in a wheel alignment friendly to modern tires, with lots of caster. That just about necessitates power steering, and the most expensive single chassis bit may turn out to be a Borgeson steering box. The Bendix ram-assisted steering and I have a checkered past, and the 16:1 and 19:1 stock steering boxes are very old school.

Most of the chassis I've described can carry a 275-305 width tire on all corners, depending on model, and be very close to stock height overall on a 17" wheel. That's enough room for later model Mustang brakes with decent sized rotors, and for some combos there are even caliper brackets available. Plenty adequate for the usage I have in mind on cars that are 2900-3300 lbs and WAY less money than Wilwood, Baer, or other track-quality systems.

Given all that, why not just stick with leaf springs? Maybe I will, by that time, but with probably 400-425hp and everything else updated, IMO the leaf springs will be the sketchiest part of the car. Options like a triangulated 4 link or a 3 link would require cutting up the car pretty severely. More so than a torque arm, which seems to work well from both a packaging and performance standpoint on a lot of cars. The hard part of the Panhard bar will be building a frame mount which positions the bar low, flat, and long for best motion. The trailing links can be fabbed up ahead of time to bolt up to the front spring mount and the leaf spring saddles. Dead easy stuff.

Coilover mounts aren't so bad, it's just a matter of where to put them, which is where my question came from. Can't just bolt them to stock shock mounts, but it's not rocket science. There's enough stuff back there to share the load into. Frame rails, trunk floor, shock mounts, perhaps even the pinion snubber mount. Maybe put a steel firewall behind the rear seat to help spread the load into the rear torque boxes, package tray, wheel tubs, and up into the C pillars.

That just leaves the torque arm itself. Plenty of ways to build one of those. I like the way the Maximum Motorsports TA for Fox body Mustangs is built, but with spring saddles on the axle tubes to make it stronger. I'm not quite sure what to do about the front mount. The RRS style of crossmember is one possibility. Or maybe something built up into the tunnel so it stiffens that structure, forms a driveshaft loop, and lets the torque arm mount underneath. The front mount still has me concerned. No heim joints, remember? That would apply to unsealed telescoping joints as well. And there's only so much space under there. Maybe a BMW trailing arm link. They're pretty small. A builder I trust told me he's had good luck using a Ford pickup radius arm bushing. It's big, squishy, and designed to make all the same motions a torque arm has to make.

Hope I haven't gone from undersharing to oversharing, but that's the scoop.

[marolf101x]

I've broken down your post and added my 2 cents.

None of this "handle like a new Corvette" nonsense, but I should be able to throw it into a cloverleaf, blow through a roundabout, or work the pedals on a twisty road enough to get my heart rate up without scaring me half to death. Or killing me to death.
--Why not "handle like a new Corvette"? We have to have a benchmark. . .something to shoot for. The Vette is the closest thing to our old muscle cars we can get in the form of a new car (SLA front suspension. . .no struts, powerful, quiet, good ride quality, etc)
--I guess if you have an aversion to GM products you could make a case for "handle like a Viper", but I found them to be much less forgiving than the Vette when driven at the limit and not as "relatable" as the Vette overall, while feeling more like a kit car than a production car (though, I only drove old ones, never the later versions, so they surely got better over time).


I love the magazine quality builds on the Projects page, but I don't have that kind of money. Besides, there's a secret hidden in that part of the forum, and a lot of others. How many threads start with big plans, get some parts bought, big chunks of the car cutaway, and then they go dead? Cars should be on the road as much as possible, within reason.
--I suffer from 90% of this. I don't buy many parts as I like the design and building phase. However, my ambition is much greater than my abilities and/or time available, so I end up with what's described above. Currently I have a 68 Camaro with a full tube chassis that's nowhere near done, and a 66 Lincoln Continental convertible with a Crown Vic front and a S550 independent rear that's not been worked on in probably two years. I daily a 64 Chevelle 4 door as I want to drive something old and "cool" but have to shuttle kids to daycare/school and athletic practices, so a 4 door was a must but I just couldn't talk myself into a Honda Accord or the like.


About those stages, which of course will vary based on the principle that Job One is to make sure it's safe and reliable. First, Monte Carlo bar and Export Brace, maybe some other details like Boss 302-style belly bar or some of the other shock tower reinforcements that were used on various 1st gen Mustangs. Rollerized spring saddles. Shelby/Arning drop. Sway bars. My preference is for a soft spring/stiff(ish) bar setup. I don't like the movement that can come from the stock strut rod bushings, but I'm also no fan of heim joints or other unsealed, metal on metal joints on the street. That stuff is for race cars, which get checked, cleaned lubed, and replaced constantly. Opentracker has Delrin monoball bushings which look like a good option. They're not metal on metal and the concave washers may do a good job of wiping dirt out of the bits. Dial in a wheel alignment friendly to modern tires, with lots of caster. That just about necessitates power steering, and the most expensive single chassis bit may turn out to be a Borgeson steering box. The Bendix ram-assisted steering and I have a checkered past, and the 16:1 and 19:1 stock steering boxes are very old school.
--I agree with the overall idea presented above. . .tighten everything up, modernize what you can.
--There are a lot of new options regarding joints. As long as you don't purchase the cheapest heim from Speedway Motors you can find it'll live for quite a while and be quiet. Delrin (especially with PTFE) is excellent for our applications.


Given all that, why not just stick with leaf springs? Maybe I will, by that time, but with probably 400-425hp and everything else updated, IMO the leaf springs will be the sketchiest part of the car. Options like a triangulated 4 link or a 3 link would require cutting up the car pretty severely.
--Not necessarily. There are many kits out there that don't require major surgery to install. . .one I know for a fact requires no cutting. If you don't want to purchase a kit use images, the instructions, a suspension design program and a little research to design and build your own.

More so than a torque arm, which seems to work well from both a packaging and performance standpoint on a lot of cars. The hard part of the Panhard bar will be building a frame mount which positions the bar low, flat, and long for best motion. The trailing links can be fabbed up ahead of time to bolt up to the front spring mount and the leaf spring saddles. Dead easy stuff.
--I always found two difficulties when designing/building a torque arm:
1-the front mount. It has to have articulation in multiple directions and be able to move for/aft.
2-mounting to the rear end. For someone building one at home I would use a "fabricated" 9" housing. Anything to which you can weld your attachment points. That allows you to do about whatever you want.


Coil over mounts aren't so bad, it's just a matter of where to put them, which is where my question came from. Can't just bolt them to stock shock mounts, but it's not rocket science. There's enough stuff back there to share the load into. Frame rails, trunk floor, shock mounts, perhaps even the pinion snubber mount. Maybe put a steel firewall behind the rear seat to help spread the load into the rear torque boxes, package tray, wheel tubs, and up into the C pillars.
--To me this is probably the easiest part. Weld (or bolt-in) a bar across the two frame rails. Weld upper shock mounts to said bar. Done.


That just leaves the torque arm itself. Plenty of ways to build one of those. I like the way the Maximum Motorsports TA for Fox body Mustangs is built, but with spring saddles on the axle tubes to make it stronger. I'm not quite sure what to do about the front mount. The RRS style of crossmember is one possibility. Or maybe something built up into the tunnel so it stiffens that structure, forms a driveshaft loop, and lets the torque arm mount underneath. The front mount still has me concerned. No heim joints, remember? That would apply to unsealed telescoping joints as well. And there's only so much space under there. Maybe a BMW trailing arm link. They're pretty small. A builder I trust told me he's had good luck using a Ford pickup radius arm bushing. It's big, squishy, and designed to make all the same motions a torque arm has to make.
--Like I said above, the front mount is the most problematic.
--The frame/body side of said mount is not difficult, but if it were me I'd cut the floor and fabricate a structure that tied into the frame rails (or rockers) and provided the TA mount. It could also serve as a trans mount and/or driveshaft loop if you wanted.

[jaybee]

Thanks very much for the feedback. It all makes sense to me and I appreciate it. Sounds like I'm on the path to a viable plan. The cars I'm looking for are still out there, just a matter of finding the right car in the right place at the right time. Every Ford fan wants a Mustang, and I'm not sure how many are aware that just about every one of the compact and intermediate Fords of that era are mechanically very similar. As always there are gotchas. After all, it takes 5 different kinds of bolt and hex stud to install a water pump.