Truck-arm Rear Suspension

[redss86]

Hey guys, I need some info/ opinions on Nascar style Truck-arm rear suspenions. I am planning on building my own setup buy buying the parts from stockcarproducts.com. I plan on buying the monoball arms along w/ their crossmember. All this I plan on incorporating into a tubular frame that will be for an 86 Monte Carlo SS.

My biggest problem is that I am not totally sure on the correct heights to mount this suspension for optimum performance. The car will be used primarily for street use, w/ the occasional track times. I am wanting this to handle extremely well. Along w/ the heights, I am also curious about the panhard heights, angles, etc...

One other thing is that I am thinking about setting this up w/ a full floater 9". What is the general opinion about this type of rearend? Any big advantages or dissadvantages?

Any and all help is greatly appreciated.

[Poopy]

I'm building one from scratch, so far its been fairly straight forward, although I dont have the greatest grasp on all the suspension engineering aspects involved....but with the truck arm theres only two links and a panhard to screw up, so I'm not overly worried about it!

Good luck!

Heres a couple threads that have been discussed already:


https://www.pro-touring.com/forum/showthread.php?t=4817&highlight=truck

https://www.pro-touring.com/forum/showthread.php?t=595&highlight=truck

[JMarsa]

No offense, but I doubt anyone is going to answer your post with a recipe for how to set up you car (I hope I'm wrong). There are people here who are very helpful and folks put alot of work into their projects. There are also vendors and site sponsors who frown on people giving away their liveihood. That said. Research. Here and over at cornercarvers.com (be prepared to know your stuff) and anywhere else you can pick up info, buy some software. People here will help you if you try to figure it out yourself (like RC, IC and all those other terms and calculations). Also, my understanding is that even if you live in NASCAR country the truck arm set-up is like magic, and it only stays MAGIC if everyone and their brother doesn't know the trick.

I'm not trying to be a jerk; I bought a truck arm kit. If I had the brains I'd be trying to do what you are, building my own. I just wanted to make sure you got a reply and give you some insight.


Regards,

--JMarsa

[dennis68]

No offense, but I doubt anyone is going to answer your post with a recipe for how to set up you car (I hope I'm wrong). There are people here who are very helpful and folks put alot of work into their projects. There are also vendors and site sponsors who frown on people giving away their liveihood. That said. Research. Here and over at cornercarvers.com (be prepared to know your stuff) and anywhere else you can pick up info, buy some software. People here will help you if you try to figure it out yourself (like RC, IC and all those other terms and calculations). Also, my understanding is that even if you live in NASCAR country the truck arm set-up is like magic, and it only stays MAGIC if everyone and their brother doesn't know the trick.

I'm not trying to be a jerk; I bought a truck arm kit. If I had the brains I'd be trying to do what you are, building my own. I just wanted to make sure you got a reply and give you some insight.


Regards,

--JMarsa

Actually, there is no magic involved in fabbing your own truck-arm system. It is one of the easiest systems to build. Most guys are just too lazy or don't have the tools necessary to scratch build the system.

[gchandler]

I would just like to say that there is more then meets the eye to the truckarm system. I have been involved in the installation of around 50 kits on all types of car, and I can tell you that suttle nuances of the system are responsible for major changes in how the system functions. I will also say that the system as it appears on the early chevy trucks leaves much to be desired.

As for the floater setup just make sure that you get the heavy duty setup that is designed for a car of your weight as I seem to remember the race floaters being offered in various load ratings. Basically I think that they simply use different steel on teh axle tubes.

I am unable to give you any assistance in figuring out how to package and setup a truckarm system, but I can tell you that the prices that Steve at HTH charges for his kits are quite reasonable when you consider the time and effort that has been put into their design and testing.

[wally8]

Jmarti81,

I'm with Denny, there's not much too it. Sounds like you are going to buy your truck arms which will get past one of the common errors. The arms need to be able to twist to work correctly which is why you wouldn't want to fab them out of tubing.

You can see from the HTH webpage where they mount the crossmember so you can get the right idea of length. After that it's just some spring pads, shock mounts and panhard mounts and a bar. Simple stuff that can be sourced from any number of racing suppliers.

You'll be fine with any of the low cost floaters like those from randy's racemart. They'll hold up fine for your app. Be prepared for some extra weight unless you're going to go the extra mile with light parts.

No offense, gchandler, but giving a response of "There's more than meets the eye" without offering any detail is a fairly worthless bit of information. He obviously knows that, which is why he asked the question..... Since you've installed 50 of them, I assume you might have some tech to offer?......


Wally

[dennis68]

Geoff used to work for HTH so out of respect for Steve he's not going to cough any info. I do think he is playing a bit of the part of Steve however making one beleive that is a fairly complex and difficult system to design. It's a pair of torque arms attached to steel crossmember, all of which can purchased at any number of circle track suppliers (which is where I suspect Steve gets his).

I don't want to sound like I am in any way putting down Steve or HTH, he found a market, thats great. He did not however pioneer some great new design that needs that requires hours of design engineering prior to installation.

Leave yourself some room for adjustment at the crossmember for pivot height and at the PHB for adjustment. Start with a PHB height equal to the centerline of the axle and the arms just below frame rail height.

[Norm Peterson]

Actually, there is no magic involved in fabbing your own truck-arm system. It is one of the easiest systems to build. Most guys are just too lazy or don't have the tools necessary to scratch build the system.Easy enough to build, but I'd add 'understanding of the kinematics and desired flexibilities/compliances' to that list if you want to tune it to its potential. I think the kinematics is what the original post was inquiring about.

I don't think it's giving much away to say that the PHB should be level with the car at rest (ideally, loaded as it will be driven), that the height to the center of the PHB should remain a bit above that of the virtual intersection of the truck arms under all conditions, and that the PHB should be as long as practical (especially with the monoball arms).

Norm

[wally8]

Norm brings up a good point; it's good to know the relationships of the parts you're putting together.

However, this is a pretty well developed application and as Denny said, if you leave yourself some adjustment you'll be in the ballpark. From there you can tune once it's on the road. Nothing too magic about integrating a bunch of off the shelf parts. Good advice on the PHB mounting.

There's a lot of theory here and that's definitely good but you can build it and tune it around to work. Rear suspensions are much easier to do copycat engineering on than fronts. Break out the welder and go, I say.


Wally

[redss86]

Thank you guys for the info. The more the better. Don't stop.

About the phb, when it is in the center of adjustment, it should be just above the truck arm virtual intersect point and level parallel to the rearend. Or should it be higher or lower in the adjustment range?

Also on the floating rearend. I was going to go w/ the Stockcar Products BN hubs and snouts. I would probably use the steel drive plates. Would these hubs be able to support the load that I would be putting on them. Remember this in under an 86 Monte Carlo SS. Here is a link to the hubs: http://www.stockcarproducts.com/rear12e.htm

thanks again, jmarti81

[scogin918]

i bought the HTH set-up from Steve,and let me tell you; i'm glad he did the hard work for me. Every car is different and he's taken the time to make kits for a bunch of them. That's what sets him apart from the DIY'er. You could probably do a good job on your own, but he's already been there and has experienced the pitfalls and developed the tricks to doing it. I can put a price on time and experience and i'll willingly pay for it.

on the floater, there are two different types of hubs. one for Nextel Cup and one for Busch. they don't interchange becaused the snouts are different. the busch one is cool because you can use the stock bolt pattern. I had to change the center section of my wheels to fit the Nextel Cup 5 on 5 pattern. The rearends should be bulletproof. They also have a groove behind the yoke for a pulley if you want to run a rear end fluid cooler. if you want to go Nascar, you might as well go all the way.

[wally8]

Those hubs will work fine. You mentioned snouts so I assume you'll be welding them on to a housing you already have? Just make sure it's done in a jig and have the housing straightened afterwards. Any circle track fab shop should be able to do it for you. Most have inserts and do it with a porta power.

Funny side story. I've seen a floater completely ripped out of a car from catching on the guard rail and it just needed to be tweaked straight afterwards. No problems other than that. The rim was a total loss, though :-)

Start there but give yourself plenty of adjustment on the PHB up and down. (I would say mostly up from there but my experience is with dirt cars so don't go by my word on that part.) This isn't a two hole sort of adjustment situation. I like the infinitely adjustable slotted mounts. They'll give you several inches. Again, you can get them from all of the stockcar suppliers.

I personally think HTH is unbelievably expensive for what you're getting but that's just my worthless opinion. Not that it's not a nice package.....

Wally

[BRIAN]

I know I am outsider hear but hey HTH had a good idea and packaged it well. I hear a lot of bad opinions about the set up but have never seen a post in regards to the installation. So maybe they are providing a well thought out piece that justifies the price So why pay DSE $375 for springs you could have made for $225? Because you know it is worked out and is bolt in without any hassle.
On the other hand it does look like fairly easy set up and have thought about it myself. To the suspension gurus are there any mtg points to start as reference or just use where the arms fall on front crossmember. I know most suspensions are based on mtg points. I know you would want the arms to wind up as far out on the rear but are you telling me that is it, just bolt them on and go. Panhard bar is to be level as with any set up. If it is that easy I will give it a shot.
I know most don't like set up but you have to admit it is strong and pretty simple to keep novices out of trouble. Also every mag test with a car equipped has been pretty impressive. Just my ideas.

[dennis68]

The arms determine the crossmember mounting location. Mount the arms to the axle and see where the pivots sit, pretty straight forward.

PS, I won't pay DSE 375 for springs, I won't even pay 225. Why not go straight to the spring builder and spec your own?

[yody]

ummm, dennis how many springs have you had speced to your own?...sounds good. How many hours of research will you have to put in trying to get the right specs? is that worth $100 or a little more? and maybe your specs aren't even all that great? Not everyone has suspension guru friends that are willing to share their secrets and tell us how to make a spring and give us the specs. However I could see how somebody would want to as "fun" i might do that down the road, once the car is finished and i have nothing left to do, but when building a complete car, it takes too long to do stuff like that along with every other darn singe thing. One thing i can throw in here(pretty useless huh!) is that the truckarms are notorious for making a lot of noise...at leasts thats what i hear...there was an entire 2 or 3 page post here about the truckarm, do a search.

[68protouring454]

it would cost you at least 400 for a set of custom leafs, anywhere, anywhere, like others have said, someone who knows little about suspension would be way better off to buy a kit, then to fab his own, ****, there are not to many on here that have raced there cars, so does it really matter?
jake

[Poopy]

Here's where I'm at with the homemade truck arm setup I used part of the GM factory crossmember for the basis of my crossmember:

https://static1.pt-content.com/images/noimg.gif
https://static1.pt-content.com/images/noimg.gif

[gchandler]

A while back there was an article run in chevy high performance about an el camino that we equipped with truckarm as well as the HTH front kit.

Between Steve and myself we installed both the front kit and rear kit in one day and drove the truck in testing the following day. The car had a full interior and was a complete running, driving car when it came into the shop and left in the same condition the following day.

This is what you pay for when you build a kit, ease of installation, proven performance and the work that goes into acheving those.

I no longer work for Steve and my statements about the complexity are not intended to sell kits. I am participating in the information exchange that is the heart and sole of this site. I am a satisfied customer and run truckarm on all of my vehicles.

I am not trying to be coy, there are simply rules about disclosure of proprietary information even after you are no longer employed by someone.

My statements are not intended to sell products, I am simply trying to give an idea about what you are jumping into when you set out to design, build, and install a custom suspension system.

Nothing is as easy as it first appears, remember that a suspension system does not exist in a vaccum, it needs to be incorporated into the chassis of the car that it drives.

[dennis68]

ummm, dennis how many springs have you had speced to your own?...sounds good. A few dozen, takes a couple tries to get the frequency f to r a close match and get a rate you are happy with.
How many hours of research will you have to put in trying to get the right specs? yeah, it takes a few hours.
and maybe your specs aren't even all that great? Better than some guys sitting a few thousand miles away that has no ides what else has been done to the car nor it's intended driving conditions
Not everyone has suspension guru friends that are willing to share their secrets and tell us how to make a spring and give us the specs. How about simply spending a few hours a night for a couple weeks learning suspension design on your own then you won't friends to tell you what to buy :hmm:

[MrQuick]

you guys get a room already....
i agree, it looks easy, hell throw a few bracket together and weld here weld there...your done right? Wrong.
It takes a lot to engineer a suspension and have it right the first time. It just won't happen. If I didn't have welding or some minute suspension experience I would be hesitant to try to DIY. How much is it gonna cost when your untested suspension desides to unload itself doing 65 mph down the highway. Please leave the suspensions to the experts...or at least do lotsa home work.

[dennis68]

Psssst, MrQuicky. you need to weld the HTH kit in too.

BTW, holy **** the arms are friken awesome. I'll have some more to post latter in the week. Let me get a dry day to play first, the water is killing me, it just gets all out of shape...no fun at 60MPH with tractor pulling doubles riding my ass.

[MrQuick]

cool, let me know how it all works together... I know but they have done the testing and have honest experience. Carefull is all I wish to add. :scared:

[wally8]

If we were going to leave the suspension stuff to the experts shouldn't we shut this forum down?

My opinion is that if you want to delve into the world of suspension fabrication, there is no better place to start than with a live axle rear suspension. Yes, you need to know how to weld, yes, you should have at least some rudimentary knowledge of suspensions and yes, you're going to have to tune it yourself, but you definitely don't need to be an expert. There is absolutely no better way to learn than to build it, tune it and race it. All the books in the world won't make you faster than the guy who's done it.

Please excuse me if this seems like a rant. My pet peeve on the 'net are the people who give no information but constantly hand out warnings about the danger and impending doom of this or that. If you're not that guy then forget about it. If you are, then I'm ranting about you......


Wally

[Norm Peterson]

Might want to add "and have a logical approach to technical/mechanical things" to that list, Wally. Otherwise, guess which way the "hit-or-miss" approach to tuning will mostly end up.

In the pics on the previous page, I keep thinking that small diagonal braces running forward and outward toward from opposite the truck arm chassis pickups to the main rails where the next lateral members connect would be a structurally better approach than placing the full demand of tire traction load (times some impact factor) on that crossmember with the huge hole cut alone. The tube size that I have in mind would weigh less than 3 lbs per foot and provide both higher local rigidity at the truck arm pickups and greater fatigue resistance to the crossmember (you really wouldn't want that thing to crack while in service).

Yes, this may sound like I'm being a bit too conservative, but the NASCAR designs include similar bracing for their truck arm crossmembers (which don't have d/s hole cuts and are subject to far more frequent inspection than any street car would ever get). Sounds like you'd get a ton of peace of mind for less than 20 lbs of metal that's attached down low and near the mass centroid.

Norm

[Mean 69]

Interesting thread. Seems to me that there are "basically" three types of folks that are interested in modifying their suspension. The first type generally believes that if you just replace all the bushings with polyurethane, and some powder coated springs and maybe a new sway bar, you are ready for Road Atlanta, look out world. The second type are a bit more deliberate, and these are the types of folks that DSE, HTH, WDE, and others supply to. These folks see or drive a pretty cool car, and want to duplicate it for themselves, because it "must" work really well. Heck, the guy that built that other car "must" know exactly what he is doing. These folks are willing to make compromises, but nothing terribly inconvenient or inventive on their part. They may try to learn a few concepts, and are probably the first to spurt out terms like "camber gain" or "roll center," but not really willing to learn that all of the issues are intertwined. And by the way, there is nothing wrong at all with either of these types of folks, nothing wrong at all.

Then, there's the third group. These folks are never satisfied, usually or always feeling that there is a better way to do things. They research, learn, attempt, and if they fail they try again. These folks also understand that there will always be a compromise, that there is not a perfect solution, and make their decisions based upon what they feel are the most important attributes. If these folks bought a suspension kit, it would be because it's good, not marketing good, but functionally good. They'd probably only buy it in the first place if it was too inconvenient to build themselves. These folks actually DO drive their cars, fast, on the track, and are honest with themselves about how it performs.

It's really all perspective, you will hear from all three classes of folks, certainly here due to the rapidly growing interest in this sector of the hobby. So when folks state that their feeling is that one solution is better than another, just keep in mind where they are coming from.

So how does this all relate to the truck arm setup? In my OPINION, if you were to build a suspension setup on your own, there are other types of setups that offer fewer compromises than the Truck Arm. So far, in this thread and others as they relate to the truck arms, there is a serious lack of technical argument as to WHY they work "so well," and it is understandable from a proprietary standpoint from HTH, but honestly, the system is very, very basic.


I keep thinking that small diagonal braces running forward and outward toward from opposite the truck arm chassis pickups to the main rails where the next lateral members connect would be a structurally better approach than placing the full demand of tire traction load (times some impact factor) on that crossmember with the huge hole cut alone.

In addition, I would consider moving the existing angular links that run back and out, closer to the pickup point for the T/A mounts, i.e. move them inward as far as possible towards the vehicle centerline. You can run some small extensions that would tie these back to the frame connectors (the runs that run parallel to the vehicle centerline). This would also help reduce the bending moment that the crossmember would see. You don't need to run super thick wall tubing, it is all about triangulation.

Mark

[Norm Peterson]

So far, in this thread and others as they relate to the truck arms, there is a serious lack of technical argument as to WHY they work "so well," and it is understandable from a proprietary standpoint from HTH, but honestly, the system is very, very basic.The most obvious reason that they work as well as they do is because rear axle roll steer can not only be made a small value of vehicle roll understeer, but also because the roll steer won't vary a whole lot over suspension travel due to the length of the truck arms. That goes toward 'predictability' and 'driver confidence'. I can picture a couple of other considerations that might be part of a good truck arm setup but I have no derivation or proof of same (this may be where 'proprietary' begins . . .)

Norm

[MrQuick]

Forgive me Wally for my glass half empty look towards this but Im just trying to avoid having a novice builder looking at this thread and saying "hey I could build that myself". I try to offer as much advice as I can but this is the best advice I can give in this situation...its alot better than a ueligy at a funeral where im apologizing.
Again just a warning to those that may not have the experience others have. This kit or others isn't just bolting on a pair of subframe connectors. This is something that can be potentialy deadly. Tuning an proper welding tecniques are required here.
Besides having pasts failiure due to improper welds or inferior metal there are also things like snap oversteer and bind unloading (don't know proper term) that can cause someone to loose control on a high speed bump.
Having worked in a performance shop for several years I have seen and heard horror stories of do it yourselfers dying or getting very close to dying. One guy with a home made R&P set up, his cheap steering shaft set up consisting of 3 u-joints broke free during a high speed jaunt due to an inadequate design, potentialy deadly for others since he was on the highway and hit a pot hole. Another guy, with a home made four link lost control when his home made lower link to frame bracket broke loose during a panic stop situation. This was caused by metal fatigue due to exsessive heat from his gas and stick welder.I asked him why he didn't have a safety plate to secure the lower link if the spherical were to break...his answer " I didn't know I needed one, there wasn't one in the picture." This also happened on a public highway. Remember there are proper areas to test and not everyone here is going to do so.
Ok to validate this post as something about truck arm suspensions Having riden in a 70 Chevelle equipt with a HTH truck are set up, I must say the system improved the car over stock. The most praise I have heard about this kit is its ease of adjustment.

[wally8]

Norm,

You're right you need to be able to tune in a reasonable manner. Some guys will just never get it. Most here seem to be capable though.

That plays in to what I think Quick is really saying too. I take for granted that you tune cars on a race track and not the street but that isn't the case for most I suppose. Point taken.

I've seen some pretty stupidly fabricated things on race tracks too where cars are supposed to be inspected. I saw a car with a black pipe roll cage and a fiberglass racing seat. The guy got hit, rolled and broke his back. Now he's in a wheel chair.

Life's a full contact sport and it is dangerous to a certain extent. No harm in warning others to be careful of unintended consequences, though.

I was thinking about the truck arm too but like M69 said, I think a 3 link or torque arm is a better design overall (less compromises). I'm going the torque arm route. I'm putting a lot of thought into LCA length though. I'm not sure how I'll get the mounts moved forward yet but it seems worth doing. However, this starts to be part of the problem that I had with the truck arm design to begin with (too long, no floor pan clearance for a lowered car). More compromises.....


Wally

[redss86]

Start there but give yourself plenty of adjustment on the PHB up and down. (I would say mostly up from there but my experience is with dirt cars so don't go by my word on that part.) This isn't a two hole sort of adjustment situation. I like the infinitely adjustable slotted mounts. They'll give you several inches. Again, you can get them from all of the stockcar suppliers.

So w/ the arm mounts as low as I can get them, the phb just above the virtual intersect point and parallel to the rearend when it is in the middle of its adjustability. I would be at a good starting point, correct?

What about the spring and shock locations? I was trying to decide wether to mount the springs on the axle or on the arms, what would be better. Remember, I am using a 9" so the perches are not already on the rearend. As far as the shocks go, I have seen them mounted on the tail end of the arms. Is this a good location?

[wally8]

Any of those mounting scenarios should be fine. You'll just have to figure your spring rate based on whatever motion ratio you end up with for your mounting application. Same thing for shocks.



Wally

[69boo307]

Having riden in a 70 Chevelle equipt with a HTH truck are set up, I must say the system improved the car over stock. The most praise I have heard about this kit is its ease of adjustment[/I].

My '69 chevelle has the HTH kit, I have done a little tinkering with tuning it. It does have a couple of different holes for the attachement of the truckarms, although 9 times out of 10 you'd use the bottom holes. I can tweak the panhard rod and spring jacks literally in just a couple of minutes. I have the panhard set basically level when the car is at rest, with the length adjusted to center the rearend under the car. Adjusting the rear springs is just a matter of sticking a 1/2" drive rachet in the trunk and turning it. I don't have any quantitative data, my 'tuning' was all seat of the pants, but it's definitely easy to do. I found that if I had the rear too high the car felt floaty when I turned and too lively over bumps. Too low, it felt kinda 'dead' like the rear suspension was kind of inhibited from moving freely. In the right spot it feels neutral and smooth through corners and just as the HTH guys have said in other posts, the more throttle you give it the more it digs in and holds. When you do exceed the traction limit it does so predictibly.
I posted an autocross review with the setup a while back, do a search. Cliff notes: the car was much better than stock and performed well, but I could still tell I was driving a big, heavy, 40 year old car.

One dissagreeable behavior I've noticed, although this is present to some extent with any live axle setup with a pretty stiff suspension, if you hit bumps mid-corner it can be unsettling. The entire rear of the car may jump to one side or the other slightly. I had this behavior with my 4th gen camaro too though, but it wasn't quite as pronounced as with the chevelle. It definitely behaves better on smooth pavement.

If you went to the track with a 1/2" rachet, a couple of big sockets, 1 wrench, a tape measure, and a pair of channel-locks, you can tune the HTH kit without raising the car off the ground. It would take you maybe 3-4 minutes between runs.

[Mean 69]

One dissagreeable behavior I've noticed, although this is present to some extent with any live axle setup with a pretty stiff suspension, if you hit bumps mid-corner it can be unsettling. The entire rear of the car may jump to one side or the other slightly.

Do you know what spring rate you are running on the car? I concur, it is not too fun when the car scampers about in a turn, but you might be able to mitigate this somewhat by running a softer spring. If your car doesn't bottom out over bumps, you may able to soften things up a bit, just look at what the free height of the spring is, and contact Coleman or some of the other circle track suppliers. Might be worth a try. I read another post where the guy who had the car felt it was a bit stiff, he also didn't like the noise associated with the setup. I have no clue about the HTH guys, but folks seems to over-spring cars a lot of the times. BTW, the setup doesn't run an anti-sway bar, does it?

And by the way, short of hard numbers, the ass-o-meter is a usually good indicator of performance, if you are honest (which is clearly the case with your description above). Thanks for the feedback!

Mark

[69boo307]

Mean 69, I have no idea what the spring rates are, they are the ones that come with the kit, and I have the front ones to match. The Carrera shocks they send with the kit are supposedly matched to the springs. There is no rear sway bar, and I run the stock sway bar on the front. The car doesn't feel too stiff to me in general, it just has some little gremlins that show up when you hit a bump :).

I replied in the 'noise' thread too, the panhard has heim joints and is connected to a heavy bracket that is welded to the frame of the car, so some noise is not a surprise, especially for me since I'm running poly body mounts.