Good tip on using the crossmember, Leevon. That will come in handy when I build my truck. I spent last Saturday at junkyard pulling some trailings for use on my coupe.
The '67 is a little off-topic for this board, but I will cover the general suspension stuff. Quarter elliptic springs curve toward the ground as they go away from where they mount on the chassis. Generally, the farther away from the axle that they mount on the chassis, the greater the curve. Go far enough away, and the ends of the springs will be touching the ground. You could use a flatter spring, but the ride would not be as good. The longer the spring is, the stiffer it has to be to do its job, and the more force it puts on the chassis mounts. It takes more than the center bolt to mount them. Typically, I have held them down with six fasteners of 7/16" or better, three on each side of the spring, through a plate, and the frame. As for the Johnny Joints, they are overkill on the street. You'd be better off with a nice poly or rubber bushing. You don't need, or want, that kind of flex in a street vehicle.
Maybe a silly question, but with the u-bolts going over the rear axle tube at an angle, wouldn't that mean that they have an inside diameter greater than the diameter of the axle tube (leaf spring u-bolts mount perpendicular to the tube, so you use one that fits the diameter). With it being a greater diameter, the relatively flatter area at the top of the u-bolt could distort, or dent the tube... Or am I just being too anal and it's not that important? I was doing a Clark-Style I beam truck arms and notching the top and bottom of ther "I" and bending and re-welding so that they are perpendicular where they go under the axle tubes... Would I just be better off leaving them and the ubolts at an angle?
the arms are 51inches cl of axle to cl of front bushing. this is stock from the trucks and most nascar as well, but be careful as they do have 47s I believe and more than likely more...they run them offset sometimes depending on the track
As for the Johnny Joints, they are overkill on the street. You'd be better off with a nice poly or rubber bushing. You don't need, or want, that kind of flex in a street vehicle.[/QUOTE] You never want your joint, as in your bushing , be it poly or rubber, to be a influence in the LACK of freedom in your system...this is what your springs and shocks are for....if your bushings can cause so much resistance to movement, they will fail in a far shorter time than they were designed for....yes, they will give resistance, just don't put that into your design as this factor will change, for the worse, with age/use. The best system is a suspension with complete freedom(or flex) with no binding or resistance in it's range of movement(this is without springs or shocks, just talking connecting arms/links here)....and for your "control" to come from properly setup springs and shocks....the trend is to go with a lower rate spring and better shocks than in the old days. This give a much better ride, but at greater expense as good shocks are not cheap (Ohlins, etc) and in my book...overkill is good.. Hans Hans
Make exhaust systems hard to do.They work well but so do other types.Worked with this type of suspension for 20+yrs.wouldn't use on my project.
I have been curious where the truck arms front centerline, should be. I noticed the pics show the bottom of the arm somewhat flush with the bottom of the frame. I have a couple of cars to do, and have pondered this quite often. Appreciate any info!
Some update pics. The crossmember took maybe an hour to fab, I cut the ends off flush with the inside of the frame and welded on some heavy c-channel that slips into the frame, which will be bolted for ease of removal in the future. I tweaked the arms inboard a bit for locating the bag mounts and so the u-bolts would clear the c-notch and I could go lower. I used a universal panhard from suicidedoors.com and located it to be parallel / square at ride height. From full extension to full drop the arc moves the rear maybe 1/2" side to side. In the range I'll actually be using the suspension it's less than 1/4". Only thing left to do is mount the shocks, set the pinion angle and weld the axle brackets for good. And I agree with Harley Man on the exhaust, that's why I'm going to be dumping it before the axle.
Just went out and checked... the centerline of my arm bolts are located about 5" down from the top of the frame or roughly within 1/2" of the bottom of the frame as you suggested, this mirrors the stock geometry closely.
I would also like to know the answer to this jay , and what's the shortest the arms can be with out messing up ride quility, since I'm actually thinking about using this type of setup I'm my wagon
The longer the arm, the smoother the ride. I think of it as a fulcrum.. the longer the arm and farther forward it is, the easier it is to control the weight. It's like a bicycle with the handle bars moved all the way forward.. try to do a wheelie and you have no leverage to get it up(no pun). Because the weight is spread out forward. Move em back(which is a short control arm) an it's easier to pull up the front. My Dad has a 70 Chevy Shortbed. A friend has a sportmans class/Nascar chassis made for his 55 2dr post. I am convinced it can be tuned and perform to my highest expectations. I am just going to have to mock everything up, per vehicle.
Similar set up to 42-48 Oldsmobile. Similar year Chev, Caddy & I believe Buick used leaf spring rear suspension. My 46 model 76 sedanette uses those long style long lower arms that mount rear of transmission mount. No top arms, only a panhard bad.
So I know the the longer the arm the better but does aney one know how short is too short before its sacrificing the ride quality ?
woodpecker, the short arms start messing with the ride quality about the same time the start messing up your pinion angle through the travel or your suspension.......seems to work that way....
I know a late 60 s chevy pick up traling arm are around 50 some inches I'm looking at building trailing Arms for my wagon that are around 43 inches max is that going to be to short for good ride quality ?
While you are 100% correct, I disagree. The theory is sound, and makes perfect sense on the track, or the trail, it may not make sense on the street, under non-ideal conditions. There are aspects of a rubber or polyurethane bushing that hare very desirable that are not provided by a low friction joint. First, heim joints (rod ends) or Johnny Joints provide little or no vibration dampening. This can result in a large percentage of road vibration to transferred to the occupants of the vehicle. I have ridden in and driven in vehicles with all heim joints in the suspension, some track cars, some with huge soft tires. The ride of all of them left me hating life after just a few miles. The second is torsional dampening. A properly setup rubber or poly joint (no pre-load at ride height) will aid in the suspension returning to center. Yes, in an ideal world, this should all be done by the shock absorbers. Yes, modern shock absorbers are much better than the shock absorbers of days gone by, even so, most are only available in one or possibly two valving configurations, unless you opt for some very expensive ones. Sure Ohlins and other high-end shocks are awesome, but most folks will balk at the price, right off. Those who will spring for them might regret it if finding the right setup becomes difficult or tedious. Getting that valving wrong, or coupling a low-friction suspension setup with a "regular" shock may result in unacceptable ride quality, and uncomfortable if not dangerous handling. This is especially compounded by what my experience has shown me, which is that most cars are too stiffly sprung, often by several hundred inch/pounds. Bushings will give a more comfortable ride, even if they are a theoretical hinderance to suspension movement, and a "band-aid" for lesser shocks, and require virtually no maintenance, which cannot be said of any low friction joints. Properly sized for the application and movement range, they will easily last for decades.
Has anyone used the bolt in crossmember from Classic Performance. or the one by Early Classic? There was an article about putting this suspension on a 49 Chevy in Rod and Custom. They used the drop crossmember from Classic Performance but when I contacted them they said that project was a prototype and they have not made any others like the one they used. I was just wondering if anyone had used either of these cross members and how they had modified them to fit.
one draw back with truck arms is seat bottom and floor board clearance if your car is lowered. if the car you are building is goingto be low to the ground,,,go with a 3 or 4 link.
Although my car isn't as low as a lot of people like, I did consider this, and rear seat clearance was one of the reasons I considered truck arms in the first place. With a triangulated 4-bar, you'll definitely have a turf war between the rear seat and the upper bars (regardless of whether the upper bars are pointed in at the front or the rear). A regular 4-bar or 4-link is still pretty questionable, though not as bad. With the truck arms, the amount of arm movement under the rear seat is pretty minimal compared to the axle itself, since they are closer to the center of the arc of motion. With either type of suspension, you can put your bags/coils/coilovers/shockwaves behind the axle to allow even more rear seat room. This is at the expense of some trunk space, though. (My coilovers are in front of the axle to allow room to route exhaust over the rear axle and still clear a decent sized fuel tank, the panhard bar, and the rear sway bar.)
This is the prototype crossmember that was used on the 49 Chevy Purple Pig in the Rod and Custom article. I'm thinking of making one just like it. It is bolted to the frame with 6 3/8" grade 8 bolts. It is not bolted to the inner frame and the top of the crossmember does not attach to the frame. If you have a truck arm suspension, does this design look like it will work? Or what else needs to be done to it? Thanks, Bill
i made a truck arm setup for my buick, it works very well, rides good and i didn`t have to cut into the floor one little bit. the setup there looks very nice, i`d run it.........good luck
I'm not sure if it's been mentioned but these type of suspensions work best with I-beam section control arms. I-beams are not torsionally stiff, they allow the rear end to articulate with out putting all the strain on the bushings like a box tube or round tube control arm. GM knew what they were doing. just throwing it out there I've seen a bunch of back and forth about the types of bushings and blah blah blah. I had a '64 3/4 ton It chewed up a lot of carrier bearings, but never needed control arm bushings.
I would want to have an attachment to the top of the frame or at least the sides so the cross member wasn't trying to twist itself off the lower mount, making it into a "K" member (with diagonals meeting near the center and going either forward or aft to the frame rails) would be ideal. But I tend to be a bit paranoid about that sort of thing.
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