Hello Folks ! Have four link in the back of 30 Coupe amd would like to swap them out for something different . The distance between the bolts in the rear appear to be 5 & 3/8 . My question is does anyone know if there are any ladder bars with that same distance between their bolts ? Would like to keep the brackets that are currently welded to the axle for the four link but again , swap them out with something with a single bolt mount in the front . Thanks in advance yall ! Eric
I doubt you will find any ladder bar that will have the same dimension. If you can weld you can make up a set yourself. Good luck. Pat
As 1934 coupe said, it will be near impossible to find bars with your same centers, offset, and will fit your pinion angle. If you can build your own, this is a sample of my fixture and finished product. Simple angle iron with the critical holes in the proper places.
1. For a street car you want the ladder bars angled to meet at a point in the centre of the car, if long enough. If shorter , then at least along that imaginary line. 2. 4 bar brackets are set up to point straight forward. On that basis, I would cut them off and start again.
By the ***le... "Rear" ladder bars"...I guess that's better than front ladder bars. Anyway. Why go backward in design ? With a four bar or four link (similar but different), the pinion gear angle stays the same through out the up and down axle travel. With a ladder bar suspension, the pinion angle changes continuously ! NOT...particularly good for U-joints. Have people run ladder bars on the street, sure, but again, the four bar is a much better method for a long lasting pinion bearing, u-joint and yoke on the drive shaft. While you don't say if you are building a race car or a street car (we NEED details !), for a street driven car, the four bar is a MUCH better arrangement than a ladder bar ***embly. IF...you are building a race car of some sort, the four bar is still a bit better a solution for axle (yes, the rear) control. Mike
Gotta be worth giving p&j a call. I had, still have in fact, some p&j ladder bars which turned out to be an inch too short due to an error in the placement of the mounting crossmember. They were able to make another pair an inch longer with no fuss whatsoever, and they fitted perfectly to the existing axle brackets (although one inch might not make that much difference to the spacing, but it must be something). Chris
Doing this would be a huge mistake, unless this is a dedicated drag race car, that will never see the street. A 4-link, parallel, or triangulated, allows the axle to articulate based on the constraints of the swing of each link. This is super handy if you live in a world where there are bumps in the road, potholes, driveway transitions, etc. It also allows for a bit of body roll when turning a corner, so as not to harshly upset the ch***is, causing a loss of lateral traction. The installation of a set of parallel ladder bars turns the entire ladder bar and rear axle housing combination into one big anti-sway bar, with absolutely zero flex. It would essentially be a swingarm. Not only would this upset the entire rear of the ch***is every time that one rear wheel goes over a bump, or a pothole, it will lead to sever oversteer in a corner. While it might be fun for you to play Johnny drift racer on every exit ramp, that will get old, and your luck in controlling it might one day run out. There is only one ladder bar arrangement that does not have this glaring defect, and those are the Pete and Jake's ones, or others built in that style: These bars are close together at the leading end, which in combination with the ladder bars themselves twisting, allows the axle to articulate over bumps. Only folks who do not understand how suspension works will tell you that hot rods are supposed to ride and handle like ****.
I'm actually doing the opposite on a '29 Roadster build at the moment; removing the P&J's ladder bars and fabricating a 4-link for the rear. For all the reasons Gimpy mentioned in addition to the fact that the design chews up a LOT of real estate under the car where the exhaust and mufflers would like to reside. I'll take some measurements of the ladder bars if you're interested in them, I'll make you a good deal on them, including the rearend mounts. You'll need a front crossmember of at the very least four ch***is tabs to attach the arms to, but that's easy. I might even be able to scare up a set of those...
As far as I'm concerned, the only articulation in that kind of suspension design, with semi rigid bushings up front is the twisting of the bars themselves. The front joints have little to no twist available, regardless of how close or far the joints are from one another, so the only thing that's going to give are the bars. Many split bones are setup that way. The bone tubes are the only thing providing articulation and are twisting back and forth. There are many instances of the original cast ends of the bones, at the diff housing failing from the twisting action and breaking in half. When that happens, its disaster. When the bars are mounted rigid to the axle housing, the joints in the front of the bar have to in essence, be able to flop side to side, to provide articulation. With 85 year old split bones, this is a serious issue. I think even with ladder bar type suspension, this twisting action, over time will become an issue also. I have 40 split bones on my 32, but done with tie rod ends at the front, and the bones are bent outward, which multiplies the articulation available at the tie rod end joint. My bones can in essence flop back and forth in the tie rod end, preventing the twisting. I have more articulation in the rear suspension than I will ever need. Bill
& iirc, the original OEM version of P&J's "ladder bars" was called Converging Trailing Arms, aka "Truck Arms". By GM. Not only did the steel-sleeved rubber bushings give-n-twist, so did the actual arms, as they were designed to do this(think 'C'channel, riveted back-to-back together to form a lightweight flexible 'I'-beam). Some folks think they can out-engineer gm on this, & build them out of 1-peice rectangular or round tubing = no twist. Bad idea, even though some get away w/it, like split early ford bones. Yayayaya, it'll work, up to a point, 'till it doesn't. Then, usually, things can get "exciting" for a moment or two. Ideally, P&J's bars would converge under the u-joint, w/1 very large H.D. heim, or better, a large Johnny-Joint. Little ugly, but better engineering. BTW, if you ever get to crawl under a 40' MANN bus, the rearaxle was held in place just like that. I tried, but never actually got, one of the super-size heim-joints. Would've been a nice conversation piece. . Marcus...
The 4-link on my Model A has Johnny Joints at the leading ends of the links. They are deep enough into the brackets that they cannot be seen easily. They come in a variety of sizes from Currie, and now come in polished stainless steel, for a much improved appearance.
So what are shackles doing that's any different? The front of the spring is attached to the frame like the ladder bar, ladder bar attaches to the rear end housing like the U-bolts attach the leafs to the housing. Ladder bar still has a spring behind the rear end just like the last half of the leaf on the leaf spring. From frame mount to housing both setups allow the rear end to move in an arc. I'm not seeing the difference where one "can't" be driven on the street and one is m*** produced by car manufacturers.
Ok, let me see if I can strip the Automotive Engineer speak out of this: Parallel ladder bars are rigid front to rear. They move in a fixed arc. Leaf springs are NOT. They move in a variable arc. The distance between the axle and the pivot of a parallel ladder bar is fixed. The distance between the axle and the front pivot of a leaf spring is not fixed. That effective length varies as the spring cycles One leaf spring can be at a fixed distance away from the frame, while the other is moved up and down. This is possible because the spring that is not moving up and down is being longitudinally twisted. This is not possible with parallel ladder bars. While the ladder bar that is on the side that is moving up and down can be twisted, deflect its bushing, or pivot on its heim joint, the side that would be moved up and down would need to move in an arc. Both conditions cannot exist at the same time! Since parallel ladder bars require either a diagonal link, a Panhard bar, or a Watts link, the axle is constrained from deflection by that link. This is instant bind. The only way that the axle can move is the whole thing, up, or down. This will lead to link failure, bracket failure, and/or joint failure over time, a harsh ride, and poor cornering performance. There are NO OEM examples of parallel ladder bars of the kind that are found in the aftermarket.
^^^^ One of my kin fock street driven a 32 in early 90s with ladder-bars, (155 mph low 9s 1/4) constantly breaking welds & hiem joints , switch to 4 link No more issues , Ladder bars on Drag set up with soft side walls less binding/ stress on welds / suspension when turning , All the(S D) ladder bar set ups I knew of on hard side walls had issues
If your coupe is fenderless, I understand why you would want to make that change. The common TCI, P&J front 4 bar mounts just look too “Street Rod” hanging down on a traditional hot rod but if you’re going to run fenders don’t worry about it, they don’t show. My coupe has P&J 4 bar in the rear and you can’t see them from the side and you can’t tell the difference from the rear. It does ride pretty nice for what it is. If your car is going to be a traditional style and fenderless, I’d do as Marty suggested and make your own, it’s easy. Do make them converge at the front though not parallel to each other. It’s the best compromise between style, safety and ride quality. I’ve seen failed Heim joints, cracked welds and brackets as well as broken ladder bars on parallel ladder bar setups used a lot on the street.
Bob, I had a 32 in here with ladder bars, and a diagonal track locater, and panhard bar as well. Pretty bound up !
Splitting hairs, perhaps, but there is nothing imparting torsion to the ladder bars, provided the front joints can accommodate the ±5° of axial rotation either way it's likely to see. Perhaps that's what you mean by "flop side to side"? —which is entirely correct. What happens, however, is: in a left turn, the front joint of the left ladder bar is pulled upwards and that of the right ladder bar is pushed downwards. This imparts compression in the upper chord of the left ladder bar and the lower chord of the right ladder bar, and tension in the upper chord of the right ladder bar and the lower chord of the left ladder bar. And, of course, vice versa in a right turn. The same conditions are experienced with single-wheel bumps. The configuration of the ladder bars is such that they resist these compressions and tensions quite effectively, with no strain to speak of. The forces are instead transmitted onto the plates on the axle. I suspect that the failure point is going to be at (one of) those four clevises, either by shearing the bolts or elongating the holes in the plate. The magnitude of these forces varies with the horizontal distance between the front joints. The problem disappears completely when that distance is zero, e.g. a single joint above or below the drive shaft or even, if you want to be fancy, concentric with the front U-joint on the drive shaft, in which case you've effectively got a torque tube. A ladder bar setup idealizes to a torque tube setup with much better beam strength for vertical loads.
Take note of post 21. I don't know how many of these parallel setups you've seen in real life - especially after some use - but I can tell you @19Eddy30 is not making things up.
I have two cars with ladder bar setups, they're purposely built for straight line excceleration but also have many street miles on them, I don't slow down to 1 mph to take turns either. If you count the t-bucket with it's buggy spring then I have 3 cars. The cars weren't built to be rock climbers or go off roading that need to articulate with one tire 3 ft higher than the opposite side. They do however drive over pothole streets and up steep driveways, some of you guys are way over exaggerating things here. There are many many cars doing race week type events driving across the U.S. and racing along the way with ladder bar setups. Does a person build a ladder bar car to go road racing, absolutely not, just like a guy into 200 mph landspeed racing doesn't attempt it in a city bus. But in both cases the vehicle can make the trip, just not as fast as the purpose built machine. Apples to apples and oranges to oranges.
I had an off-topic Nova that was tubbed and had parallel ladder bars. I put a lot of street miles on that car. I drove it to a show 180 miles away and ... the ladder bar broke. Luckily it made itself obvious without me ending up on my roof or crashing into an innocent. A former friend with an off-topic tubbed car with parallel ladder bars broke a heim end while driving it on the street. He got lucky too as he was not going fast when it broke. As others have mentioned, parallel ladders bars turn the rear end into a SOLID sway bar. During normal street driving, some part of your rear suspension is being stressed. Lots of people have put plenty of street miles on cars with parallel ladder bars without issue ... lots of people have walked on ridiculously thin ice and not fallen through too. Walking on thin ice and not falling through does NOT erase the fact that you were in fact actually walking on dangerously thin ice. Having had a ladder bar break, I am now very aware of correct geometry and now choose correct geometry over "that'll work just fine, been doing it for years". I will NEVER run parallel ladders bars on the street again.
There are actual Automotive Engineers on this thread. It might be a good idea if you actually listened to them. You are en***led to your own opinion, but you are not en***led to your own facts. There is a reason why they are not called The Friendly Suggestions of Physics. They are incontrovertible laws.
The Jalopy Journal
