Here is mine. Just a wrecking yard panhard bar shortend for my use. Mounted in double shear on the frame (left) side and what appears to be a bolt is actually a 1 inch piece of thick wall tubing the bolt is only there to hold the washer and bushing halves together. Its pretty stout and exactly how it was mounted on the Pathfinder I removed it from. Its also fairly centered height wise with the centerline of the axle and very near the same roll center as the front.
The only thing I see correct on this rear suspension is the panhard bar , but this is academic [ it wouldn’t matter if it was mounted on a 30° angle because the suspension is that stiff that there is not enough movement to cause bump steer ] The roll stiffness isn’t a concern either [ it doesn’t even come into the equation here ] with this ladder bar suspension you end up with a 4’ wide swing arm, so it wouldn’t matter if you simply had one coil spring on the centre of the diff head. I recommended earlier to lower the spring rate down to 90 lbs / in [ this is actually on the stiffer side for a bucket / roadster ] For comparison is a 69 Camaro has 89 lb/in leafs and a 69 Stang has 110 lb/in leafs in cars that weigh approx 3500 lbs with 45% rear weight bias. The high performance road racing homologation specials , like the Z28 Camaro had 131 lb/in leafs , and the Boss Mustang had 152 lb/in leafs. 240 lb/in coils do not belong in that car [ with relatively low sprung weight ] You seriously need to get rid of those ladder bars, and lower the spring stiffness. A good starting point would be to weigh the rear of the car, then pull the springs out and weigh the wheels again [ while the car is on stands ] to deduct the unsprung weight. Once you know the sprung weight divide this by 4 to 5 to get the total spring stiffness [ then divide by 2 to get each spring ] Dividing by 5 would give you a softer more comfortable ride. [ if you don’t understand this, go out and jack up your daily driver and measure how many inches it will lift before the wheel leaves the ground ] When you put softer springs in, they need to be taller [ this is referred to as “spring load” which is not to be confused with spring rate ] I also noticed a rear seat in this car, so I assume this car isn’t a road racer [ go for the comfort ]
ok 23 tub thanks for the report this is whats up. With your car on jack stands and from your trial you indicate that you have 1/8" side motion on your axle. This is where your problem starts. The front pivots for the radius rods are heim ends that are basicly ball bearings with a hole. This application allows for motion but only constrains the longitudinal mount of the vehicle. Because of the design the lateral movement is still possible within the angle of operation of the heim end thus you get side to side movement up to the max degree of the end. If you disconnect your panard rod the axle can move side to side the arc of the heim end allowed. This side to side movement creates an arc in relationship to the center line of the vehicle so any lateral movement will now cause the axle to point in that direction and track in that direction. To control that you need a constraint of some kind in this case a panard rod. In your case the panard rod of choice has two rotary ends which work fine but in only one position. However as the axle bumps the angle of the axle changes and the two rotary panard rod ends reset at the new angle skewing the axle because it rotates on the front mount heims.Kind of like a parallelogram. By exchanging the heim end on one end of the panard rod to a fixed end this forms a constraint that cancels out the lateral movement of the ladder bar heim end because it removes the hinge point. The ladder bars now can only operate up and down and the axle tracks true. The heim end on the other side of the panard rod only has to deal with the torsional misalignment and the minor operating arc deflection which is taken up by the ball motion of the end. This is also why its important to keep the panard rod and the axle in concentric arc operation. After you have gotten your ride to track straight you can then address the spring ride rate.
That's quite a bit, and I'm sure it's even more when being acted upon by the dynamic spung and unsrung weight of your bucket. Kind of like the old bananna bikes with split frame. Whoo hoo hold on. Listen to what dick is telling you. He's on the money
Oh , and be sure to post some pics when you get this part If you go with George's economical idea of 1 240 pounder, don't post pics. I've had all I can take in the oven cleaner thread.
I'll be sure to post pictures of any strippers I can find to help in choosing my springs. After staring at this thing for awhile today - and grabbing the panhard bar and heaving (on the bar, not my guts), I have a sneaking suspicion that it's flexing. Thought before that it was stout enough, but on second (or third or whatever) look, I'm not so sure. The tie rod they had on this thing was too flimsy too, which gave me a severely fluttering right front wheel (standard, not cross steering). Replaced it with a stouter bar and no more flutter. So I got online and ordered a new one from Speedway along with the bushing end Dick recommended. Should be in late this coming week, depending on how slow the pony express is from Nebraska to Socal. There are many, many possibilities, but being s stubborn cuss, I need to prove that the obvious is or is not the problem before going for the more complicated fixes. BTW, I also ordered some 14", 150 pound springs for you spring aficionados as the 150# 12 inchers I have on it now ride just a bit too low. Ride is decent other than the twitching. Stay tuned.....
You have hair pins on the front with a tube axle. That makes for extreame roll stifness because the tube axle will not twist. The rear is the same design but worst because the rear axle is even stiffer. You need to go to 4 bar suspension on both ends. The rear spring rate should be near 100 lbs/ in. The pan hard bar is excellent as is. I have seen a bunch of simular suspensions fail and sometimes at speed on the highway. It is a critical design flaw that needs to be changed for safety sake. It should be fine then.
Between Dick, Koz, Kerry and Andy, you've got a rodder's best consults. They help the rest of us 'unwashed' types, and I've learned a bit from these notes, so thanks guys.
Great thread, very interesting. Listen to Dicks advice and change one thing at a time. Change the one panhard heim out for the fixed one and then road test before installing the new springs. Changing multiple things at once often leads to even more confusion.
Absolutely on one thing at a time. Scientific method. Leaned that years ago. Otherwise you will never know exactly what the problem (or fix) was...
Haven't tried that. It'll go on the list. My favorite test expansion joint is on a relative busy freeway nearby, so I'll need to find a time lends itself to a coasting test.
I still think the extreme roll stiffness is the problem. For fun, try jacking one rear wheel up and see if the other side comes up too.
Try 15# in the rear tires. 180# rear spring.The rear hair pins are acting like a sway bar but won't make rear step out. The pan hard should be level to the ground at ride height. What is the wheel base on the car.
Wheel base is 100 inches. Panhard bar should be pretty close to level to the ground when I put in the 14" springs.
New panhard bar and springs arrived. Installed the springs. Received the wrong Heims with it, so had to order the correct ones. Tried an install, but the panhard bar will hit the differential cover. So gotta get the mount changed. Since I can't weld, gotta take it somewhere to get that done. Also received the part Dick suggested. It won't fit either because of the chassis end panhard mount. So the story goes on. I'll post results after I get the welding done. Thanks to all for the suggestions.
I'm still amazed ! six pages and not one other person is curious about the front end set up. Rear set up is very basic, the problems could be coming from the front. OK I'm done !!!!!!!!!!!
Old springs (14 inch 250 lb) were much too stiff. Was just trying to limit the amount of up and down travel in the rear end as an experiment. I then installed some 150 Lb. 12 inchers, but the car sat a bit too low even though the ride was MUCH better. So I ordered the 14 inch 150s. Test run this coming Saturday. Not holding out too much hope as I had 14 inch 170s in it once before and the problem was still there. All I was able to do this time was to do a little front to back spacing tweak on the panhard bar where it mounted to the axle. It was about 1/2" closer to the axle on the axle mount end. Just a matter of changing a few spacers. Sure wish I could weld.
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