Most people are familiar with bump steer. I have no problem what so ever with bump steer. What I do have I'll call torque steer for lack of a better description. If I jump on that Hemi it pulls right enough that it takes about 1/8 turn of the steering wheel to the left to keep it straight down the road. When I back off the opposite takes place, pulls left requiring a turn to the right. I have checked to see if the wheel base is right, rearend square with the world. Everything is tight. Panhard bar on the front mounted from the left frame rail to a bracket welded on the right radius rod. Panhard on the rearend from the left frame rail to a bracket welded to the rearend as far toward the right frame rail as I could mount it. Ladder bars with coil overs on the rear and a monoleaf spring on the front. I really don't have a idea what to look for next other than take it to a front end shop and have them check to see if everything is in the chassis like it is suppose to be. I don't think the frame is flexing. It is 3/16 box tubing with 11 ga duece style frame covers welded to the front part and the body has 16 ga floors with a 1x1 and 1x2 box tubing reinforcement. The car weighs 2800 and change. Any Ideas?
I had an A pick uo with a 327. It did the same thing. the rear end was shifting. Have you checked that?
sounds like bad steering geometry. when you jump on it, the front lifts a bit - right. When you let off, it drops - left. how is your drag link hooked up?
As far as I can tell with a tape measure the rear is square. Thats one reason I may take it to a front end shop and have a 4 wheel alignment done. The steering box is a new vega type with cross steer. The drag link is parallel with the tie rod car at rest.
The rear springs are 250 lb springs. They are so stiff that above about 60 mph and going across a long bridge it can feel a bit squirley. They beat the hell out of me.
you might try to straighten your ladder bars ,seems as they pivot at the same center point. just a thought
My money is also on the frame or ladder bars flexing and moving the rear end out of alignment. The right rear tire is almost certainly moving forward under power. I know having the ladder bars angled in at the front reduces bind in roll, but I'd like to see a good picture of the ladder bar's front mount.
The ladder bar mounts need to be out nearer to the axle flanges. And a lot beefier. Send me a beer when you figure out I'm right.
I would check your ladder bar brackets on the rear axle housing for signs of flexing. If those single plate brackets are not causing problems now,they almost surely will. I would strongly advise going to boxed double plate bracket where the heim joints on the rear of each ladder bar are bolted between two axle housing brackets. Most of my experience is with drag racing setups and I can assure you that your current setup with a single bracket with a clevis would not hold up. Remember all the torque is transferring through those brackets to the ladder bars and then to chassis. That makes those brackets the first potentially weak leak.
humor me and pull the rear panhard off and go for a short ride and see what happens. with triagulated rear ladder bars the panhard is not needed. It also throws another arc into the mix and may be causing the rear end to bind as it travels. I could be wrong but its worth a shot.
No way Tinman...thats not a great idea IMO! Pretend the ladder bars are an original Ford torque tube for a sec...with one pivot point up front and the coilovers out back. (Instead of a transverse leaf spring). Running without a Panhard bar, the rearend would arc side to side very easily due to the single pivot up front...correct? Here you have two ladder bars with two pivot points, perhaps a foot apart, up front...but now you don't need a Panhard? The binding caused by 12 inches of separation is enough to keep the rear axle located perfectly under any driving conditions? No way. You NEED a Panhard bar or some other type of link to control axle positioning even with triangulated ladder bars.
Mr Hackerbuilt is playing it safe and I'd have to agree with him. Esp if the panhard is both long, and level when it's loaded. The lower outer rear shock/spring mount looks like a better region to consider for a mounting, then carry bars forward to a [K] braced form of heavy section crossmember?
I would look at frame twist. Had a more door car did the same thing. After driving the car for several years with white knuckles I built a new frame and installed a large heavey wall K member and had a great driving car for another 60K miles. WALTER
250 lb. springs does seem to stiff for a 2800 lb car. You can do the math and get pretty close to spring rate you need. Since we don't the details of your car we'll have to make a few assumptions. First we need rear vehicle weight. Assuming 50/50 weight distribution that would be 1400 lbs. Now we need rear sprung weight. Total rear weight-unsprung weight=sprung weight. Unsprung weight= wheels,tires,brakes,axle + 1/2 weight of ladder bars,shocks,panhard bar and driveshaft. We'll use 350lbs(aprox.) for unsprung weight. 1400lbs-350= 1050 lbs rear sprung weight 1050/2 =525 lbs sprung weight per shock At ride height you want your shocks 50 to60 % compressed,assuming your shocks have 5" of travel and they are 50% compressed,that would be 2.5 inches. 525 lbs divided by 2.5= 210 lbs per in Because your shocks are mounted at an angle,you have to apply a correction factor to the spring rate.(The shock maker can provide the correct factor based on angle your shocks are mounted.) We'll use .89 210 lbs/in *.89=186.9 lbs per inch. Spent some time with some scales and substitute in the values for your car and can dial the spring rate you need.
First guess would be, the torque twists the frame and picks one front corner up, throwing the front geometry off kilter. Second guess, the front goes 'way up, and the cross steer link pulls the steering to the right. The Panhard bar should prevent that, though. The car is open-wheeled, get a buddy to ride and watch the front end closely while you work the throttle. Sharp eyes might see the movement, where-ever it is.
Frame flex and corner weighting are up there on the culprit list. Panhard rod is backward too. Should be mounted to the axle on the driver (left) side and to the frame on the Pass (right) to help with torque steer.
I have looked at the pictures of the frame and to me it is quite simply really. When you get on it the front end unloads and raises up. This in turn lengthens the distance from the steering box to the spindle arm. Since the steering box is rigid mounted the car can only do one thing and that is pull right. Hence you must put some left turn in it to bring it back straight. When you get off of it the suspension settles and the left turn you put in before is now making it turn left and you must put the wheel back to the original position to achieve straight ahead.
My Comet did the same thing (ladder bars, leaf springs, with sliders) I had to preload one ladder bar to make it run strait
Funny to read all these different opinions as to cause. My '32 coupe with an enlarged Flathead and all Ford rearend (torque tube, transverse spring, and stock radius rods) does the same thing. Frame has been boxed forward of the k-member but it does have P & J four bar and Mustang steering gear. The draglink is parallel to the bars but slightly shorter. Stab the throtte at 60 and it goes right, back off and it goes left. Sorta scary-definetely don't want to try Bonneville with it .
"Panhard rod is backward too. Should be mounted to the axle on the driver (left) side and to the frame on the Pass (right) to help with torque steer." ELpolacko: Do you do it this way ONLY on high-torque cars or are all your chassis set up this way?
My car started doing this when the cheap aluminum lowering block sheered the pin. I agree with everyone else, the rear end is moving.
With cross steer I'd be looking at spring travel (front). Unless you have a very long drag link Your going to get some directional change in the steering. You could use an old sprint car trick to check travel. Put a small zip tie around the shock stem, push it down against the shock body. Now on level ground drive the car slowly gaining speed (no jack rabbit start), then put on the brake and come to a complete stop. If the spring is letting the car (front end) drop to much it will be shown by how far the zip tie was pushed up the stem. I would look for no more than an inch to an inch and a half. If it moves to much you are going to have a problem as you have discribed with directional control. The upward movement will also cause the same effect. Good luck and let us know the results.
A quick glimpse of the picture you have provided and the description of you problem first assumption is that it is a rear steer issue as the chassis rolls from engine torque. Quick look of your chassis and your description indicated that you have a panard rod operating at an angle to the rear axle. This rod must operate parallel to the axle housing for best results. First guess is that as the chassis rolls, the rear axle skews left because of the distance change of panard bars operating alignment shortens. The change changes the lateral position of the axle thus driving to the right. Do not disconnect the panard rod as you do need it for lateral locating. Just reposition the axle mount parallel with the axle and you should find that it drives much better.
I don't see a substantail K member, it looks like there is some kind of tube associated with the trans mount but it isn't very effective. Look at what ford did when they put a 60hp flattie in thier chassis, they have a huge K member. Other people have noted different problems: panhard bar angle, direrection; single-plate axle brackets; steering arm geometry etc all of which are mentioned enough that i am thinking that all of the above are factors into correcting your problem, the hard choice is which one to go to work on first, and i would choose the K member.
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