Good Friday morning! We recently built a home built car loosely based on a model A- my buddy who owns the car is about ready to bash his head against a wall! The car has a wheel hop above 45mph- A list of what we have and have done- the car is a 2x3 tube frame car, with a model A axle, Speedway cross-steer, with speedway disc brake kit- 15" radials 205*60*15, the front end is way out there- about 10" in front of the engine (302 with AOD) total front axle weight is 1160lbs- The front spring is correct and also new- stock type posies spring- did the same thing with the stock spring and the new spring- the shocks are rear shocks for a crown Vic- we have tried a stiffer shock to no avail. Here is the fun part- He put a 2x4 between the axle and the spring 6.5" tall- and the car sings down the road with NO wheel hop. We have balanced the tires, checked for true on the wheels, balanced the rotors- and still the same. We have tried different tire and wheel combos, adding leafs to the spring- toe is set at 1/8" tried going drastic to 1/4" no help. ARGH! Any help is greatly appreciated!
When you blocked it solid, you stopped the harmonics. I bet there's a Wierd frequency between the spings and the extended frame. Check for frame flex, try stiffer shocks yet.
It sounds like you have checked all, i have no idea. Are you sure about the tire/wheel balance? Maybe one or both aren't centered, or the studs could be machined off center?
We are going to try stiffer shocks yet- he is concerned about his shackle angle, he is at about 20 degrees or so loaded- could this cause the issue? I have seen worse drive better, but at the same time, speedway recommends 40-45 degrees.
a loose kingpin would normally be culprit. but Ill say this... sounds like your front end is trying to go in a circular motion... so try adding a panhard bar to it I think it will fix the issue as long as you have enough caster in that axle settup you should be fine also there. play with tire pressure also... drop em down 5 to 10 lbs and you will be amazed what it can do... and also set toe at 1/16" to 1/8"
wheels sit perfectly on the hub center- and we are sure everything is balanced- tried spin balance and static.
Give us some good pictures of the front end setup......otherwise we are all just guessing. What exactly do you mean by wheel hop ? Could you be experiencing Death Wobble, where the car shakes violently from side to side ? (Like you see on a shopping cart when one of the casters on the front starts to go from side to side) Don
Lock one of the shackels only so it dose not move and try it[you can buy one that dose that at Cal. Cus it sounds like from your info it may need that
No death wobble- it seems to oscillate from side to side as if "teetering" on the center of the spring- I will try locking down 1 shackle and see what that does- and I will get good pics this afternoon. As for the angle when blocked up- he blocked it until he got *40- but would that not be irrelevant if the suspension cant move?
Or check the balance of the engine. When you use a light frame front end stretched sometimes your harmonics from the engine become magnified though the chassis. I proved it last year when we swapped my balanced small block for the raven's late model small block. His mill that dame thing had a major death wobble, my engine it went away.
Ok quick question on the shackles then- this is a stock model A axle, with Speedway perches (item #:91033047) which are at the same angle and height as stock- We also verified the distance between perches with a second axle- all was well- and the new spring is the same length as the old spring. Should I have the spring eyes turned in a bit to get the shackle angle correct?
I had the exact same thing happening in my 31' sedan. Mine was very violent/scary/nerve wrecking the car would be driving fine and then BAM, the front would teter so harsh you could see each tire jumping off the pavement 10". I searched and searched until I found that one of the rear hairpin mounts were wore out and I had play at the connection. Once I fixed that the problem went away.
The extended axle is loading the spring more and shortening the spring might help, but even with the correct shackle angle or a dead perch, the radius rods could flex enough to cause you problems. Converting to side steer might be a better choice unless you can manage to snake a panhard bar directly to the axle, seems unlikely though.
Also, if you do a dead perch, the spring will still need to be shortened and it probably matters which side it's on as well.
It is not hitting the perch- but it is sure close. I am going to get the spring turned in a bit and will get back when we test it out! Any other ideas let me know.
It's really close in the static pic, what's it do when the front end bounces ? Spring flattens out, when that happens it gets longer, then ,,,,,,, Well ...... then the front end bounces all over, your buddy beats his head on the wall , and you post on the HAMB. Lol
The pictures helped a lot. I agree there is not enough shackle angle there and the frame is rocking on the shackles. I would also add a dead perch to the drivers side, and get a new main leaf that is shorter. Something I notice too is that you are running those thin steel steering arms, those can contribute to some flex in the front end. Lock up the front wheels so they can't turn from side to side and crank the wheel. You will see those arms flex like you won't believe. When we built my Son's T bucket we used them and we were shocked to see how far they will move under load. They got pulled off and we modified some Chassis Engineering forged steel arms to work and the chrome flat ones went in the trash. Don
A dead perch should be treated the same way as a panhard bar! The dead perch needs to be on the opposite side of the steering box so that when it arcs on a radius from the centerbolt of the spring, it is approximate to the arc of the drag link. This method is more effective with a R&P because the drag link is shorter [ closer to the length of half the spring width ] You NEVER have a panhard bar or dead perch on the opposite side to a drag link, pivoting on opposing arcs is a recipe for bump steer
I think a few guys have gave you the most likely answer, that long or flat spring cannot be helping matters. It sure looks like it would hit with the slightest about of travel.
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