First let me describe the car. It's a 23 T modified with a pinto 4 banger. The front end is a speedway tube with hair pins. The body being gl*** and aluminum makes the car quite light (1400#) and with the motor set back the empty weight favors the rear (750# rear). The caster is 10 degrees. 7 degrees is usually used but it steers fine with 10 and 10 should make it more stable. The front shocks are lever arm of the rear of an MG Midget. A couple days ago going about 30 mph on a rough road I got a speed wobble (front wheels going right and left). Yesterday on a smooth road and a little above 60mph it started to wobble and then got real bad. I got a good scare slowing it down to a stop. The wobble continued until I got to a dead stop. I took off and all was fine as I didn't go over 50mph. I'm using a covair box and the drag link crosses the rear hair pin attachment so bump steer should not be a problem. The wheels were balanced with a harbour fright bubble balancer. Could balance be a problem? However it did happen at low speed on a rough road. I am running the main leaf spring and one very short leaf on the front (almost a mono leaf) because of the light front end. Could I be too soft? Any coments and sugustions would be appriciated. Nick
this has happened to me when the drag link is out front of the axle and not alighned correct.sounds like the wheels are pointing outward
There are a number of threads about this problem, put "death wobble" (or for one extensive thread, "deth wobbel") into the search.
King pins are tight? The pin should install w/a thumb-press-fit, or ever so slight interference, where lube helps. Other issues may be balance, out of roundness or steering component wear (sometimes in combination).
the first thing I'd look at for a wobble between 40-70 mph would be tire balance. used to be very comman with bias tires
put the axle at 6-7 degrees. more than that decreases your turning ability and makes steering harder. The added stabilty is nice on a drag car, but on a street car its nice to be able to change lanes. So you have shocks? start by "nut & bolting" the entire front end. This means tighten every nut and bolt on teh front end. check the wheel bearings too. check toe next, if it changed then somethings bent and you gotta find it. This is just a good starting point.
Some things to check, if it has no panard bar, make one for it. If the car has bias ply tires, give it 1/8 toe in. If it has radials, give it less. Look at the car from the front. If you draw an imaginary line through the king pins to the ground, draw another through the center of the tire. They should meet at the graound. If they dont, change the wheels untill the lines meet. On a car that light, 10 degrees leaning back at the top of the king pin is good. Tie pressure at about 28 to 30? Good to start there, if you need a softer ride, adjust TP after the handleing problem is solved.
I agree with the Da Tinman, start from square one, caster about 4 degrees max 6, on a light car this should be OK... King pin's adjusted properly...tires computer balanced..all ball or heim joints good, and good and tight...shocks? a must have...make sure all of your adjusting thread's on steer links, cross links, hair pin's etc have lock nuts on them and are tight after all final adjustments are made, if you don't have the lock nut's eventually your threaded adjustments will wobble out and destroy these points.....toe in 1/8" this can be done with 2 straight edges clamped with spacers off the face of the rims. All of this should cure your problem but the first thing to check is your front and rear axle alignments they need to be square with each other and square with the frame, this can also be done with spacers, straight edges and strings.
This is my take on this. The start of the post indicated that the vehicle was being driven on a rough road. This indicates that the front axle is cycling up and down according to the road conditions. As the axle cycles one side rises and the other side drops. This action produces changes in geometry of the axle from static. As the axle rises or falls this changes the toe of the vehicle. As the spinning tire wants to correct itself to center it initiates an action that is p***ed thru the tie rod to the opposite tire. This realignment action now draws the other tire out of alignment and they start to fight for neutural dynamic alignment, this is your wobble. My starting point on this is to first check for any loose or excessive play connections from the steering box to the spindles. Any loose connection with excessive play will also start this action, especially incorrectly adjusted steering boxes. Make sure there is not an excessive amount of wobble in the king pins as king pin resistance is an important part in controlling wobble. King pins should be greased well and rotate easily but should not have side to side play or sloppy fit. The second step is to roll out some of the caster, 10* is way to much, this is one of the cases where more isn't better. My take is 4-6* is plenty based upon your tire foot print. What I think is the excess caster under bump creates an excessive toe out that is p***ed to the tire contact patch and the tire patch creates a long lever action dynamic to the tire that tries to center the tread. This creates the unstable side to side action. Make sure that you have eqaul tire pressure in your tires and if you havent done this recheck the sqaure of the axles to your ch***is. This dynamic can also be caused by having one tire lead the other due to the axle not being installed sqaure. Remember setting toe only points the tires inward or out ward it does not sqaure the spindles to the axle for straight ahead. Let us know what happened..
Most of the stuff recomended has been adressed but much has not. Thanks for the help. Now back to the shop. I'll repost my findings.
If you are above 25#s your tires are superballs. Afraid to drive through the wobble are ya? I had one at 65, by the time we hit 70 she was gone.............................
Try different wheels and tires. Some tires just aren't compatible with some solid axle cars. A twisted belt can cause a death wobble. Slamming into curbs is the worst way to twist one. Can you post some pics of the front end? That might help.
****, I'm not certain about the red words above...esp w/a cross ch***is tie-rod. I'm havin' a little trouble here! If the drag link (crossing link) was sloped down, then a pulsed wobble could result.
Pitman.... Sloping up or down of the drag link only effects steering arm ratio to steer input. Don't think of the axle as a solid axle. Remember the spindles turn and are controlled by the steering arms which do not run parallel with the spindle but a a predetermined Ackerman setting. As the axle goes into bump the wheel rises and there is an arc created at the opposing tire center line and ground. The bump tire moves closer to the center of vehicle because of the arc created. Because the Ackerman steering arm angle and the bump radius are not the same this rotates the spindle and creates a slight toe change on the spindle to track ..Now this is just fractions of inches but enough to create a dynamics problem with a spinning wheel. Compounded with excess caster you get a shopping cart wobble effect as the speed increases.
If excessive caster can cause this on a light car, how did/do all the dragsters and lakes cars run that caster and not have death wobble?
Death wobble starts at a very, very slow speed. It always starts with an irregularity in the road surface, and once you get past a certain speed, it won't/can't restart that low speed wobble. You need giant stones to try to drive through it If you ever had a car with true low speed wobble, you can get a better idea of what is actually happening, and can better understand what people like **** say about the causes. My first old time rod I bought 40 years ago was fine until I swapped on mags with more offset. It went into a violent wobble 100 feet from leaving the driveway. I tried to avoid bumps at low speed for that summer, but it got worse. After I swapped the wheels back, it still did it and I ***ume something got damaged or bent during all those events. The last time I ever drove that car, it went into such a bad shake, that the roadster windshield frame popped out of the stantions, doors flew open and the hood top got tossed into the road....all this at maybe 10-15 MPH
Here's what I found. My left rim was bent slightly, about 1/8" off. I replaced it and had the wheels electronically balanced. I found that the right arm going from the spindle to the cross link was a little loose, now it's tight. I also found that steering box was a little loose, now it's adjusted. No more wobble. I took it up to 75Mph and smooth. I took it down the rough road where I got a slow speed wobble before and it was fine. Thanks for all the input.
x2 on that.. a tire imbalance with cross link steering can cause just that.. jeep wranglers do the same thing...
Checking vintage wheels for run out should be the first thing done even before tires are mounted. Years of potholes and curb bumps take their toll. "Nut and Bolt" checks are always a good idea. Have a buddy do this, they always seem to find the loose ones. Caster should be kept at around 5 degrees for best handling both around town and on the hiway. Remember, if you need to change your caster, you will also need to change your toe-in. This can vary from car to car. I've had some that acually had toe-out. Usually from some kind of bad suspension engeneering. Lastly, a 4 wheel alignment is a must. You be surprised how many times the wheel base on a problem car is longer on one side than it is on the other. You can get pretty close with a plumb bob, chaulk and a tape. Balancing should be done with the wheels mounted on the car especially if you are running bias tires. Besure to mark each wheel so they go back on the same corner in the same position on the hub. Just my 2 cents. Ron
Years ago I bought a running Model A and drove it home. Half way there I got the "death wobble" that started at about 30 mph and wouldn't stop until I came to complete stop. Both ends of the tie-rod were not locked in position and were threading back and forth. I locked them back in and the wobble stopped. Proper toe in is also important or the front end will fight with each other for center with aggressively. Nut and bolt the whole front end first.
I should mention that the tires are radial. I had balanced them on a Harbor Fright bubble balancer before. After having them both electronicly balanced I noticed that they put about the same amount of weights on the right one that I had removed (the left one had the bent rim). Out of curisoity I checked them on the bubble balancer before mounting and the bubble was right in the center. I think that the balance was probably OK and the other things caused the problem.
I had this happen to me with my two young sons in my rod and needless to say it scared me and still does when I think about it. A fellow rodder suggested installing a steering damper which I did and it never happened again.Not the prettiest thing on a fenderless rod but it works
you should really find out what the problem is, fix it and then use the dampner. deth wobble has a cause, the dampner hides the cause. when the cause gets critical the dampner wont help you.
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