Reently I experienced a severe front end low speed front end wobble in my Roadster, much like a motorcycle tank slapper. The car has a torsion bar front suspension. The wobble is extremely violent, during the first incident it loosened all four 5/16 grade 8 bolts that mount the steering box to the frame. I replaced the steering box and all the hardware with new ARP grade 8 bolts.

The steering box sector shaft and worm gear are perfect, zero play.

The caster is set at 8 degrees.

The toe-in is at 1/16 (in).

The camber is zero.

The bump steer is zero.

It has new king pins and bushings in a new, thicker than original front axle.

The drag link is new, chrome moly.

All the high quality heim ends in the steering assembly are new.

All the hemi ends have specialty tapered washers that prevent the shoulders of the heim ends from binding.

The left spindle (has at most) 1/32 top to bottom play, the right has none.

The steering arms are flat, equal in angle and tight.

The front wheel bearings are new and have zero lateral play.

Motor and transmission mounts are all good

The front wheels are true with zero run out. I took the tires off and spun them on a wheel/ tire balancer.

The front tires are new (Hoosier’s) and have very little run out, the assembly (Tires and rims)are balanced to within .5 a gram. In fact ALL the wheels are balanced to within .05 a gram.

The wobble has only happened after the front end sets down after a wheel stand and goes away once the car gains a little speed, this is a throttle stop car so the initial speed gain is minimal. After the wheel stand it appears (on video) that both front wheels hit the ground at the same time, this is not a case where one wheel strikes the ground before the other.

This suddenly ocurred with no apparent reason (after hundreds of clean runs) but has now happened twice even after checking and replacing everything. I am not looking for it to happen again. The front end geometry seems fine, I can not figure out why this suddenly began.

Has anyone experienced this same anomaly? Does anyone have experience with installing a steering damper on a torsion bar front suspension? If so, where did you buy the damper?

Bob

You may look to off road buggies and jeep parts suppliers. I have a family member in Arizona who plays with sand buggies and desert racers. Think moog also used to sell a universal one with u bolts to attach to the vehicle.

I don't know about torsion bar frt. suspension. But on my strut frt. I had the same thing. On my car it's an old VW bug steering stabilizer. Mine is a kit from Quay but it's nothing that couldn't be fabbed up. Bracket on the frame and a bracket welded to the center link. Cured my death wobble and it was violent.
https://www.summitracing.com/p...view/make/volkswagen

Whats your caster? I know some old FED's had a lot and would have same issue. Seems most are now in 15 to 20* range now. I was told anything more and you might have occasional issue with wobble.

quote:

Originally posted by wideopen231:
Whats your caster?

First post 8°

Bob, have you changed anything on the front before this happened?

Caster is at 8 1/2 degrees.

The only change to the front end was made last year when I replaced the steering box with a new one, same manufacturer, same model. When I did, I used the old pitman arm from the broken steering box but I lowered the drag link position. Since that change the drag link has been at the lowest of the three positions on the pitman arm so it created a significant amount of resistance required to turn the wheel, it increased the turning radius but it was very hard to turn the wheel. The new box had a much shorter pitman arm. This morning I replaced the original pitman arm with the shorter arm to see if that helps.

Moving the location on the pitman arm also leveled the drag link, which might have contributed to the wobble issue.

Installing a steering damper will be more than just welding a few brackets, the fiberglass nose piece will create a significant interference issue. Lots to think about, not an easy task.

Bob

I had an altered for a few years with this type suspesion. When i bought it the previous owner had removed a damper on the tie rod, said it wasnt needed. Well first time i went out with it i had what you experienced. I was fortunate to find the damper that it was designed to have at S&W race cars in Pennsylvania. I was told its original application was for a Honda goldwing motorcycle. It was only about 7 inches long and was also adjustable . This took care of the problem 100 %. I doubt the pitman arm location will solve your problem totally. What starts it is caused by the extra caster these front ends are designed with in combination with light flexible undampened steering components. Lots of caster is good for directional stability but when the front wheels set down from being unloaded and one tire hits first it kicks that tire in towards the center of the car and it just takes off from there. If you could take a couple of degrees of caster out that would help but there probably isnt enough adjustment since its kind of set when built. I dont think think these cars need 8 deg to drive well down track , often times if the steering doesnt feel comfortable its because the front end is being unloaded. Moving some weight forward can help. Good luck with it.

Since I have my first torsion bar front, I’m following this, with a lot of interest. Mine has a funny car type steering box also.

The issue I have suddenly experienced is the same as your’s K107, it begins as soon as the front wheels hit the ground. I thought that it might have been caused by the drag link flexing so we built a new thicker wall chrome moly unit, that did not fix the issue. We then built a new thicker wall chrome moly tie rod thinking it might be flexing, same result. I’m also going to slow down the throttle stop to soften the landing when the tires hit the ground. I recently ran it wide open and lowered the wheelie bars, that stopped the problem but significantly hurt the reaction time too much for a competitive Super Gas .400 Pro Tree.

My last item is to change the pitman arm and reduce the caster from 8 1/2 to 7 degrees and see if that corrects the low speed wobble. The only concern I have with reducing the caster is how it drives/steers in high gear, this car has a gang of mph for a torsion Bar Roadster.

Reducing the caster and using the shorter pitman arm should at least reduce the effort needed to steer the car while backing up.

If and when I finally discover what eliminates the wobble I’ll post the results. The S&W damper may be the item that finally fixes the problem, the issue is how it clears the fiberglass front nose piece. That’s going to be a challenge.

Bob

My altered did that when I throttle stopped it for Super/comp. It would also do it occasionally while backing up. My steering box mounts were cracked, and finally failed. After fixing it, with additional bracing, it's been rock solid ever since. I haven't throttle stopped it much though.