Steve Hoelscher
True Classic
I have been checking in on this thread from time to time and am surprised that the issue hasn't been found and fixed. I should note that the X1/9 is susceptible to front end vibration at about 65 mph. I have noticed this on a couple of my cars and a few others. This has typically been tied to a combination of worn components and out of round/balance front tires.
Its important to remember a few fundamentals here: 1) all mechanical assemblies have a resonating frequency. 2) Such problems are seldom one single issue but an intersection of two or more smaller issues. 3) when you can't identify a problem, take a step back, reconsider the situation and start from the basics and move up from there.
When ever I get stumped by such things, like an engine that won't start, I always go back to the basics and start from there. Fuel, air, spark, timing, compression. If I have all of these, in the appropriate quantities, the engine will run. So in this case what causes a speed related vibration. And that answer is an un-dampened oscillation. So we have two problems; 1) something that has more motion than is normal, and 2) that motion is undampened.
So continuing down the diagnostic path using the above, the first step is to find the source of the excess motion. To find that, check everything that turns with the road wheels: Tires, wheels, hubs, brake rotors and wheel bearings. Have the wheels/tires spun up on a wheel balancer and check the runout and balance. Assuming they are good, then check the wheel to hub mounting surface and ensure the wheel is fitting flush to the hub. Next, check the hubs for runout. That's pretty easy with a dial indicator mounted to the hub carrier. Also check that the wheel bearings are tight and smooth. Finally, check the brake rotors for runout.
Next is to find what is permitting the harmonic excess motion. Start at the suspension mounts and inspect for cracks and worn mounting holes. More than once I have found a cracked suspension mount on a track car that caused me all kinds of headaches. Next the bushings, control arms and ball joints. And don't forget the tie rod ends and toe adjusters. Also check that the struts are in good condition and that the inserts aren't loose in the housing.
Finally, the alignment. Assuming you have done all of the above, I would suggest investing in taking it to a competent shop and having them put in on a commercial rack. I'll be the first to tell you I don't trust most alignment shops or techs and do all of my own alignments on everything but my wife's SUV and my truck. And those go to a friends shop where I can observe the tech's work. Two reasons for taking it to a shop. First, its a way to verify your own measurements and you can get a caster measurement. Unless you are pretty good at doing your own alignments, and have the tools to do it, you won't be able to get a caster measurement at home.
The reason I noted caster is an interesting one. Too little caster can cause exactly your problem. While I have never experienced an X having a steering vibration resulting from to little caster, its a major problem in other vehicles. Jeeps are notorious for the problem and its not an uncommon problem in late model Ford SuperDuty 4wd pickups. The cause is a combination of a worn track bar, or steering stabilizer, and a lower than normal caster angle. The factory caster spec is 2.8 to 3.3 degrees on the Ford truck. That's not a lot (an X1/9 is about 7 or 8). In the case of the Ford, a huge percentage of owners either install "lift" or "level" kits. Either one raises the front of the truck and because the front suspension is simple (reverse) trailing arm setup, simply raising the front ride height reclocks the front axle and reduces caster. Its not uncommon for caster to end up at less than 2 degrees. This is problematic as its caster that provides for the steering self-centering and therefore the steering stability. So reducing caster significantly will reduce the natural geometry function of stabilizing the steering. Reduce it enough and the lack of caster can't prevent the natural oscillating frequency from being triggered by the simplest of things. A slightly out of balance or out of round tire. Or, in the case of the big Ford pickups, crossing a bridge/pavement seam at 60 mph. In the case of the big Ford truck or Jeep, its compounded by the lift/level kit and the almost universal addition of much larger (read increased mass and inertia) wheels and tires on lifted trucks.
All of that to explain that if you replaced the radius arm bushings you really need to ensure that the caster is correct. Its entirely possible that the new bushings reduced the caster and that is the primary cause of the problem.
Its important to remember a few fundamentals here: 1) all mechanical assemblies have a resonating frequency. 2) Such problems are seldom one single issue but an intersection of two or more smaller issues. 3) when you can't identify a problem, take a step back, reconsider the situation and start from the basics and move up from there.
When ever I get stumped by such things, like an engine that won't start, I always go back to the basics and start from there. Fuel, air, spark, timing, compression. If I have all of these, in the appropriate quantities, the engine will run. So in this case what causes a speed related vibration. And that answer is an un-dampened oscillation. So we have two problems; 1) something that has more motion than is normal, and 2) that motion is undampened.
So continuing down the diagnostic path using the above, the first step is to find the source of the excess motion. To find that, check everything that turns with the road wheels: Tires, wheels, hubs, brake rotors and wheel bearings. Have the wheels/tires spun up on a wheel balancer and check the runout and balance. Assuming they are good, then check the wheel to hub mounting surface and ensure the wheel is fitting flush to the hub. Next, check the hubs for runout. That's pretty easy with a dial indicator mounted to the hub carrier. Also check that the wheel bearings are tight and smooth. Finally, check the brake rotors for runout.
Next is to find what is permitting the harmonic excess motion. Start at the suspension mounts and inspect for cracks and worn mounting holes. More than once I have found a cracked suspension mount on a track car that caused me all kinds of headaches. Next the bushings, control arms and ball joints. And don't forget the tie rod ends and toe adjusters. Also check that the struts are in good condition and that the inserts aren't loose in the housing.
Finally, the alignment. Assuming you have done all of the above, I would suggest investing in taking it to a competent shop and having them put in on a commercial rack. I'll be the first to tell you I don't trust most alignment shops or techs and do all of my own alignments on everything but my wife's SUV and my truck. And those go to a friends shop where I can observe the tech's work. Two reasons for taking it to a shop. First, its a way to verify your own measurements and you can get a caster measurement. Unless you are pretty good at doing your own alignments, and have the tools to do it, you won't be able to get a caster measurement at home.
The reason I noted caster is an interesting one. Too little caster can cause exactly your problem. While I have never experienced an X having a steering vibration resulting from to little caster, its a major problem in other vehicles. Jeeps are notorious for the problem and its not an uncommon problem in late model Ford SuperDuty 4wd pickups. The cause is a combination of a worn track bar, or steering stabilizer, and a lower than normal caster angle. The factory caster spec is 2.8 to 3.3 degrees on the Ford truck. That's not a lot (an X1/9 is about 7 or 8). In the case of the Ford, a huge percentage of owners either install "lift" or "level" kits. Either one raises the front of the truck and because the front suspension is simple (reverse) trailing arm setup, simply raising the front ride height reclocks the front axle and reduces caster. Its not uncommon for caster to end up at less than 2 degrees. This is problematic as its caster that provides for the steering self-centering and therefore the steering stability. So reducing caster significantly will reduce the natural geometry function of stabilizing the steering. Reduce it enough and the lack of caster can't prevent the natural oscillating frequency from being triggered by the simplest of things. A slightly out of balance or out of round tire. Or, in the case of the big Ford pickups, crossing a bridge/pavement seam at 60 mph. In the case of the big Ford truck or Jeep, its compounded by the lift/level kit and the almost universal addition of much larger (read increased mass and inertia) wheels and tires on lifted trucks.
All of that to explain that if you replaced the radius arm bushings you really need to ensure that the caster is correct. Its entirely possible that the new bushings reduced the caster and that is the primary cause of the problem.
