I'm doing a restore on a 1973 Bronco that I bought 1 1/2 months ago. When I bought the Bronco, it had the radius arms disconnected from the area they should be, but they were still attached to the front axle. The vibration that I speak of is comparable to the space shuttle during take-off. When the vibration does occur and I look out the window at the front axle, it looks like after-burners in full idle ready for launch. After installing the 3 1/2" lift ( bushings, shocks, coil springs, and leaf springs), the vibration stopped, but now at times the vibration is slight and once in a while it comes back to shake me back into orbit but not as bad as at first. Also any bumps in the road can spark the rocket motors. The lift kit is on correctly and tight to specifications. I will be buying new rims and tires this week, which I hope will help. I'm puzzled by this freak problem. Do you have any suggestions? Your help is greatly needed.
This is not a freak problem but one of the most common problems with the Bronco. It always has to do with the track bar, track bar bushings, track bar bracket, and the tires. When you look out your window and see the front end shaking violently back and forth, the only thing keeping it in place from right to left is the track bar.
We have found a great video illustrating this problem on a website belonging to a gentleman by the name of Greg Banfield, aka Motoman. You can take a look at it here: http://www.emotoman.com/videos/dw.mpg
How to diagnose the problem:
Have someone rock the steering wheel back and forth putting pressure on the steering and front end. The number one culprit of this problem is worn-out upper trac bar bushings. Check the trac bar bolt and the bolt hole as you check the following items. Replace or repair as necessary.
What to look for:
1. Lower bushing - Look for excess movement which could be caused by a worn out bushing or broken tack weld on lower track bar bolt. This is the bolt that goes through the track bar bracket which is welded to the front end.
2. Upper bushing - This is the most common source of the problem. Look for excess movement which could be caused by a worn out bushing. Check bolt hole for egging out of the hole. Bolt size for 66-75 is 9/16". Bolt size for 76-77 is 5/8".
3. Upper track bar bracket - Most early Bronco suspension systems use a drop bracket for the track bar. This bracket must be properly welded to the frame. If the bracket is rocking back and forth on the frame during the test, this is the source of the problem or at least part of it. Bolting on this bracket is not enough! It must be welded and welded securely. We weld all attaching surfaces when we do the lifts here in the shop.
4. Factory upper track bar bracket - In severe cases (which we have seen a number of times), the factory bracket will be separating from the frame. Thoroughly clean and inspect the frame where the bracket is welded to it. Sometimes rocking the steering wheel will not expose this problem and so careful inspection is needed. If you see cracks in the frame, this must be fixed. Small cracks may be fixed by welding. Large cracks and breaks will need to be reinforced with new metal.
5. Tires - The taller, wider, and cooler-looking the tire, the more likely to have steering and handling problems. Usually the culprit is worn or out-of-balance tires. We are not paid by these guys to say this but BFG and Goodyear tires have our stamp of approval. We drive our Broncos on a daily basis and these will provide the best all around use. We have seen this problem go away with a tire change. In this case the actual source of the problem may still be there, but with the better tires, the problem doesn't show up.
6. Front end alignment - Bad alignment will make this problem worse and more common. Make sure your front end wheel bearings are checked and greased regularly.