I got a '69 recently and I've been trying to research what my vibration could be. I was assuming it was bad shocks, out of balance tires, imbalanced drive shafts, or flat spots. I have an F150 with the same tires (BFG A/T KO2 but they're 37s on the F150, 33s on the Bronco) and after it was stored for a long time, there was a shake in it from flat spots on 2 separate occasions. I attributed it to flat spots, ran freeway miles and speeds, and it eventually went away. It was a mere nuisance but not concerning. I've got aftermarket mid travel, triple bypass shocks, etc. so it's smooth as butter except when those tires sit and get flat. I'd love to get that suspension performance out of my Bronco, but let's be honest here... haha
But the Bronco feels like it wants to shake apart, as if the tire is egg shaped and bouncing/shaking or there's a bolt gone and there's a part of the suspension that's loose. Starts at 55 mph and (if I remember right) it will kind of chill out at 70. I didn't want to go that fast, but I had to figure out if faster would cause a change. It actually helped on my Raptor when it had that shake that ended up being the tires, but I had to get to 80. It sometimes goes away with smooth pavement, but not every time. CO highways are also an absolute waste of taxpayer's money, so that doesn't help. I can run my F150 over washboard terrain and it won't shake like those highways will make it shake. But if the pavement smooths out, the shake sometimes does too. It'll come back on the Bronco more often than not, though. Only when I'm turning on a curve in the highway at higher speeds will the shake transfer to the steering wheel, but just enough to feel a jiggle without remotely feeling uncomfortable. Otherwise the wheel is steady. I'll get lucky and the whole truck will get to a little bit of harmony at speeds faster than 55 for a short time, until some input disrupts the peace. The only reason I'm concerned it's not the tires is the intensity of the shake. To borrow someone else's description, it's like I'm in a space shuttle launch. Or even like I'm driving over a washboard. Or getting wheel hop at 55 mph. The shake you get in the body of the vehicle from the start of wheel hop is the best way to describe it. Just without loss of traction. The part of wheel hop where it starts fast, right before the bounces gets wider apart as the suspension bounces more, only it never gets wider apart.
I've looked at the suspension and nothing is missing, but I'll need to get into a shop with tools to check for tightness and condition of bushings. I got to smooth backroads to make sure it wasn't the poor road quality of the undulating highways and it'll still pick up right at 55, so I don't think it's rough input from the road causing an uncontrollable bounce (LIKE wheel hop, but not. My description earlier wasn't saying that's what it is). So suspension is likely out the window.
The track bar upper bushing looks new, but I can't see if the hole is deformed. The shake isn't in the steering wheel, so I'm not sure it's a "death wobble". That's actually one thing no one ever states specifically, is if the death wobble is transferred to the steering wheel. I assume it would be, because all the videos I've seen the pitman arm is moving. It's a curious thing no one has stated that, though. Obviously a death wobble is a whole truck shake, but my truck has nothing in the steering wheel. Also means it's not a front tire if it's the tires. Because I'm not well versed in that issue, I'm not ruling that out until someone here has a compelling argument against it being the cause.
I'll also check to see that the 23 gallon gas tank is strapped in solid too. I didn't think of that until writing this. It's not a rubber strap though, it's a solid bar and bolts. Just physics of the sloshing fluid wouldn't make it shake, maybe unevenly wobble/jiggle, so that's likely not it.
I can't verify if the frame is bent, but I've seen no cracked welds or frame damage.
It could most likely be the tires, so I'll start there. The fact that it'll come and go makes me feel it's a tire issue more than shock/suspension. Plus it starts at a specific speed, but in the past I've felt out of balance tires start wobbling at 45 not 55. But it shakes the hood and rattles the truck hard, so it makes me feel there's more than just an imbalanced tire. Hence the reason to post and get ideas. A hub bearing could be the culprit, but I don't hear a drone/metallic whine from any corner of the truck.
It'll be about 2 weeks at the earliest until I can get to it, but I can't stop trying to figure it out. I'll also be an hour from Wild Horses once I'm back in town, so maybe I'll stop by there and see what they say if they're willing to look at it.
I just got it, so I'm trying to identify all the PO's mods and upgrades. I'll list them so folks have an idea of what the truck has.
'69 Bronco soft top
-3 speed (rebuilt 3k miles ago) with D20: no leaks
-2.5" lift (?): no labels on the shocks but the truck sits up a little and has a progressive rate coil spring, 11 leaf pack, and a 4" drop pitman arm; stock radius arms, track bar, steering linkage, and knuckles
-No body lift (?); I can't ID body lifts on an EB due to no experience, plus I've never done a body lift because I've just modified fenders to make tires work. But at most it's a 1" lift, if at all.
-Power steering, but gear box has play in it; unknown model
-4 wheel power disc brakes
-Worked over 302 that runs strong, aftermarket radiator, ignition
-23 gallon fuel tank
- Drive shafts look new, stock D30 and 9"
Any thoughts or questions?
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