Shaking front end.

[Southbronco1]

Hello Friends, about a year ago I bought a 1970 Bronco. 302, manual, stock, no lift. I recently successfully bled the brakes and slightly adjusted the shoes (using a screwdriver on the star-wheel) on all four wheels. It was the first time since I owned the car that I had the wheels off and the car on jack stands. During the initial test drive (the brakes worked perfectly), I felt a slight rapid hop that soon went away. The next day, I began to feel the hop again, but again it soon went away. However towards the end of the three mile drive a got a really strong shimmy through what felt like the front wheels, that became a near violent shake that went straight up through the steering wheel. I slowed down as quickly as possible and the shake went away. I have been driving it a lot to try and discern a pattern for when the shaking starts, but it seems very random. I thought perhaps I over adjusted one of the front shoes by too many turns on the star-wheel adjuster, so I went back in and backed it off a couple clicks on each wheel. Each wheel spins with the same amount of drag and the car stays perfectly straight under heavy application of the brakes, so I dont think that is the issue. Alignment seems fine as car stays straight down the road. The car has the original leaf springs that I intend to replace this winter, but previous to my doing the brakes, never caused any problem. So I am at a loss for this shimmy/shake on the front end. Clearly I unintentionally screwed something up while doing the brake job. Any thoughts on what this could be? Or what I should do to trouble shoot? I am very much a rookie with the mechanical end of things. Any thoughts at all are greatly appreciated.

Steve

 

[Broncobowsher]

Sounds like a light case of "death wobble". Typically track bar bushings, but not always.

 

[Southbronco1]

Thank you..

 

[Jimboss77]

All the symptoms except for the brake adjustments sounds like a bad ball joint to me. Had a 70's model 4x4 F150 that had a bone jarring shake like you described that would come and go. Thought it was a tire out of balance until I took it to a tire shop and they found it.

 

[B RON CO]

Hi, if you had the brake drums off for inspection, I would jack up the front end and make sure the hubs are properly tightened. Do not drive anymore until you make sure the hubs are not coming loose.There are particular techniques for installing the hubs, and any error can cause a big problem.
If that is ok some of the basic things to do is rotate the tires. While the front end is in the air look at each connection, any firmly grab and wiggle each part, including the brake drums, to check the ball joint and steering parts. Did you grease all the grease fittings? Are your tires in good shape?
Time to check and double check things until you figure it out.
Good luck

 

[Hinmaton]

I know this sounds stupid, but are you sure the lug nuts are tight? Ask me how I know.

Hinmaton


Sent from my iPhone using Tapatalk

 

[DirtDonk]

Speaking of tires... How old are the ones on your bronco? Tires do age out even if they still have tread left on them, so that could be at least part of the issue.
If you still have the original Dana 30 front axle assembly you would have king pin bearings that can wear out. Or possibly just need re-greasing and resetting of tolerances.

 

[Southbronco1]

Thanks all. I appreciate the comments. I'll do some trouble shooting on these points. I don't know the age of the tires but plenty of tread and they don't look pretty new (I've only owned the car for a year, so not entirely sure). Not sure tires are the issue anyway as this condition started right after I had jacked up the truck for the first time. So I'm assuming in doing so I put something out of kilter.

 

[lars]

First thought: what is popularly known as Death Wobble. Volumes have been written about it, and it can be a symptom of many issues. Bad tires, poor steering geometry (don't assume that because it's stock that it's ok- plenty of early Broncos left the factory with out of spec steering geometry, due to loose manufacturing quality control), worn kingpins (yours is a 1970 thus likely a Dana 30 with kingpins), worn suspension bushings, worn steering linkage, etc. When I bought my 1970 Bronco 25 years ago it suffered from all of the above. The shaking would sometimes start as low as 20 mph. Unfortunately it's not always easy to parse out exactly what is causing it. Fortunately most of the bits and pieces necessary to correct the above described ills aren't terribly expensive.

 

[Yeller]

Failing belt in an old tire?

Track bar bushing is probably it but jack it up and spin the wheels and see if the tires are round. And double down on Himaton's comment lugnuts tight? Work on stuff long enough sooner or later you won't do final torque...

Torque spec is 85-95ftlbs.

I use the general rule if your wife can't loosen the lugnuts with a normal 18” lug wrench they are probably too tight.

 

[Southbronco1]

Thank you gents. I'll check the tires again but they are pretty new and had no previous problems before jacking it up on stands. Ha, on the lug nuts I made sure they were all torqued to 100 ftlbs.

 

[Southbronco1]

Very helpful. Thank you all.

 

[DirtDonk]

You say the tires ARE pretty new, or ARE NOT?
If newer than 20 years or so, they will have a date code on the sidewall. If they predate the date coding, like we've seen still mounted on a lot of older vehicles, then they are too old.
If they're more than ten years old, they're likely too old as well.
Just some food for thought.

And yes, if it happened right after you did something, then this is suspect. But it could also fall into the misleading category of "coincidental failures" that happen all the time on our old rigs.
Things like changing a tail light bulb, then having the headlights start to flicker. Possibly related, but very unlikely. Just a coincidental failure that had been waiting to happen and just chose that moment in time.

Removing and re-installing the tires and wheels would not normally cause any issues. Adjusting the brakes would not normally cause your symptoms either. But I suppose it's possible.
As others have said, maybe your work set the king-pin bearings over the edge. Maybe it's being driven more in this last year than in the last thirty years, and some things are just wearing out finally.

If you have not already, and don't know if it was done previous to you owning it, you really should re-pack and re-adjust the front wheel bearings. At that time since the drums will be removed you can fully inspect the brakes for anything amiss.
And you can at least test for excess play in the king pin bearings at that time as well.

In the meantime, before you put it back up on jack stands, do the steering test where, with the tires fully on the ground and the full weight of the vehicle on them, a helper turns the steering wheel back and forth a half-turn in each direction while you watch every joint, rod, or other component in the front of the vehicle. Everything from the steering shaft into the box, the box itself on the frame, and all the rod ends. You can even see wheel bearing and king-pin movement when this is being done.
Basically you're pitting the weight of the vehicle against the torque of the steering system and anything that is loose will show up. Where you might not have seen it with the normal testing by hand.

Well worth the five minutes it takes to perform.

Paul

 

[Broncobowsher]

For the date code look on the sidewall. There will be a DOT code. It is only on one side of the tire so you may need to look at the inside sidewall to find it. There are 3 blocks of alpha-numeric. The last block will be a 4 digit number. If a 3-digit number, pre-2000 tire. The first two digits of the 4-digit block are the week. This will be a number between 01 and 52. The last two digits are the year, 07=2007.

 

[Southbronco1]

DirtDonk and Broncobowsher - This is VERY helpful info. I really appreciate it.

 

[Rustytruck]

Jack up the front and put it on jack stands grab a tire at 12 0-clock and 6 o-clock and try to wiggle the tire in and out. then grab at 9 o-clock and 3 o-clock and wiggle in and out if anything moves then it must be fixed. take the tires and have them run on a spin balancer and make sure they are in balance and running true could be a flat spot or out of round tire from sitting. then replace the top and bottom track bar bushings.