Front End light vibration and travel

[Myersalec]

Hey all, first post.

I have a 1990 Jeep MJ I've done a LOT of work to over the years. Rebuilt 4.0 engine, lifted 3 inches, adjustable track bar, adjustable lower control arms, new damper, new ball joints (all), newish 32" tires. Balanced and aligned, twice because I can't figure this problem out: I still have front end shake after years. Used to be death wobble, but since replacing all the suspension compontents other threads have suggested (joints, arms, bars) it's since reduced. I get vibration between 50 and 55, and it likes to travel in the lane even slower than that.

 

I'm thinking it's the caster, which a lot of people say should be unaffected at a 3" lift at stock 4.2°. Mine is sitting at 6.4°. 

My next thought is unaligned driveshaft pinions, since the lift pulled the t-case higher than the axle, but not much further. I've read that can cause shake and oscillations.

 

Any help is appreciated. I do all my own work, and am knowledgable enough to fix what's broken, but some things I still need a hand with.

[thecodemonk]

Pull the front driveshaft from the front axle and see if the problem goes away. You can probably just unbolt on the axle side and bungie it up for a quick test. That'll tell you if it's related to the driveline spinning or not.

If it still vibrates, check tire balance next? If the vibes stop, it's something to do with the driveline balance or angle.

Sent from my Pixel 4 using Tapatalk

[Pete M]

tires are notorious for vibrating at around 50mph.   

 

also, stock caster should be between 7 and 8 degrees. 

[Minuit]

What's the "play in the steering wheel" situation? Slop in the steering box is one of the things that can allow a small tire shake to turn into death wobble.

 

For what it's worth, both of my death wobble experiences can be directly blamed on the tires. My '91 has never gotten death wobble except for when a tire was being held on by two lug nuts at about 50 mph in a gentle right turn, and a recurring problem with it on my '89 can be summed up as a dynamic tire imbalance side-to-side shake that hit just the right frequency to DW at about 50 miles per hour in a slight left turn. A visibly out of round Cooper tire and a possibly bent wheel were the culprit. Once the offending tire and wheel combination were punted into the dumpster with reckless abandon, no more wobble.

[75sv1]

As has been suggested, driveshafts and steering box are things to check. Have you rebuilt the drive shafts? Also, check the frame at the steering box for cracks. If you have the aluminum steering box bracket, I'd replace it with one of the steel after market ones. Also, rotate tires. Also, the DW might have damages parts. I've been through DW myself. There were a few culprits. Part of mine was probably the RC upper control arms holes were worn out. 

 

Edit: Two things to check are the engine and trans mounts, and the harmonic balancer. Also, might have it aligned by a shop that does Jeep 4X4s. 

Edit again: You mention travel in the lane. Is this wandering or side to side ? Possibly steering box or trackbar is loose. I had a bushing on my trackbar that was sloted. 

 

[JMO413]

My total of 2 real experiences with death wobble were both Cooper tires. I have drove multiple customer vehicles that they said had death wobble. None of them were that bad in my eyes. Most were a tire problem and one was a steering damper. Road force balancing a tire is the end all for showing a bad tire.

[omega_rugal]

On 5/13/2020 at 2:53 PM, Myersalec said:

I get vibration between 50 and 55

 

does the vibration goes up when you accelerate? does it stop when you coast?

[Pete M]

just for a point of clarification so we're all talking about the same thing, a vibration at speed is not Death Wobble, even if it wiggles the steering wheel. 

 

DW is when the front end shakes so violently and out of control that you slam on the brakes and start praying to your deity of choice. 

[thecodemonk]

4 minutes ago, Pete M said:

just for a point of clarification so we're all talking about the same thing, a vibration at speed is not Death Wobble, even if it wiggles the steering wheel. 

 

DW is when the front end shakes so violently and out of control that you slam on the brakes and start praying to your deity of choice. 

 

This ^

 

A lot of people mix the two up.  Death wobble is something you never forget when it happens.

[Minuit]

Point of clarification to your point of clarification - a certain breed of tire balance issue can progress to death wobble under the right conditions. The tire shake itself is not death wobble, but it very well can be what starts the suspension oscillating. If anyone disagrees, I would invite them to take trip back in time and drive my 89 in its original configuration of square Cooper front tires, very loose steering box, completely dead steering stabilizer, and multiple ruined tie rod ends.

 

@JMO413 - ditto. After my experiences you couldn't pay me to drive on a set of Cooper tires again. The damn things were more square than round. I had to see them run on a machine to believe it.

[rokinn]

I've actually had a pretty good experience with Cooper Discoverer M&S running on my Subaru.  I in fact just swapped them back off yesterday.  I bought them a few years ago after I retired when I was living off grid and had to drive about 5 miles off the highway up a pretty bad sometimes steep dirt road.  I got them mainly because of the aggressive tread.  They never skipped a beat going up that road.  I run Michelin's normally and can't say the difference is particularly noticeable.  The only issue I had with them is they can track the sections of the highway that have especially crooked grooves in concrete highways a little too well. 

[Eagle]

On 5/13/2020 at 3:53 PM, Myersalec said:

I'm thinking it's the caster, which a lot of people say should be unaffected at a 3" lift at stock 4.2°. Mine is sitting at 6.4°. 

My next thought is unaligned driveshaft pinions, since the lift pulled the t-case higher than the axle, but not much further. I've read that can cause shake and oscillations.

 

 

Caster range is 7 to 8 degrees, with 7-1/2 preferred.

[BeatCJ]

On 5/27/2020 at 7:22 AM, Pete M said:

just for a point of clarification so we're all talking about the same thing, a vibration at speed is not Death Wobble, even if it wiggles the steering wheel. 

 

DW is when the front end shakes so violently and out of control that you slam on the brakes and start praying to your deity of choice. 

One time I was following a late 80's early 90's Dodge 1 ton, DRW flatbed at work on a long trip. On the way home, down a long steep (shift down to keep from running away, heating your brakes steep) downgrade, it started shimmying, and progressed to the point that the front tires were actually alternating off of the ground. It was impressive/scary, to say the least. The owner finally isolated the problem, a steering component that would work loose over time. As long as they kept it tight, it wasn't an issue. I want to say frame side track bar, just like our problems.

[JMO413]

On 5/27/2020 at 9:22 AM, Pete M said:

just for a point of clarification so we're all talking about the same thing, a vibration at speed is not Death Wobble, even if it wiggles the steering wheel. 

 

DW is when the front end shakes so violently and out of control that you slam on the brakes and start praying to your deity of choice. 

I fully understand. Both of mine were death wobble as in lots of curse words and brake pedal though the floor board.  

And the passenger possibly needing fresh underwear.

 

All the customer vehicles that I have had to drive were a vibration felt in the steering wheel. Trying to explain the difference to most customers is pointless though. Had a 1 ton Dodge in today that got a pretty good shimmy over 55. It's was easily manageable by a slight increase our decrease in speed. Steering stabilizer and track bar fixed it.

[Eagle]

5 hours ago, JMO413 said:

All the customer vehicles that I have had to drive were a vibration felt in the steering wheel. Trying to explain the difference to most customers is pointless though. Had a 1 ton Dodge in today that got a pretty good shimmy over 55. It's was easily manageable by a slight increase our decrease in speed. Steering stabilizer and track bar fixed it.

 

With all due respect, if the shimmy started at 55 MPH, the stabilizer and track bar didn't fix it, they just hid it.

 

I can't explain why it's always at 55 MPH, regardless of tire size, but a shimmy that materializes at 55 MPH and goes away at 60 or 65 MPH is always caused by tire balance. This has been the case since even before I got my driver's license. I remember my mother being concerned about a shimmy in her then-new 1958 Rambler station wagon. 55 MPH. Tire balance cured it.

 

An automotive tire-wheel assembly is a gyroscope. If it's properly balanced and the wheel isn't bent or out of round, it can't shimmy. If it does -- it's either out of balance or out of round.

[Myersalec]

Thanks all. I will go ahead and recheck everything underneath for shifting, and also get those tires balanced. Appreciate it!

[Pete M]

1 hour ago, Myersalec said:

Thanks all. I will go ahead and recheck everything underneath for shifting, and also get those tires balanced. Appreciate it!

 

be sure to add your truck to the registry  

[Myersalec]

Very much a newbie here: you're referring to the registry on this forum? Or is there another place to register?

[Pete M]

yup     that way you can get a build sheet and birthday for your baby.    oh, and add your truck's basic details to your signature.  it helps out a lot with answering questions.

 

https://comancheclub.com/forum/28-comanche-registry/