Low speed shimmy / vibration

Jshadwick

Jshadwick

New Member
Joined
Aug 15, 2020
Messages
8
Location
Wichita Ks
Hey all,

Just joined. I have an issue maybe someone on here could help me with.
First off I have a 1998 tj sahara with the 32rh trans. A while back I had some vibrations when doing highway speeds but smooth as silk with in town cruising. Did some digging and discovered the double cardon joint on my front drive shaft was toast. Since I was lucky enough to buy some warranty with my tj instead of having the joint rebuilt they got me a replacement Tom woods shaft. Well my issue now is, there is a shimmy even at low speeds. I don’t have fancy tools or angle gauges. But could someone possibly point me in the right direction?
 
Get your tires balanced and tell the manager that they need to be perfect or you’ll feel it.

You can do a dry steer test as well by watching the steering links for movement while someone turns the wheels back and forth. A loose track bar bolt will also create shimmy but unbalanced tires will exacerbate any worn or loose links and even cause shimmy when everything else is tight.
 
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Thank you Ajrango. I actually just came from looking underneath the front end. The track bar on the axle side does have just a tiny wiggle I’m thinking that may be my culprit. Right now driving without the drone drive shaft isn’t a big deal due to Kansas summers not calling for 4wd but I’m hell bent on getting it sorted out by winter
 
Sounds like your track bar bolts are in need of the proper torque spec.
 
Trackbar bolts are tight as can be. Had the brother in-law dry steer it while I watched and the track bar does have some lateral play on the axle side. I have an adjustable one to replace it but it requires cutting off the frame mount and welding in a new frame mount. I’m not comfortable enough in my welding skills for such a critical weld.
 
Jshadwick said:
Hey all,
Well my issue now is, there is a shimmy even at low speeds. I don’t have fancy tools or angle gauges. But could someone possibly point me in the right direction?
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I agree with @AjRagno with getting your tires balanced. A rotation might also be in order if there is any uneven wearing of the tires. Since you didn't give specific details I'm under the assumption the shimmy you're talking about is felt in the steering wheel? That can be caused by tire balance or wheel/tire runout. When you take it to have the tires balanced, also have them make sure there is no side to side wobble in the tire or wheel both while on the balancer and on the Jeep. Very low speed wobbles/shimmies are more often caused by something not spinning true, (wobbling side to side) than they are an imbalance.
 
I’ve have the tires rotated and balanced twice. But I’m pretty sure it is the trackbar. If not? The lateral movement needs addressed anyways. So I might be crazy but I’m gonna take my new bar in and see if we can match a tie rod end up on it so that way I don’t have to do any cutting or welding.
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When I first got it, it rode smooth until 60mph. That what made me think balance issue. Took them to a local 4x4 shop and had them rebalanced. No change. Read some forums and the remove the front shaft was talked about so I tried that and boom. Smooth as silk all the way up to 90. Took a look at the shaft and the cardon joint was pretty much trashed. So instead of rebuild I talked the dealer into getting me a Tom woods shaft. Put that in and then the shakes started at lower speeds.
 
A shimmy you can see and feel, but not hear (except maybe rattling), is usually the tires, wheels, or something within that assembly. Driveline vibrations are usually much higher frequency, in the audible range. You wouldn’t see them (except maybe the mirrors get fuzzy), but you would probably hear a pulsing roar. You may see or feel driveline vibrations (below the audible range) at low speeds.

You can think in terms of revolutions per minute and frequency in Hz. If the driveshaft is spinning 3600 RPM (freeway speeds), it would be heard at either 60 or 120 Hz. Meanwhile, the tires would shake at roughly 15 hertz, depending upon your gear ratio (imaginary 4.00 axle ratio used in this example). 15 Hz is too low to hear, but you could probably see the individual vibrations.
 
Jshadwick said:
When I first got it, it rode smooth until 60mph. That what made me think balance issue. Took them to a local 4x4 shop and had them rebalanced. No change. Read some forums and the remove the front shaft was talked about so I tried that and boom. Smooth as silk all the way up to 90. Took a look at the shaft and the cardon joint was pretty much trashed. So instead of rebuild I talked the dealer into getting me a Tom woods shaft. Put that in and then the shakes started at lower speeds.
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Maybe I misunderstood your complaint. In my experience vibrations caused by drive shafts are not related to a "shimmy". A shimmy is descriptive of the steering wheel shaking back and forth, or a side to side shift feeling in the seat. The prior being the front end and the latter being the rear. A shimmy can be compounded by a worn track bar joint or bushing but the track bar will not cause a "shimmy". Low speed shimmy can be cause by a bent wheel, malformed tire casing, bent axle or unit bearing hub. High speed shimmy is usually caused by improperly dynamically balanced tires as well as the prior mentioned causes.

All that aside you also mentioned your vibration came back when you installed the new drive shaft. I would suggest pulling the drive shaft out again and see if the vibration goes away again. If it does then I would check pinion angle, pinion bearing, or possibly transfer case yoke bearing.
 
I apologize. By shimmy I was meaning vibrating. But got the new adjustable trackbar installed and re centered the axle. No more vibrations. But now I need to get an alignment. Jeep tracks straight. But now my steering wheel is 90 degrees off.
 
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Jshadwick said:
I apologize. By shimmy I was meaning vibrating. But got the new adjustable trackbar installed and re centered the axle. No more vibrations. But now I need to get an alignment. Jeep tracks straight. But now my steering wheel is 90 degrees off.
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You can simply shorten or lengthen the drag link to adjust steering wheel center. It won't affect the toe in. Only adjusting the tie rod will affect the toe in. There should be an adjustment collar on the drag link
 
Ok awesome. Thank you very much. I’m guessing putting my budget blocks “3in spring spacers” in off centered my front axle and threw my drive shaft angle out of whack? Either way now that it’s recentered it’s not vibrating anymore. Hopefully it stays that way. Thank you all very much for the input.
 
Jshadwick said:
Ok awesome. Thank you very much. I’m guessing putting my budget blocks “3in spring spacers” in off centered my front axle and threw my drive shaft angle out of whack? Either way now that it’s recentered it’s not vibrating anymore. Hopefully it stays that way. Thank you all very much for the input.
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Most likely. The trackbar tends to pull the axle to the driver's side when a Jeep is lifted. It makes an arc throughout its motion, just like the control arms do. Using an adjustable trackbar allows it to be recentered.

Be sure to check your toe-in while you're at it. The toe will also change when the Jeep is lifted, because the inverted-Y steering gets taller and slightly narrower. If this is out of spec, your tires will go bald very quickly.

Here's a how to guide:
https://wranglertjforum.com/threads/how-to-align-your-jeep-wrangler-tj.85/
The only other thing you might be able to adjust is pinion angle/caster, if you either have cam bolts or adjustable control arms. On lifted Jeeps, the pinion angle is ideally set one degree below the angle of the driveshaft and the caster at 7 degrees, but because of the fixed relationship between pinion angle and caster, a compromise between the two must be made on lifted Jeeps. The goal is to find a tolerable level of caster that doesn't allow the driveshaft to vibrate.

Camber is fixed and not adjustable. If your camber is out of specification, you have either bent your axle or caused other damage elsewhere.

So basically after that, you have 100% done your own alignment.
 
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