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55mph shimmy & shake

P

ParkCityXJ

NAXJA Forum User
Location
Park City, Utah
I get a strange vibration in the front end right at about 55mph. It's fine at 50 and below and 60 and above. I thought it was my tires being out of balance, but after buying new tires that I needed anyway it hasn't gone away...Any ideas??

Thanks
 
Start with the steering stabilizer. It's the most likely suspect. If that doesn't help, start looking for other worn parts in the front end, and alignment issues. My 87 got a wobble when a bad ball joint put the camber off.
 
Is the shimmy still at exactly the same speed? A steering stabilizer does not and cannot PREVENT shimmy, all it can do is dampen it to hide the effect from the driver a bit. 55 MPH is the magic speed for shimmy caused by improperly balanced tires, and just because you have new tires does NOT guarantee that the guy who slapped weights on your rims knows how to run the machine. I would take it back to the tire shop and ask the manager to re-check the balance on the front tires.
 
I agree with Eagle. Every single time this has happened to me its been the front tires out of balance and sometimes not even by very much. A few times it only took it being off by half an ounce which is pretty easy to screw up when balancing and I knoiw of a lot of shops that will say half an ounce is close enough but it isn't. Definetely bring them back.

Dean
 
If your tires are balanced, check the LCA bushings. I put in new RE LCAs and my 50 mph shimmy completely went away. Just replaced the UCAs and the ride now is like butta. You may be able to get the same results by changing the bushings in the stock control arms.
 
Rotate the front tires to the back and see if you still have the shimmy.
Could be just the front tires out of whack.
If not, got the route of looking for suspension components worn.
 
Make sure that the tire shop road forces tires (not everyone does). Tires that fail road force tests give off vibes too. Ask to watch them being forced/balanced. Balancing/forcing is VERY easy (depending on tire/rim size) to do, but many of the chain shops around here don't bother doing it. We constantly get customers from other shops whose tires are all out of wack from places like tires plus,jiffy lube, ect. They are slack, and that's all there is to it.
 
A few weeks ago, I checked Hunter's website for a tire dealer in town that has their road force balancing capability. That turned out to be a local 4X4 shop, Chux Trux. The guy there tells me they can't handle large tires on the machine(33's in my case).

They did do a good job of dynamic balancing, though. Made a noticable difference over the job done by Firestone.

I'd consider dynamic balancing the minimum. I picked up my spare tires after I dropped them off at Firestone last week and the had all the weights on the inside of the rims. I asked the guy if they dynamic balanced them and he said "no, the manager said not to bother". That was news to me. I took them back out of my Jeep and waited for the guy to redo them all. You can't bubble balance a large tire and expect it to work well on the front of a solid axle vehicle.
 
Yes, that is true. Tires are only road forced up to about 285's or so. After that, it makes no difference what the road force is.
 
Dynamic balancing is critical, but it also has to be done right. I've watched the guys at a local tire chain (Town Fair Tire) do it. They barely get the tire rolling before they shut the machine down and start whacking on weights. There's no way the tire is spinning at close to 55 MPH, and that's the speed when shimmy usually starts to kick in. The slow roll may be fine for showing up gross imbalance, but it won't show up small imbalances. It doesn't take much eccentric weight on the outside edge of a big tire to raise havoc with the steering.
 
Eagle, I don't know what kind of machines they have, but ours stop automatically. I don't know how fast they get the wheel to, but if we try to stop it early, it errors out. Also, if the wheel isn't VERY tight on the machine, it can throw the balance off.
 
Mine did the same thing at about 50mph, while checking it out I found I had a busted u-joint at the front axle. Replaced it and problem fixed.
 
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