Help with shimmy - slightly different than I am used to

[Jon K]

Hey guys - car is back on the road and got a new p/s pump in it finally so I want to get into driving it more often. I had my p/s pump bypassed with a shorter belt, and noticed a pretty nasty shimmy (i'd call it more like a shake... it was pretty violent!) one day at maybe 40 - 45 mph when I hit some averagely rough pavement (lumpy is a good description..not rough), the front end did a pretty nasty shake. I slowed down and managed to get it under control - it was on the way to work and was the sort of shake that makes you go "holy ****!". This was on stock bottle caps.

I had driven the car about 100 - 150 miles without another instance of this happening, and had the car on original wheels up to like 80 mph without issue. Then I put my small drag wheels back on the other day and got it up to 40 - 45 mph again and immediately got this shimmy. It seems almost like if I steered away from the center point of the steering wheel I could work the nasty ass shake out... or if I slowed down - usually I slowed down. It was a pretty nasty/violent shimmy though.

So - I am used to the 55 - 60 mph slight vibe or nasty vibe while braking. I have Grunt urethane control arms in the rear most position (I forget if thats upper or lowers, but its closes to the firewall). I have 4 year old stock bushings in the other position. I have a good amount of steering wheel play. I need help because I want to drive my car regularly now that I have power steering but I don't want to die. Thanks!

[Bill R.]

most likely thrust arms, then tierod ends, then idler arm and finally ball joints.. I'd start at thrust arm bushings though first.

[Jon K]

Bill - yeah thats what I figured. Was hoping the mph range spelled something else. Can you refresh me - which are the thrust arms? The ones whose bushings are closer to the radiator or closer to the firewall? I have the urethane bushings in the closer to firewall arms - hopefully they're not bad. Gonna probably just buy new tie rods and rod ends and idler arm or see if I can notice any weird jiggle in it. What about the drag bar?

[BMWDriver]

If your rear is raised as in your sig pic, then there is likely a weight shift towards the front, and so additionnal stress on the front wheels and all that supports them.

[Jon K]

If your rear is raised as in your sig pic, then there is likely a weight shift towards the front, and so additionnal stress on the front wheels and all that supports them.

No the rear is not raised and that really wouldn't change weight distribution

[bubba966]

If your thrust arm bushings are rather bad they'll get nasty at 40-45 MPH. Mine are rather nasty and do this now. have the new arms, but don't want to put them in with the mostly dead shocks as that'll just kill 'em right quick. So I've been living with it when it pops up...

[Paul in NZ]

No the rear is not raised and that really wouldn't change weight distribution

make sure wheel balancece and tire pressures are good too!

[Jon K]

If your thrust arm bushings are rather bad they'll get nasty at 40-45 MPH. Mine are rather nasty and do this now. have the new arms, but don't want to put them in with the mostly dead shocks as that'll just kill 'em right quick. So I've been living with it when it pops up...

This is like nasty like if you're not paying attention and you hit it its like WTF. Which are the thrust arms and which are the others? I always confuse the two.

[Scott C]

Why do you have play in your steering wheel (is it the box adjustment)? or the idler arm. Others have already mentioned the arms/bushings/joints ....

Scott

[bubba966]

This is like nasty like if you're not paying attention and you hit it its like WTF. Which are the thrust arms and which are the others? I always confuse the two.

Yeah, by nasty I mean violently shaking/hoping. Well beyond your typical thrust bushing shimmy.

And I don't remember either offhand which are the thrust arms and which are the control arms...:(

[Sam-Son]

upper is thrust lower is control
or so I believe

[Jon K]

Why do you have play in your steering wheel (is it the box adjustment)? or the idler arm. Others have already mentioned the arms/bushings/joints ....

Scott

I dunno - I've got play :)

How do we get the play out of the wheel? I'll replace the idler arm if thats it. How does the box on the M50 car get adjusted?

[Scott C]

I actually couldn't find the box adjustment in the Bently... You can frog the box if the internal backlash is not adjusted properly (too tight - lack of castering /wheel centering are the symptom).

Check out this for several other things to check prior to box adjustment
http://www.bimmernut.com/forum/showthread.php?t=3926&highlight=steering+adjustment

[Jr ///M5]

Wait until you get new control arms in the car before you start playing with the adjustment on the steering.

Just remember, the upper control arms deal with "fore and aft" force, the lowers deal with side to side motion.

While your car is up in the air, squeeze the ball joints upward/downward with a large pair of channel locks to see if the joint has any play. None is allowed. Do this on all the larger control arm joints and the smaller steering wheel linkage joints. You can also have someone in the car with it not running to gently move the steering wheel back and forth and you will see/feel the play in the defective joints. Follow Bill R's instruction about the order in which they are checked/replaced. You can check the thrust arm bushings for play by driving the car at about 2-3 mph and quickly apply the brakes, if the bushing is shot you will see the front wheel go back about 2 inches.

JR

[russiankid]

You can get tie rod from Autohausaz for $50 each, its a complete assembly. I had the same nasty shake as you did, it felt like the front end is playing hop scotch on the road. New thrust arms, tie rods, sway bar end links and bushings solved the issue.

[Jon K]

See I dont think its my thrust arms because I have the urethane bushings in :(

[bubba966]

See I dont think its my thrust arms because I have the urethane bushings in :(

The ball joints on the thrust arms could be shot.

When you put the urethane bushings in did you re-use the same thrust arms you had in there before?

[Jon K]

The ball joints on the thrust arms could be shot.

When you put the urethane bushings in did you re-use the same thrust arms you had in there before?

Yes but at the time they only had about 3k miles on them. These are my cars second set of thrust arms that I put in prob abour 130 - 150k miles, and the 750i bushings were in there, then I popped in the urethanes in less than 3 - 5k miles.

[Bill R.]

are junk. And they are causing your problem





Yes but at the time they only had about 3k miles on them. These are my cars second set of thrust arms that I put in prob abour 130 - 150k miles, and the 750i bushings were in there, then I popped in the urethanes in less than 3 - 5k miles.

[Jon K]

are junk. And they are causing your problem

I dunno bill the remedied my shimmy last time :(

[cammo]

had a weird shimmy. got all 4 wheels aligned n balanced. all good now. sorry if this does not help. its just you mentioned you hit something on the road

[Paul in NZ]

I dunno bill the remedied my shimmy last time :(

Jon i had a positively evil shimmy..it got so bad that if i was forced to travel at 90 k it was violent enough to start a knocking/rattling in the front end and make it feel like i was about to slide off the road(just relax it wont but it sure feels like it will)it came out of nowhere and got worse and worse over a two week period.
I needed new tires so i got some,and the guy said the balance on my old ones was bad...(i told them to check balance carefully when putting new tires on) Shimmy disappeared!.Perhaps you have lost a weight?Check your pressures and presence or lack of hubcenrtric rings??

[ahlem]

I had the same problem and minimized it with tie rod ends and a replacement idler arm, so far. I still have a little wobble at 50. I have 18" rims and fat tires and adjustable camber plates that need to be unegative-cambered a bit. You can see movement if you properly place the car on jackstands and apply pressure to the front or back of a wheel with the steering wheel locked. that will tell you the minimum components to replace. I fear I need to do the thrust arms as well.

[632 Regal]

they will remedy it again too, just have to replace them every 3-5k and good to go.

I dunno bill the remedied my shimmy last time :(

[Jon K]

3 - 5k? I've had them in there for over 70k