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...