Bump Steer Causes?

Anyone know what would cause bump steer?  It use to be real bad but after I changed my tires it wasn't as bad.

Everytime i hit a good bump or go on a bumpy road the steering wheel shakes, if i am going on freeway and hit a bump the steering feels like it jerks hella fast and makes me feel like i lose control for a split second. kinda scary.  

I know some bumpy feeling is natural but this is more than the average shake.  I just got my rack and pinion done and I asked my shady now ex-mechanic and he keeps telling me its normal and gives his "explanation of why it does it".. this shake is abnormal as I go through the same bumps with different cars and get no jerk.  

just some causes.. ive been searching online but if anyone is experiences with this please let me know.

thank you

I don't really have an awnser.

Did it do this before the new rack? Is it a new rack?
What was it doing before that rack work?; how did you come to the detirmenation it needed rack work?

Did you get it alighned?

How are your struts?

Is the car modified in any way?

You could take a pry bar to it to see if there's exessive play in the joints or bushings.

zastabaMaybe he forgot to put in one of the steering rack bolts...  

what exactly is bump steer anyway? i always thought it was when you went around a sharp corner and the car would start hopping/bouncing because something was not aligned causing the wheels to fight against them self and hop the car. i had this prob with my car after i lowered it until it was aligned with proper control arms.

Bumpsteer, technically, is when the movement of the wheel through out it's suspension travel causes the wheel to turn.

What he's getting is heavy shock feedback through the steering wheel.

No problem for me except grinding stuff...
Check your car quickly!
Before tried to tight them, loose them. Why? It's better to know the "torque" that mess than overtighted.

Sorry for my sentences, i'm french...

As JonB stated this doesn't sound like bump steer. Get a proepr garage to look at it.
For comedy effect what does Mr Shady say exactly ?

The exact definition of bump steer is failure of the bottom suspension arm and steering arm to maintain a parallelagram during suspenion travel.  

Hmmm.. another explantion of bump steer...

When your wheels go up and down, so do the tie rods from the rack.. as they go up or down, it shortens or lengthens them following the radius that the ends travel on, so when the wheel drops, the tie rods have to go downwards, and it pulls them inwards a bit. when they get pulled in, so does the tire.

If its bump steer causing your issue, then it would likely kinda jerk the steering wheel off to one side when you hit a bump with one wheel versus 2.

If the whole car kinda seems to almost "slide" kinda thing when hitting the bumps then its kinda like an overly stiff suspension, and likely your shocks/struts/springs arent realy doing thier job anymore. If its your shocks, the car will be bouncy. with the springs shot it generaly rides like a tank.

If you hear a kinda knocking sound everytime you hit a mild little bump, 85% of the time its struts.

Check your bushings, my car does this, its the bushings, the springs, and rear struts for me, pretty meh right now.

MaxpowCheck your bushings, my car does this, its the bushings, the springs, and rear struts for me, pretty meh right now.

ArroQFT

QFT is "Quoted For Truth"

take a look at this image;



Notice how the steering arm and lower suspension arm maitain their positions (relative to one-another) during suspension travel.
Failure to do so would cause a change of track on bump aka bumpsteer.
Also note this isn't so important with high mounted steering rack ie; Audi and (IIRC) some Hondas ?

CamInHeadtake a look at this image;



Notice how the steering arm and lower suspension arm maitain their positions (relative to one-another) during suspension travel.
Failure to do so would cause a change of track on bump aka bumpsteer.
Also note this isn't so important with high mounted steering rack ie; Audi and (IIRC) some Hondas ?

CamInHeadtake a look at this image;



Notice how the steering arm and lower suspension arm maitain their positions (relative to one-another) during suspension travel.
Failure to do so would cause a change of track on bump aka bumpsteer.
Also note this isn't so important with high mounted steering rack ie; Audi and (IIRC) some Hondas ?

Jsvob03Audi/VW uses the setup you are referring to, as well as some honda/acura vehicles. even older chryslers, and GM cars used that setup.. (high mounted steering rack). if you do alignments, you know just how terrible those cars are. (honda's are by far the easiest, but still not a walk in the park.)

also, the AUDI/VW (some) setup has a means to adjust the "toe curve". thats the arc that the rod travels thru. gl w/ that, lol..

Yeah the most likely cause of bump steer in a factory designed car is somekind of failure in the TRE balljoint. I think poor location of the steering rack can also cause it but
1) that simply wouldn't happen in a facotry design
2) I've never worked outside of mildly modified OEM designs

Also you're correct saying double wihbones usually are of different sizes. Usually described as "unequal length" or SLA "short/long arm".
A longer lower link makes the outer wheel, of any given turn, see negative camber which effectily increases ovberall grip.

Tha actual theory for those extra VAG balljoints is quite simple BTW. With a single joint it all pivots off that one point and provides the axis for the various geometry.
With a pair of balljoints the centre is actually throretical, at a point where, if you were to project a line from each balljoint, they would converge.
Desireable if the best position of the pivot isn't pratical. I'll shove up a picture as it's easier to see than describe.

thanks all for your replies.. and sorry i wasn't able to get back to you all as i have been busy over the holidays without a computer.

I guess I wasn't too sure what bump steer was but it seemed to be the appropriate term for what was going on.  JonB might have said it best as calling it "HEAVY SHOCK FEEDBACK THROUGH THE STEERING WHEEL"

but also if I am driving on a really bumpy road ill have to grip the steering wheel tight to keep it from shaking so much and following the bumps.  

My car is not modified in anyway.  I will get an alignment done as soon as possible.  It did not do this before I got my rack rebuilt.. I needed my rack rebuilt because I got my steering rack bushings and tie ends replaced and my steering was still being wierd as it would be late responsive and improperly aligned even after getting an alignment.  

mr shady says that its normal and it happens in his car too even after I told him this has never happen to me in any other car I drove.  We tested a bump I know that it happens on this car and not on a normal average working car.  I pretty much forgot what he said but he was basically saying bologna to say that it was perfectly normal.

Yeah once I get another job as my hours have been cut ill have it checked at a more legit shop.  
So what type of bushings do I need to have replaced?

I know my front struts need to be replaced as well but I was just kinda waiting until i had enough to buy some lowering springs or a good coilover set to come about.  

thanks for the help all.  what else would I need to get done to solve this.

tie rods

ball joints

steering rack bushings

tension rod bushings

control arm bushings

intermediate shaft play (between steering rack and steering column)

torque of all fasteners

things I would look at, somewhat in this order.  The situation you describe is very common to s12s and can make for a scary drive.