Topic: what causes steering drift / bump steer

[j.p.sloan]

I am having trouble with my '90 YJ drifting on smooth roads, and hard to keep on my side of the road on bumpy roads.  It has a 3 inch suspension lift and 2 inch body lift,  dropped control arm, etc..  I'm running 33x12.50 MTX tires.  
  Is it the sway bar, control arm, steering box, or what?  I had it up on the lift and everything feels tight.  I know this is a fairly common issue, so I am hoping you guys can help me out.  I'm fairly new to the Jeep scene, and just not sure what I'm looking for.

Thanks; John

[zeitlerusmc]

does your jeep have a steering stabalizer? has it been aligned since you lifted it? you could have a stuck caliper that could make it pull to one side. there are alot of things that could be the cause. does it do it at specific speeds? and does it pull when you brake?

[Krod]

Still have your factory trac-bar and sway bars installed?   They help with those issues

[j.p.sloan]

I do still have the trak bars installed.  It does have a steering stabilizer.  It doesn't pull when I brake, and it doesn't pull in the same direction each time.  It feels like I will have tension on the wheel to keep it from drifting in one direction, then I hit a bump and it jumps in the other direction.  Also, and I don't know if this has any bearing on this issue or not, when I'm off road and going over some rough terrain, it starts to make this grinding kind of clunking noise in the rear.  

Thanks for your input;John

[chardrc]

i have somthing like that when i have 4wheel drive in when of hard surfaces.. the front axel binds and eventualy slips but the od part is that i dont have a locker or limited slip in front which is what i thought did that.. so im stupid on my problem.. i just got to remember asfult =2wd...:)

[zeitlerusmc]

I would go spend the money and get a steering stabalizer, its  real simple to put onyou can do it your self, and also get it aligned see what happens then!

[SMC4WD]

There are a few different factors that could cause bump steer and 'drifting'.  One thing to keep in the back or your mind is the crown of the road.  A lot of people don't understand that the road is not flat.  It's curved, or crowned on the top so water doesn't puddle.  

Now I'm far from an authority on this one, and specific degrees are not my forte, so I'll try to wing it.

It's a YJ, so the only rear alignment that could be done on this is the toe.  Toe in or out is the direction the tires are facing.  Follow this link to some alignment basics:
http://www.familycar.com/Alignment.htm

If the vehicle is aligned correctly, this could eliminate some of the drifting.  What is difficult to do, is to fix the caster.  In order to change the Jeeps caster, you must also change the pinion angle.  This causes front drive line vibrations.  So you've gotta find a 'happy medium'.

Then there's bump steer...  That's too difficult for me to explain, and this web site I found has a bit more to do with racing than Jeeping.
http://www.bakerprecision.com/longacr17a.htm
The idea is to keep your tie rod at the same plane are your drag link.  If those two pieces are as close to the same plane, you'll help in eliminate that issue as well.  Drop pitman arms help with bump steer, high steer or over-the-top knuckles or tie rod ends.

I hope that this clears up some of your issues, or at least informed a few of you.  A disclosure on my behalf...  I'm the furthest from an authority on this subject.  This is most of what I know on this subject.

[zeitlerusmc]

bump steer is kind of like when you pick a cart when your walking in the grocery store and the front wheels are turned the wrong way, and the front wheels shake left to right real fast. kind of the same deal with your jeep, the pitch of your axle is not right. and i don't know if some of you have heard this but there is no such thing as bump steer in the rear of your jeep. some kid try to convince me that my bump steer was coming from the rear axle. i laughed and asked for another sales person.

[Jeffy]

OK, I guess I'll drop my 2 cents in.  Bumpsteer is caused by incorrect steering geometry.   The drag-link and the tie-rod need to be parallel with each other.  (aka; on the same plain.)  What happens is the drag-link is set to a certain size that is fixed in length.  When your suspension is at rest and your drag-link and tie-rod is not parallel your drag-link sorta looks like this, /.  It angles down from the pitman arm to the tie-rod.  In the case of the TJ/XJ/ZJ the end of the tie-rod is also the end of the drag-link.

When the suspension compresses as when hitting a bump the distance between the pitman arm and the tie-rod decreases.  Well, the drag-link cannot change length on the fly so something has to give.  This is where you come into play.  If you're holding the wheel tight, you'll feel the wheel push clockwise.  Since you're holding it firmly you prevent this from happening so the wheel will turn to the left instead.  Now as the suspension rebounds, you're usually holding the wheel straight still and have corrected for the initial bound.  Now as the suspension expands the reverse happens.

Bumpsteer will usually happen on taller Jeeps that don't have hi-steer setup.  It will happen more so on softer sprung Jeeps.  You'll also see it happen when you hit the brakes hard.  The track-bar will help but is not a cure.

Drifting is a bit different.  the most common form of drifting occures more often when you go with larger tires.  They tend to grap the grooves and cracks in the roads and follows them.  If it happend all the time then it could well be an alignment problem.  You don't want to test it on a residential street since the roads are arched so water runs to the drains.

Here's a guess though.  You're driving up a residential street on the right side.  The arch in the road will cause you to drift right.  Hitting the brakes hard will cause you to bumpsteer left also but you might be catching ti on the rebound as it straigthens the wheel and pulls right.  

Oh and a steering stabilizer doesn't do too much other then deaden the feel at the steering wheel when hitting smaller bumps.  If your steering geometry is right on the money you won't need a steering stabilizer.  It sort of masks any problems.

[j.p.sloan]

Okay, after further investigation, I don't have a dropped pitman arm. The drag link is angled down as Jeffy described.  I will install a dropped pitman arm and see if that takes care of it.  What Jeffy described as far as controling the bump steer is EXACTLY what I am going through.

Thanks for all your input guys,  I appreciate it immensly.  i was afraid I was going to have to replace the steering box or something.  I will let you know how it turns out after the change out of the pitman arm.

Thanks; John

[zeitlerusmc]

Good to go a$$hole. i thought my shopping cart analogy was awesome, and then you gotta come in and make me look like a 3rd grader with your squared away technical explination and all that trash. Smart a$$!!!!!!!!!!! :D  (im just kidding by the way gents don't get all mad SMC4WD!!!)

[SMC4WD]

It's alright man, I thought I explained it pretty good too.  But Jeffy's smart...   I give the guy alot of credit.

The shopping cart thing was a great explaination.  If one wheel on a cart is all bent out of shape, that will cause that wheel to rattle all over the place.

Rear bump steer...   Maybe if you have rear-steer.  In a TJ, the rear is very similar to the front.  5 link...  The rear has a trackbar, and 4 control arms.  The front has the same...  

Now tire balancing...  That wasn't discussed...   Tires outta balance will get a vehicle hopping all over the road.  But that doesn't sound like that's a issue.