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Bump Steer

73EB

Sr. Member
Joined
Feb 21, 2010
Messages
534
Loc.
Bentonville, Ar
So what causes bump steer? I thought it was drastic angle in the steering linkage but does the alignment of the steering linkage and track bar cause this as well?

My rig has bullet proof steering, no drop pitman arm. The track bar angle is greater than the bar that goes from the gear box to the pass side spindle. I just assumed it needed a drop pitman arm but I saw in another thread that someone said not to have one.

So when I'm driving and go over a dip or sag in the road my EB goes left quick. its consistant and nothing feels loose. Thanks
 

broncnaz

Bronco Guru
Joined
May 22, 2003
Messages
24,341
Mostly the angle differances between the drag link and trac bar but there are also lenght differances that can cause it as well. You hit a bump and one bar is moving more than the other and causes the steering wheel to move since its the only moveable part.

If your rig has 3.5in of lift or higher you usually need a drop pitman arm. You also need a drop trac bar bracket or trac bar riser. Some pics and more info of your setup may help
 

Deano

Bronco Guru
Joined
Jan 9, 2010
Messages
1,182
I've got a pic on my flickr page with the track bar riser and a tierod over setup and I have no bumpsteer. If that helps.
 

Broncobowsher

Total hack
Joined
Jun 4, 2002
Messages
34,834
So what causes bump steer? I thought it was drastic angle in the steering linkage but does the alignment of the steering linkage and track bar cause this as well?
Yes!

The axle does not move in a true vertical path. There is some side shifting going on due to the arc that the track bar takes. Match that arc with the steering linkage and no bump steer. Perfect match is almost impossible but really close is what you are after.

I was amazed while working mine out that ¼" of height change on the steering linkage would make a noticable difference. To get it right can take a lot of work.

The best way I found to see bumpsteer is to remove the front shocks (so you can get some good bouncing and travel in the driveway). Some vise grips and scrap metal to lock the tierod to the axle tube. That is so ALL the bumpsteer will show up in the steering wheel. Bounce the front suspension and watch the steering wheel. When you get the steering wheel to stop turning while bouncing the bumpsteer is gone.

Another thing to consider...
I mentioned the axle does not travel a true vertical path, it follows the arc of the track bar. Well when that track bar starts getting some angle to it the axle shifts off center. Some fix it with a longer/adjustable track bar. Well that centers it under the body but does nothing for the angle. When you hit a dip in the road you will experience a lot of axle shift. When this happens it feels like the suspension is crooked. The dips in the road cause the vehicle to rotate. Well the body rotates but the truck drives straight and it can do this with no bumpsteer.

There are a lot of things that can be done wrong.
I start with the basics. Is the track bar right? does the suspension travel up and down without side to side movment? Then go after bumpsteer.

My history:
Lift, springs only. No bumpsteer but now bounced sideways in dips.
Track bar riser. Drove straight in dips now but angles off on steering, bumpsteer.
Heim joint steering. (no drop pitman arm) played with over/under and some spacers. Drove great after that.
 

broncnaz

Bronco Guru
Joined
May 22, 2003
Messages
24,341
How much lift do you have and what components are installed? Doesnt appear to be any drop brackets or anything else.
 
OP
OP
73EB

73EB

Sr. Member
Joined
Feb 21, 2010
Messages
534
Loc.
Bentonville, Ar
It has a 3.5" lift. frt springs are WH. stock radius arms, It doesn't seem to have a drop bracket or an adjustable track bar. Flat pitman arm. The axle appears to be centered. I bought it with the lift already on it. Did they make a longer track that could used?
 
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