The Stovebolt Site Forums The Shop Area General Truck Talk Answer me this

Can anyone explain bumpsteer to me? Is it good? Do I want it?

When your wheels are not centered at the bearing, a bump can cause the wheel to veer. If the wheel is offset a bump will have the effect of pushing the wheel back, effectively steering the vehicle in the direction of the wheel that hit the bump. Getting into something soft, like dropping a wheel off the pavement onto a soft shoulder can drag the vehicle right into the ditch. If the wheel is inset, the steer is in the opposite direction. If you hit a bump on the right the vehicle steers left.

Do you want it? Depends. Do you like to wrestle?

Bumpsteer is the name given to the affect of bumps in the road causing the truck to veer off course without input from the driver. The geometry of the front end is designed to avoid this. Some changes that can cause bumpsteer are changes in ride height and front wheels that are offset outside the original track.

I have never heard of this and it describes one of my problems. Is the fix new bearings, races, and seals? Or possibly spindles and hubs?

When I first got my 64 it had been "updated" with power steering. PO had just bolted the box on wherever it was the easiest. The drag link was at an angle to the crossmember, & the bumpsteer was incredible. The truck would move over half a lane on a good bump. I got about 1/4 mile down the road & was scared to drive it back. Brian

Would backset on the front wheels also cause bumpsteer? From what I can gather from Brad B and Truckernix this is not a desireable situation. Do I understand that the wheel must be centered between the 2 front bearings to avoid bumpsteer? If so how much offset or backset is too much? The term "bumpsteer" has always puzzled me and I knew I would get some answers from all you bolts. Weeds

Weeds, Bumpsteer is the towing in and out of the front wheels when the suspension travels up and down in there normal position. To correct this problem you need correct the angle or height of the tie rods so when the suspension travels up and down it does not pull or push the wheel in or out. Sometimes you can add shims to the outer tie rod end to correct bumpsteer. A bumpsteer gauge is available and has two dial indicators mounted on a frame that sits on the ground and a plate is bolted in place of the front wheel that rest against the dial indicators to tell if the front wheel is towing in or out when you jack up or let down the suspension. Both front wheels need to have there bumpsteer set seperatly. I hope this explains it a little for you.
Jamo

Weeds,
if you look at the front axles, from the front, you will notice that the kingpins slant outward from top to bottom. In theory, the line through the kingpins is supposed to intersect the ground in the middle of the tire tread. I don't think that small changes here are a big deal, myself. Even using tires of a different diameter will change this relationship and this is a pretty common situation.

True bumpsteer can be caused by a draglink that is not horizontal, but on an angle. This can happen if the ride height is changed. What happens is when the wheel goes up or down, the arc of the drag link causes movement in the horizontal forward/aft direction causing the steering arm to turn.

Chuck the truck,T-nix, Erics 46 and Brad B thanks for educating me. Now I have to further display my ignorance by asking what a draglink is. I understand the terminology for upper and lower control arm, idler arm and pitman arm, tie rods and tie rod ends but whats a draglink? Chuck I printed your link and am going to study it to see what if anything I have done wrong so far in building my IFS. Talk about an education! Wow. Weeds

Weeds, the drag link is the long arm across the front that the tie rods and the steering box hook to, so that the gearbox can turn the wheels.
Jamo

Eric,
the drag link goes between the Pitman arm and the steering knuckle. On the old trucks, the steering box moves an arm called the Pitman arm. Between the Pitman arm and the steering knuckle, on the driver's side, is the drag link. Now, to make the passenger's side turn in the same manner, it is connected across with the tie rod.

E46,Tnix, thanks for explaining draglink to me. Ask a question get an answer. What a site this Bolt! Weeds