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Read what I found out abot Bump steer

Discussion in 'OffRoad Design' started by Klef72K5, May 5, 2001.

  1. Klef72K5

    Klef72K5 1/2 ton status

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    I just bought this 72 Blazer and it has a 6 in. lift with 33's under it. When I drive down back roads and hit a bump it chases it. Is this what they call bump steer? How can I improve it? Would double shocks help? I did notice that my bearing on the gear box (the one that the drop pitman is attached to) has a little play in it, could that be the problem? I also posted this in the 69-72 section, I wasn't for sure where to post it at.
    Thanks in advance all!
    [​IMG]

    <P ID="edit"><FONT SIZE=-1>Edited by Klef72K5 on 05/07/01 02:34 PM (server time).</FONT></P>
     
  2. Greg72

    Greg72 "Might As Well..." Staff Member Super Moderator

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    Re: Bump steer?

    I'm no expert, but I'll get you started and let someone else confirm or correct what I say here: [​IMG]

    When you lift a K5 you will increase the angle of the tie rods relative to the wheels. This change in geometry will cause "bump steer" as well as cause you to have a larger turning radius than when the truck was at stock height.

    The most common solution for K5's with 6" of lift is to go to a "crossover steering" conversion. It re-aligns all of the front steering geometry and reduces bump steer, as well as giving you a nice tight turning circle again.

    FWIW - Check all the "little stuff" too....like the steering box adjustment...front ball joints, drag link ends, etc. If those are worn, it will contribute to sloppy steering and you'll be disappointed with the results of your crossover steering conversion.

    Hope this gets you started. There are plenty of Tech Articles on this site about the conversion, so you should be able to get plenty of info to make a decision.

    Good Luck, and be sure to let us know what you decide to do.

    -Greg72
     
  3. Klef72K5

    Klef72K5 1/2 ton status

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    Re: Bump steer?

    Greg,
    What about on a 4 inch lift? I thought about lowering it 2 in. It has 33's on it now and I don't want to go any bigger. Would I still be in the same situation?

    <A target="_blank" HREF=http://wsphotofews.excite.com/031/rw/Jo/og/t488200.jpg>http://wsphotofews.excite.com/031/rw/Jo/og/t488200.jpg</A>
     
  4. Greg72

    Greg72 "Might As Well..." Staff Member Super Moderator

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    Re: Bump steer?

    I think it will still be fine on a 4" lift. Most people woudn't go to all that trouble and expense for a 4" lift, because the truck won't be that 'out of whack' in the steering department. But certainly if you've got problems with your 6" lift, it should work fine with 4" of lift later. The only problem may be some interference with the crossover bar and the engine support bracket....but the parts to deal with that are out there....!!

    Good Luck

    -Greg72
     
  5. Klef72K5

    Klef72K5 1/2 ton status

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    Re: Bump steer?

    I found this information about Bump steer and thought I would share it with everyone.

    Question:When I hit a bump, my car suddenly jerks to one side. Is anything wrong?

    Answer:Yes. The condition is called "bump steer," and it means your steering linkage is not mounted parallel in the chassis possibly as a result of collision or frame damage, a bent steering arm, misalignment in the chassis, or an improperly mounted steering rack.

    Bump steer is not a very common condition, but it can be a very unnerving thing to experience if you're unfortunate enough to encounter it. It is usually most noticeable when crossing a major dip or bump at speed, as when crossing a railroad crossing or passing through an intersection with a lot of road crown. As the suspension bounces over the bump, it suddenly feels as if someone tugged on the steering wheel. The car twitches or jerks to one side as if it has a mind of its own. This occurs because of unequal toe changes that occur as the suspension extends and compresses.

    In a properly aligned car, the toe alignment of both front wheels changes equally as the suspension moves up and down. But if something causes more of a toe change in one wheel than the other, it will jerk the steering towards the side with the greatest toe change.

    The thing that needs to be checked is the parallelism of the steering rack and linkage with respect to the ground. This can be done by simply measuring the distance between both ends of the rack and the ground. If one end of the rack is sitting higher than the other, the rack is misaligned in the chassis. If it can't be corrected by loosening and retightening the rack mounts, the subframe or crossmember on which the rack is mounted may be bent or damaged. This will require special straightening equipment or replacement to correct.

    The height of the outer ends of the tie rods with respect to the ground should also be measured. If one tie rod is higher than the other, one of the steering arms is probably bent. The cure here is to replace the steering knuckle.

    CAUTION: Bending a steering arm to "correct" a bump steer condition is not recommended because doing so may weaken the arm and increase the danger of it breaking.




    <A target="_blank" HREF=http://wsphotofews.excite.com/031/rw/Jo/og/t488200.jpg>http://wsphotofews.excite.com/031/rw/Jo/og/t488200.jpg</A>
     
  6. JoeAngelicchio

    JoeAngelicchio 1/2 ton status

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    Re: Bump steer?

    With a 4" lift a raised steering arm would be all you need to correct any bump steer. I've got a 4" Rancho lift with a steering arm and don't notice any bumpsteer. Truck handles great.

    <font color=green>Joe Angelicchio
    86 Jimmy 4+3, 35-&gt;39.5 tires,4spd
    </font color=green>
    [​IMG][​IMG]
     
  7. michaelm

    michaelm 1/2 ton status

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    Re: Bump steer?

    well klef nice quotes but they have absolutely nothing to do with your solid axle steering. all chevs have bumpsteer because the short drag link cannot duplicate the actions of the leafsprung axle. your truck is worse than stock because the springs are longer and move differently than the factory designed. as well as it is possible that you dont have a proper raised steering arm or drop pitman arm that help some.
     
  8. coopertwpk

    coopertwpk 1/2 ton status

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    Do you have a steering box brace?if not thats first on your list next would be a raised steering arm .also replace the ball joints and tie rod ends if they need it .

    88k5 silverado w4"lift soon to have <font color=orange>d44 and corp14ff</font color=orange> with 4.56s
     
  9. Klef72K5

    Klef72K5 1/2 ton status

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    From what I understand there is no brace for the 69 - 72 blazers. I would need to design one for it.
    I noticed the other day that there was some play in the shaft that the drop pitman arm is connected to. It was supposably a new (rebuilt) gearbox, but I beleive the lower bearings are out. I'm hoping that this is my "bump steer". I thought that if it was that I would have play in the steering wheel when going straight on a smooth road. Maybe that's only the worm gear though.

    <A target="_blank" HREF=http://wsphotofews.excite.com/031/rw/Jo/og/t488200.jpg>http://wsphotofews.excite.com/031/rw/Jo/og/t488200.jpg</A>
     
  10. michaelm

    michaelm 1/2 ton status

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    the play in the box doesnt help but it isnt the root cause of your bump steer.
    the drag link is connected to the steering box in a relatively fixed position, on suspension compression or extension (if the steering box was held still) the draglink will travel in an arc. on compression of a lifted leaf spring the spring gets longer pushing the axle rearward, if your draglink was level at ride hieght it is now moving upward in an arc getting shorter steering the vehicle to the left.
    on extension of a lifted leaf spring the spring gets shorter pulling the axle forward, if your draglink was level at ride hieght it is now moving downward in an arc getting shorter, now if it matched the rate of length change the spring was doing it would be fine but they dont so it still affects your steering.
    did that help any?
    the reason the crossover is popular is that the longer the arm the less it changes length through suspension travel.
     

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