Re: Re[2]: Drop pitman arms and bump steer

["T.R.E. Jr." <T_R_E_Jr@xxxxxxxxxxx>]

-Thank you Ken,

---What you tell me is just what I was thinking. The bump steer is caused by 
a combination of changes to the steering (alignment and components) without 
the correction of one or more. It all comes down to the length of the drag 
link in relation to the distance between the steering knuckle and the pitman 
arm.

---As I already know, I have a "larger than stock" angle on my drag link's 
rod ends and that to me is the most concern when it comes to the lift. With 
5" of lift, the angle is quite much compared to stock 
http://aka3toes.cornbinder.com/images/draglnk.jpg and it is obvious that 
since the drag link is not adjustable in length, the toe in is extreme on 
both wheels. If you don't change the caster when adding the lift (as I have 
not yet), you are adding more to the toe in. Doing this would greatly effect 
your steering and lifting or dropping the wheel on either side would effect 
the steering/toe even more. So, if you bring the pitman arm and steering 
knuckle mounting surfaces to the same height, set the front end to the 
correct alignment, you measure the distance between the two mounting 
surfaces and see if your stock drag link fits the bill, if not, you will 
still experience improper steering alignment (aka bumpsteer), caused by a 
combination of changes to the steering without the correction of one or 
more. Unless you add a drag link of the proper length. Changing the angle of 
the drag link without lengthening it will pull the steering knuckle end of 
the drag link closer to the pitman arm end.

---My Scout does get a little touchy at higher speeds and that is most 
likely the case with mine and others, but Jeff B.'s suspension being stock 
is most likely due to the front body mounts being shot and pushing the 
steering knuckle end further away from the gear box... or bad ball joints 
allowing the tire to flop around when he hits a bump.

---The major downfall to not correcting the angle of the drag link is not so 
much the bumpsteer to me, it is the improper angle of the joints at the end 
of the draglink. That will cause premature rod end failure and possibly even 
breakage when on the trail. His Heim joints, if applied to the drag link, 
are correcting the extreme angle of the rod ends, but if on the tie rod do 
nothing more than make the suspension more comfortable when performing 
normal duties (and easier to work) and quite possibly will last longer than 
OEM joints.. if greaseable.

---Thank you,
-T.R.E.Jr.
-`73 Scout II (StoneThrower)
-`51 Farmall H (Heinz)
-`49 IH fridge (presently unnamed and in need of a compressor)
-`49 Plymouth Special Deluxe 4-door Sedan (Papapalooza)


----- Original Message ----- 
From: "ken.dunnington" <ken.dunnington@domain.elided>
To: "T.R.E. Jr." <T_R_E_Jr@domain.elided>
Sent: Thursday, July 03, 2003 11:01 AM
Subject: Re[2]: Drop pitman arms and bump steer


> Hello TRE,
>
> Perhaps I can be of help in understanding bumpsteer.
>
> Bumpsteer is caused by the movement of the steering knuckle relative
> to the pitman during compression/rebound of the suspension.
>
> I drew up an example to help explain.  You can find it at:
>
> http://www.hemkosys.com/kenstuff/images/bumpsteer.jpg
>
> It's a little large and not oriented correctly but you can download it
> and turn it if you like.
>
> Anyway, note how link A-B, as the suspension compresses, moves the
> steering knuckle outward, thus causing the steering of the tires to
> deflect to the right of the vehicle, thus "bumpsteer".  With link
> A-C(parallel to the ground), the drag link on a stock set-up will
> deflect in a similar manner but much less.  As the angle at static
> position between the hypotenuse(A-B) and the long leg(A-C) increases,
> the bumpsteer worsens, as the magnitude of the deflection of B will
> increase with a given amount of suspension compression/rebound.
>
> Ken Dunnington
>
> Thursday, July 3, 2003, 2:19:33 AM,  T.R.E. Jr. wrote:
>
> TREJ> ---I don't quite get the bump steer concept myself. I know if you 
> raise the
> TREJ> distance between the steering knuckle and the pitman arm then you 
> need to
> TREJ> lengthen the drag link that connects them. I also know that when you 
> lift
> TREJ> the vehicle and change the caster, you need to correct the caster. 
> Lastly,
> TREJ> when you lift the vehicle and change the angle of the drag link's 
> rod ends,
> TREJ> you are sacrificing the angle that the joint can travel and taking a 
> chance
> TREJ> on binding the joint if you articulate beyond the joint's ability to 
> move.
> TREJ> So, when the vehicle is lifted, you need to bring the caster back to
> TREJ> correct, you need to justify the angle of the drag link for the sake 
> of the
> TREJ> rod ends and you need to bring the pitman arm and steering knuckle 
> to a
> TREJ> level plane, place the wheels in the correct position for alignment 
> and
> TREJ> measure the distance between the steering knuckle and the pitman 
> arm. This
> TREJ> to me seems to be what everyone refers to as bump steer, a 
> combination of
> TREJ> changes to the steering without the correction of one or more.
>
> TREJ> ---Anyone care to drill a hole in my head and fill me with 
> information?
>
> TREJ> ---Thank you,
> TREJ> -T.R.E.Jr.
> TREJ> -`73 Scout II (StoneThrower)
> TREJ> -`51 Farmall H (Heinz)
> TREJ> -`49 IH fridge (presently unnamed and in need of a compressor)
> TREJ> -`49 Plymouth Special Deluxe 4-door Sedan (Papapalooza)
>
>
> TREJ> ----- Original Message ----- 
> TREJ> From: "joel brodsky" <travelall1974@domain.elided>
> TREJ> To: <ihc@domain.elided>
> TREJ> Sent: Thursday, July 03, 2003 2:51 AM
> TREJ> Subject: Drop pitman arms and bump steer
>
>
> >> Okay, this is now the 6th Lift I've put in a truck of
> >> mine, and guess what?  Well, I purposely left the
> >> front shocks off so that I could more easily
> >> demonstrate bump steer.  I went over a speed hump in
> >> my neighborhood, the kind that you can confortably go
> >> about 15 over without any jarring at all.  As I
> >> traversed the hump while holding the steering wheel
> >> straight, the front end of the truck went down/left
> >> and up/right in the oscillations.  This is clearly
> >> bump steer.  The reason eludes me though.  It would
> >> seem that the reason is that the drag link, while
> >> being held still at the steering box, tries to get
> >> longer in horizontal distance from the PS box as it
> >> subscribes the arc traveling upwards.  As this
> >> happens, it pushes the right front wheel out to make a
> >> right turn.  then the rebound is the other way, up
> >> gives a turn to the left.  But, the actual bump steer
> >> is just the opposite, down and LEFT, instead of the
> >> explano of down and right.  Anyone?
> >>
> >> So, the solution can only be a dropped pitman arm.
> >> Now, with the drop and stock arms, the difference is
> >> 2.5".  The stock pitman arm radius is 9.5" and the
> >> drop is 1.5".  The droped arm is 7" radius and 3.5
> >> inches of drop.  So will the 2" help with the bump
> >> steer?  I certainly hope so.  Will the steering be
> >> affected?  Yes.  Will it matter?  I'm not so sure.
> >> The stock steering arm at the knuckle is 9.5" making
> >> the ratio of steering input to wheel reaction
> >> 9.5"(input)/9.5"(output), thus it is considered to be
> >> one to one.  The new setup is 7"/9.5" or .736842.
> >> Thus it runs about 3/4 as sharp as it used to.  So,
> >> what does this mean to me/you/anyone?  Well, if the
> >> turning circle was right at 50 feet before, now it's
> >> 35.7% bigger.  Remember that to get to 100% from
> >> .736842 it's 1/.736842 so that 1.35714, or 35.7% more.
> >>  So, that sounds like it sux bad!  Anyone have numbers
> >> on steering radii for Scout 80, 800, ScoutII,
> >> Traveler, PU, TA, Travelette, etc.?  I'm wondering if
> >> my turning will even be close to a Scout 80, which is
> >> atrocious on the trail anyway.
> >>
> >> Better a wider turning circle than bump steer, I
> >> believe.  I'm going to try the drop arm this weekend
> >> and report back.  I have been running bump steer for
> >> about 8 years now and no wonder I've thought these
> >> trucks handled poorly.  Now that I understand what's
> >> going on, I can believe that it's this bad!
> >>
> >> Bronco II or not, there ought to be a way to get a
> >> longer radius pitman arm, with about 4" of drop in it,
> >> to correct a Scout steering to a place where it can
> >> compare to the stock numbers.
> >>
> >> Any ideas anyone?  Now, why again shouldn't I heat and
> >> bend an stock arm to do the tests?
> >>
> >> Thanks for your support,
> >>
> >> JoelB
> >> -time to get some shut-eye
> >>
> >> __________________________________
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