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#2419944 - 12/17/17 03:28 PM Less bump steer with '73+ suspension?
AndyF Online   content
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I have a '72 Duster which I'm working on. I don't like the early suspension design with the tapers point up since it is impossible to work on with headers. So I was going to switch to the '73 style steering linkage but I can't figure out what to do with the tie rods.

The '72 style has a shorter center link so the tie rod ends sit inboard of the LCA pivot. That would seem to be a bump steer issue? The '73 center link is longer so the tie rod ends are close to the LCA pivot. That seems like a much better design.

Anyone bump these two designs and compare them? I'm assuming when it came time to design the '73 suspension the engineers much have known the '72 style wasn't the best so that is why they changed it?


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#2420050 - 12/17/17 07:34 PM Re: Less bump steer with '73+ suspension? [Re: AndyF]
astjp2 Offline
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Andy, I think that was covered in the old Mopar circle track and the performance manuals...
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#2420132 - 12/17/17 10:17 PM Re: Less bump steer with '73+ suspension? [Re: AndyF]
autoxcuda Offline
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I bet you find the linkage points very close in both designs.

I don't think the critical points at the inner tie rods holes are a different width center to center.

I've bump steered the 73 style, but the tie rod ends where hotchkis spherical set up.
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#2420430 - 12/18/17 02:23 PM Re: Less bump steer with '73+ suspension? [Re: AndyF]
AndyF Online   content
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The inner tie rod holes are different between '72 and '73 by a fair amount. At least 1/2 inch, maybe closer to 3/4 inch on each side. So it looks like the '72 style would have more bump steer than the '73 style since the inner tie rod is located inboard of the LCA pivot.

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#2420435 - 12/18/17 02:30 PM Re: Less bump steer with '73+ suspension? [Re: AndyF]
AndyF Online   content
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Now the big question is can I use the '73 center link with the '72 lower ball joint? It all fits but there is a lot of angle on the tie rod since the inner taper points down and the outer taper points up.

I could remachine the lower ball joint so the taper points down but that is a lot of work.


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#2420450 - 12/18/17 02:45 PM Re: Less bump steer with '73+ suspension? [Re: AndyF]
autoxcuda Offline
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Originally Posted By AndyF
Now the big question is can I use the '73 center link with the '72 lower ball joint? It all fits but there is a lot of angle on the tie rod since the inner taper points down and the outer taper points up.

I could remachine the lower ball joint so the taper points down but that is a lot of work.


Ok. Didn't think there was a width difference between the center links.

The 73-76 LBJ also has the tie rod taper pointing up. What's the geometry difference between the 67-72 disc and the 73-76 disc LBJ's (steering arms) ??
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#2420524 - 12/18/17 04:04 PM Re: Less bump steer with '73+ suspension? [Re: AndyF]
autoxcuda Offline
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Would be interesting to have an adjustable center link like thir ines we used in circle track racing.

Mopars center links are non wear...Less expensive to build/design.

Like this but pitman and idler to the inside of the tie rod pick up points



Then you adjust with these slugs

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#2420810 - 12/19/17 12:36 AM Re: Less bump steer with '73+ suspension? [Re: AndyF]
DoctorDiff Offline
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Tie rod end design changed for the 1970 model year.

In other words, '70-'76 tie rod ends interchange, but they are different than the'69 and older version.
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#2420831 - 12/19/17 03:33 AM Re: Less bump steer with '73+ suspension? [Re: DoctorDiff]
autoxcuda Offline
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Originally Posted By DoctorDiff
Tie rod end design changed for the 1970 model year.

In other words, '70-'76 tie rod ends interchange, but they are different than the'69 and older version.


But the centerlink didn't change until 1973.
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#2421396 - 12/20/17 09:25 AM Re: Less bump steer with '73+ suspension? [Re: AndyF]
csk Online   work
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if you move the outer tie rod to the top it will have more bad bump steer

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#2421414 - 12/20/17 10:13 AM Re: Less bump steer with '73+ suspension? [Re: AndyF]
TC@HP2 Offline
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Without actually mapping it out, I'd suspect they actually have similar bump characteristics.

Looking at the suspension from the front or rear, if you project a line from the upper arm inner bushings through the lower arm inner bushing, and the upper ball joint through the lower ball joint, you would find the tie rod ends are still inside this plane,which is the preferred place to minimizing the bump issue. Is it slightly better or worse, I don't know right off hand.

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#2422048 - 12/21/17 07:02 PM Re: Less bump steer with '73+ suspension? [Re: AndyF]
AndyF Online   content
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I'm going to put the suspension back in the car and see what it looks like. I'll also swap in a set of '73+ knuckles to see what they look like. I don't really like the '72 center link since it is impossible to work on with the headers in the car. I'm not so sure I like the '73 tie rod setup with the one taper up and one taper down but I guess that is the way the engineers designed it.

If the '73 center link doesn't fit with my oil pan and headers then I might need to make my own or find someone who makes them. I've been told that the NHRA Super Stock guys fab their own centerlinks so I'll check there first.

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#2444800 - 02/01/18 04:16 PM Re: Less bump steer with '73+ suspension? [Re: AndyF]
NV69B7RR Offline
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Which of the two center links is best for optimal handling when using the 73+ Disc brakes and ball joints?


Edited by NV69B7RR (02/01/18 04:44 PM)
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#2445259 - 02/02/18 01:48 PM Re: Less bump steer with '73+ suspension? [Re: NV69B7RR]
autoxcuda Offline
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Originally Posted By NV69B7RR
Which of the two center links is best for optimal handling when using the 73+ Disc brakes and ball joints?


Would have to bump both setups in same car. Must align it for each change.

Need to do it on many cars to confirm a trend.

There are other variables effecting the bump steer. Alignment, suspension parts used, alignment adjustments, straightness of frame, production tolerances may all, some, or one effect the bumpsteer results.



Edited by autoxcuda (02/02/18 03:40 PM)
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#2446218 - 02/04/18 11:29 AM Re: Less bump steer with '73+ suspension? [Re: AndyF]
AndyF Online   content
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My tape measure says the '73 center link reduces bump steer. The engineers moved the inner tie rod location out slightly on each side so it is more in line with the lca pivot. That should reduce bump steer. I don't know how much since I didn't actually measure the bump steer.

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#2451096 - 02/13/18 05:35 AM Re: Less bump steer with '73+ suspension? [Re: AndyF]
Dilbert Offline
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Ask Bill Reilly of RMS if you want some good data and information.
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#2459147 - 02/28/18 08:37 PM Re: Less bump steer with '73+ suspension? [Re: AndyF]
375inStroke Offline
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Aren't the lower ball joints different, too? If the tie rods are the same length between the two styles because the tie rod mount location on the ball joint is relocated the same amount that it is on the drag link, bumpsteer would be the same, right?


Edited by 375inStroke (02/28/18 08:45 PM)

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#2459431 - 03/01/18 12:19 PM Re: Less bump steer with '73+ suspension? [Re: AndyF]
AndyF Online   content
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The tie rod length is not the same between the two designs. The '73 style inner pivot point is moved out so it lines up with the LCA pivot point. Looks to me like the design engineers figured out that they had a problem with the '72 design and they fixed in the '73 design.

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#2459486 - 03/01/18 02:34 PM Re: Less bump steer with '73+ suspension? [Re: AndyF]
EagleDuster Offline
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So this makes me curious about my car, I have a '70 Duster that I upgraded to '73-up spindles and brakes, if I'm still using the older-style steering centerlink will that cause bump steer issues?
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#2459545 - 03/01/18 04:14 PM Re: Less bump steer with '73+ suspension? [Re: EagleDuster]
autoxcuda Offline
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Originally Posted By EagleDuster
So this makes me curious about my car, I have a '70 Duster that I upgraded to '73-up spindles and brakes, if I'm still using the older-style steering centerlink will that cause bump steer issues?


No “issues”

It will be in an acceptable range of a stock setup.

Very few of these cars will have the same exact bumpsteer to the 0.001 inch.
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