Topic Options
#2419944 - 12/17/17 03:28 PM Less bump steer with '73+ suspension?
AndyF Offline
Too Many Posts

Registered: 01/20/03
Posts: 23624
Loc: Oregon
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?


Attachments
DSC_1777 (Large).JPG

DSC_1782 (Large).JPG



Top
#2420050 - 12/17/17 07:34 PM Re: Less bump steer with '73+ suspension? [Re: AndyF]
astjp2 Offline
master

Registered: 01/18/11
Posts: 4124
Loc: Utah and Alaska
Andy, I think that was covered in the old Mopar circle track and the performance manuals...
_________________________
1941 Taylorcraft
1968 Charger
1994 Wrangler
1998 Wrangler
2008 Kia Rio
2017 Jetta

I didn't do 4 years and 9 months of Graduate School to be called Mister!

Top
#2420132 - 12/17/17 10:17 PM Re: Less bump steer with '73+ suspension? [Re: AndyF]
autoxcuda Offline
Too Many Posts

Registered: 01/20/03
Posts: 25581
Loc: So Cal
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.
_________________________
Spring Fling XXII
April 14 & 15, 2018
Woodley Park, Van Nuys CA
www.cpwclub.com
700 show cars, 300+ swap, manf. midways
Malibu Cruise, Track Day, Cruise-In
Free Spectator Admission!

Top
#2420430 - 12/18/17 02:23 PM Re: Less bump steer with '73+ suspension? [Re: AndyF]
AndyF Offline
Too Many Posts

Registered: 01/20/03
Posts: 23624
Loc: Oregon
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.

Top
#2420435 - 12/18/17 02:30 PM Re: Less bump steer with '73+ suspension? [Re: AndyF]
AndyF Offline
Too Many Posts

Registered: 01/20/03
Posts: 23624
Loc: Oregon
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.


Attachments
DSC_1784 (Large).JPG



Top
#2420450 - 12/18/17 02:45 PM Re: Less bump steer with '73+ suspension? [Re: AndyF]
autoxcuda Offline
Too Many Posts

Registered: 01/20/03
Posts: 25581
Loc: So Cal
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) ??
_________________________
Spring Fling XXII
April 14 & 15, 2018
Woodley Park, Van Nuys CA
www.cpwclub.com
700 show cars, 300+ swap, manf. midways
Malibu Cruise, Track Day, Cruise-In
Free Spectator Admission!

Top
#2420524 - 12/18/17 04:04 PM Re: Less bump steer with '73+ suspension? [Re: AndyF]
autoxcuda Offline
Too Many Posts

Registered: 01/20/03
Posts: 25581
Loc: So Cal
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

_________________________
Spring Fling XXII
April 14 & 15, 2018
Woodley Park, Van Nuys CA
www.cpwclub.com
700 show cars, 300+ swap, manf. midways
Malibu Cruise, Track Day, Cruise-In
Free Spectator Admission!

Top
#2420810 - 12/19/17 12:36 AM Re: Less bump steer with '73+ suspension? [Re: AndyF]
DoctorDiff Offline
master

Registered: 01/20/03
Posts: 7805
Loc: Polson, MT
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.
_________________________
Contact info

Top
#2420831 - 12/19/17 03:33 AM Re: Less bump steer with '73+ suspension? [Re: DoctorDiff]
autoxcuda Offline
Too Many Posts

Registered: 01/20/03
Posts: 25581
Loc: So Cal
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.
_________________________
Spring Fling XXII
April 14 & 15, 2018
Woodley Park, Van Nuys CA
www.cpwclub.com
700 show cars, 300+ swap, manf. midways
Malibu Cruise, Track Day, Cruise-In
Free Spectator Admission!

Top
#2421396 - 12/20/17 09:25 AM Re: Less bump steer with '73+ suspension? [Re: AndyF]
csk Offline
super stock

Registered: 08/13/11
Posts: 939
Loc: KATY TEXAS
if you move the outer tie rod to the top it will have more bad bump steer

Top
#2421414 - 12/20/17 10:13 AM Re: Less bump steer with '73+ suspension? [Re: AndyF]
TC@HP2 Offline
master

Registered: 01/23/03
Posts: 4781
Loc: Pikes Peak Country
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.

Top
#2422048 - 12/21/17 07:02 PM Re: Less bump steer with '73+ suspension? [Re: AndyF]
AndyF Offline
Too Many Posts

Registered: 01/20/03
Posts: 23624
Loc: Oregon
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.

Top
#2444800 - 02/01/18 04:16 PM Re: Less bump steer with '73+ suspension? [Re: AndyF]
NV69B7RR Offline
master

Registered: 11/08/06
Posts: 5749
Loc: Reno, Nevada
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)
_________________________
68 AMX track car
72 Demon 340
71 Duster 340 Resto http://board.moparts.org/ubbthreads/show...part=1&vc=1

Top
#2445259 - 02/02/18 01:48 PM Re: Less bump steer with '73+ suspension? [Re: NV69B7RR]
autoxcuda Offline
Too Many Posts

Registered: 01/20/03
Posts: 25581
Loc: So Cal
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)
_________________________
Spring Fling XXII
April 14 & 15, 2018
Woodley Park, Van Nuys CA
www.cpwclub.com
700 show cars, 300+ swap, manf. midways
Malibu Cruise, Track Day, Cruise-In
Free Spectator Admission!

Top
#2446218 - 02/04/18 11:29 AM Re: Less bump steer with '73+ suspension? [Re: AndyF]
AndyF Offline
Too Many Posts

Registered: 01/20/03
Posts: 23624
Loc: Oregon
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.

Top
#2451096 - 02/13/18 05:35 AM Re: Less bump steer with '73+ suspension? [Re: AndyF]
Dilbert Offline
top fuel

Registered: 08/21/03
Posts: 2281
Loc: out riding & passing you
Ask Bill Reilly of RMS if you want some good data and information.
Bill was very helpful with technical support when i built the 2 cars to run Watkins Glenn

Top

Advertisement
Sponsored Link
Forum Stats
25,145 Registered Members
32 Forums
186,700 Topics
2,172,234 Posts

Most users ever online: 882 @ 03/05/17 10:15 PM
Moparts Newest Topics
Brake booster help needed
by 70runner
02/21/18 01:05 AM
Slant 6 cross ram
by theraif
02/21/18 12:35 AM
'71 Roadrunner Air Grabber
by intruder71
02/20/18 11:43 PM
Pressure check a Hemi or whatever block
by cudaman1969
02/20/18 10:17 PM