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Re: 12" wheelstand then the tires shimmy when it comes down
[Re: Tig]
#1389622
02/18/13 08:16 PM
02/18/13 08:16 PM
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Joined: Jun 2003
Posts: 52,972
Romeo MI
MR_P_BODY
Master
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Master
Joined: Jun 2003
Posts: 52,972
Romeo MI
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Not wishing to Hijack the thread but the car has solid strut's with the Heim joints, tubular uca's with Heims, boxed lca's with poly bushes. The idler arm was replaced too. A good set up helped but you can't get away from the physics of the set up. The upper, lower and track rod arms all run through different arcs and pull the wheel every which way through the travel. Limiters help but really just mask the problem we have them too. Only real cure is going to a strut type front suspension I'd guess. In real time, at it's worst, it was a brief shimmy of the steering wheel on touch down. If you watch some of the old Super stock vids on you tube a lot of the mopes do it. I just put it down as inherent but made worse by a poor set up / alignment job. Again apologies to the OP for hijacking but hopefully this helps some.
The initial problem is the 2 different length arms...
the upper being shorter is fine for going around corners
but was never meant to have the front tires come off
the ground... if the upper arm was the same length
as the lower AND both the upper and lower pivoted
from the same inner pivot points(same point inward)
then the spindle would stay vertical... then all
you have to do is make sure the inner tie rod point
is at the same pivot point(inward pivot of the lower
arm) and at the height of the arm.. then just make
sure the tie rod is level at curb height... they would
all pivot in the same arc... but the stock front end
wasnt designed to pull wheelies on a straight line...
it was designed to corner
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Re: 12" wheelstand then the tires shimmy when it comes down
[Re: Tig]
#1389623
02/18/13 08:20 PM
02/18/13 08:20 PM
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Joined: Mar 2006
Posts: 9,848
MI, usa
dvw
master
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master
Joined: Mar 2006
Posts: 9,848
MI, usa
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Quote:
Quote:
Quote:
Check this out
http://www.youtube.com/watch?v=91dmTS-UvDc
We've made it better but it still does it  
We have over 7 inches of travel on the front end, it was never designed for that much.
I may be wrong but in this case I don't think static bump steer is the issue. There are inches of toe change with almost zero ride height change. Stop/start the video after the return to earth. There's definitely a toe change happening. I think it's a combination of flex , bushing compression and expansion. My bet the number one culprit here are the strut rod bushings. Possibly the control arm bushings as well. Add a little flex and whala. My 2 cents.
Doug
Not wishing to Hijack the thread but the car has solid strut's with the Heim joints, tubular uca's with Heims, boxed lca's with poly bushes. The idler arm was replaced too. A good set up helped but you can't get away from the physics of the set up. The upper, lower and track rod arms all run through different arcs and pull the wheel every which way through the travel. Limiters help but really just mask the problem we have them too. Only real cure is going to a strut type front suspension I'd guess.
In real time, at it's worst, it was a brief shimmy of the steering wheel on touch down.
If you watch some of the old Super stock vids on you tube a lot of the mopes do it.
I just put it down as inherent but made worse by a poor set up / alignment job.
Again apologies to the OP for hijacking but hopefully this helps some.
I guess that shoots my theory. Maybe we're looking at it all wrong. Maybe the toe is remaining constant and the whole steering assembly is moving right and left.
In that case the steering damper helping to control the problem makes sense. Now we're back to the question of cause of the oscillation. I still believe there is toe change (both sides changing equally) as the cars that exhibit this problem continue to go straight. How about the fact that when the wheels are off the ground the track dimension narrows. When contact is made with the ground the tires need to scrub outward to the original dimension. Could this be the cause? Maybe that's why limiting travel helps. It reduces the change in track dimension.
Doug
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Re: 12" wheelstand then the tires shimmy when it comes down
[Re: dvw]
#1389624
02/18/13 08:38 PM
02/18/13 08:38 PM
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Joined: Jan 2003
Posts: 2,924
A shed in England
Tig
master
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master
Joined: Jan 2003
Posts: 2,924
A shed in England
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Here's a vid from a different angle, you can see both wheels. They seem to be following the same angle.  http://www.youtube.com/watch?v=4-w-tGU0Nks
'74 Challenger..9.46 @ 145.9 1/4, 6.001 @ 118 1/8 so far. 4023lb !!! # N/A, Marsh performance 655ci, Indy Maxx, T/R, Indy 600-13 X's, Street legal, pump gas, full interior, Cal-Tracs, mufflers, 3:73's and real 10.5 radials.
9.51 @ 142.4 1/4, 6.003 @ 114 1/8 with our old mule KB, 572-13, 580 wedge.
RHD '68 Barracuda Fastback 323ci street/strip. Best ET 13.88 @ 99.03
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Re: 12" wheelstand then the tires shimmy when it comes down
[Re: dvw]
#1389625
02/18/13 08:44 PM
02/18/13 08:44 PM
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Joined: May 2004
Posts: 3,210
robin hood country
deaks
master
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master
Joined: May 2004
Posts: 3,210
robin hood country
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I've often wondered if the strut rods with heim joints, exacerbated the problem.
My car does the shimmy quite bad but i never really notice it.
I cut my bump stops down for more front end travel but it seems to spend a long time going up and not going forward. So this year, i'm going to fit stock ones to shorten the travel.
Mick
69 Dart GTS 440 mopar .590 cam, Edelbrock heads, 3200#
best et 6.45, 106.78, 10.14, 132.88 mph, 1.47 60ft
best 60ft 1.36
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Re: 12" wheelstand then the tires shimmy when it comes down
[Re: deaks]
#1389626
02/18/13 08:49 PM
02/18/13 08:49 PM
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Joined: Jan 2003
Posts: 2,924
A shed in England
Tig
master
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master
Joined: Jan 2003
Posts: 2,924
A shed in England
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Quote:
I've often wondered if the strut rods with heim joints, exacerbated the problem.
My car does the shimmy quite bad but i never really notice it.
I cut my bump stops down for more front end travel but it seems to spend a long time going up and not going forward. So this year, i'm going to fit stock ones to shorten the travel.
Mick
All I know Mick is that the more front rise / travel we could get, the better the 60ft ( the back wheel ones baffled us for a time though  )
'74 Challenger..9.46 @ 145.9 1/4, 6.001 @ 118 1/8 so far. 4023lb !!! # N/A, Marsh performance 655ci, Indy Maxx, T/R, Indy 600-13 X's, Street legal, pump gas, full interior, Cal-Tracs, mufflers, 3:73's and real 10.5 radials.
9.51 @ 142.4 1/4, 6.003 @ 114 1/8 with our old mule KB, 572-13, 580 wedge.
RHD '68 Barracuda Fastback 323ci street/strip. Best ET 13.88 @ 99.03
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Re: 12" wheelstand then the tires shimmy when it comes down
[Re: Tig]
#1389627
02/18/13 10:38 PM
02/18/13 10:38 PM
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Joined: Feb 2004
Posts: 6,257
acworth / N. georgia - south e...
cheapstreetdustr
master
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master
Joined: Feb 2004
Posts: 6,257
acworth / N. georgia - south e...
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i dont mean to distract...but i gotta ask..how do you get those super slow mo videos.?
365" Iron J heads,,3480lbs best 1.39 60ft on SS springs.10.54,124 mph ...6.67 1/8th et.average 60fts 1.46 w/ small cam &.063 no2 pill tagged & insured
[image][/image]
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Re: 12" wheelstand then the tires shimmy when it comes down
[Re: MR_P_BODY]
#1389629
02/18/13 11:36 PM
02/18/13 11:36 PM
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Joined: Sep 2011
Posts: 369
California, USA!!!
WheelsUp73
enthusiast
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enthusiast
Joined: Sep 2011
Posts: 369
California, USA!!!
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Quote:
Not wishing to Hijack the thread but the car has solid strut's with the Heim joints, tubular uca's with Heims, boxed lca's with poly bushes. The idler arm was replaced too. A good set up helped but you can't get away from the physics of the set up. The upper, lower and track rod arms all run through different arcs and pull the wheel every which way through the travel. Limiters help but really just mask the problem we have them too. Only real cure is going to a strut type front suspension I'd guess.
In real time, at it's worst, it was a brief shimmy of the steering wheel on touch down.
If you watch some of the old Super stock vids on you tube a lot of the mopes do it.
I just put it down as inherent but made worse by a poor set up / alignment job.
Again apologies to the OP for hijacking but hopefully this helps some.
The initial problem is the 2 different length arms...
the upper being shorter is fine for going around corners
but was never meant to have the front tires come off
the ground... if the upper arm was the same length
as the lower AND both the upper and lower pivoted
from the same inner pivot points(same point inward)
then the spindle would stay vertical... then all
you have to do is make sure the inner tie rod point
is at the same pivot point(inward pivot of the lower
arm) and at the height of the arm.. then just make
sure the tie rod is level at curb height... they would
all pivot in the same arc... but the stock front end
wasnt designed to pull wheelies on a straight line...
it was designed to corner
My suspension has been rebuilt as Mr P discribed in his first paragraph with strut rods with heim joints, tube upper arms ,boxed lowers and here is a vid of the front wheel.
http://youtu.be/LWD9sbw_UWk
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Re: 12" wheelstand then the tires shimmy when it comes down
[Re: cheapstreetdustr]
#1389630
02/19/13 12:22 AM
02/19/13 12:22 AM
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Joined: Jan 2003
Posts: 32,394
Quicktree
I Win
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I Win
Joined: Jan 2003
Posts: 32,394
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Quote:
i dont mean to distract...but i gotta ask..how do you get those super slow mo videos.?
what he said
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