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12" wheelstand then the tires shimmy when it comes down
#1389601
02/18/13 11:58 AM
02/18/13 11:58 AM
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Joined: Jan 2012
Posts: 2,690
Stuttgart, Arkansas
rickseeman
OP
master
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OP
master
Joined: Jan 2012
Posts: 2,690
Stuttgart, Arkansas
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My buddy's 68 Barracuda bracket car does a nice little wheelstand at the launch, but when it comes down, the front tires shimmy for a little bit. Looks bad/dangerous. What do we need to do to fix this? Is this a bump steer issue? Thanks for your help.
2011 Drag Pak Challenger
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Re: 12" wheelstand then the tires shimmy when it comes down
[Re: MR_P_BODY]
#1389603
02/18/13 12:14 PM
02/18/13 12:14 PM
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Joined: Jan 2004
Posts: 13,247
Mt. Vernon, Ohio
dartman366
I Live Here
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I Live Here
Joined: Jan 2004
Posts: 13,247
Mt. Vernon, Ohio
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Quote:
Stock front end... look at all the parts but I would
think pitman or idler arms
I agree, had a similar issue and had a idler arm getting loose, it don't take much, so I would check everything. 
Light travels faster than the speed of sound,,,this is why some people seem bright untill you hear them speak.
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Re: 12" wheelstand then the tires shimmy when it comes down
[Re: rickseeman]
#1389605
02/18/13 12:44 PM
02/18/13 12:44 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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With the stock front end, it could be the toe change causing it.. you might not even feel a bad part.. it could be flexing the front end parts and flexing the weakest point
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Re: 12" wheelstand then the tires shimmy when it comes down
[Re: Dyno1]
#1389606
02/18/13 12:50 PM
02/18/13 12:50 PM
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Joined: Feb 2009
Posts: 401
dayton,ohio
ROSSIO
mopar
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mopar
Joined: Feb 2009
Posts: 401
dayton,ohio
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I have the same thing happen all the time All my susp.stuff is new and it still happens I've checked everything,it's all tight and align Good 
1970 DART B1MC N/A
8.86@ [Email]155
3200 lb on 275 DR
5.30 @ 130 1/8
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Re: 12" wheelstand then the tires shimmy when it comes down
[Re: ROSSIO]
#1389607
02/18/13 12:56 PM
02/18/13 12:56 PM
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Joined: Jan 2012
Posts: 2,690
Stuttgart, Arkansas
rickseeman
OP
master
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OP
master
Joined: Jan 2012
Posts: 2,690
Stuttgart, Arkansas
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One guy told me it was a "bump steer" thing. Like when the front end is off the ground, it has either toe in or out, and when it comes back down it has to straighten up. He thought there was a "bump steer" kit to put on it that would fix it. I hope he is right.
2011 Drag Pak Challenger
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Re: 12" wheelstand then the tires shimmy when it comes down
[Re: rickseeman]
#1389608
02/18/13 01:11 PM
02/18/13 01:11 PM
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Joined: Nov 2004
Posts: 4,330
Lynchburg, VA
Leon441
master
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master
Joined: Nov 2004
Posts: 4,330
Lynchburg, VA
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Yep remeber those days. Video the front wheel and then play it back in slow motion if want to get real nervous. The front wheel steers back and forth a few times. You feel it in the steering wheel.
I reduced it but it was still there. New joints bushings. Equalized the tie rods and centered the wheel. Limited bump travel. This all helped. But, would not get rid of all of it. Probably still had some bump steer.
Replaced front end with tubular stuff and a rack and pinion. Now have zero bump steer and no shimmers.
Note...
Not all aftermarket frontends fix cars some make them worse.
Career best 8.02 @ 169 at 3050# and 10" tires small block power.
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Re: 12" wheelstand then the tires shimmy when it comes down
[Re: Leon441]
#1389609
02/18/13 03:30 PM
02/18/13 03:30 PM
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Joined: Jan 2003
Posts: 2,937
A shed in England
Tig
master
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master
Joined: Jan 2003
Posts: 2,937
A shed in England
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Check this out http://www.youtube.com/watch?v=91dmTS-UvDcWe'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.
'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: Leon441]
#1389615
02/18/13 06:47 PM
02/18/13 06:47 PM
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Joined: Jan 2003
Posts: 2,937
A shed in England
Tig
master
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master
Joined: Jan 2003
Posts: 2,937
A shed in England
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We had C/E 3 ways on back then. Now we have Afco d/a's with the BNC valving  I hear ya on the nitrous hit though, Maybe's we could get to the 1/8th  http://www.youtube.com/watch?v=01qA0_3sBZY
Last edited by Tig; 02/18/13 06:52 PM.
'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: Leon441]
#1389616
02/18/13 06:48 PM
02/18/13 06:48 PM
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Joined: Dec 2005
Posts: 1,495
Shelby mi.
JAKE68
pro stock
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pro stock
Joined: Dec 2005
Posts: 1,495
Shelby mi.
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Bump steer has a huge affect on that problem but there is something else contributing to it. When the front end is going threw its travel caster is changing big time. When up in air and coming down it could change as much as 5deg. that is why limiting travel helps allot. If you can keep toe change to asclose to 0 as possible it helps. The problem is if you look at the angle of the upper control arm pivot point you will see how that happens. It is hard to change that without like doing a chassis car type front end wich would have the upper control arms pivot level to the pivot the the lower goes threw. So caster does not change. So for most cars to bring it to minimal use the mopar chassisbook guide lines for correcting toe change and that will help allot.
Last edited by JAKE68; 02/18/13 06:49 PM.
JAKES AUTOMOTIVE
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Re: 12" wheelstand then the tires shimmy when it comes down
[Re: Tig]
#1389617
02/18/13 06:51 PM
02/18/13 06:51 PM
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Joined: Mar 2006
Posts: 9,893
MI, usa
dvw
master
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master
Joined: Mar 2006
Posts: 9,893
MI, usa
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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
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Re: 12" wheelstand then the tires shimmy when it comes down
[Re: dvw]
#1389619
02/18/13 07:13 PM
02/18/13 07:13 PM
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Joined: Jan 2003
Posts: 2,937
A shed in England
Tig
master
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master
Joined: Jan 2003
Posts: 2,937
A shed in England
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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.
'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]
#1389620
02/18/13 07:21 PM
02/18/13 07:21 PM
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Joined: Dec 2009
Posts: 20,696
in a cattle trailer down by th...
Guitar Jones
Paddle faster! I hear banjo music!
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Paddle faster! I hear banjo music!
Joined: Dec 2009
Posts: 20,696
in a cattle trailer down by th...
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I see a lot of the stock front suspension cars doing this not just the mopes. My Duster did it too but wasn't a handling or control concern, it just did it and quit.
"Follow me the wise man said, but he walked behind"
'92 D250 Club Cab CTD, 47RH conversion, pump tweaks, injectors, rear disc and hydroboost conversion.
'74 W200 Crew Cab 360, NV4500, D44, D60 and NP205 divorced transfer case. Rear disc and hydroboost conversion.
2019 1500 Long Horn Crew Cab 4WD, 5.7 Hemi.
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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: 9,893
MI, usa
dvw
master
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master
Joined: Mar 2006
Posts: 9,893
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: 2,937
A shed in England
Tig
master
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master
Joined: Jan 2003
Posts: 2,937
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: 2,937
A shed in England
Tig
master
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master
Joined: Jan 2003
Posts: 2,937
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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