Wheel shimmy after wheelie

[dvw]

Has your car done it? And if so were you able to cure it. Does anyone know the real cause. Many I've talked to have added urethane bushings, tubing control arms, zeroed bump steer, all with limited results.
Doug

[nhrastocker]

Has your car done it? And if so were you able to cure it. Does anyone know the real cause. Many I've talked to have added urethane bushings, tubing control arms, zeroed bump steer, all with limited results.
Doug

First, you have to say what make of car you are racing. There are different front suspension designs based on the car make.

[af2]

Has your car done it? And if so were you able to cure it. Does anyone know the real cause. Many I've talked to have added urethane bushings, tubing control arms, zeroed bump steer, all with limited results.
Doug

First, you have to say what make of car you are racing. There are different front suspension designs based on the car make.

And what caster, what wheels and tires/balanced?

[dvw]

Car is brand new. Ready to get aligned. I'm looking at preventing the problem before it happens. 64 Belvedere,poly strut rod & lower bushings,offset rubber upper bushings,6 cylinder bars. Strut rods have been shortened slightly, this along with the offset uppers should make 3 1/2-4 degrees of caster attainable. I will check the toe pattern after the caster is set and correct as necessary. Shocks are single adj QA1. If needed I will upgrade to double adjustables. Rear is ladder bar with Koni doubles,125 springs.,10.5wx31,4.10 Dana. Car weight should come in at about 3350lbs. I expect to run N/SS 9.25 index on footbrake.
Doug

[af2]

Car is brand new. Ready to get aligned. I'm looking at preventing the problem before it happens. 64 Belvedere,poly strut rod & lower bushings,offset rubber upper bushings,6 cylinder bars. Strut rods have been shortened slightly, this along with the offset uppers should make 3 1/2-4 degrees of caster attainable. I will check the toe pattern after the caster is set and correct as necessary. Shocks are single adj QA1. If needed I will upgrade to double adjustables. Rear is ladder bar with Koni doubles,125 springs.,10.5wx31,4.10 Dana. Car weight should come in at about 3350lbs. I expect to run N/SS 9.25 index on footbrake.
Doug

NICE!!!!! Check toe when up and down. 3+ caster will work. You do mean torsion bars I hope when you said strut bars???

[dvw]

Car is brand new. Ready to get aligned. I'm looking at preventing the problem before it happens. 64 Belvedere,poly strut rod & lower bushings,offset rubber upper bushings,6 cylinder bars. Strut rods have been shortened slightly, this along with the offset uppers should make 3 1/2-4 degrees of caster attainable. I will check the toe pattern after the caster is set and correct as necessary. Shocks are single adj QA1. If needed I will upgrade to double adjustables. Rear is ladder bar with Koni doubles,125 springs.,10.5wx31,4.10 Dana. Car weight should come in at about 3350lbs. I expect to run N/SS 9.25 index on footbrake.
Doug

NICE!!!!! Check toe when up and down. 3+ caster will work. You do mean torsion bars I hope when you said strut bars???

6 cylinder torsion bars twisted tight for more stored energy. If wheelies become a problem( the wheel base has been shortened up to 113") I have thicker 318 bars. The strut rods are made from 4130 tubing. I shortened them 1/4" to pull the lower control arm slightly forward. This was done while fabbing them up to increase caster. They aren't shortened enough to cause any bind through the travel.
Doug

[af2]

Car is brand new. Ready to get aligned. I'm looking at preventing the problem before it happens. 64 Belvedere,poly strut rod & lower bushings,offset rubber upper bushings,6 cylinder bars. Strut rods have been shortened slightly, this along with the offset uppers should make 3 1/2-4 degrees of caster attainable. I will check the toe pattern after the caster is set and correct as necessary. Shocks are single adj QA1. If needed I will upgrade to double adjustables. Rear is ladder bar with Koni doubles,125 springs.,10.5wx31,4.10 Dana. Car weight should come in at about 3350lbs. I expect to run N/SS 9.25 index on footbrake.
Doug

NICE!!!!! Check toe when up and down. 3+ caster will work. You do mean torsion bars I hope when you said strut bars???

6 cylinder torsion bars twisted tight for more stored energy. If wheelies become a problem( the wheel base has been shortened up to 113") I have thicker 318 bars. The strut rods are made from 4130 tubing. I shortened them 1/4" to pull the lower control arm slightly forward. This was done while fabbing them up to increase caster. They aren't shortened enough to cause any bind through the travel.
Doug

You say twisted tight for more stored energy??? Please rethink if you are way up on the launch. You might need to keep the (stored) energy out of the chassis..

[dvw]

May not need the light bars to help pitch rotation. If so I'll go to the thicker bars that I have,easy swap. Still wondering if there is anything I should do to prevent shimmy in this stage of the build.
Doug

[nhrastocker]

The twisted torsion bars do not help.
Also, I would recommend you use the aftermarket strut rods with the spherical bearings.
http://www.qa1.net/qa1_motorsports/drag ... -bars.html

[dvw]

The twisted torsion bars do not help.
Also, I would recommend you use the aftermarket strut rods with the spherical bearings.
http://www.qa1.net/qa1_motorsports/drag ... -bars.html

A" twisted bar Does not help" as in controlling the shimmy ? A smaller diameter bar tightened to maintain the same ride height as a thicker bar would have more stored energy. Not that it would help shimmy at all.
Doug

[nhrastocker]

The twisted torsion bars do not help.
Also, I would recommend you use the aftermarket strut rods with the spherical bearings.
http://www.qa1.net/qa1_motorsports/drag ... -bars.html

A" twisted bar Does not help" as in controlling the shimmy ? A smaller diameter bar tightened to maintain the same ride height as a thicker bar would have more stored energy. Not that it would help shimmy at all.
Doug

I tried it years ago when I raced a Mopar in NHRA Stock Eliminator and the car was inconsistent during the launch.
All current NHRA Super Stock Mopar's are using the the aftermarket strut rod with the spherical bushing.

[Olefud]

I usually lurk and learn here; but maybe I can contribute from an engineering viewpoint.
Assuming you have a good dynamic wheel balance, shimmy can be caused by gyroscopic forces. When the axle tilts down during a wheelie it generates a gyro reactive force 90° from the tilt direction. Then, if there is suspension slop, the reactive force causes another axle tilt which in turn produces yet another reactive force, etc. Formally this is known as whirling mode, but we call it shimmy.
The cure is a tight suspension that prevents the reactive movement. Ball joints are the worst suspects in that when unloaded, as during a wheelie, any excess clearance in the ball and socket can allow axle tilting movement – and many of the available ball joints from China have excess clearance out of the box. Also, many ball joints have nylon liners that are OK for street use but won’t do well with wheelies. Of course steering and bushings also have to be tight and of high quality.
So, use the highest quality parts without plastic liners and make sure everything is tight.

[Mario428]

Very simple, put a steering damper shock on it. Proven fix on many drag cars.

http://www.summitracing.com/parts/mon-sc2917/overview/

[nhrastocker]

Very simple, put a steering damper shock on it. Proven fix on many drag cars.

http://www.summitracing.com/parts/mon-sc2917/overview/

A steering damper will not work in a Mopar or Ford application where you have a strut rod.

Read the postings regarding this issue that not only affects the launch, but also high speed braking:

http://classracer.com/classforum/showthread.php?t=44796

[af2]

Very simple, put a steering damper shock on it. Proven fix on many drag cars.

http://www.summitracing.com/parts/mon-sc2917/overview/

A steering damper will not work in a Mopar or Ford application where you have a strut rod.

Read the postings regarding this issue that not only affects the launch, but also high speed braking:

http://classracer.com/classforum/showthread.php?t=44796

Thank you from another that has been there!!!!!!!!