High speed instability issue

Posted By: FastOrange

High speed instability issue - 02/21/09 05:05 PM

70 challenger. ladder bar/coil over car with front shocks on 90/10 setting. Strange double adjustables in back. Extension set at max, rebound set in the middle. Big Block torsion bars. 35 psi air pressure in radial tires. Stock suspension. Car hooks nice and straight but gets unstable at high speed. Ran 129 mph twice last night

but it was all I could do to finish the run. I had to lift on a 3rd run because it started getting sideways.

My front end is aligned but it is mechanically limited on caster degrees and is set at around zero. I'm not sure if the shocks are keeping the front end nosed up unloading the tires or more positive caster will fix the issue. Any suggestions?

Also, what front shocks and settings are usually good with a ladder bar car?

Posted By: QWK_ENUF

Re: High speed instability issue - 02/21/09 05:32 PM

no caster means big trouble
get adjustable upper control arms and put 6 degrees in it , it will be like you are on rails

Posted By: Edge

Re: High speed instability issue - 02/21/09 05:37 PM

I agree aftermarket tubular upper control arm can give you the caster you need to to help the car self center, zero caster could be pretty dangerous IMHO

good luck

Posted By: MR_P_BODY

Re: High speed instability issue - 02/21/09 05:38 PM

0 caster or negitive will mess you up.
On the front shock, run them just loose enough to
get the front to rise on the launch. Also make sure
there's
no binding in the front end
EDIT
also make sure your not toed out with the body up
1"(1" up is where the alignment should be done at)

Posted By: FastOrange

Re: High speed instability issue - 02/21/09 06:43 PM

Thanks fellas.

The alignment was done at 1" raised. About
Tubular A arms. What choices do I have? Pros/Cons?

I would prefer a simple Bolt-in if possible.
Sounds like I need to try another shock setting too.

Posted By: QWK_ENUF

Re: High speed instability issue - 02/21/09 06:46 PM

Bondo Bob makes a nice set and he is a board member

Posted By: B1Fish540

Re: High speed instability issue - 02/21/09 07:10 PM

Here is a pic of the ones i had installed on the challey..far as i know(IIRC) it was just a "bolt on".

Posted By: TheBlackCar

Re: High speed instability issue - 02/21/09 07:26 PM

My e-body regularly run 139+ with stock front end and close to 150 with some "persuasion". Never any stability issues. Check your calipers for drag, re-align car (front and rear). As mentioned, more caster will help high speed stability. Can either buy control arms or slide K-member forward. Also, preload setting in chassis can give you a scare if you just step of gas pedal at the stripe. Hope this helps. Good Luck

Posted By: FastOrange

Re: High speed instability issue - 02/22/09 01:28 AM

Fish540 , Where did you get those? I was also wondering about the ones Mancini sells with the heim joints?

Posted By: B1Fish540

Re: High speed instability issue - 02/22/09 02:23 AM

Quote:

Fish540 , Where did you get those? I was also wondering about the ones Mancini sells with the heim joints?

FO, I got them from RMS Chassis Components:

http://www.reillymotorsports.com/

Posted By: B1Fish540

Re: High speed instability issue - 02/22/09 02:27 AM

Heres a better link. i also got his struts.

http://www.reillymotorsports.com/store/home.php?cat=265

Posted By: dvw

Re: High speed instability issue - 02/22/09 01:52 PM

Offset upper bushings in the forward location will help. Are the strut rod bushings tight and in good condition? Shortening the the strut rods a 1/4" will help as well. Also often forgoten is the fact adding a lot of caster effects toe change. By adding caster (which is good) the steering arm (stock style rear steer) outer tie rod pivot location drops. The oter tie rod position may need to be raised by bending the steering arm. I have driven cars with -1 degree of caster (not recomending this) at 135 mph with no issues. However they had a good toe pattern.
Doug

Posted By: FastOrange

Re: High speed instability issue - 02/22/09 02:19 PM

That is some good info to consider.

I already have the offset bushings in the upper arms and the strut rods are tight and have poly bushings.
I'm still questioning the shock settings at 90/10. I wonder if the front end is maybe higher than one inch raised at the end of the track which changes the toe setting?. I have had the car aligned twice

with the same results.

Posted By: cgall

Re: High speed instability issue - 02/22/09 02:32 PM

Check the circumference of your rear tires. If they are off by more than 3/8", it wil cause rocking at high speed.

Posted By: FastOrange

Re: High speed instability issue - 02/22/09 03:05 PM

Thanks. I will check the circumference.

Thanks for the link 540FISH

Posted By: go green

Re: High speed instability issue - 02/22/09 03:59 PM

Check the number of turns in the torsion bar adjustment, they should be fairly close.

I got mine back from the alignment shop once and it did the same thing .( They had one torsion bar cranked up )

I went home and redid every thing with a tape measure and a smart level .

I put as much caster as I could.

Had the wheels strait up and down with 1/8 toe .

After that ,I would hardly even correct the wheel.