Tell me what I did!!!

[shookler]

First of all, thanks to all of you for this wonderful forum. I am learning a ton!!

This is what I did. I took a hard hooking, good driving, stable 10.5 @ 127 car, (backhalved 4-link Olds) and ruined it. The front end height was about 4 inches above the height of the rear. Well, I decided to lower it and lower it I did. I removed a coil and then heated the spring for the final drop to level the car.

When I went back to the track, the car would hook but the right rear squatted and the left front rose, Violently. Car stayed squatted through the entire quarter so bad that it rubbed the top of the wheel tub.. At about 110 mph it became very squirrley, darting back and forth and I let out. I tried to stiffen the right rear shock but to no avail.

(correct me if I am wrong) I now realize that with changing th center of gravity, and the fact that I rotated the rear 4 link bars downward, I basically created a mess. My theory on this is, that I need to raise the front of the upper and bottom bar on the 4 link to compensate for this. My other big question is, should I raise the car back up or get aftermarket springs? Do I try to eliminate the bumpsteer problem that I have created or is it a product of my screwed up rear suspension?

I have a picture of the last launch where it bent the pass. side front four link bracket. Who can I send it to to post for me? I am going to the Richmond seminar to see Dave, but I really want to start working on the car now. Any help will be greatly appreciated.

Thanks

LEroy

[Dave Morgan]

LeRoy,
Wow, there are several things you could have done...
1) Cutting the coils out of the front springs made them stiffer. Not only is it harder for the car to pitch rotate rearward and transfer weight, when the car does pitch rotate, it is pivoting off the front suspension, not the center of the car.
2) You've got a good sense of the rear suspenion relationship, but you need to create a map of how to locate the instant center. Also understand there is a kinematic relationship, this has to do with the linkage itself. We'll get into how the torque is transfered through the drivetrain and to the tires.
3) Bumpsteer- you know you did something here. The good news is that you can fix it easily and cheaply (probably less than $2.00). The seminar I will present will not cover bumpsteer as most racers want me to focus on the rear suspension, so let's make sure we spend some private time together and I'll give you some tips.
4) Yes, you did change the CG height, but I doubt you fouled that up enough to make a huge difference. In either case, I'll show you how to locate it, both front-to-rear and height.
If you get in a hurry and want to work on the car before the seminar, just e-mail me at staaytuned@aol.com.
I hope this helps and I look forward to meeting you in Richmond.
Stay Tuned,
Dave

[ERV JR]

You should never heat a spring it will kill it fast and will add to your problems

[Bob West]

Yep, heat the spring, cut a coil and lost any chance of weight transfer, gotta have it unless you got all kinds of horsepower like JOHN .

[shookler]

Ok, I realize that I screwed the springs up. How then, would I lower the front of the car? without doing spring surgury. Also, before the lowering, the rear stiffened and I had no squat and it had weight transfer, hooked hard and went forward. Now, (I really need to show you this picture) it squats hard, still hooks but drives my wheel tub down on the top of the tire. I am assuming that my instant center point is now below the neutral line and it is squatting. What do I do about the spring situation? I am sure it will run high 9's but I am telling you, its so screwed up now that past 100 mph, it scares the heck out of me.

Can I send this pic to one of you more computer savy guys?

thanks

leroy

[John_Heard]

Leroy email it to admin@dragstuff.com and I'll post it for ya.

[Mike Peters]

Ok, I realize that I screwed the springs up. How then, would I lower the front of the car? without doing spring surgury. Also, before the lowering, the rear stiffened and I had no squat and it had weight transfer, hooked hard and went forward. Now, (I really need to show you this picture) it squats hard, still hooks but drives my wheel tub down on the top of the tire. I am assuming that my instant center point is now below the neutral line and it is squatting. What do I do about the spring situation? I am sure it will run high 9's but I am telling you, its so screwed up now that past 100 mph, it scares the heck out of me.

Can I send this pic to one of you more computer savy guys?

thanks

leroy

Check the angle of your lower rear suspension links. If the bar is at a downward angle towards the chassis, this is probably why the body of the car is getting sucked down towards the tire. The rear end housing is trying drive itself over the chassis mounting point of the lower link. When it does this, the tire moves upward towards the body. The lower bar needs to be level or 1 to 2 degrees pointing down to the chassis. Once you lowered the front of the car, you changed ride height of the entire car along with the relationship between the suspension mounting points on the housing and suspension mounting points on the car. Not trying to insult you but, it sounds like you're in need of finding a chassis guy who has been down this road before to help you get it sorted out again. Making these adjustments without prior experience can be hazardous to your health.

[Mike Peters]

Ok, I realize that I screwed the springs up. How then, would I lower the front of the car? without doing spring surgury. Also, before the lowering, the rear stiffened and I had no squat and it had weight transfer, hooked hard and went forward. Now, (I really need to show you this picture) it squats hard, still hooks but drives my wheel tub down on the top of the tire. I am assuming that my instant center point is now below the neutral line and it is squatting. What do I do about the spring situation? I am sure it will run high 9's but I am telling you, its so screwed up now that past 100 mph, it scares the heck out of me.

Can I send this pic to one of you more computer savy guys?

thanks

leroy

Also, Leroy, possibly part of the reason the car is handling so poorly at speed is because you're experiencing some roll steer. Roll steer is when the housing is trying to drive the car. This again, is possibly due to your housing trying to drive above the plane of thrust the lower suspension links give you when they are parallel to the track under power. Roll steer is also why really fast cars which use the South Side Machine bars philosophy usually need a driver's diaper at the big end. The housing tries to drive underneath the car instead of pushing it. Yours is possibly tring to drive over the car since I'm assuming your lower links are now pointed downward after you lowered your front end.

But then, what do I know, I'm just a bicycle rider.............

[shookler]

Trust me, your not insulting me. I am learning and soaking it all up. This is a whole different ballgame than my low 11 chevelle. I realized that with lowering it I messed it all up. I had it right to begin with, but, in the pursuit of fasterness, had to mess with it. Could I put it back to my prelowered ride height, measure the angles of the bars then try to duplicate the angles with the new ride height? I will move the bottom link to near level, but what about the top link?

I understand the theory and the neutral line and so forth, I just need to put it all into practice.

and what about the front springs??? Get rid of them? Replace them with what?

thanks

leroy

[John_Heard]

[shookler]

I am the one in the car, not the truck. What the pic does not show is the pass. rear (body) continues to go on down until the tub hits the tire. Front driver side ends up way in the air. Then about half track, the tire grows and rubs the tub again. I understand what you are saying about the way it is trying to drive over itself, but the part that really got me was that it drove the entire quarter like that.

Thanks for posting that pic, it is all much appreciated.

By the way, I didnt build the car, I bought it as a project form another guy that had to get out from under it. I have no idea why the front end was that high. I do know that it did run very well that way though.

I just want to fix it, and understand how I fixed it.

thanks again

leroy

[sunsation540]

nice car Don't scratch it all up>>>

[Mike Peters]

Leroy,

Do you have an anti-roll bar in the car? If so, it's exhibiting what appears to be a lot of roll rotation or "twist" on the launch. If not, I would run, not walk, to the nearest competent chassis builder and have one installed.

[JeffMcKC]

When you worked on the front spring it may have changed the preload in the car that was helping, sort of. I would put in the Anti roll bar and have less preload it in. If you want the front lower put in a lighter spring but dont let it go into coil bind. Moroso trick springs work well if its a stock control arm maybe the 212 if its light.

[Stickshifter 55]

When you change the frame height from front to back you also change the caster of the front spindles. You should get the front end aligned and the caster and camber reset. That is in addition to all the other points made in this thread...