So, this post is gonna be mainly about suspension and steering geometry and that sort of things. I actually had this post ready, yet unpublished, but decided to add something on it before publishing it. The name of this post was gonna be "Steering stuff", but I had to change the name to better suit the new content :D
So, One thing that I wanted add on was this picture. As you may see, it is Signet on the roof of a Chevrolet wagon. THIS is the place where it spend all of it's junkyard years. And I did not have a picture of it! Until last Sunday when one of my readers sent me this picture. Sure it don't look like going anywhere, not anymore, ha ha. But things can change, and as you know very well in this case, they actually did. Really did. The reason why I did not shoot this kinda picture by my self is that when we went to pick up Signet from the junkyard, the guys there were already started before we got there and pulled it to place where we could easily load it up on the light truck we were using to carry her home. Sometimes little things can make you happy. And this
picture was that little thing to me:)
So, some of my readers probably are familiar with vehicle suspension technology, what is what, what is does and how everything works together. For those who are not, but are interested to learn I suggest you to read the links below for brief explanation of this stuff. Good sites, things put simple.
Signet, just like many other (most) older cars have a suspension that was originally engineered for somewhat different driving conditions than what we see today. We drive faster, most roads are paved and we're using radial type tires instead of old fashioned bias-ply. All these thing together may lead you to a point where you wonder "how in the hell anybody were able to drive these machines. EVER!". Been there. Of course, worn out parts or bad tires are the most common reasons causing horrible driving experience, but sometimes rebuilding your suspension just wont cut it. It make no better. At this point, when you're sure there is no mechanical reason for your vehicles morbidly fatal behavior, it would be time to go deeper what would seems to be the problem.
I have done some empirical research over these things and I found (along with many others enthusiast) that there is one "easy to do" thing that seems to have more positive influence on vehicles handling than any other. That is called "Caster angle". Many older cars from the 60's and early 70's were originally engineered and adjusted for caster near to "zero" or very little positive caster. Some, like Signet, had NEGATIVE caster that seems to be "the straight way hell"-solution for radial tires. It seems like there is no reason in any case to go caster less than 3 degrees positive. Of course, this won't help much if your car has bad suspension design in general, or if it is in bad shape. But re-adjusting from near to zero caster to something like 3-4 degrees positive, usually improves high speed stability, cornering and steering centering by a lot. Other adjustments are critical as well, but seems to be more case specific and original alignments are usually good to start with.
Signet, just like all a-body mopars suffer from limited steering alignment abilities. If you want to get more caster, you usually have to give up some camber alignment. If you're building a daily driver it is not a good idea, because too much negative camber causes more tire wear and can cause some wondering and leaning. So, how you'd like your car to handle is, of course, pretty much a matter of taste. With my experience, I have found these adjustments to work the best for me, no pulling to a side or another, no exces wondering and pretty nice cornering;
Camber; 0,0Deg. Left and right.
Caster; 3,5-4 Deg. Must be the same for Left and right.
Toe; about 1,5-3mm total. Seems to be not very critical.
The only problem with these adjustments are that you are most likely not gonna be able to get there without some modification to the suspension parts.(I'm talking about a-body mopars now). What I'm gonna show you next is my own idea which I have found to work very well, but I want to point out clearly that I won't be responsible for any troubles you may face by doing the mods as explained next. If you use it, use it on your own risk. And check your local laws and regulation first! If you're not 100% sure what you're doing, don't do it.
To get an easy adjustments on caster and to be able get it to desired range of 3,5-4 Deg. positive (If you like very heavy steering with lost of "road feel" you can go up to 8Deg, positive, but going over 4Deg. is not advisable for normal street driving.) you can modify either the upper or lower control arms. I have tried both and found lower ones to be the easiest way to go by far. Actually, you don't need to modify the control arm itself, but the strut rod that holds the lower control arm in place. (it is a rod supporting the outer end of the control arm to the sub-frame.) Shortening the rod will move the control arm towards front of the vehicle giving you more positive camber and leaving other adjustments virtually untouched.
Below is a slide show that I've put together to explain the deeds:)