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Discussion Starter · #1 ·
As some of you are aware, I'm planning on dropping my impala drivetrain into a 92 sonoma. Since I kind of decided on an "impanoma" theme, I'm going to put a set of impala rims on the truck with GMC hubcaps (assuming I can ever find any that fit). However, the impy rims have a tad too much backspacing. I have to replace the upper a-arms, springs, spindles, and shocks anyway, so replacing the lower a-arm so the impy rims will fit is cheaper than buying new rims.

This, along with the tie rod location on the b-body spindles I'm planning on using (so I can run bigger brakes), is going to create some suspension geometry problems. Not seriously bad ones, but since I'm basically replacing the front suspension anyway, it won't cost any more to make it right than it will to just throw parts on there.

Now to the problem: I don't know how to design it right. Anybody have some favorite books and/or websites that teach you how to design suspension geometry?
 
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Discussion Starter · #2 ·
Take a look at these guys:
http://www.auto-ware.com/

I have their "Front Suspension Geometry Pro" package and found it very helpful working on control arms.
Since I wasn't messing with tie rod relocation I'm not sure if it will help with that or not. I can check it out tonight.
 
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Discussion Starter · #3 ·
My short list:

Chassis Engineering - Herb Adams
How to make your car handle - Fred Puhn
Race car engineering & mechanics - Paul Van Valkenburgh

These should get you started pretty well, and depending on where you are at the present, there are more books out there that'll make you head spin! (Mine did in the start btw)

Forums where you can ask talented people: (Sorry ImpySSforum.com - not that high tech-level in suspension here)
Corner.Carvers.com forum
Lateral-G.net forum
Pro-Touring.com forum
Do a lot of searches in the archives, there's PLENTY good info stored in all of these forums. Having suspension-engineers and others with it 'under their skin' answering your questions are way better than having to re-do it all later, when you're more educated.

The programs most seem to be using are these two:
The cheaper, but powerful Perf. Trends Susp. Analyzer,
or the more professional Bill Mitchell Wingeo3.
But before these two do you any good, you have to understand WHY and WHAT the numbers shown are, and what to try and get/minimize/improve. After reading a lot, you'll really understand things like why the tall-spindle swap on A-bodies is crap, even though it flips the FVIC to the inside and gives negative camber-gain. You'll find ways to improve Impalas and Caprices too - they're not that good to begin with... (Springs and bars help conceal most of it)

Hope it helps, and good luck - it's a great journey!
 
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Discussion Starter · #5 ·
Got Herb Adams' Chassis Engineering book in the mail today. Holy crap, this subject is complicated! Almost as bad as cam design...
 
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Discussion Starter · #6 ·
Originally posted by stonebreaker:
Got Herb Adams' Chassis Engineering book in the mail today. Holy crap, this subject is complicated! Almost as bad as cam design...
Honestly, that is the "entry level" book on that subject (and a very good read - lots of helpful diagrams, calculations, and formulas)

After reading it, you'll understand how it all works, and what changes make what effect, but there's not quite enough info in there to determine the compromises you'll need to make when designing your own chassis.
 
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Discussion Starter · #7 ·
Well, I'm not designing the whole chassis. I just want to optimize the suspension on the truck when I lower it. Rick (my son) wants to autocross it, and since we're swapping the motor anyway, we might as well optimize the suspension as long as we're going to have the truck stripped down anyway.
 
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Discussion Starter · #8 ·
Your Sonoma chassis is the same as the S10/S15 right? Which shares components from the 78-88 G-body (Metric chassis). I have heard about people using the Hotchkis tubular UCAs and B-body spindles on S10s, this gives you better brakes and a more favorable spindle height (and if you keep the 5x5" boltcircle, the use of Impala SS wheels). This swap uses the stock LCAs, that already have the same lower balljoints as the Impala. The downfall with the swap is huge amounts of bump-steer, due to the incorrect position of the outer tie-rod. (I think too low, usually is on the tall spindles). Read up on this swap and make sure it applies to your vehicle, I don't want to encourage wasting money on wrong parts.

HOWE makes modular balljoints for a lot of cars/chassis, ours and S10 as well - available in stock height to 0.5" extended in 0.1" increments, this gives you some possibilities in modifying the FVSA/FVIC/RC, and lessen the bump-steer some. (As in; too low outer tie-rods = extended LBJs for example). The width of your centerlink can also be wrong, and there are several Stock-Car racing products out there that can be used. In really bad cases, like the tall-spindle swap in an A-body/Chevelle, you have to relocate the steeringbox and idler down ~1" to make BS tolerable, but it does nothing for the fact that the steeringarms are too long (slowing steering ratio, and lessening wheel steering angle) on that chassis.

I had tall-spindles next to some '79 Malibu spindles some time ago, and the steering arms did seem close to each other in length, though I may remember wrong. Either way - If you go the tall-spindle route, buy some suspension software and get the geometry right at your intended ride height FIRST, then tune handling/balance with springs/bars/shocks later. You have a lot of reading in front of you, to be able to decide on what compromises work best for your car and intended usage - there is no "fits-all perfect suspension" out there I'm afraid.

If you search in the pro-touring.com-forum for "book list", you'll find a longer list. Not all books may suit you, I have a small list on the website in my "public info", with some comments. Just ask if you wonder about something, though there are lots of people more suited to answer than I am ont the forums listed above.
 
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Discussion Starter · #9 ·
Christian,

Yes, the sonoma is the same as the s-10.

When you say 'metric chassis', will all the midsize metric chassis components fit? Bushings, a-arms, stuff like that? I was thinking about using delrin or nylon bushings like Herb Adams suggested.

The bump steer issue is one of the things I'm preparing to deal with - I'm currently taking a mig/tig welding class in order to be able to do things like move the steering box on the chassis. (the prof in that class is a real, uh, 'perfectionist'...yeah, that's the term I was looking for! ;) He's teaching us to weld 18 gauge stainless. Hard as hell, especially with no gas to cover the back of the weld.) BTW, I only learned what bump steer is, exactly, last night reading that book. I've had several people on the s-10 forums suggest using spacers to fix the backspacing problem, but those would actually make the bump steer worse. I see no problem with changing the tie rod length and/or moving the steering box in order to deal with bump steer.

As far as the turning ratio, I have the impala steering box. If that's not quick enough by itself, I can always put a shorter arm on it to quicken the steering ratio. Summit also sells a little planetary gearset that adds either 30% or 50% overdrive to the steering.

I don't really plan on completely redesigning the front suspension (but then, I was only planning an engine swap originally<VBG>); I just want to make it as correct as possible when I put the impy wheels on it and lower the truck, as opposed to those who drop the truck and then accept the poor handling as the cost of looking good.
 
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Discussion Starter · #10 ·
I didn't realize they used the same chassis components. I knew the brakes & spindles were the same, but the rest I thought was different.

SC&C sells some of the best products for the G-body chassis, so you may want to talk to them and see if he's ever done any S10 stuff. ( www.scanc.com )
 
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Discussion Starter · #11 ·
Those sc&c adjustable a-arms look really trick. It makes me a little nervous, though, that they have all those nuts and bolts to work loose.
 
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Discussion Starter · #12 ·
Since you're going to be messing with the front suspension so much, something else to pay attention to that I haven't seen mentioned yet is the scrub radius...depending on how you achieve your goal of narrowing the suspension so that the impala wheels backspacing works in the truck will have an effect on it.

The reason why everyone loves enormous swaybars and beefy springs in these cars is because they EXTENSIVELY limit suspension travel...which masks the fact that just about every aspect of the suspension geometry in these cars flat out sucks...kinda amazing how well they can corner (especially considering the weight) when you look at just how bad the geometry is.
 
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Discussion Starter · #13 ·
Originally posted by MikeOD:
Since you're going to be messing with the front suspension so much, something else to pay attention to that I haven't seen mentioned yet is the scrub radius...depending on how you achieve your goal of narrowing the suspension so that the impala wheels backspacing works in the truck will have an effect on it.
Actually, I'll be WIDENING the suspension, so the impala backspacing will work. Several guys suggested using spacers to fit the wheels, but as you mentioned, that will increase the scrub radius and thus the bump steer.

I'm kind of thinking about building my own a-arms. I need to rationalize buying that tig welder, after all... :D
 
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Discussion Starter · #14 ·
Originally posted by stonebreaker:
When you say 'metric chassis', will all the midsize metric chassis components fit? Bushings, a-arms, stuff like that? I was thinking about using delrin or nylon bushings like Herb Adams suggested.
Measure the center to center distance between the bolts that hold the UCAs and alignmentshims to the frame - My measurement off a '79 Malibu (G-body) is 6-7/8". Other than that, I have heard folks with Monte Carlos using LCAs from S10s and 3rd gen F-bodies (Camaro/Firebird 82-92), but the last may require trimming of the steering stops. (Strut suspension, but "same" LCA). The balljoints are the same, as is the one from the Impala (except the 95/96 equipped with the MOOG K6141 5/8"). You can try mounting an Impala spindle to the stock S10 CAs, though the UCA will be too long to get a meaningful alignment (a ton of shims, and still positive camber)


The bump steer issue is one of the things I'm preparing to deal with - I've had several people on the s-10 forums suggest using spacers to fix the backspacing problem, but those would actually make the bump steer worse. I see no problem with changing the tie rod length and/or moving the steering box in order to deal with bump steer.
You must be mixing up here, wheel offset or backspacing has nothing to do with bump-steer, but as mentioned all to do with scrub radius. (Distance from where the KPI hits the ground to the centre of the tire patch viewed from the front/rear)

See page 53 of the Adams book; The picture doesn't show it as good, but all the lines should be lengthened till they intersect at the IC - That shows why the outer and inner tie-rod should be at the correct height. The lines showing the inner- and outer pivot points of the suspension shows why the links have to be a certain length, and why the correct centerlink is important. Adjusting the tie-rod lenght only changes your toe. While the outer tie-rod may be further outboard on your spindles than those lines, the "steering link" can be displaced laterally, as long as the length is the same as between those two lines. (Then comes the problem that plan/top view geometry plays it's part as well, further complicating) Did I mention that you should get some suspension analysis software???



As far as the turning ratio, I have the impala steering box. If that's not quick enough by itself, I can always put a shorter arm on it to quicken the steering ratio. Summit also sells a little planetary gearset that adds either 30% or 50% overdrive to the steering.
The problem with longer steeringarms on the spindles (not so sure it's a problem here, like on the old A-bodies), is that the steering box has internal "stops" that prevent the pitman arm from turning so far - so if the steeringarms are longer, needing more "sweep" from the pitman to turn the same amount, the box or "steering quickener" won't help (unless the internal stops are different, allowing more sweep). A shorter pitman arm will slow down the steering ratio due to less sweep, as shorter steering arms on the spindles will increase steering ratio as they need less sweep to rotate the spindles the same amount.

None of this is meant to prove you wrong, I'm actually impressed that you learn so fast and think out other problems and solutions. Some more reading, some software, and help from some suspension guru's will have you covered in a short period of time. Don't worry if it doesn't get "perfect" - it will anyway be far better than stock, that's what I'm after mostly - to get the basic geometry as good as a novice can, while having someone with more experience check in on things, and warn about pitfalls before there's done something irreversible.

Nice project, and a good thread!
 
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Discussion Starter · #15 ·
Speaking of bump steer...

Are these cars better off at stock (civilian-type) ride height or the Impala SS ride height? Aren't the tie-rods more parallel to the ground at Impala SS ride height? I know the chassis was designed long before they thought of lowering it but I've been wondering this...
 
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Discussion Starter · #16 ·
I see I'm going to have to be more precise in my vocabulary. Yes, I meant to include the center link when I was talking about changing the tie rod length, as I was trying to indicate lining up the inner tie rod end with the UCA and LCA bushings to minimize bump steer; as well as using bushings to raise or lower the outer tie rod end to align it.

As far as mixing up the bump steer and the scrub radius, I must have read Adams wrong - I could have sworn he said that increasing the scrub radius increases the bump steer because it moves the tire's centerline away from the, uh, kingpin axis, I think he said. You don't get an increase in degrees of rotation, but you do get an increase in tire displacement because of the longer scrub radius. At least, that's what I thought I read. I'll have to check tonight when I get home to make sure I have the terms right.

It turns out that the s-10 chassis uses the same UCA as the 79-88 g-body chassis. I looked it up on GMPartsDirect and the UCA part number from GM is identical for both vehicles. The LCA numbers are different, though.

On the steering, I wasn't referring to sweep as much as I was referring to ratios. I have read, although I have not yet confirmed it, that the stock s-10 spindles have a shorter steering arm than the b-body spindles, which causes enough change in the steering ratio to be noticeable to some drivers. Thus, I was wondering if a longer arm coming out of the steering box would compensate for the longer arms on the b-body spindles. But then I realized that if I just use the impala steering box, the impy has a stock ratio of 13:1, I believe, which should be adequate. Of course, I could always use this steering quickener to drop the steering ratio down to about 8:1, but that's probably overkill.

BTW, what's a Pittman arm?
 
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Discussion Starter · #17 ·
Originally posted by Kevin Moore:
Speaking of bump steer...

Are these cars better off at stock (civilian-type) ride height or the Impala SS ride height? Aren't the tie-rods more parallel to the ground at Impala SS ride height? I know the chassis was designed long before they thought of lowering it but I've been wondering this...
We're actually talking about S-10's, not impalas in this thread. You might want to start your own thread for that question.
 
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Discussion Starter · #18 ·
Well, we are discussing Impala parts on a Sonoma, in an Impala suspension forum..? ;) I was hoping that Rustic or AutocroSSer would chime in, I assume they have bump-steer'ed their cars to check it out. All I know is that the outer tie-rod/steering arm are too low, and buying a bump-steer "kit" (rod end, adapter, and spacers) won't help, as all you can do is shim it further down. Dialing in more positive caster (with Rustic UCAs) helps, as it raises the outer tie-rod. I just can't offer any numbers I'm afraid...

I agree with you on the increased front/rear tire displacement, and that the rotation of the spindle itself is the same. You should generally try and minimize such things, as well as side-scrub (track change with bump/droop) I would just see where the stock Impala wheel and spindle takes you, find a solution to the UCA, maybe build the lowers if the resulting track is too narrow (or the wheels hit the UCA/LCAs), and just go from there on the RCH, FVswing arms and bump-steer. The UCAs from SC&C listed above are very flexible in length, and I have yet to hear about the jam-nuts and bolts loosening. The arms are from PolePosition btw, and lots of people use them.

On the steering, what I meant is that you shouldn't only look at turning ratio; The pitman arm (Connects the steering box to the centerlink, looks like the idler on the passenger side) length, combined with the max amount of rotation you can get from the sector shaft (on the steering box) determine the "sweep" length of the centerlink, and your potential for turning radius. With longer steering arms on the spindles, the more travel of the centerlink sideways is needed for the same rotation of the spindles, and therefore turning radius. The limiting factors are the internal steering stops in the steering box, and the spindles hitting the steering stops on the LCAs (and the tires hitting the swaybars/frame). If the steering box is the limiting factor, it is possible to alter the internal stops.
All clear as mud now


With the Impala SS steering box, I don't think the need for a steering quickener is there, but that's up to the end user. Hotrods never get finished anyway, right?
 
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Discussion Starter · #19 ·
OK, so in order to lessen the bump steer with the b-body spindles, then, I need to raise the spindle in relation to the center link, is that right?

I know there's something wrong with that picture, because all that suggests to me is that I can lessen bump steer by lowering the truck until the spindle steering arm lines up with the center link, and finding the correct center link and tie rods to align the inner tie rod end with the a-arm bushings.

What am I missing?
 
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Discussion Starter · #20 ·
You have to understand that you get the UCA and LCA to point where you want, giving you the geometry you're looking for, THEN do what it takes to correct bump-steer.

Imagine the lines drawn through the inner and outer pivit points on the CAs, and extending them until they intersect (This is the IC, and determines the FVSA and RCH). A line drawn through the inner and outer pivot points on the tie-rods must ALSO point at the IC, if not - either the height of the inner or outer tie-rod is wrong, and you get bump-steer. Then in this position, the length between the inner and outer tie-rod pivot points must be along the lines drawn between the upper and lower inner bushing/pivot point of the CAs, and between the upper and lower BJ pivot. This length can be offset inwards or outwards, but must have the length between those two lines. This is the basic principle.

Complicating this, are the "skew" of the CAs inner pivot line in relation to the vehicle centerline in top/plan view, and the side view tilt of the UCA mount, which makes the CAs go in different paths (Castergain in bump, the tilt is for Anti-Dive). Again, you won't be able to get this worked out without some suspension analysis software, or atleast without a LOT of trial and error...

Regarding the Hotchkis tubular UCAs for the G-body, this link should be interesting, it's from the Hotchkis homepage, look at page 4:
Tubular arm mounting instructions
If you want to make your own, that's nice, but they do exist and fit
 
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