186 posts in this topic

Very good idea,Mike. Even a cable with a threaded chain loop to make it a quick to use tool. I'll use the idea next time. Thanks.


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Unfortunately, I forgot to take a picture of the next step.... I tried to mount the top of the shock and there was not enough stud length to go through the mount, both washers and the frame mount. I didn't want to shorten the factory rubber bushings fearing that the shock might get into a bind.... So I discovered that if you flip the cup washer upside down, it will adapt the upper stock Caddy shock mount. And that cup sat down far enough that I had some shock stud to grab onto. This worked out really well and looks "trick". The shock hangs from the upper Caddy mount like its an umbrella.

Now for the lower mount. The washers worked just as planned, however, they were a pain to install. I spent more time on this one step than the whole spring replacement process. Finally had to tape some washers together to hold them in place while I wiggled the bolt through them. Very frustrating and made me run short on time for the day.

0629141400a.jpg

If I had the time and money, I would have had the machine shop build four 10 MM spacers with tapered edges for easy installation.


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Not only was I running out of time, but I also got the rear bar in a bind. Initially, I hung it on the frame with the factory bushings and wanted to install the end links before I drilled the holes for the new frame bushings... Somehow, I got one side of the bar hung under one of the lower A-Arms and killed another half hour fighting with it to get it topside. Then had trouble with the end links being in a bind when the suspension was at full extension. To solve this, I propped a wrench on the jack and used the cavity in the A-Arm as a guide. This allowed me to get the bar high enough to free the end links.

0629141555.jpg


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Installed!!! (except for polyurethane bushings).

0629141601.jpg

That is one massive looking spring!!!

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0629141601a.jpg

That rear bar is only 1MM smaller than my stock front bar!!!

Whoo Hoo! Behold the rear suspension!!

Edited by Cody

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Moment of truth; ride height, ride quality, and handling.......

Ooops! 4 inches too high at the rear fenders and very embarrassing rear end height!!! The spring pad spacers and the un-calculated pre -load pushed the deck lid up to the sky! Oh no!, I have to give my son a ride to work like this! Oh no!

But as soon as I get back, The spring pads come out and I do a recheck.

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0629141645.jpg

Yikes! Yikes! Yikes! How do you spell bad taste!

0629141645a.jpg


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Getting rid of the spring idolaters dropped it just over an inch because they also kept the spring from seating all the way in the pocket. This is still way too high in the back, but at least I can drive it like this until my next day off without trying to hide.

0629142301b.jpg

The ride quality is sporty but not firm. The shocks keep the back wheels planted. Not harsh over potholes and was able to cross railroad tracks at 50 MPH without bouncing. So ride quality is spot on with room for even more spring rate.

The cornering is flat for the most part. However, The forward rake has shifted my front to rear weight ratio making it nose heavy like a Grand Prix. The rake also removed a favorable caster angle... I get front tire noise earlier. It holds the road well and no oversteer so far, even on corners with loose gravel....

So, except for the ride height and steering geometry issues it is causing, the suspension mod is a success and this feels like a Camaro!

Edited by Cody

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Fixed it.

MODERATOR: Please remove (or gut) my post #72 as it has become redundant and it takes a lot of room. The Edit option has expired and I can't do it.

Cody: I love the dog sleeping in the shade under the car.

You have a massive victory in getting your rear suspension into a high-performance state on the first try, even if it is an inch or two too high. Congratulations.

If the springs aren't seated completely, you may get another inch or so after driving the car for a week or two.


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Thanks, Jim... Well, I cut another 3/4" off of the springs... According to the coil spring calculator, they are now rated at 1,000 lbs. per inch.

I am working on the rear sway bar bushing installation now. Sure is easier to get to with the lower A-arms and shocks out of the way. The delay on the bushings was that the factory bushings elevate the bar 16MM from the frame surface and the polyurethane bushings only space it 6MM away from the frame. At first, I didn't think it would matter, but the clearances are too tight to move the bar more than a couple of millimeters and the design of the end links would cause binding if it gets moved much at all. So I spent a few hours working on that problem while a new coat of paint dried on the springs.

I never could get an answer on the mathematical equation needed, and was struck between a 3/4" cut and a 1-1/2" cut, so I chose the smaller cut size and will give it a try. When it comes together again, it will either be just right or still 1-1/2" too high at the rear fender well.

Oh well, back to work on it.


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I used the factory bushings to locate the rear sway bar correctly and marked the center of it perpendicular to the frame. I also measured the distance between the bar and the frame.

0704141733a.jpg

There is an opening in the frame on the inboard side allowing finger and wrench access. This means I can get a washer and nut in there, which removes the need to drill all the way through the frame.

0704141734b.jpg

This is the spacer I made from a couple of mending brackets I bought at Lowe's. I cut them in such a way that I was able to use one of the holes already there. I just had to open them up a little.

0704142114b-1.jpg

And this is how it looks installed. I was able to get 9.6 of the 10MM I needed.

0704142220.jpg


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I discovered that a fender washer would properly locate the lower bolt of the bushing's A-frame bracket so that it would line up with the car's factory lower bolt location. And that the stock bolt was long enough to go through the new hardware.

The factory bushings have a slot in the top mounting location so a new hole must be drilled. I used the new spacers as a jig to locate the holes. I also test fitted the bushings before drilling to ensure proper alignment with the tapered bar.

You need a 1-1/4" or 1-1/2" bolt with a washer and lock washer because the slot in the frame is tight and the wrench must access the nut at an angle.

0704142220b.jpg

Whenever you drill a hole in the exterior of a car, especially the frame, you need to paint that hole before bolting your part on or you will create a new place for rust to begin. Also, drilling creates metal shavings that rust super fast and will spawn a very bad rust out problem, even in the South. If you can remove the shavings via air gun or alcohol wash, great.... If not, then seal them in with paint... I sprayed the frame cavity in every angle through every hole in the area until paint was running out in a continuous stream.

0705141344b.jpg

By painting the inside of the frame Red, I made a cool accent for the suspension.

0705141523.jpg

0705141525.jpg


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This is what the Caddy top shock mount looks like after being adapted to the standard sized shock stud. This modification was easy. Just use the cup shaped washer from the standard shock mount and turn it upside down on top of the Caddy shock mount.

0705141529a.jpg

0705141529b.jpg


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The shorter the spring is cut, The closer it comes to not being long enough to make contact with the upper pocket and the outboard side of the pocket in the lower A-arm. Not knowing if I would need a third cut, I decided to go ahead and test my idea of a lower spring retainer. With these springs being 1/4" larger in diameter than the stock springs, The inner spring guide is not contacting the inboard part of the spring. Therefore, the spring can walk toward the outer pocket lip and if it is not fully seated, it can slip out of the lower pocket.... And that would be a bad thing... So I used a U-bolt as a retainer.

0705141524.jpg

Dog included for Jim's entertainment, lol!

0705141509.jpg

0705141508a.jpg

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BTW; the dog's name is Security, and he's 15 years old.


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Thank you very much for the photos of Security, and for the tip with photos on the spring retainer.


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The 3/4" spring cut that created 1,000 lb. / inch springs dropped the car about 1-1/2". The rear fenders are about 1" higher than the front. So, this is not the final ride height or spring rate. At least one more cut is in the near future. However, it no longer is an embarrassment to drive and I have two other cars in need of immediate repairs ( plus my cooling fan problem ). So, I have to make this a temporary stopping point in the suspension modification. The rear suspension is now race ready (accept for the ride height adjustment ). The car is still firm, but not uncomfortable to drive... My wife's Grand Am actually rides rougher with its bad struts.

Here are some pictures of the suspension as it sits now. Notice the tight sway bar clearance.

0705141523b.jpg

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0705141528a.jpg

0705141529.jpg

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I have not yet measured at ride height, but at full extension, I have room for 7-1/8" backspace wheels. Looks like more as it compresses. 10" or 11" wide wheels are in my future.

0705141534.jpg


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Here's how the car looks now with a forward 1" RWD hotrod rake. It sits with the same stance as the Red Mustang in the background. If my primary racing was going to be drag racing, then I would leave it with this stance since it would help prevent weight transfer from the front wheels at launch. But since my primary goal is to dodge cones and take high speed corners, I need a level to slight rear rake for better weight distribution and caster.

0707140656-1_1.jpg

0707140656a-1.jpg

0707140656b-1.jpg

0707140856-1.jpg

Edited by Cody

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It may be possible for me to lower my car correctly after all. Before I get into talking about the things I am thinking about doing, I wanted to pass along the basics about Roll centers and center of gravity.

The follwing is from thecartech.com and is for those who have not yet studied suspension design; this is a copy/paste, not my own work:

What is a Roll Center?

A “roll center” (RC) is a theoretical point around which the chassis rolls, and is determined by the design of the suspension. Front and rear suspensions have different roll centers.

A “roll axis” is an imaginary line between the front and rear roll centers.

The amount that a chassis rolls in a corner depends on the position of the roll axis relative to the car’s center-of-gravity (CG). The closer the roll axis is to the center of gravity, the less the chassis will roll in a corner. Chassis rolling at one end of the car or the other gives more grip to that end of the car.

Roll center is one of the most under-utilized adjustments on a car, but one of the most powerful. This is because roll center has an immediate effect on a car’s handling, whereas anti roll bars, shocks and springs require the car to roll before they produce an effect.

For the purpose of this article, I have borrowed explanations from a variety of sources, and I will try to paint a clear picture of how roll center works.

Roll Center Basics

Here are some basic facts about roll center (RC) and center-of-gravity (CG).

* Roll center (RC) is the point around which the car rolls

* Each end of the car (front and rear) has its own roll center

* Center-of-gravity (CG) is where all cornering force is directed

* RC and CG are (ideally) in the middle (left-right middle) of the car

* RC is vertically below the CG in cars

* Rolling produces more grip

Where is the Roll Center?

Roll center is determined by the cars suspension geometry. Each end of the car has its own roll center, determined by the suspension geometry at that end of the car.

RC001.jpg

The following diagram shows how you can find a car’s roll center at one end of the car or the other.

This looks a little bit complicated, but here is a breakdown:

* Line ‘A’ is parallel to the upper arm.

* Line ‘B’ is parallel to the lower arm.

* Line ‘A’ and line ‘B’ intersect at point ‘IP’

* Line ‘C’ goes from the wheel contact point (WC — bottom center of the wheel) to point IP

* The point at which line ‘C’ crosses the car’s centerline (CL) is the roil center

Adjusting Roll Center

You can adjust roll center by changing the angle of the suspension arms.

IMPORTANT:

Always ensure that left and right sides of the car have the same settings!

Adjusting roll center can be done in a variety of ways, depending on the car. You can change either end of a suspension arm to change roll center. Sometimes it is easier to change the inner pivot point of the suspension arms (nearest the chassis), while other times it is easier to change the outer pivot point of the suspension arms (nearest the wheels).

RC002.jpg

RC003.jpg

Car manufacturers have come up with some innovative ways to do this on their car. Most modern, intermediate-to-pro-level cars have SOME way to adjust roll center.

When adjusting roll center, changes to the upper arms result in small RC changes, while changes to the lower arms result in larger RC changes.

(Since the lower arms are closer to the roll-center itself, making changes in the lower arm angle will have a very large effect on roll center position.)

* To give a lower roll center, make the suspension arms flatter (more horizontal).

* To give a higher roll center, make the suspension arms more angled. Upper arms would have more of an upward angle where they meet the wheels; lower arms would have more a downward angle where they meet the wheels.

How Does Roll Center Work?

When cornering, centrifugal force is applied to the car’s CG, which tends to push the car to the outside of a corner. This causes the CG to rotate around the RC. Since the RC is below the CG, cornering force causes the car to rotate AWAY from the force. Hence, the car rolls to the OUTSIDE of the corner.

RC004.jpg

RC005.jpg

* When the RC is far away from CG (lower RC), when the car corners the CG has more leverage on the RC, so the car will roll more.

* When the RC is closer to CG (higher RC), when the car corners the CG has less leverage on the RC, so the car will roll less.

* If the RC was right on top of the CG, when the car corners the CG has no leverage on the RC, so the car would not roll at all.

Depending on what the car is doing, you will want one end or the other to roll more or less. You change the height of the RC accordingly to make it closer or further from the CG (which for all intents is a fixed point).

Effects of Front Roll Center Adjustment

Front roll center has most effect on on-throttle steering during mid-corner and corner exit.

LOWER front roll center

* More on-throttle steering

* Car is less responsive

* Better on smooth, high grip tracks with long fast corners

HIGHER front roll center

* Less on-throttle steering

* Car is more responsive

* Use in high grip conditions to avoid traction rolling

* Use on tracks with quick direction changes (chicanes)

Effects of Rear Roll Center Adjustment

Rear roll center affects on- and off-throttle situations in all cornering stages (entry, mid, exit)

LOWER rear roll center

* More on-throttle grip

* Less grip under braking

* Use to avoid traction rolling at corner entry (increases rear grip)

* Use under low traction conditions

* Increases traction, reduces rear tire wear

HIGHER rear roll center

* Less on-throttle steering

* Car is more responsive

* Use in high grip conditions to avoid traction rolling

* Use on tracks with quick direction changes (chicanes)

Edited by Cody

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This is what happens to the roll center of a Macpherson strut suspension when the car is lowered. It may look cool, but dropping the roll center is counterproductive to handling. See the diagram below:

trollcenter.jpg

So to lower the car correctly, the suspension angles must be managed to avoid lowering the roll center.


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All of the following cars are (or were) based on GM's W-body platform and shared a Macpherson strut front suspension that is a close cousin to the suspension in my Eldorado:

Buick Century

Buick LaCrosse

Buick Regal

Chevrolet Impala

Chevrolet Lumina

Chevrolet Monte Carlo

Oldsmobile Cutlass Supreme

Oldsmobile Intrigue

Pontiac Grand Prix

My wife and I are both fans of the 97 up Grand Prix GT and GTP; I am a member of one of the enthusiast's forums. Even though a base model Eldorado will accelerate, corner and stop faster, by far, than even the supercharged GTP, there is a following for these cars that would make you drop your mouth open in wonder... I learned a lot about how to modify my Eldorado by reading forum posts made about its slower cousin.

Most people who lower these cars are doing it for looks and never attempt to correct the roll center problem they create. However, there is a big database on the solutions to other problems that happen when a W-body platform gets lowered and the same type of problems are sure to be prevalent with any Cadillac of a similar suspension setup.

Some of the problems are:

Bump steer

Torque steer

Bouncing K-frame

Tire wear

Blowing out struts

Bouncy ride

Rough ride

Ball joints wearing out faster

And I think there are a few more problems too.

So not only am I facing a dropped roll center problem, I would be faced with all of these too.... And all for a 1" to 1.5" drop in ride height...... It's just not worth it.

Unless, there's a fix to all of these things..... And I think I have found it. I just need more time with a measuring tape under my car. If I am right, then I can avoid all of the suspension related problems.

I will post again about this after I look into it.

Edited by Cody

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To avoid changing the roll center, you are going to need a raised spindle, and avoid rotating the lower control arm.

To avoid toque steer and bump steer, you need to adjust the offset so that the strut axis (the "kingpin axis") passes through the center of the tire patch when the steering is straight ahead.


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-- Click Here for my personal page to download my OBD code list as an Excel file, plus other Cadillac data
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Yes, I was Jims_97_ETC before I changed cars.

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Yes, a spindle, of the same length, with a wheel bearing hight that has been raised instead of using lowering springs is one valid approach, but no one makes them for this application and I can't afford a " one - off " fabrication.

Another option is to use lowering springs, but add the equivalent length of the drop back to the bottom of the spindle to space the ball joint attachment down to its original location.... A cheaper alternative to a one-off strut build, but still out of my budget.

What I am looking into is the removal of the K-frame mounts to raise the whole thing the same amount of the lowering spring drop. This would keep the drive shaft angles and steering rack angles in the correct alignment while raising the inner A-Arm attachment point to prevent an angle change there as well. And it would only cost a few hours of time. I just need to make sure it wouldn't put anything else in a bind... This would also prevent K-frame bounce and accelerated wear of the ball joints.


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The U-bolt spring retainer test was successful. They don't make noise against the spring and they have not changed position. I know they look ugly and unprofessional, but they work as one option. My other design for a retainer that would not be noticeable involves drilling one hole just inboard of the lower spring seat for mounting. However I want to discuss that with an engineer first to make sure it won't weaken the A-arm.

But, as stated before, I do not need the retainers at this time and hope that I don't need them after the next cut.

BTW ; I took several family members to church in a carpool ride. My 6 month old grandson's car seat was in the back and he fell asleep shortly after the trip started. My daughter in law could not tell that the ride had gotten any rougher and my son in law, who fell asleep in the front seat said that the car rides much better and softer than their 05 Kia Spectra

Not bad for 1,000 lb springs.

Edited by Cody

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What's happening with the Edorado?


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-- Click Here for CaddyInfo page on "How To" Read Your OBD Codes
-- Click Here for my personal page to download my OBD code list as an Excel file, plus other Cadillac data
-- See my CaddyInfo car blogs: 2011 CTS-V, 1997 ETC
Yes, I was Jims_97_ETC before I changed cars.

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Hey, Jim. Did measurements for wheels. I found a set of 18 X 10s that will work. Trying to get them while they are on ½ price clearance (can get the whole set for $380.

I will run 275/40s on it under the fenders in all four corners.

I also found some looseness in the rear springs after I removed the retainers; I know what fix needs to be made (a ¼” spacer on the inboard side of the spring at the A-arm mount). I will show pictures when I do the mod. It’s safe to drive, just makes a minor popping noise at times when the spring shifts positions as the arm angle changes.

The car handles so good I’m almost tempted to leave the front suspension soft. But I will try the mods as planned earlier when I can.

Talked with an alignment shop that can slot the holes in the strut mounts for better camber and caster.

Will do the alignment after I eliminate the sub frame spacers to change the angle of the lower front A-Arms.

Still trying to get the money right so I can work on it.

Have been having fun with sports cars on curvy roads…. Lots of fun. This thing is a blast to drive. The rear suspension turned it into a different car.


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The rubber mounts of the subframe are there to decouple engine/road noise and vibration. You might look to keep something there, like sheet rubber from a truck inner tube.


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-- Click Here for CaddyInfo page on "How To" Read Your OBD Codes
-- Click Here for my personal page to download my OBD code list as an Excel file, plus other Cadillac data
-- See my CaddyInfo car blogs: 2011 CTS-V, 1997 ETC
Yes, I was Jims_97_ETC before I changed cars.

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