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It's a good thing I scored some super beefy springs. I got a more exact measure of my rear spring motion ratio; distance from inner arm pivot point to spring center is 7 inches. Distance from inner pivot to center of outer bolt hole is 14.25 inches. I had originally thought that the spring was exactly half the distance which would have been a .25 ratio. But 14.25 divided by 7 squared is .2413... So, if I wanted a 200 lb. Wheel Rate like the stock Cobra, I would need an 829 lb. spring.

But let's say I wanted a 225 lb wheel rate...

225 divided by .2143 is 1,049.9. The extra 1/4 inch length I discovered really effects the math when calculating spring rates. At a .2413 ratio, it takes a whole lot of spring rate increase to make a small increase at the wheels.

I will be able to cut these springs for desired ride height and don't have to worry about it becoming too stiff. The extra firmness will be insurance against bottoming out if I go with a very low ride height.

When I start working with the front suspension, it will be a very different story because small changes make a real difference. But I will worry about the front later.

Edited by Cody

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I was at the local Pick -N-Pull in Little Rock today and found three more Sevilles with 23 MM front sway bars and 18 mm rear sway bars. (I tested the accuracy of my caliper by measuring my tape measure and it was dead on. I also found Eldorados and Sevilles with the 19 mm and 21 mm fronts and 14 mm and 16 mm rears. I thought my find was very rare. I guess not after all. Now it bugs me that I can't find replacement sway bar bushings for them.

The Seville STS cars with the giant bars were 93, 95, and 96. Mine came off of a 97. So it is safe to assume that the 93-97 Sevilles all had the same bars with the sport performance suspension. I will go back when it is dry and see if I can find the part numbers of the big bar cars. It was raining and I was between jobs.

Also discovered that the upper and lower mounting diameter of the Grand Prix front coil spring looks very close to that of the bottom mounting diameter of the Eldorado coil. It may be possible to swap strut mounts and use the aftermarket GTP lowering springs up front with the variable rate advertised as 450 lbs. /in.


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Since the production sway bar insulators (as they call them) are rubber, a part for a 21 mm stabilizer bar should work well with a 22 mm or 23 mm stabilizer bar. In the Rock Auto parts for a 2002 Eldorado, I seep stabilizer bar bushings for 19 mm, 21 mm, 29 mm, and 31 mm. The part numbers are AC/Delco 45G1454/19111128 through 45G1457/19111131, and Raybestos part numbers 5501454 through 5501457.

I don't see rear stabilizer bar bushings for the rear. When I got them I got mine from GM Parts Direct and they were AC/Delco part number 25662287, so if you search around that part number you should find bushings that will work for you.


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-- See my CaddyInfo car blogs: 2011 CTS-V, 1997 ETC
Yes, I was Jims_97_ETC before I changed cars.

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Since the production sway bar insulators (as they call them) are rubber, a part for a 21 mm stabilizer bar should work well with a 22 mm or 23 mm stabilizer bar. In the Rock Auto parts for a 2002 Eldorado, I seep stabilizer bar bushings for 19 mm, 21 mm, 29 mm, and 31 mm. The part numbers are AC/Delco 45G1454/19111128 through 45G1457/19111131, and Raybestos part numbers 5501454 through 5501457.

I don't see rear stabilizer bar bushings for the rear. When I got them I got mine from GM Parts Direct and they were AC/Delco part number 25662287, so if you search around that part number you should find bushings that will work for you.

Thank you, Jim. Yes, I have also found the 29 mm and 31 mm “isolators” listed online and at the auto parts stores. I wish they would not do things like that; I searched the salvage yards several times before figuring out they were issuing a “catchall” listing of the bushings without really researching what was available for each year. The 21 mm was the base model bar for the 85-91 Eldorado/Seville and the 31 mm was the touring coupe or performance sway bar. When Cadillac introduced the last generation Eldo/Seville, the front suspension, engine and transmission were carried over from the 85 – 91 design. Even after the 90-91 Eldorados started appearing with smaller diameter sway bars that attached to the strut, the hole remained in the A-Arm for the old style bars until the suspension redesign/update (which I think was 97, but could have been 96. It is possible to put the 29 and 31 mm bars on a 93- 95 (or 96) car by converting to the old style end links. However, nothing is gained by doing so. The information I have been finding shows that bars that attach to the strut are an average of 40% more efficient than bars that attach to the A-arm. Thus, a 19mm bar (strut attached) is equivalent to a 26.6 mm bar (a-arm attached), and a 21 mm bar (strut attached)is equivalent of a 29.4 mm bar (a-arm attached). This would mean that the 23 mm (strut attached) performance bars would be the equivalent of a 32.2 mm (a-arm attached bar).

I have actually started a conversation with an aftermarket company about casting a 31 mm bar as a strut attached racing bar. No information yet about pricing. The conversation included my racing efforts being used to develop a GT or SS racing kit for the car for that company to sell… but that is in its infancy stages, so it doesn’t mean anything yet.

Cody


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However, since the % of sway bar efficiency is an average (not a one size fits all cars singularity) I did some figuring:

If the 29 mm old bar equals the 19 mm new bar,

And if the 31 mm old bar equals the 21 mm new bar,

Then that would be approximately 46% more efficient.

In that case, the 23 mm sway bar (strut mounted) I found would be the equivalent of a 34 mm sway bar (a-arm mounted)…. I hope that is the case.


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I'm guessing, based on bar strength being proportional to moment of inertia of the cross-section, e.g. the square of the diameter, and the spring rate being proportional to the square of the lever ratio, that the effect on wheel rate is improved when you mount the stabilizer bar nearer the ball joint as opposed to on the A frame between the ball joint and the pivot, so a smaller stabilizer is more effective when it's on the strut, which is attached to the ball joint.

The key thing to remember is that you square both the lever ratio from the place where the link attaches to the suspension and the diameter of the stabilizer bar for the same effect.


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-- 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
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You are correct, Jim. Although I have not yet studied the sway bar formula to calculate the exact strength, I do know the basics. The diameter is only one aspect of the equation like coil diameter is only part of the spring and wheel rate equation... Sway bars are basically a "U" shape. The part that reaches from the left side of the car to the right side would be the base of the U and it is where most of the twisting occurs. The "arms" that reach forward are the levers. The longer the lever, the more twist will occur in the bar center with the same force. The same effect as the spring motion ratio of a coil spring effected by the length and position on the A-Arm. Also, the placement on the A-Arm or strut enacts the second leverage that twists the bar.

I made rough measurements with a tape measure from the inner part of the bushing to the center of the hole at the end of the bar on both new and old sway bar designs. The old design had 11 ish inch levers while the new design had 9ish inch arms (a big difference ). This is possible because the strut leans inboard slightly and the bar end links attach high enough to be closer to the body, yet the strut attaches above the ball joint (as you mentioned ) giving it better leverage than the A-Arm attachment point.

Because the forces are squared, a little bit of leverage makes a big difference.

This is why increasing the diameter of my rear brake rotors by 3/4 of an inch is a worthwhile upgrade.

One other consideration is solid vs hollow bar. All of the Eldorado /Seville bars are solid and so they are stiffer than a hollow bar that would be 2 mm bigger.

On a BMW racing forum, I read where, even using the same bar, mounting it to the strut vs the A-Arm was worth a 40% efficiency gain. This was by using a mounting kit and making no other changes.


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Another big parameter for stabilizer bars is length. The principal spring "give" is torsional spring action along the long roughly straight portion. The "spring rate" seen at the links is inversely proportional to that length.

Hollow stabilizer bars don't lose much stiffness. That's because the stiffness is proportional to the "moment of inertia" about the axis of spring rotation. That means that the stiffness of a solid bar is proportional to R^2, and the stiffness of a hollow bar is R^2 - r^2, where r is the radius of the hole. So, a hole that is half the diameter of the bar will reduce the stiffness by only 25%. It reduces the weight by only 25% too.


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-- See my CaddyInfo car blogs: 2011 CTS-V, 1997 ETC
Yes, I was Jims_97_ETC before I changed cars.

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Very true.. I didn't cover the length of the bar (bottom of the "U") since I was comparing bars that were of equal length and shape between the bushings. The factory did a great job following the contour of the frame and angling it for clearance as it moves so that it misses the exhaust. They doing a good job of " the shortest distance between two points is a straight line ". I looked at other bars trying to find one that I could swap it with, but most of the other bars have unnecessary length due to bends that seem to be generic for multiple car fitment.

As far as a hollow bar, I would think that the loss of 25% strength would be, as the teenagers say, " an epic fail ". I have seen several broken hollow bars in the salvage yards and the hole in the middle looks to be more like 50%- 75% of the total diameter. For racing, I want the most strength possible.

The exception would be in one of those custom -cut to length - racing bars that are over 100 mm in diameter with triangular bolt on ends that look like ladder bars. Those things are huge and a solid one would weigh about 100 pounds. For a total custom build, that is the way to go, but I can't make one fit without a blowtorch and a custom exhaust system.


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If I did the math right, I cut the springs to 11.25". That makes them 888 lb. / inch springs. My desired ride height happens when the spring is compressed to 8". That puts the spring pressure at 2,885 lbs. Given my. 2413 spring ratio, that means the spring will be supporting 696 lbs /in. at each wheel. I figured 100 lbs. unsprung weight, meaning that I needed 606 pounds of support to hold up the weight of the car. The. 2413 ratio means that there is an extra 21.7 pounds of support at each rear wheel. If you add 17 to 19 gallons of gas and my 225 lb. weight (consider placement of the weight ) and it should work out about right... The desired ride height is when the fender lip is level with the top of the tire at just over 26.5" above ground level. I have given myself a plus or minus half inch in ride height.

Oh, and my wheel rate will be 214.3 lbs. (SVT Cobra is 200 lbs. )

I cleaned up the springs today and will soon hand them off to a friend for cutting. Then it is paint and install time (if I have the shocks ready by then.

Drum roll, please..............


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I think that the roll center in the rear is higher for Cadillac than for Mustang. I don't know about the later ones with SLA rear suspension but swing axles are notorious for low roll axis; without a lot of work it tends to be the center of the differential! With canted shocks and stabilizer bars, it can be raised to the level of the trunk but with an SLA suspension you can put it where you want it. The Eldorado was designed for sports sedan handling with a low wheel rate, which implies a high roll center at the rear. This is very important because of the weight distribution. If the wheel rate is too high on the rear as compared to the front, the rear will tend to come around on rough roads or with irregular throttle. If you notice that, increase the spring rate and/or stabilizer strength in the front to balance the handling at the limits of traction.


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-- 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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Thank you, Jim. The Short Arm Long Arm (SLA) Independent Rear Suspension (IRS) of the previous generation Mustang (from mid 90s to 2004) was a bolt on modular replacement for the solid axle rear end. It can be adapted into other cars. ( I put words to the abbreviations above for readers less familiar with the terms).

I don't know exactly how much higher the roll center is on the stock Eldorado compared to the Cobra, but mine is much lower than stock due to a leak in my air shocks that lets my car squat about 2.5" lower in the back than the front. My exhaust hangs a little low do to rotten hangers and I have to be careful on my gravel driveway not to drag it... 11.25" is the shortest my rear coils can be and remain touching all of the lower A-Arm pocket. When the car sits with the coils compressed to 8" and the fender lip is even with the top of the tire, it will be about a 1.5" to 2" drop from the stock ride. (someone with a functional air ride system can check that, as I have no way of knowing for sure).

I will fix the exhaust sag soon.

Anyway, the roll center is low now and will stay lower than stock.

Also, when I reroute my exhaust system into a "U" shape instead of a "V" shape, I will have room to put a battery box under the spare tire. That will not only transfer 50 lbs. From in front of the front tires to the back, but it will also hang even with the mufflers as a means of getting a lower center of gravity.

Remembering that, I remarked my springs to be cut at an even 900 lbs. / inch.

I may also relocate my window washing fluid to that area as well.

The target for a front spring rate is 450 variable.


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I ran across an inexpensive caliper that is suitable for occasional use in measuring stabilizer bar and spring coil diameter. It's accurate to about 0.005" and seems suitable for occasional use:

th_IMG_7019_Caliper-1.png

I ran across it in a hobbies and crafts store. It's about $5 plus tax, and has inches (to 1/128") and metric (to 0.05 mm) scales. It's intended to measure beads and such but it should work fine for a stabilizer bar or spring or two.


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-- 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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Here's how the car sits now with bad air shocks.

0603141713.jpg

The finished rear suspension will only be about an inch higher.

0603141700a.jpg

Then the front will be dropped to match it.


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The auto-level is designed to have about 7 psi in it with nothing in the trunk or back seat.


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Yes, I was Jims_97_ETC before I changed cars.

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Wow, only 7 psi!!! No wonder it rides so gushy soft. Remarkable that it can handle so well and feel like you are flying a hovercraft.


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Actually if the shocks have less than 50,000 miles on them, you have a well-controlled ride. Then, there's the electronic shock stiffness adjustment that kicks in on washboard or rough roads, hard cornering, or speed above about 50 mph. Even though the car may pass the bounce test, most people forgot how their car drove with fresh shocks.

I'm speaking from experience here. I changed my shocks and struts for AC/Delco electronic units when GM closed them out and the priced dropped. My car had about 155,000 miles on it at the time and the car still passed the bounce test. But the improvement in the ride, and how the car drove, was phenomenal.


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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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Mine had 67,800 miles on it when I got it last November. It has almost 83,000 now.

I got word today that my rear springs have been cut down to size.

Also, my shocks arrived at the store, but there was a misquoted price issue so I did not pick them up. I will order a set online if the issue is not resolved.....I waited a month for the special order to get here....

I hope to do the install on Sunday.


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Wow, only 7 psi!!! No wonder it rides so gushy soft. Remarkable that it can handle so well and feel like you are flying a hovercraft.

The air bags aren't for spring stiffness and add little to it. All the air bags do is adjust the height of the rear.


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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
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Yeah, watch that price switch. Just this week I was about to write a check for an appliance when as our handshake was about to happen there appeared an extra $100 "for delivery and installation." A few seconds investigation from home showed that the same exact appliance is available locally for very closely the same price, and the price *includes* delivery and installation.

But it does happen. Retailers get jerked around too, and mistakes do happen. I've seen cases where delivery costs appear on the bill that were never there in negotiations and discussions. Then, there's always the "price subject to change without notice" even while the product is in transit.


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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
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Yes, I was Jims_97_ETC before I changed cars.

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It was a no-go with the shocks today. The retailer wanted to stick with his mistaken second attempt to price the shocks which was $20 higher than average retail.


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Perhaps he is ordering them from the same place that you can, or a place with similar prices, and he didn't get a wholesale discount. Sad, but not uncommon. I think that's what my appliance salesman was looking at. If I ordered it and had it delivered here, it came with free delivery and installation. If it is delivered to his store, there is no installation and the store has to deliver and install it themselves, with no markup, clearly a non-starter for them. I knew what was happening instantly, of course, and the saddest part is that if he had asked $20 I would have considered it just to buy local. But the appliance wholesaler that I had in mind is in the next town over.

True bait-and-switch does happen and is not as rare as it should be in this day and age when anyone can do a price check on the Internet. I once went into an auto parts store and asked for a quarter-inch drive torque wrench for spark plugs and small bolts in aluminum threads, because mine is 45 years old and I wanted one with more recent calibration. The clerk asked where I got my spark plugs and I said online, and he got testy. Then he quoted me a price of $275 for a $35 torque wrench. I said thanks - but no thanks - and left, and got it online for $35.


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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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The problem was with a markup Keystone wa putting on the parts. If a parts store special orders a part from them, the parts store is the retail customer. It happened to me at another retailer as well. They did not stock the $40 mufflers that I want for my car... to get them from them through Keystone, my price was going to be $125 each. But from Autozone, who does not order this part from Keystone, my price was still $40. .... I have since found the muffler online for $35 and would already have them on my car if it were not for the failing rear shocks making a different priority.


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My policy is that if anyone says that they have to order something for me, I tell them that I can do that. Unless it's manufactured to order, or in a price-protected supply structure, you can get it for the same price as anyone.


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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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The racing shocks are on order as of Friday from 4 Wheel Drive Parts through EBay. Paid $41.99 each with no sales tax, free shipping, no handling fees, and they were shipped the same day. They are Pro Comp ES9000 series (same as the Toxic Shocks for sports trucks, but with different stickers). They have a ten stage valving system that adjusts itself to driving and road conditions. They can handle 1100 lb. /in. I springs and customer feedback online talks about how soft they ride.

I also Ebayed some Prothane polyurethane sway bar bushings for the 18mm rear bar.

I am getting ready to order Red dust boots for the shocks since this part number does not come with them.

Got my springs and sway bars painted Red.

The parts kit for the rear end rebuild is finally coming together.

Edited by Cody

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