Ultimate Spring Setup
By Scott Mueller.
OK, I finally have figured this out and have settled on what I think is the best possible set of rear springs for the Impala. The 9C1 springs do lift the car about 1 to 1.5 inches, but they do not add appreciable stiffness which is something I wanted. I have tried several different sets of springs in my car and finally have what I think is the best set. They are 9C1 springs, but they are from the '90 and earlier models, which I have found are significantly stiffer than the ones used in the '91 and up models.
I am now recommending the springs which I currently have in my car, which are '90 GM 9C1 springs p/n 482086 (cost about $40 each) and which are much stiffer than the '94-'96 9C1 springs. I had a set used from previous 9C1 spring experiments with my '88 9C1, so I had them Jet Hot coated in black! They will never corrode, and the black finish is essentially permanent (much better than even powder coating, but of course much more expensive).
These springs will also lift the rear of the car approximately 1 to 1.5 inches, and with them the bottom of my rear wheelwell is at exactly 28.5 inches off the ground on each side, and that is with a full tank of gas but an otherwise empty trunk. I do have air bags, but I normally run them with no air (or the minimum amount) as I use them only to lift the suspension if I am carrying a heavy load. With the air bags, no matter how much weight I put in the car (people, stuff, a trailer hitch, etc.) I can easily bring the rear back to the normal height, plus increase the spring rate at the same time.
IMHO, these '90 9C1 springs I am recommending are absolutely perfect for the Impala, and will result in a level to slightly raked appearance, not to mention much better handling due to the stiffer rate. The car is by no means too stiff, but it does handle MUCH better.
I did have one sort of weird problem with my car, and that was with the front springs. I have installed the factory 8X3 Bilstein shocks, and since they are a very high pressure gas design, they put more of an upward push on the suspension than the stock Decarbons. This is especially true of the fronts, which try to expand so forcefully that they are actually somewhat difficult to install. You have to push up on the base of the shock with a great deal of force to hold it from expanding while installing the screws through the shock into the lower control arm.
Anyway, with these shocks, I found that my front end was now riding much higher than before, and higher than anybody elses Impala I had ever seen. The bottom of the front wheelwell was 28-5/8 inches off the ground, which was slightly higher than the rear with no air in the bags, or even with some air in the bags. Since my rear end height could be lifted further and trimmed out with the airbags, it was not terrible, but over time it actually seemed to get higher in the front! The car was level, but I seemed to lose the slightly raked appearance I think looks best on these cars.
I knew that this "problem" would only get worse when I installed the LT4 engine, as the aluminum heads shave 50 lbs off of the front of the car! I saw Dave Morgans Impala after he had Lingenfelter ported aluminum LT1 heads installed, and his front end was noticibly higher as well. He solved his front end height problem by installing lowering springs from Eibach, but I wanted to try a different solution.
The other night I removed my front springs and cut 1/2 a coil from each one. This was actually very easy to do, and the only special tool required was a die grinder with a cutoff wheel. Just as a note you must never cut a spring with a torch as the heat will ruin the spring steel temper, but a cutoff wheel zipped right through the hardened spring metal in a minute or so per side, without heating the spring at all. The springs were very easy to remove and you don't even need a spring compressor if you use the technique of jacking up on the control arm, and removing the two bolts that attach the arm to the front crossmember, and then lowering the jack to release the control arm and subsequently the spring. It will literally fall out! The swaybar does have to be disconnected first (but not removed), and the front shocks have to be removed before starting.
YOu do NOT want to follow the technique listed in the service manual, which requires that you disconnect the steering linkage, as well as the lower ball joint, to separate the control arms. This is a LOT more work than the technique mentioned here. Interestingly enough, the easier technique is the one that is shown in my '78 B-car service manual, while the '88 and newer ones show the much more difficult (and tool intensive) technique. Using the older method, no special tools are required, while the newer method they show requires a ball joint separator tool to separate the steering linkage (tie rod) and the lower ball joint, as well as a spring compressor to remove the spring.
BTW, since I did this the night before the Skips show, I of course took the opportunity to clean and detail EVERTHING as I removed and re-installed it!
The front springs are wound flat on the top and pigtailed on the bottom, so cutting them is easy and they retain their proper shape. The pigtail bottom inserts into a special pocket on the lower control arm. I cut off 1/2 of a coil on each spring, after estimating how much that would lower the car.
Upon re-installation the front end is now riding at exactly 28" from the ground to the bottom of the wheelwell moulding (at the highest point)! Note that after first re-installing them the full lowering effect will not be noticed until you drive the car a little to get everything to settle.
The 28" front is now slightly lower than the rear, and the car takes on a slighly raked appearance. This is because the placement of the wheel openings on the body is such that the rear one is lower on the body, so if it is at the same height off the ground as the front, the car will appear raked a little.
So 1/2 a coil lowered the front of the car 5/8 of an inch to 28", which is back to what I consider normal, but which is still probably a little higher than most other Impalas. I would be interested in what other people measure from the ground to the bottom of the wheel opening moulding at both the front and rear wheel openings. Mine are now 28" front and 28.5" rear with no weight in the car.
Cutting the front springs in this fashion also increases the spring rate, in other words the springs are stiffened slightly. Since this is so easy to do, I would not recommend anybody get the Eibach or other springs, as cutting the stock ones can give you equal or better results, besides you can trim them more or less to achieve the exact height you want. I am sure I will have to trim the front springs again when I install the LT4, but that will be easy, and the rate will be increase further, which I like!
Note that unlike the front springs, the rear springs have specifically shaped ends on both the top and bottom, it is not possible to cut them, you have to purchase different ones to raise or lower the rear of the car.
One interesting thing I noticed was that the front right spring was about 3" longer in coil length than the left. GM installs different part number springs sometimes from side to side to compensate for the weight distribution of the car. In my case the front RH spring is slightly taller than the front LH spring, probably to account for the weight of the battery (50 lbs) as well as the coolant reservoir and AC system which is all on the RH side of the car.
Interestingly enough this caused my RH side to ride about 1/8 of an inch higher than the left, so I am trimming the extra 3" off the LH front spring coil such that the car rides equal in height from side to side. In fact I usually prefer a slightly higher setting for the LH side, as that is where the driver sits, and I do end up driving the car alone alot. That is the cool thing about trimming the front springs, you can basically fine tune the ride height as you see fit.
You will definitely need spring compressors to put the 9C1 springs in, though. On the floor, they stand about 1-1/2 to 2" taller.
I have done quite a few spring R&Rs on B-cars over the years, and I have NEVER needed to use a spring compressor for the rear! There is more than enough room to insert the springs in without compressing them, and if it is a little tight, just have somebody push down on the wheel from the side of the car. With both shocks off and the rear axle fully lowered, the tilt of the axle with somebody pushing down on the wheel results in more than enough room to push the spring up to seat it. No special tools are required to change either the front or rear springs if you know the technique!
Another handling tip for the rear springs is to leave off the rubber insulator that goes between the bottom of the rear spring and the axle. Always use the insulator on the top of the spring, but if you leave the lower insulator off, the axle will be more controlled and handling will improve. I have run several B-cars with both setups, that is both with and without the lower insulator, and without it is clearly better. All high performance (9C1, F41, etc.) B-cars before the Impala never used the lower insulator, in fact they were only used on the wagons to help eliminate road noise.
The factory engineers probably were concerned about noise in the Impala, and decided to use the lower insulator at the expense of some handling and control, but I recommend removing them. You will not likely notice any additional noise, but the increased handling is noticible to me after back to back testing I did a few years ago on my '88 9C1 and a '78 Riviera (B-car 2-door with a 403 Olds motor and a THM-400 trans!). Scott.