I get alot of PM's, and I have seen this come up a quite few times in threads.

About a year ago, there was quite a bit of experimentation done with methods for lowering the rears of our cars. There weren't any known, inexpensive, g-body application specific springs that would lower the rear any more than 1" or so. The proposed solutions that come to mind were cutting IROC cargo coils, and using QA1 coil-over springs, without the central strut. There are inherent problems with both of these methods.

The stock rear springs for the G-body are "pigtailed" on both ends. This means that the spring diameter reduces from roughly 8-9" to about 3-4", and the end slip over the spring seat on the frame and on the rear end axle tube. On the upper spring perch, however, there is a "pocket" that will also support a "box" end spring, albeit this was not the intended design.

Pigtailed ends (both top and bottom)


Tangential on bottom, boxed on top


By cutting a cargo coil or any other spring, you end up with not a pigtail, not a box end, but a tangential end. This leaves a very small area for the spring to contact the upper spring "perch" (it's not really even a perch). The entire corner weight must be transfered through that small contact area, causing high stresses on the frame, and possibly damage. This can be somewhat mitigated with a spring isolator, but the isolator will take quite a bit of abuse because of the stresses. If you want to see an application that the tangential end spring was designed for, take a look at the lower control arms up front. They have the tangential pattern stamped into them, which is why the spring has to be "clocked" correctly.

Another problem associated with cutting the rear springs is that the spring can come unseated rather easily. Again, the frame is not designed for any type of spring other than the pigtailed one. So any type of spirited driving could potentially dislodge the spring and then you have big problems. I was able to unseat a cut IROC cargo rear spring during an autocross run once, and I was VERY lucky that I didn't do any further damage.

Cutting springs also increases the springs "rate" which is a measure of the springs stiffness. The foce (in pounds) required to compress the spring 1 inch is it's rate. The spring rate, and more specifically the distribution of spring rate from front to rear, plays a prominent role in determing how the car handles. So if you cut cargo coils (you will have to cut them ALOT to get down to even a 2-3" drop) then you will end up with very stiff rear springs. The cargo coils are already stiff to begin with, you can see how thick the wire is that is used to make them. The long and the short of it is, you end up with a car that tends to oversteer. It is "loose" in stock car terms, or basically, the rear of the car will lose traction first in steady state cornering. (Search "Roll Stiffness" for more information.) This becomes hard to control at times (think emergency lane change maneauvers) and is not a good thing for racing... especially with V8 torque. Again, I know this from experience. Overall, cut springs are a very bad comprimise for the money saved, and there are much better solutions.

Some have tried running the QA1 coilover springs, as they can be ordered with many different spring rates and dimensions. They fit the pigtail, from what I have read on this forum, and they can provide the ride-height drop that many desire. However, as pointed out by many of the guru's on this site that are much smarter and experience than I, they are designed for coilovers, and as such, using them without the central supporting strut can cause problems. The length to diameter ratio of the spring is very large, which lends well to buckling. Just for understanding's sake, imagine you had a spring that was 1" in diameter, and 2 feet long. Trying to compress it would likely cause it to fold up rather than compress uniaxially. The coilover springs are obviously not this bad of a case, but they are getting to the point where they could potentially buckle instead of functioning properly. I have personally never tried running these springs, so I cannot comment on how they work in practice under all conditions, or how the car handles with them.

Finally, there are the springs that are pigtailed on both ends, and provide a 2 or 3" drop. OPG offers the only 2+" drop springs that I know of that are marketed as "G-body springs", but they cost $170/pair. There is one other option that I know of...

Classic Performance Products sells springs that are marketed for '67-72 A-bodies, and they advertise a 2 or 3" drop. When these springs are used in our cars, the "2 inch" springs provide an actual 3 or 3.5" drop, and the "3 inch" springs are far too short for the G body. The best part is that they sell for right around $100 shipped. They are pigtailed on both ends. Many other companies also sell A body springs, Belltech sells 1.5" drop springs for the G-body, and between all of the manufacturers, you are bound to find a spring that puts you where you want to be, safely.

Now that we know of springs that will drop the ride height to where you want it, there are some other things to consider... at least for drops of around 3+ inches.

The stock frame side bumpstops will begin contacting on a regular basis. I have removed mine completely, but left the pinion snubber.

The big problem with droping the rear 3+ inches is the suspension link geometry. The springs only locate the rear end in the car vertically. The upper and lower trailing arms are left to do the work of locating the rear laterally and longitudinally (left/right and fore/aft). The lower the car is, the more the trailing arms are pointed downward on the front (frame) side and upward on the rear (axle) side.

As you would expect, the trailing arms pivot about their frame mounts, and the result is that the axle mount travels in an arc path. At stock height, the arms are parallel to the ground. When the car makes a turn, the body rolls towards the outside of the turn. The outside spring goes into compression, and the spring on side of the car that is on the inside of the turn goes into droop. So the outside trailing arm travels upwards in its arc, and the inside one goes down. If the arms are parallel to begin with, there is no problem because the axle mounts are still the same distance from the rear end.

With a severely lowered car, and no further modifications to correct suspension geometry, the trailing arms are not parallel to the ground. When the body rolls during a turn, the outside arm travels further up in it's arch, and the inside arm travels down in its arch, ending up closer to parallel with the ground. This means that the outside arm pulls the rear end further foward, and the inside arm pushes the rear end further back towards the rear of the car. The rear ends up actually steering the car, as it is no longer perpendicular with the centerline of the car. This is called "rollsteer", and it is not something that you generally want, at least not in sever amounts. (See picture- The wheel would travel down with the axle side of the control arm, illsutrated by the heavy grey line above and below the heavy black line. The black line is where the control arm is at static ride height, and the grey lines illustrate the inner/outter arms under body roll. Upper trailing arms have been omitted for simplicity, but the concept is the same.)



There are relocation brackets that will lower the axle side mount of the lower trailing arm, and get it pretty close to parallel with the ground. I am not aware of any solution for the upper trailing arms though. I have the BMR lower trailing arm relocation brackets, and they help, but there is still a very noticable amount of rollsteer in the rear of my car (~3.5" drop). It is enough to make me very cautious when entering and exiting turns. I still have to solve this issue, but I think it is going to entail relocating the frame-side mounts for the upper arms.

Finally... there is the issue of pinion angle. Because of the arcs that the arms travel on, and the fact that the upper arms are shorter than the lower ones (and because they are angled in, further reducing the longitudinal distance between the frame mount and the axle mount) the pinion angle becomes more severe, the lower you go. Adjustable upper trailing arms are needed to remedy this, and with stock arms and a 3.5" drop, the driveline vibrations were absolutely unbearable on the highway. I have the Currie Enterprises Curectrac adjustable upper arms with the johnny joints, and so far, so good. I have also noticed that by using the BMR reloation brackets, and adjusting my upper arms to be longer (to account for the pinion angle) that the rear axle actually sits further back in the wheel well. It looks a bit funny, and I'm sure that it hurts the corner weight distribution a little bit by making the rear axle a hair lighter than it used to be. I even went as far as putting a longer yoke on my driveshaft just to make sure that it was engaged well enough.

I hope that this sheds some light on lowering the ride height on the G-body. As with most mechanical systems, you cannot simply alter one aspect and expect that it will not affect something else.

Great write up Bernie! Should be sticky'd

X2!!! Awesome write up bernie! this will help answer a lot of questions!

Yes, quite a writeup! There are a few Moogs numbers that lower it pretty well. They are high rate, low height springs. Not to sit on the bumpstops of course, but a good bit lower.

Hey Bernie - great info!

One thing I think should be added is that everyone can use a 3" drop spring for the rear.. and say you only want 2" of drop, find 'spring spacers' for the rear. Basically they are used for lift by the donk crowd, but they are made to fit the perch very well and the pig tail top fits in there nice too. And since they are aluminum, they can be trimmed if you really want to dial in the rear height. So they could be used in conjunction with the CCP springs that you mention.

Also I'll add that OPG does (last time I checked) offer rear springs for g-bodies in 1, 2 and 3" of drop. They are nice and fairly accurate from my experience. Yes they are pricey, but doing it once and right is always cheaper in the long run.

Again, you could go with a 3" OPG drop spring for the rear and use the spacers I mentioned to dial in a 2.5" drop.

I have the OPG 3" drop spring in the car. They are good but VERY stiff. My car never bottoms out. You can not put the car down at all.

...Bill

Hey I looked on OPG's website and couldn't find the drop springs for the Monte. Do they still make them for the rear?

They're under 78-88, low profile srings, down toward the bottom of the page:
http://www.opgi.com/product.asp?topcatid...&yearrange=
If you're looking to buy this month there's a discount code that I got for 10% off, I think it's OCTDISC
Larry.

i was looking for the springs myself...thanks whitess

Wow Bernie that was very good, I actually learned something today. The drawings turned the light on for me. If I don't have a print to reason it out in my head I'm blind.

So you have some issues with the set up. Have you ever considered putting a corvette rear and suspension under the Monte?

i need to check into those lowering springs!

Thanks it was really starting to bug me!!!

You're welcome. Their site is kinda wierd to use sometimes.

$330 for opgi's springs?? WOW

no it's $155 a pair

http://www.classicperform.com/chevelle.htm

RCS60342 will lower the G body 3". That's what is in my car in this pic (and currently)

[img]http://www.sickspeedmonte.com/ProShot.bmp[/img]





I have considered that, but that is dreaming big. Maybe one day... I have seen it done to a few Novas and even '50's pickup, and it involves re-engineering the frame from the ground up (or should I say from the suspension mounting points in.) I would do that for different reasons though, namely the weight distribution advantages of the rear transaxle, the torsional rigidity of the torque tube tying the frame points together, the LS series engine, the independent suspension's ride quality and ability to absorb bumps.

Simply relocating the frame mounts of the suspension and getting the correct length arms should sove the issues that I addressed in the original post.

There is an interesting 3 link convorsation going on as well in the chassis forum.

This thread also addresses something else to consider when lowering the rear of the G body, as well as proposed solutions.

http://www.montecarloss.com/community/ubbthreads.php?ubb=showflat&Number=737111#Post737111

if you know how much weight to hold up, you can use 2.50 diameter hypercoils. just do some math using spring rate and spring free length. to determine how much to lower the car. at the given amount of weight to hold up at a given spring compressed height
$60 a pop

Geez good research and writeup. But most of my mods get done by accident!

I got some Intrax Impala SS for my Fleetwood but they dropped it silly low, so I put them on my son's '88 and they're perfect. I had to use an industrial tiewrap around the top since they're almost 1" shorter at rest than the axle drop. Good ride especially with the Bilstiens.

I didnt see that part number on the chevelle site. Will this part number work?

FCS6330D 1967-72 Front Coil Springs 1-1/2" drop, pair

Moog CC507 cargo coil (72 and older Monte etc) work in our cars; with 5662's in the front with 1/2 a coil cut off and CC507's in the back car is just slightly raked - going back to the alignment rack with it to get a good look at lower rear trailing arms to see if they are parrallel with ground - front lower control arms are level when viewed from the front - just put a post up for info on drop spindles.

Have always had a pronounced vibration 80-85 mph and up; this is mentioned in tech section as a rear suspension/pinion angle problem without a defined cause. Since I pulled the CC627 coils out in favor of the CC507's it has abated somewhat; the 627's had the rear approx 2" higher than it is now - also had the 5662's in at full length, car was really up high (I called it my 'urban suspension'). Any info on this symptom?

RCS6034

Sorry about that, I don't know why I had a 2 in there.

Is the first gen Monte an A body?

I touched on pinion angle in the original post of this thread as well.

It's because the universal joint is not a constant velocity joint. The velocity of the shaft on the output side of the U joint goes by a sine wave pattern, which is a funciton on the input velocity and the angle between the slip yoke and driveshaft, (or the driveshaft and pinion). If you have equal U joint angles on both ends of the driveshaft, the sine waves cancle out and you get a constant velocity at the pinion flange. (This requires that the u joints are "clocked" correctly, but every driveshaft shop knows to do this, as does the OEM)

So in short, make sure that your pinion axis of rotation is parallel with your slip yoke axis of rotation, and you'll be good. Drag racers put the pinion a degree or two down in relation to the yoke, because the pinion tends to "climb" upward under hard acceleration. This causes the pinion to be parallel with the yoke under hard acceleration, and gives the smoothest power transfer to the ground.

Personally, I have 4:10 gears and a 26" tire, so my driveshaft spins pretty quickly. I was unable to dial in any pinion down "pre-load" if you will, as even 1 degree caused vibrations at highway speeds. They are parallel, and smooth as butter now.

The 1st gen Monte is basically an A body. Thanks for the reply - will have to do some checking with the angle finder. GM made more than one upper arm for the rear axle with degree footnotes so you could dial in the pinion angle; what you're saying makes perfect sense. Now to find a flat surface on the trans tailshaft...

I had to go to a jiffy lube and request to use their pit for a few minutes to get an accurate figure with the rear suspension at ride height. Just an idea.