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If that were my car, I would not hesitate to put on a Van Steel low-arch monospring, perhaps one that has been shortened 1/2" on each side. From what I can tell, their low-arch springs are similar to the VB&P springs. The Hyperco springs are likely similar to the high-arch TRW springs that cause the same problem you are trying to fix with your steel spring. Certainly call them first, though.
Here's a shortened VB&P monospring in my 80, with 8" bolts.
Last edited by Bikespace; Dec 11, 2019 at 04:13 PM.
I removed one leaf of my spring too. Had a 7-leaf, wich now is a 6-leaf....
Don't remember which one I removed, but I guess the effect differs with which leaf you remove so there might be some trial and error involved. Anyway, a simple job.
I have a 9 leaf set-up and was thinking of removing the top 2-3...they are real short and just moving to the bottom so the bolts lengths won't change going back into the differential, along with moving up to 8" bolts. Any advice on removing the spring and the leafs? mine is a 79
I have a 9 leaf set-up and was thinking of removing the top 2-3...they are real short and just moving to the bottom so the bolts lengths won't change going back into the differential, along with moving up to 8" bolts. Any advice on removing the spring and the leafs? mine is a 79
With all the work you'll need to go through, why not just install a new composite spring for the firmness and ride height you want and be done with it?
I'm hearing the composite will raise the rear. I don't really think changing the bolts and maybe removing a few leafs is that big of a deal. I already started in this direction and just looking for feedback.
I'm hearing the composite will raise the rear. I don't really think changing the bolts and maybe removing a few leafs is that big of a deal. I already started in this direction and just looking for feedback.
If the goal is to lower the car for aesthetics, what you propose will likely be the cheapest route. You will need to fabricate a spacer (easy, and shown above), and you will have made your spring slightly softer.
If your goal is to improve your car's performance, you may change your mind about the composite spring once you remove that heavy steel spring bundle.
FWIW, my understanding is that the wrong composite spring will raise the rear, but the correct one will not. TRW and the high-arch Van Steel springs will raise the rear. VB&P and (I've heard), the Van Steel low-arch springs will not raise the rear. The correct spring can also stiffen the rear, while still providing a smoother ride (this was certainly my experience). Stiffer may be doubly important now that you have reduced the total suspension movement. To keep from bottoming out and riding on the bump stops, you may want a stiffer spring.
I have a 9 leaf set-up and was thinking of removing the top 2-3...they are real short and just moving to the bottom so the bolts lengths won't change going back into the differential, along with moving up to 8" bolts. Any advice on removing the spring and the leafs? mine is a 79
The top 2-3 will not have so much effect on the arch, but a bit (not very much?) on the total thickness.
I would remove nr 3+6 from the top or something like that, and then try it. Ok it is some work but you'll do it in an hour or two.
Note! If you remove two or three leafs, the spring mounting bolts, or at least two of them (the ones not drilled thru in the diff mount) could possibly bottom out in the mounting hole. Measure this, or you could end up not knowing this, and just torque the bolt against the bottom of the mounting hole!
The main idea is to get the half-shaft almost exactly horizontal at normal ride height, with normal weight on it.
This isn't really the optimal position since the driveshaft acts as one of the links in the suspension. Optimally, you want the driveshaft angled down a bit to reduce induced camber as the wheel moves through the suspension travel.
The angle of the tire (camber) is determined by the lengths of the two arms attaching it to the center diff (driveshaft and strut rod), these two work in conjunction to one another. The strut rod is always angled down, so the absolute distance (horizontal plane) from the differential will ALWAYS increase when the suspension is compressed and it swings upward. This will have the effect of angling the tire in at all times.
When the driveshaft is level and parallel to the ground, the distance from the rear to the tire is at it's maximum. From this point, with any suspension travel, that absolute distance will be reduced as the driveshaft is essentially an arm swinging in a radius from the pivot point on the diff. Since the driveshaft is the upper link, the absolute distance from the rear to the tire is reduced, this will tilt the tires inward, increasing the camber. C3s like to squat upon acceleration, and this creates an uneven/reduced contact patch for the tires. Same thing in turns. This is compounded a bit by the fact that the strut rod will always want to tilt the tire inward.
With the driveshaft angled downward at rest, when the suspension travels upward, the distance from the diff to the tire (horizontal) will change and reach it's maximum as the driveshaft passes through the horizontal plane, and then it starts reducing again, reaching the starting distance when the suspension is at a point where the driveshaft is now angled upwards the same number of degrees (but in opposite direction) as when it was at rest. This combination is till not perfect, but it keeps the most tire on the ground at most times. When lowering bolts are solely used, you lose this effect the closer to the horizontal the driveshafts are at rest.
The Chevy Power Book's solution to properly lower the rear of the car is to remove the rubber mounting bushings from the differential mount crossmember and replace them with welded in steel discs, this will lower the chassis onto the differential, lowering the ride height and allowing you to keep geometry correct. I did this on my car, and it in conjunction with the VanSteel coilovers worked well. A lower arched spring should have the same effect, but it will reduce the total amount of suspension travel some, probably not a big deal.
Just trying to provide a little info to inform you in your decision.
Last edited by SLVRSHRK; Dec 12, 2019 at 11:43 AM.
This isn't really the optimal position since the driveshaft acts as one of the links in the suspension. Optimally, you want the driveshaft angled down a bit to reduce induced camber as the wheel moves through the suspension travel.
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I'm sorry but that statement is not correct. The half-shafts should be parallel to the ground. The Chevy Power book recommends a 1-1/4" D dimension on the strut rod and that is what flattens the half-shafts. There is less stress on the u-joints that way. (However drag cars should have flat half-shafts at launch and under load to enhance u-joint life). The main reason for lowering the car by raising the differential into the frame is to not increase the half-shaft angle.
The Corvette rear suspension is both one of a kind, unique, peculiar, and hard to understand. But it actually works quite well. There are however many incorrect myths about it as well. The camber curve of the rear suspension is controlled by the Instant Center where the strut rod line intersects the half-shaft line. For a stock C2 it is 48" and for a stock C3 it is approximately near the opposite tire. Because of this the rear of a Corvette has a large negative camber gain on jounce. (Rebound is positive but mostly irrelavent). The gain is relatively constant regardless of rear ride height. Many have found that the negative camber gain in the rear is too great and needs to be reduced. This is accomplished by lowering the inner strut rod mount. Lowering the strut rod mount around 1" can make the strut rods and half-shafts absolutely parallel. This would move the instant center to infinity, and would have zero camber gain, and could be useful to drag racers. A 1/2" lowering seems to be a more common adjustment for handling.Whether this is beneficial or not depends on all the other suspension parameters.
I wrote an excel spreadsheet just for C3s, which allows you to see the results of suspension setup changes in a dynamic and interactive manner.
Duntov's Rear Camber Curve here:
This is the C2 Rear Camber Curve. Lowering the rear strut lessens this.
To the OP's question of removing leaves to lower the rear: That is complicated. Multi-leaf springs are designed as a system. Adding a leaf adds both load capacity and rate and raises the rear. Removing leaves does the reverse but additionally makes the spring fatigue quicker, thus it will settle, wear out and droop under use. As these kinds of changes are pretty unpredictable, they can be frustrating. I would recommend having the spring professionally corrected, or buy a new one, preferably composite.
Last edited by leigh1322; Dec 12, 2019 at 08:37 PM.
I'm sorry but that statement is not correct. The half-shafts should be parallel to the ground. The Chevy Power book recommends a 1-1/4" D dimension on the strut rod and that is what flattens the half-shafts. There is less stress on the u-joints that way. (However drag cars should have flat half-shafts at launch and under load to enhance u-joint life). The main reason for lowering the car by raising the differential into the frame is to not increase the half-shaft angle.
The Corvette rear suspension is both one of a kind, unique, peculiar, and hard to understand. But it actually works quite well. There are however many incorrect myths about it as well. The camber curve of the rear suspension is controlled by the Instant Center where the strut rod line intersects the half-shaft line. For a stock C2 it is 48" and for a stock C3 it is approximately near the opposite tire. Because of this the rear of a Corvette has a large negative camber gain on jounce. (Rebound is positive but mostly irrelavent). The gain is relatively constant regardless of rear ride height. Many have found that the negative camber gain in the rear is too great and needs to be reduced. This is accomplished by lowering the inner strut rod mount. Lowering the strut rod mount around 1" can make the strut rods and half-shafts absolutely parallel. This would move the instant center to infinity, and would have zero camber gain, and could be useful to drag racers. A 1/2" lowering seems to be a more common adjustment for handling.Whether this is beneficial or not depends on all the other suspension parameters.
I wrote an excel spreadsheet just for C3s, which allows you to see the results of suspension setup changes in a dynamic and interactive manner.
Duntov's Rear Camber Curve here:
This is the C2 Rear Camber Curve. Lowering the rear strut lessens this.
To the OP's question of removing leaves to lower the rear: That is complicated. Multi-leaf springs are designed as a system. Adding a leaf adds both load capacity and rate and raises the rear. Removing leaves does the reverse but additionally makes the spring fatigue quicker, thus it will settle, wear out and droop under use. As these kinds of changes are pretty unpredictable, they can be frustrating. I would recommend having the spring professionally corrected, or buy a new one, preferably composite.
That's a fascinating spreadsheet. Kudos to you for taking the time to put it all together. I'm a big fan of using Excel to do modeling like you have done. Seriously.
I don't want to hijack the OP thread here, but just wanted to make a couple of points/pose a few questions.
I am in total agreement that having the half-shaft parallel to the horizontal puts the load on the U-joints at it's lowest
Lowering the body by raising the diff allows you to lower the body, and not change the suspension characteristics as you have not changed any of the angles which determine the Instant Center, that was my point above
It would seem that if you angle the half shafts down a bit, you increase the Instant center as the point of intersection of the half-shaft and strut rod will be moved further away than if the half-shaft is at the horizontal plane. This has the same effect as lowering the inner strut rod mount point does, it just does it by changing the other line.
When the half-shaft starting point is below the horizontal, wouldn't the total change in camber be smaller throughout the suspension travel range? This would be because the travel of the half shaft from below the horizontal to the horizontal would have one effect which would then be offset by the same amount at the point where the half-shaft is above the horizontal by an equal amount as when the car is at rest. So doesn't the car hold tighter to the original camber specification in this layout than when starting from horizontal because when you start at the horizontal, you only have one direction of travel.
I'm no suspension expert, didn't even sleep at a Holiday Inn last night, but I am a fan of fact and am happy to be enlightened.
That's a fascinating spreadsheet. Kudos to you for taking the time to put it all together. I'm a big fan of using Excel to do modeling like you have done. Seriously.
I don't want to hijack the OP thread here, but just wanted to make a couple of points/pose a few questions.
I am in total agreement that having the half-shaft parallel to the horizontal puts the load on the U-joints at it's lowest
Lowering the body by raising the diff allows you to lower the body, and not change the suspension characteristics as you have not changed any of the angles which determine the Instant Center, that was my point above
It would seem that if you angle the half shafts down a bit, you increase the Instant center as the point of intersection of the half-shaft and strut rod will be moved further away than if the half-shaft is at the horizontal plane. This has the same effect as lowering the inner strut rod mount point does, it just does it by changing the other line.
It's only the intersection of the two lines that matter. And there is only one intersect point.
When the half-shaft starting point is below the horizontal, wouldn't the total change in camber be smaller throughout the suspension travel range? This would be because the travel of the half shaft from below the horizontal to the horizontal would have one effect which would then be offset by the same amount at the point where the half-shaft is above the horizontal by an equal amount as when the car is at rest. So doesn't the car hold tighter to the original camber specification in this layout than when starting from horizontal because when you start at the horizontal, you only have one direction of travel.
I'm no suspension expert, didn't even sleep at a Holiday Inn last night, but I am a fan of fact and am happy to be enlightened.
So a stock C3 has about an 78" Instant Center where the two lines intersect. This is the point around which both links and the tire rotate around. Lowering the rear strut rod as mentioned by Chevy Power Book, Guldstrand and VBP, with a spacer allows about a 1.25" "D' measurement on the strut rod (with level half-shafts). This moves the Instant center point out to about 108", cuts the rear roll center height in half to about 3.5", coincidentally making it the same as the front. It also cuts the negative rear camber gain about in half compared to a C2, which has a 5.2"rear roll center. Regardless the camber change is linear and does not matter at what angle the respective arms start at. All that matters is that at 1.0 G-force the body roll (positive camber gain) is neutralized by the suspension (negative camber gain), and you wind up with zero camber at 1 G, or darn close to it.
It's only the intersection of the two lines that matter. And there is only one intersect point.
Yes, but because the upper and lower links are not equal length, that intersection point will vary as the suspension travels up and down and the angles change. There's a million potential combinations, each with a slightly different sweet spot. Your sheet does a great job of letting a person tune for a particular target (in your post above it was zero camber at a 1g turn).
I'm going to have to think on this a while. If I have questions I will follow up in a PM. Thanks for the info/discussion.
Yes, but because the upper and lower links are not equal length, that intersection point will vary as the suspension travels up and down and the angles change. There's a million potential combinations, each with a slightly different sweet spot. Your sheet does a great job of letting a person tune for a particular target (in your post above it was zero camber at a 1g turn).
I'm going to have to think on this a while. If I have questions I will follow up in a PM. Thanks for the info/discussion.
Yes the Instant center does move around some as the everything moves. Then it gets really hard to follow, except in a 3D CAD program.
And thanks for the excel sheet compliment. I knew there would be a couple people out there that got a kick out of like I do.
yea I am supporting the weight with the jack for the mock-up. Those long bolts are going and I will use the 8" ones. Here is a question...I hear people say they remove the banding to lower the rear also. Do they mean the banding in these pics that is on longer bottom leafs?
those bands should be removed. They are only for shipping to keep the spring together. I removed mine, but it didn’t change the ride hight.
Sorry to keep the topic sidetracked... But I believe that you definitely want the outboard end of the half shaft lower than the inboard end, not because of camber but because of toe. The dynamic toe angle is basically controlled by the half shaft - as the half shaft moves away from vertical it pulls the rear of the trailing arm inward towards the center of the car, resulting in toe out - it's very bad to have toe out on the outside rear in a corner, exceptionally unstable! If you start with the outer end say 0.5" below horizontal then you have an inch of upward (bump) travel through which the suspension can move before it toes out relative to the static setting (it toes further inward for the first half inch, then moves back to the static setting over the next half inch). If you have the half shaft parallel then any movement in bump results in increased toe out compared to your static settings, and so you need to run a huge amount of toe in (which is not very good for a number of reasons) to avoid the car being dangerously unstable when pushed hard into a corner. See the VIP (Vette Improvement Program) articles for further description and analysis of this.
Last edited by Metalhead140; Dec 15, 2019 at 05:59 AM.
Excellent analysis! I also agree that would be a terrific reason when fine-tuning the handling to have the wheel end 1/2 inch lower.
Metalhead I bow to your considerable handling expertise. I have seen your car run in your videos and you obviously have it "well dialed-in". Your real world tuning experience & comment just gave me another "ah-ha" moment and explained the graph below.
I found this rear bump curve in Duntov's book, and the shape of it can only be explained as you describe., Varying the height of the outer half-shaft would tilt the bump curve below. He must have had a certain amount of droop in mind to generate an almost flat toe-in bump curve in the 2-3 inch of jounce range that is so critical to handling. The curvature itself is controlled by the length of the Instant Center. But you can see that the curve is tilted & not symmetrical. Greenwood does indeed recommend a 1/2" lower outer half shaft setting for optimum handling.
In response to the original OPs question I have seen Vettes where these half-shafts were tilted down severely, or tilted up severely in attempts to either raise or lower the car. It's just not a good idea to stray too far from Duntov's original plans on ride height. Yes the Vette suspension is more complicated and adjustable than most. That also means it is easier to "foul" it up. We just have to remember that he was smarter than the average Joe!
Last edited by leigh1322; Dec 15, 2019 at 10:54 AM.
Sorry to keep the topic sidetracked... But I believe that you definitely want the outboard end of the half shaft lower than the inboard end, not because of camber but because of toe. The dynamic toe angle is basically controlled by the half shaft - as the half shaft moves away from vertical it pulls the rear of the trailing arm inward towards the center of the car, resulting in toe out - it's very bad to have toe out on the outside rear in a corner, exceptionally unstable! If you start with the outer end say 0.5" below horizontal then you have an inch of upward (bump) travel through which the suspension can move before it toes out relative to the static setting (it toes further inward for the first half inch, then moves back to the static setting over the next half inch). If you have the half shaft parallel then any movement in bump results in increased toe out compared to your static settings, and so you need to run a huge amount of toe in (which is not very good for a number of reasons) to avoid the car being dangerously unstable when pushed hard into a corner. See the VIP (Vette Improvement Program) articles for further description and analysis of this.
Originally Posted by leigh1322
Excellent analysis! I also agree that would be a terrific reason when fine-tuning the handling to have the wheel end 1/2 inch lower.
This is good information, and well thought out. It makes you wonder why GM went with this design, considering the inherent "flaws" that it possesses. On the other hand, considering that the design was on the drawing board in the 1958-59 timeframe (for a late 1962 release, for the '63 Sting Ray), and tires had only about 3" of tread width, it wasn't as big an issue, as in later years.
This is good information, and well thought out. It makes you wonder why GM went with this design, considering the inherent "flaws" that it possesses. On the other hand, considering that the design was on the drawing board in the 1958-59 timeframe (for a late 1962 release, for the '63 Sting Ray), and tires had only about 3" of tread width, it wasn't as big an issue, as in later years.
Duntov purportedly had a 4 or more link design in mind that would have had floating (non-loaded) half shafts. But there were $ costs involved. So this was the innovative loaded-half-shaft design solution that kept the costs down but also retained virtually all of the high performance handling characteristics. The biggest concession was the loss of wheel control in the case of a half-shaft or u-joint failure. And in '62 he had no idea how much power we would be putting through these rear ends many years later!
I think it is truly amazing this design is holding it's own with the passage of time as well as it's doing!
Duntov purportedly had a 4 or more link design in mind that would have had floating (non-loaded) half shafts. But there were $ costs involved. So this was the innovative loaded-half-shaft design solution that kept the costs down but also retained virtually all of the high performance handling characteristics. The biggest concession was the loss of wheel control in the case of a half-shaft or u-joint failure. And in '62 he had no idea how much power we would be putting through these rear ends many years later!
I think it is truly amazing this design is holding it's own with the passage of time as well as it's doing!
Agreed. The stories I have read suggest that the only way he got independent rear suspension was to make these compromises and pull almost the entire front suspension from the Chevrolet parts bin. I can imagine the discussions about building their sports car with Impala lower A-arms, spindles and that wonderful hydraulic cylinder based power steering....
Excellent point on the Toe. I knew this, it just didn't click at the time I wrote the response. Great add.
