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Rebuilding front and rear suspension this winter.
are aftermarket upper a-arms worth it? Looking at Vansteel or SPC
Vansteel did offset rear arms for me. - great guys there!
1968 427 conv. Building as a summer daily driver.
Adding Borgeson steering, Bilstien shocks will try cutting springs first to lower front a bit (yes I can properly measure and cut the springs)
If not happy will add new springs.
I love a good handling car but have little experience with c3 corvettes
I will add 18" wheel and tires
Is the increased caster worth the cost? The SPC are very adjustable but I will set it and forget it. I do not plan to track the car.
Leigh1322 is correct concerning the measurement and 2D plot. That plot should not have been used nor referred to here because it isn't the complete story and does not yield a true roll center dimension. I just grabbed a readily available plot and didn't give enough thought to it. The raw data (the measurements) is actually correct but understanding what data this is is important. All of this was done 15 years ago so remembering all that we did is challenging. Both analyzing and calculating dimensions that are not easily measured was performed to arrive at our design but much of what we did seems to not be accessible so I can't just toss another plot at you with that data and I apologize for not having that. We don't even have 2D AutoCad on a computer anymore.
What that plot data was is the front pivot point of the suspension. The upper a-arm has a 10 degree anti-dive geometry in it. The cross shaft is 13” long so the difference in height of the front and rear pivots of the upper a-arm is 2.257”. So if you assume an average pivot point of mid-way along the shaft you easily get an approx. 1” drop in pivot point. This gets you to a geometry where all instant centers cross the centerline. From 15 years ago I recall that we included those considerations but I can't find 2D plots to show that to you.
So yes I made some mis-statements and incorrect statements regarding the location of the instant center and the corresponding roll center. I will edit some corrections in my original posts to clarify so others can understand without having incorrect information. My original statements regarding a low roll center are still mostly correct. Therefore I still stand by the statement that the roll center stated in the Duntov SAE paper is not the same as what we are dealing with on our cars currently. Mostly because of different ride heights but we also don't know all the assumptions and settings they used so replicating that exact roll center number could prove difficult. For instance, the Z height for a 67 is 2.25” yet for a 72 it ranges from1.35 to 2.11”.
I think a civil discussion on many aspects of the front ends of these cars would be beneficial to the entire community and I welcome it. Everyone has a different way of looking at and solving problems. We can all learn from one another. Further, we never claimed to have the ultimate solution. We simply have a solution that we offer as a product. Everyone is free to disagree and not buy our products but we aren't some evil corporation that is dogmatic nor only intent on hoodwinking people to take their money. We are enthusiasts just like you.
I will address a few other points later but I wanted to post something today.
Note that they are all assembled for one side of the car, so one of them will need to be disassembled and reassembled as a mirror of the other. The longer shaft goes forward, to move the ball-joint rearward, increasing caster. I used red electrical tape to denote the left hand thread side of any turnbuckle adjustment sleeves (A-arms, steering linkage, strut rods). With the Borgeson, I think you'll want much more caster than stock. I have a LOT of caster with my manual steering 80 with the SPCs (pictured). Great on the highway, not easy to park. On my Borgeson 79, there isn't enough caster, and the steering is very light, like a modern sedan.
It looks like the SPC are very easy to set up or adjust.
do you know the available castor range? what is best for street?
Also it looks like dialing in a bit camber would be very easy.
Note -I will have a local performance shop do the final alignment.
If you don't want to spend the money and still want a very good upgrade use your stock arms. Buy the Global west Del-a-lum bushings and offset upper shafts
And as far as cutting the coils cut one full coil off. It will lower the car about an inch
Reno,
I did some reading on these a while ago. Keeping stock look might be of value someday.
What is the installation process for the Del-a-lum? are they pressed in? do I have a shop do it?
Reno,
I did some reading on these a while ago. Keeping stock look might be of value someday.
What is the installation process for the Del-a-lum? are they pressed in? do I have a shop do it?
Thanks Tom
Global West has a couple videos on how to do it. But the lowers are a bitch If you have a good shop let them do it
It looks like the SPC are very easy to set up or adjust.
do you know the available castor range? what is best for street?
Also it looks like dialing in a bit camber would be very easy.
Note -I will have a local performance shop do the final alignment.
I don't know the range offhand, but it is more than you can do with stock shims to be sure. The final caster number will be affected by your steering solution. On the Borgeson install thread, there is a flow limiter that increases the turning effort of the Borgeson. More caster will also increase steering effort, so balancing the two may be up to you. Look for threads from @cagotzmann for some DIY alignment tips and suggested measurements that will work on the street. Adding camber is certainly easy with the SPCs.
If you are changing to modern radial tires you want more caster, have a look at the amount a C4 vette has. Adding more caster was one of the best things I did to my '70 it got rid of the nervous twitchy feel the stock setting had. Not a fault its just that the suspension was originally setup for cross ply tires that required more effort to turn. I slotted the upper arm mounts by a 1/4 inch so that the arms could be moved backwards (there are posts on the forum regarding this mod which is where I got the idea from), replacement arms with more caster adjustment would have been desirable but needing expensive certification in this country.
If you don't mind doing a little grinding and machine work, here's a thread about using old Chevy Impala
tubular upper control arms. It's a relatively easy mod and A LOT less expense when compared to the
other aftermarket upper control arms.https://www.corvetteforum.com/forums/c3-tech-performance/4058443-tubular-a-arms-4.html
It's a little long, though. Just the arms themselves are designed with 4* caster.
The limiting factor on my 69 was where the SPC arm started to hit the inner fender wall cutout. I recall getting about 7 degrees of caster at that point. One of the benefits of the arm was getting rid of the shims which cleared up some room for an LS conversion. It's worth marking the red part of the arms (in the picture below) for reference to the number of turns to make adjustments.
To measure caster, I attached a pentagram with a front surface mirror and shined a laser off of it onto a white board to note the travel of the image vs. horizontal. Doesn't look like I made note of that here so I can't exactly verify the 7 degrees.
The obstruction I noted is where you might start to have difficulties getting more caster. Seven degrees is plenty and the turn-in on my car was excellent. I highly recommend the arms. The additional mod that is offered from SPC was a taller ball joint and that is also worth it.
The only downside I can think of to increased caster is that turning the wheels visibly lifts the front-end and, with my Borgeson conversion, I can see that the frame is twisting a little as it resists torquing on wide sticky tires. That's at rest, while driving I doubt that it matters.
100% worth it, extra caster makes the handling much better, both increases roadholding and stability. Especially with the Borgeson which has plenty of assist. I have the Global West uppers with extended ball joints and I think they're great, but most of the available uppers seem to have been used with success. Yes you can alternatively use slotted or offset shafts to get better caster settings also, but most of the aftermarket uppers also use an extended ball joint for increased camber gain as well.
I installed Global West upper and lower control arms on my street driven 74, along with 550lb springs, Bilstein sport shocks, 1 1/8” sway bar. Car is setup with 5 degrees positive caster and 1/2 degree negative camber, handles superb on Nitto NT550 G2 255/50/17 tires. I initially tried a budget offering that ended up a nightmare and a lengthy delay on returning my Corvette to the road; fiasco well documented in another thread. I was at least able to get my money returned. I am extremely satisfied with the quality of the Global West parts. Additionally, with the GW lowers, I have the ability to convert to coil over setup if desired in the future. I don’t foresee converting to to coil over though as I am happy with the stance and handling. The front suspension setup is used in conjunction with 7 leaf rear spring(factory spring)Van Steel heim strut rods, Bilstein sport shocks and 3/4” sway bar.
I think it all depends on how you drive, what you are looking to improve, and how much you want to spend.
For street driving, by far the best value, are stock OEM control arms with poly bushings, upper and lowers. I have had prothane poly bushings for over 12+ years now and they look perfect and do not squeak. A dramatic improvement over rubber control arm bushings and little decrease to none in ride quality.....Total cost $150. My labor to remove control arms, $50 prothane poly bushings, $50 for each control arm for installation by a machine shop for both uppers and $50 labor for both lowers.
I would go Delrin inserts in the OEM arms with the offset shafts next for the best street improvement and the race arms for obviously, racing.....
ALL ^^^^^^ will make a big improvement over stock arms with rubber bushings...Anything and everything one can do to reduce unwanted suspension movement and travel will help a c3 dramatically
The limiting factor on my 69 was where the SPC arm started to hit the inner fender wall cutout. I recall getting about 7 degrees of caster at that point. One of the benefits of the arm was getting rid of the shims which cleared up some room for an LS conversion. It's worth marking the red part of the arms (in the picture below) for reference to the number of turns to make adjustments.
To measure caster, I attached a pentagram with a front surface mirror and shined a laser off of it onto a white board to note the travel of the image vs. horizontal. Doesn't look like I made note of that here so I can't exactly verify the 7 degrees.
The obstruction I noted is where you might start to have difficulties getting more caster. Seven degrees is plenty and the turn-in on my car was excellent. I highly recommend the arms. The additional mod that is offered from SPC was a taller ball joint and that is also worth it.
The only downside I can think of to increased caster is that turning the wheels visibly lifts the front-end and, with my Borgeson conversion, I can see that the frame is twisting a little as it resists torquing on wide sticky tires. That's at rest, while driving I doubt that it matters.
All in all, nothing but positives for this change
What ball joints did you go with on your uppers, as I see you stayed with the 3-hole plates?
And did you add any suspension bumper or stop, or straps?
If not, What spring rates? Or are you limiting with shock donuts on the travel?
Last edited by TCracingCA; 12-29-2019 at 01:12 AM.
What ball joints did you go with on your uppers, as I see you stayed with the 3-hole plates?
As mentioned I went with the tall ball joints that SPC provided. That helps somewhat with your next question
And did you add any suspension bumper or stop, or straps?
The lack of stops bothered me but I didn't do anything about it. Savitske claimed the shock damping would be enough. I have a 1.25 bar up front which probably helps and I haven't seen any dents or blems in the frame or arms so there's never been hard contact. I thought about maybe cementing a rubber pad at the contact point but other than that I don't see an easy way to limit the arm. The arms do rest on the frame when the car is jacked up so the shocks are not at their limit..
If not, What spring rates? Or are you limiting with shock donuts on the travel?
Front-end ended up lighter and I cut off a coil to get back to stock height. I don't remember the spring rate but it was mid-range as I knew the rate would increase with the cut
Parenthetical note - my autocross opportunities dried up and I am not working the car as hard. Basically just street driving. Car is boxed in right now I will have another look when I get access. I have changed the shocks out and went back to Bilsteins. Not sure I can say where the travel is limited anymore. I will take a look and measure the clearance later with the car on the ground.
I have the SPC arms and really like them for my application where we're doing a lot of autocross/track days and are making occasional changes.
However, I would recommend just going with the Vansteel arms for your car. They make great products and have outstanding customer support. Also, they're a simple, straightforward replacement part, so you won't have to worry about fabbing anything or periodically checking all the hardware on these SPC arms, and it will keep the standard alignment procedures (shims) for whoever does your alignment work.
Whichever way you go, be sure to use updated alignment settings, especially with the Borgeson box in there.
These are pretty close to what Vansteel, VBP, and others recommend for street use: Front
Toe, 1/32" In
Camber, 0 deg
Caster, 6-8 deg Rear
Toe, 1/8" In
Camber, .25 deg (Neg Cmber)
Good Luck with your project, whichever way you decide to go.
-Chris
Parenthetical note - my autocross opportunities dried up and I am not working the car as hard. Basically just street driving. Car is boxed in right now I will have another look when I get access. I have changed the shocks out and went back to Bilsteins. Not sure I can say where the travel is limited anymore. I will take a look and measure the clearance later with the car on the ground.
As arms can move up and down, I am a heavy spring advocate (have the Homologated 860s PN #3986032s) and a rear Daytona PN #6258056 (6 leaf config thou) with Swiss cheesing the upper three blades, but it will make for a super rough ride, but the inability of the road to compress the springs, based on car weigh is a limiting factor for suspension travel. Going softer would necessitate some limiting feature, as in the stick suspensions, they hope you aren’t going that fast when you land on the bumpers. We have all hit a road condition, that fully taxed the suspension!
On the SPC arm config, it is advised to go with aftermarket ball joints, and I saw the four bolt plate units as the unit to select, I think off of the top of my brain precision Howe units to have the geometry arm orientation correct.
I have SPCs new in the box, but have only run the Pole Position forefather arms to the SPCs! I bought the SPCs to freshen up the car, as things were just not all shiny nice on the underside. I am still deep into the rebuild, of that car. I keep going off track literally, like just bought a new Dual Sport motorcycle! As my compulsive disorder for new toys keeps getting in the way of my ultimate rebuild, I might never finish! So I understand! Just curious on shared project engineering toward the ultimate, from like minded people.
The new version of my car will have the Tom’s Diff stuff, but better, everything NOS L88, but in an all Aluminum SBC Bow Tie block and heads with all Vintage Bow Tie engine component stuff mostly, the special built HD ROD 6 speed is going back in, the Guldstrand rear multi-link, but with twists, and telescoping halfshafts, upper link, going full coilover, not a mix of full and semi, so cutting spring pockets in the front, and going up on my flares from Jongbloed modular 3 piece racing Mag rims in 10 & 8.5 to 11 & 10s, etc. and still planning on metalflake 1960s purple on the C2 racer (my Top Secret Project). The other C2 will stay Stock gussets as GW suggested with Global West Del Um bushings (running those since late 80s/startvif 1990s- second Corvette in existence to run those, is what Doug told me back then, his first parts customer for those units), the rear CVC-Apex suspension, Koni Double adjusts vintage, etc. The C3 is staying more F-41 level with some bells and whistles, but as my street ride and throwing the second set Jongbloed 10 & 8s onto that car, moving the 8 inch rally rims to the 65 El Camino.
Last edited by TCracingCA; 12-29-2019 at 01:43 PM.
K.I.T.T. posted a vid over in the road racing about a C3 racecar he restored. The pre-rebuild 'burned out' car has what appear to be stock control arms. Who knows it had/has offset shafts but it did have bias-ply tires.
The Speed Direct aluminum a-arms are the only ones that change the roll center as well as adding more positive caster. I've had these on the car for about 15 years. I've run it on the track and made several Hot Rod Power Tours. They are the lightest arms of anybody.
12-23-2019, 07:08 AM
stock or aftermarket upper A-arms ?
If you have a good shop let them do it
So I understand! Just curious on shared project engineering toward the ultimate, from like minded people.
