Fabricated A-Body spindle ideas and discussion
- Thread starter DionR
- Start date
-
DionR
Well-Known Member
So, using my "basic" performance setup which is:
LCA flat
1 degree negative camber
6 degrees positive caster
275/35R18 +35mm wheel
The roll center numbers potentially are:
A-Body spindle - 5.5155"
F-Body Spindle - 6.6873"
F-Body w/ 1" ext BJ - 8.7916"
In comparison, the stock suspension roll center looks to be at 6.9489"
The other (maybe?) useful data point might be the height of the LCA pin:
Stock - 12.3684"
Performance - 10.3946"
Or almost 2" lower.
If we take these numbers and do some comparisons, here's a couple of things that jump out to me.
The stock A-Body on the performance setup is lower by 1.9738" but the RC dropped by 1.7939, so the roll couple is shorter by 0.1799". Not much, but still a shorter roll couple. Add that the center of gravity (CG) of the front of the car is down almost 2", the LCA isn't at a leverage disadvantage (side load could result in jacking in the stock orientation) and it doesn't look like it is ready to go rock crawling (no offense intended to the stock 14" wheel crowd, well ok, maybe some offense intended). So it makes sense this setup would be superior to stock.
The F-Body spindle with the same ride height drop only loses 0.2616" of height for the roll center but with the CG being 1.9738" lower the roll couple is actually shortened by 1.7122". So a lower CG and shorter roll couple suggest a win-win.
The f-Body spindle with the extended ball joint actually has a taller roll center by 1.8427" and when added to the CG drop, the roll couple is 3.8165" shorter than stock. That can't be bad, can it?
Now this flies in the face of the idea that you want a 2-4" height for your roll center. After doing some reading, I am leaning towards the thought those numbers really only apply if you already have a low CG already. I think a short roll couple is the key provided you keep the CG low and you don't have the control arms at wonky angles.
I understand that you can tune for a large roll couple with a bigger sway bar and stiffer springs, but it makes sense to me reduce the roll couple if possible rather than have to work against it.
This further solidifies my opinion that the stock TB suspension has (potentially) the best geometry of any of the Mopar A-Body systems available on the market.
LCA flat
1 degree negative camber
6 degrees positive caster
275/35R18 +35mm wheel
The roll center numbers potentially are:
A-Body spindle - 5.5155"
F-Body Spindle - 6.6873"
F-Body w/ 1" ext BJ - 8.7916"
In comparison, the stock suspension roll center looks to be at 6.9489"
The other (maybe?) useful data point might be the height of the LCA pin:
Stock - 12.3684"
Performance - 10.3946"
Or almost 2" lower.
If we take these numbers and do some comparisons, here's a couple of things that jump out to me.
The stock A-Body on the performance setup is lower by 1.9738" but the RC dropped by 1.7939, so the roll couple is shorter by 0.1799". Not much, but still a shorter roll couple. Add that the center of gravity (CG) of the front of the car is down almost 2", the LCA isn't at a leverage disadvantage (side load could result in jacking in the stock orientation) and it doesn't look like it is ready to go rock crawling (no offense intended to the stock 14" wheel crowd, well ok, maybe some offense intended). So it makes sense this setup would be superior to stock.
The F-Body spindle with the same ride height drop only loses 0.2616" of height for the roll center but with the CG being 1.9738" lower the roll couple is actually shortened by 1.7122". So a lower CG and shorter roll couple suggest a win-win.
The f-Body spindle with the extended ball joint actually has a taller roll center by 1.8427" and when added to the CG drop, the roll couple is 3.8165" shorter than stock. That can't be bad, can it?
Now this flies in the face of the idea that you want a 2-4" height for your roll center. After doing some reading, I am leaning towards the thought those numbers really only apply if you already have a low CG already. I think a short roll couple is the key provided you keep the CG low and you don't have the control arms at wonky angles.
I understand that you can tune for a large roll couple with a bigger sway bar and stiffer springs, but it makes sense to me reduce the roll couple if possible rather than have to work against it.
This further solidifies my opinion that the stock TB suspension has (potentially) the best geometry of any of the Mopar A-Body systems available on the market.
DionR
Well-Known Member
@BergmanAutoCraft can you give us your personal experience on the F-Body spindle with the extended UBJ? What improvements did you see?
Curious to hear your thoughts.
Curious to hear your thoughts.
Yes, your trends with taller spindles and higher ball joints raising roll centers is correct and consistent with my experience as well.
I would be interested in hearing Peter's feedback as he uses the F body spindle with a tall ball joint to raise the roll center, thus shortening the moment lever arm and reducing lateral leverage on the car. This also has the benefit of requiring less negative camber to compensate for the body roll and it creates a more equal roll between front and rear. Some anecdotal evidence on these changes would be nice to hear.
The rear roll center height is found at the mid-way point between the center of the axle and the imaginary line drawn through the spring eyes. So with a high arch drag race spring, the roll center height is below the spring eye plane. On something like a zero arch oval track spring, the roll center height is going to be above the spring eye plane.
So, by raising the front roll center, you are shortening the moment lever arm. Conversely, you could lower the center of gravity height, but that's much harder to do. Most old timers I've spoken to tended to estimate it as roughly camshaft height and just on the interior side of the firewall on a mostly stock, street going car. The oval track cars I was familiar with, this location was 2.5-3 feet back and lowered to a few inches above the trans tunnel.
Finding the exact center of gravity height is a major pain in the butt. Most of the things I've read say it requires four corner scales and the ability to raise the rear about two feet and the ability to put the scales back under the tires at that height. After some geometric trig, you can figure the exact COG of the car. I wish it was easier because I would have liked to do some before and after comparisons on my car to capture changes after a few mods.
FWIW, the very popular Howe spindles used in many oval track classes are only a 1" drop with 10* SAI. You then use a slotted upper control arm mount to move the inner pivot up and down to alter roll center location and different length arms or shims to adjust camber gain.
One reason we didn't go too low on front roll center was to reduce static negative camber and reduce the require spring rates to resist roll. We could then step up sway bar rates and still have some suspension travel for the nasty bump entering turn 3. I'd guess a street car would appreciate a similar set-up.
I would be interested in hearing Peter's feedback as he uses the F body spindle with a tall ball joint to raise the roll center, thus shortening the moment lever arm and reducing lateral leverage on the car. This also has the benefit of requiring less negative camber to compensate for the body roll and it creates a more equal roll between front and rear. Some anecdotal evidence on these changes would be nice to hear.
The rear roll center height is found at the mid-way point between the center of the axle and the imaginary line drawn through the spring eyes. So with a high arch drag race spring, the roll center height is below the spring eye plane. On something like a zero arch oval track spring, the roll center height is going to be above the spring eye plane.
So, by raising the front roll center, you are shortening the moment lever arm. Conversely, you could lower the center of gravity height, but that's much harder to do. Most old timers I've spoken to tended to estimate it as roughly camshaft height and just on the interior side of the firewall on a mostly stock, street going car. The oval track cars I was familiar with, this location was 2.5-3 feet back and lowered to a few inches above the trans tunnel.
Finding the exact center of gravity height is a major pain in the butt. Most of the things I've read say it requires four corner scales and the ability to raise the rear about two feet and the ability to put the scales back under the tires at that height. After some geometric trig, you can figure the exact COG of the car. I wish it was easier because I would have liked to do some before and after comparisons on my car to capture changes after a few mods.
FWIW, the very popular Howe spindles used in many oval track classes are only a 1" drop with 10* SAI. You then use a slotted upper control arm mount to move the inner pivot up and down to alter roll center location and different length arms or shims to adjust camber gain.
One reason we didn't go too low on front roll center was to reduce static negative camber and reduce the require spring rates to resist roll. We could then step up sway bar rates and still have some suspension travel for the nasty bump entering turn 3. I'd guess a street car would appreciate a similar set-up.
Last edited:
DionR
Well-Known Member
This is my current idea for the hub and caliper mount:
The difficult thing for getting the rotor located correctly is the back of the hub to caliper mount surface. My previous idea had used several stacked plates to make up the offset, which worked ok and even accounted for the LBJ bolts and captured them in the spacers.
The problem is that plate is that there is a tolerance on the thickness and the more plates you stack up, the more potential variation compared to the target thickness.
I am hoping that a part that is CNC bent by SendCutSend might have better potential for hitting the target.
The small slots are so the bends don't distort anything. These would get welded up in the final assembly.
This comes with some concessions in that nuts need to be welded.
It also has tubes and plates to fill in the corners.
The other bigger change was a single 1/2" plate for the caliper mount ears instead of two 1/4" plates. I figure the thickness tolerance doesn't matter if the spacer assembly sets the offset from that surface. It might vary the overall track width a touch, but I doubt it is more than the factory tolerance.
That's as far as I got on it. Have to build the UBJ mount and figure out what that might look like.
The difficult thing for getting the rotor located correctly is the back of the hub to caliper mount surface. My previous idea had used several stacked plates to make up the offset, which worked ok and even accounted for the LBJ bolts and captured them in the spacers.
The problem is that plate is that there is a tolerance on the thickness and the more plates you stack up, the more potential variation compared to the target thickness.
I am hoping that a part that is CNC bent by SendCutSend might have better potential for hitting the target.
The small slots are so the bends don't distort anything. These would get welded up in the final assembly.
This comes with some concessions in that nuts need to be welded.
It also has tubes and plates to fill in the corners.
The other bigger change was a single 1/2" plate for the caliper mount ears instead of two 1/4" plates. I figure the thickness tolerance doesn't matter if the spacer assembly sets the offset from that surface. It might vary the overall track width a touch, but I doubt it is more than the factory tolerance.
That's as far as I got on it. Have to build the UBJ mount and figure out what that might look like.
DionR
Well-Known Member
The above layout is still using the Scat Pack caliper and rotor info. I don't have any of the needed S197 info and I'm not sure the nut needed for the LBJ bolts would fit between the caliper mount plate and the hub. The SP rotor has a depth of 58mm overall and the Mustang one is 46mm. That's potentially a 1/2" shorter on the spacer assembly and the current setup only has 0.338" before the nut is into the hub. Not saying for sure that is the difference in height, the caliper can have a large impact on this. Just guessing right now since I don't have an info.
My thought right now is to forge on with the SP stuff and if I want 15" brakes I will use GT350 calipers and an adapter that does from the ears to a radial mount caliper. Not going to be off the shelf, though.
And I think the SP setup is the better one anyways when compared to the S197 4 piston setup. Where the S197 setup shines is being able to easily upgrade to 15" brakes, the SP stuff only really has the HC option and that doesn't fit under 18" wheels.
My thought right now is to forge on with the SP stuff and if I want 15" brakes I will use GT350 calipers and an adapter that does from the ears to a radial mount caliper. Not going to be off the shelf, though.
And I think the SP setup is the better one anyways when compared to the S197 4 piston setup. Where the S197 setup shines is being able to easily upgrade to 15" brakes, the SP stuff only really has the HC option and that doesn't fit under 18" wheels.
DionR
Well-Known Member
bjkadron
Well-Known Member
I agree. When I did my initial calculations it had very good geometry. Most of the time I planned to invest was just with tuning spring/swaybars/shocks etc.
I would think a cut piece welded to risers like the red one in post #22 would be the easiest to integrate with this. I'd also be curious what it would cost to get something machines comared to this many pieces with welding everything together. With that much welding you also open up to warping which would change dimensions.
DionR
Well-Known Member
My aversion to machined parts is cost and access. There are online places similar to SendCutSend but every time I have gotten a quote it was pretty expensive.
But I haven't tried to see what a piece like that would cost to have machined. Maybe I will git a quote and see.
That was one nice thing about using multiple flat plates, not as much welding and (in theory) should be pretty trouble free for things like warping. But it's fairly bulky.
I wouldn't be surprised if the bent plate idea is a flop and the accuracy just isn't good enough.
bjkadron
Well-Known Member
Yeah that makes sense. I'm mostly worried with the tolerance stackup and stuff actually fitting together. I think if you got creative with the design, a machined piece could be fairly reasonable. I'd like to get a mill and be able to machine stuff myself. But no luck so far.
Mopar_Taxi_Guy
Well-Known Member
The four piston S197 Brembo caliper is designed to work with a 14" rotor and an 18" wheel. Thats what the GT500s and Boss 302s had. The 15" rotor didn't come about until the 2013 GT500 which used a 6 pistion Brembo similar to the S550 6 piston caliper and 20" wheels.
The caliper brackets like the ones I have made and the ones that you can still buy from another guy, used the S197 calipers and rotors becase they were readily available years ago and cheap to get. The SRT calipers were at least double to quadruple the price at the time. Plus the same bracket can use any of the S197 brake packages allowing 15" to 18" wheel fitment with off the shelf OEM parts. Same with the cost of the S197 rotors compared to the SRT rotors. The offset of the Mustang rotor and caliper arrangement also lends itself to working very well with cut down rotors turned into hubs or the use of Dr. Diff hubs without needing an offset caliper mount when using drum brake knuckles. The caliper only needs some slight shimming to get it centered over the rotor.
Last edited:
DionR
Well-Known Member
I don't argue that the Mustang rotor works well on a cut down rotor, but I am guessing it won't fit with the S550 hub. There is only so much room between the caliper mounting plate and the hub. Not that there aren't other possible ways, nor that the offset on the caliper wouldn't fix it some. I am just guessing and my guess is that it won't fit with my design.
Maybe if the LBJ mounting bolts were a countersunk. Trick there is, the way the S550 hub mounts, you most likely have to be able to capture the fastener because the hub has to be bolted to the spindle before the LBJ is bolted up. Unless something different is done like move the hub up a little. Right now, with the hub at the same centerline as the stock spindle, it covers the LBJ bolts enough to make it a bit of a puzzle. That's why I captured the bolts and then put a final spacer over the top in my earlier iterations, and why the nut is fixed and welded in the current one.
The distance from the caliper mounting surface to the face of the hub is 2.6953" with the SP calipers and rotor. The hub is 1.8102" tall, leaving .8851". The nut I am using is 0.5471" tall, so the gap between the back of the hub and outside of the nut is only 0.338". If the S197 rotor is 12mm shorter, that means it is possible that the distance between the surface the caliper mounts to and the back of the hub could be as short as 0.4127". Not enough room for the 5/8" nut I have in there.
Looking at your part above and thinking about my kit for the SP calipers on the disk brake spindle makes me think the difference is less than the 12mm that worries me. So maybe there is room for the nut. I just don't know and I don't have any parts to try and lay it out and see. So I'm not saying it won't work, but I am saying I have concerns and decided to stick with what I have for now. I can't see spending $140 for a caliper to measure off of just to see.
As to price, the SRT rotors are a touch cheaper and the calipers about $20 more each, matching brands. There is the Cardone brand of the SP calipers that is only $7 more per caliper, or you grab the closeout calipers for $42 each. I would say there's really not much difference between the two setups.
When I started look at SP calipers, they were about the same difference, or maybe the SRT calipers were a touch cheaper. Been awhile, but it wasn't much of a difference in cost about 2 years ago when I first started trying to adapt them.
swisswill
Well-Known Member
A lot has gone on here since I last checked in and, per the usual, I continue learning from you guys.
There’s a lot here so far and I want to make sure I’m tracking with parts selection. So far the hub is S550 with SP calipers and rotors? Hard to tell from the back and forth but is there a preference toward Mustang parts but unsure if they’ll work because we don’t have measurements to confirm? If so, I’ll order a caliper and rotors and send them to you DionR, if it works awesome, if a no-go because of the steering arm, then we know and can move on with knowledge.
As for machining, once we have a design, I’ll send it to my guy and to Michigan Metalworks to get other pricing options.
I haven’t made it to my car yet to hunt of my AutoWares CD but I’ll try to get there this weekend.
There’s a lot here so far and I want to make sure I’m tracking with parts selection. So far the hub is S550 with SP calipers and rotors? Hard to tell from the back and forth but is there a preference toward Mustang parts but unsure if they’ll work because we don’t have measurements to confirm? If so, I’ll order a caliper and rotors and send them to you DionR, if it works awesome, if a no-go because of the steering arm, then we know and can move on with knowledge.
As for machining, once we have a design, I’ll send it to my guy and to Michigan Metalworks to get other pricing options.
I haven’t made it to my car yet to hunt of my AutoWares CD but I’ll try to get there this weekend.
gzig5
Well-Known Member
I'll almost guarantee you that if the base material thickness tolerance variation is a concern for you, a bent part is never going to be smaller than the couple thousandths that rolled plate varies. That has been my experience from 25 years in product design/developement/quality. What kind of tolerance are you looking for on the finished part? Depending on the material and size, there may be plate that starts out more accurate. You could have the base material Blanchard ground in lots. Or best might be to have a single machining operation to dust off the critical points after assembly, preferably an easily accessible surface. But as you know all of this costs to one degree or another. There are a lot of small one-man shops and/or hobbiests like myself that are capable of doing good work at a much lower cost than a commercial shop would charge. You have to remember there is normally a setup fee and then the piece part cost. The more parts you do at once, the cheaper it gets per piece. Sometimes volume can make or break a project. If you are just doing single pairs at a time, the machining might break it. But if you get multiple commitments or self-fund a larger lot, it may make it work. You also need to consider surface finish like powder coating or paint, to make it a more desirable product.
bjkadron
Well-Known Member
The other thing I was thinking is if you could make it modular, you could make both sides the same which would help with Machining costs and only change the steering arm and the UBJ connection point. But that may be difficult because I don't think they are symmetrical.
DionR
Well-Known Member
Correct, my model is currently laid out around the S550 hub and SP rotor/caliper.
Yes, there is a potential benefit to the S197 rotor and caliper. Upgrades to a 15" package are easy, they seem to have worked well in their application, prices aren't bad, they are probably a touch lighter than the SP setup and they should (in theory) fit the hug with no slope (the center bore on the SP rotor is bigger than the pilot on the hub).
The rotor info is easy, don't need those to measure from. It's just the centerline of the rotor to the mounting surface of the caliper that I need.
I would hate for you to spend money to send me a caliper. I hadn't thought about it until now, but I could buy one and return it after getting the measurements. There aren't any that I find locally, but I can order one from Autozone with free shipping and return it to the store so no one is out money.
I could setup a model that uses a machined spacer instead of the sheetmetal one. It would probably be a different shape than the one I have right now so it would be a different design.
DionR
Well-Known Member
Not really sure what tolerance I would want. The first design used (1) 1/4" plate, (3) 0.187" plates and (1) 0.074" plate. SendCutSend's tolerance on the 1/4" and 0.187" plates is +/- 0.008 while the 0.074 plate is +0.006 and -0.004. So the stack up could be +0.038 to -0.034 or 1/32 either way. I think at the time I figured if the stack was off a little, I would shim the caliper some, provided it wasn't short.
SendCutSend's tolerance on bent parts is +/- 0.015" bent to edge, and I would assume the material thickness tolerance would stack with that. Seems like that is potentially better than the stacked plates.
The other idea with the bent sheetmetal is to potentially throw it in a mill after the corners and crush tubes are tacked/welded and face of the ends of the flanges and other parts so the height is exact. Wouldn't be a difficult process, shouldn't even need an CNC mill. I guess you could do the same thing with the stacked plates, it just seems like more work to me.
Finish is so far down the road, I can't even see that bridge. And since I didn't get into this project with the idea of anyone selling them, I wasn't even looking at making them more desirable.
DionR
Well-Known Member
The first idea with a bunch of laser cut plates would have had the UBJ centered over the hub and would have been buildable as a left or right based on how the plates were stacked.
With the idea of moving the UBJ back and engineering in 7 degrees of positive caster, I suspect it could still be done that way. Certainly the caliper mounting plate and spacer assembly could be flopped to make it left or right.
The bigger issue is if I try and use bent plates for the top instead of varied lengths of plates and a square block.
The initial idea was to set the angle of the UBJ mount using the ends of the plates to create the surface. Like this:
But I think I am going to try more of a heavy tube and some bent parts and see if I can't make it a little more pleasing to the eye. If so, it won't be as reversible as the plates were, but it wouldn't be any more than just ordering the parts opposite.
Still working hard to avoid any machining being required. I can work something up if someone wants to get stuff machined, but so far I'm not ready to say it can't be done without it.
The original idea was something a guy in his garage could build with just a welder, a couple of clamps and a tapered ream.
swisswill
Well-Known Member
I’ll let you make that call, but I’m happy to put some skin in the game. You obviously have a lot of time on this and I’m good throwing in some coin if not time.
The bent sheet metal spindle is very similar to the Speedway Motors G Force upright, and if send cut send can do it at reasonable prices, could potentially be done in a slightly above average garage. As I look closer at that upright, seems like that might work if there was a 1” drop built into the spindle. I recall a page or two back some discussion about building in some drop.
Thinking about caster, is it really necessary to build in 7 degrees? Seems like three or four would be sufficient given stock should be able to get 3.5-4. That top piece could be square with an offset for caster, then taper-reamed out in a home garage. Just a couple thoughts.
Appreciate all your design and other work on this Dion.
Mopar_Taxi_Guy
Well-Known Member
DionR
Well-Known Member
Well, I failed but I did try. There is a Pull and Save yard about an hour from me that had a 2005 Mustang so I loaded up my tools and dial caliper and headed there in the hopes I could pull the offset between the face of the hub and the caliper mounting ears. But no dice, someone had pulled both spindles before I got there.
But the drive had benefits of it's own as I had plenty of time to noodle over the issue. And I think I have a solution so we could run the Mustang brakes and the S550 hub.
Unfortunately, I will be out of town for a week starting Monday so I won't get any time on it until I get back. And I still need the offset before I can start playing with it.
But the drive had benefits of it's own as I had plenty of time to noodle over the issue. And I think I have a solution so we could run the Mustang brakes and the S550 hub.
Unfortunately, I will be out of town for a week starting Monday so I won't get any time on it until I get back. And I still need the offset before I can start playing with it.
DionR
Well-Known Member
Appreciate that.
I don't think dropping the hub will work, but I do plan to raise the UBJ some so an extended one isn't required. That should match the F-Body spindle with the extended balljoint without the addition of a non-standard part. I still have to decide if I will move the UBJ in some to reduce scrub radius or just leave it alone, and I will need to make sure it still clears the 18" wheel since the UBJ won't be in exactly the same spot as the F-Body setup.
The 7 degrees is all me. I've been researching late model cars and found the S197 Boss 302 had 7 degrees, plus others. @72bluNblu mentioned once (if memory serves) that he ran 7 degrees for awhile and then dialed it back to 6. I figure if I build in 7, 1 degree could be dialed out if desired or 7 could be run. And by engineering it in, the LBJ stays level and the OTR is in more of the as-designed location.
Thanks. Been working on this idea since SEMA 2023.
DionR
Well-Known Member
That's great info! Definitely will need that at some point.
But no, I wanted one of these pieces of info at 90 degrees to the above dimensions:
Either the distance from the CL of rotor or hub mounting surface to the mounting surface of the caliper ears. The above numbers are for the SP caliper/rotor.
With one of those numbers, I could figure out how much room there is between the back of the S550 hub and the plane of the caliper ears on the new spindle.
So I have run as much as +8° caster on my Duster. Currently I’m running +6.5°, which is pretty close to the tipping point for the steering becoming much heavier with turning.
With +8° the steering was noticeably heavier, and the jacking effect from the positive caster was very noticeable as well. I did run the car for quite awhile like that though.
The steering gets quite a bit easier dropping below 7°, but dropping below 6° with the 275’s and the tracking issue starts to become noticeable and the steering doesn’t get all that much lighter.
So I generally set about +6.5°. No less than +6° and no more than +7°.
That upper number though has a lot to do with my 16:1 manual steering! With power steering it wouldn’t be as much of an issue, although I do think the jacking effect would mean you’d want to keep it under +8°.
DionR
Well-Known Member
So here are Hotchkis' recommendations for alignment in their UCA kit for A-Bodies.
Seems like designing in 7 degreed positive caster maybe isn't so far off the mark.
Seems like designing in 7 degreed positive caster maybe isn't so far off the mark.
-
Similar threads
