Oooohhh preeetty

quote Originally posted by Bloozberry: That should be a really challenging project Will. You'll need to start a thread in the "Other Cars" section as I'm sure there will be a lot of interest. One of the challenges I'm sure you've already considered is how you're going to mount the longitudinal 348 engine into the 308's engine bay designed for a transverse engine. I'll subscribe if you start a thread.

I will eventually.
I have other things going on in life right now.
The 308 and Fiero have similar wheel bases, but are proportioned very differently. The 308 has a much larger engine bay and the occupants are pushed further forward than in a Fiero. People have done "358" builds using 355 drivetrains in 308 bodies. The 355 drivetrain is dimensionally the same as the 348 drivetrain, so I know there's enough room. What makes it work is the oddball layout of the 348 and 355 transaxles. They put the diff immediately behind the engine and the clutch at the very back end of the transmission.

I've occasionally had similar problems with Summit. They always make it right. I've also had some very good results with them, in terms of adding parts to their catalog that weren't previously there. As long as one of their suppliers carries it, they can get it, whether they show it or not.

Spent the last hour catching up Blooz - as always - unbelievable work you are doing. I learn new tricks every time I come in this thread. Thanks again for taking the time to share all your hard work.

Pat

How's the quality of the shocks? They look nice, are they for a street car or a track car?

Thanks for your feedback BlackEmrald, katatak, and zkhennings. It's always rewarding to see someone is interested. For zkhennings, the quality of the shocks seems pretty high given the replaceable bushings and the rebuildable nature of the shocks. They're really light weight too, and if price is any indication they should be pretty good. I'm not sure how to tell if they're for a street car or a track car... but I suspect the rebound adjustability using the 18 position knob will allow the characteristics to be changed to suit several applications. Time will tell whether they dampen my 350 lb/in springs effectively.

I'm a little behind where I'd like to be in the rear suspension construction, but then again it's summer. I also just got back from visiting the Yarmouth area for a week and checking out PFF member Yarmouth Fiero's convertible frame modifications. I brought down a bunch of the F355 fiberglass body panels for him to try out on his car... it looks stunning with the roof removed. Check his progress out here: www.fiero.nl/forum/Forum3/HTML/000137-7.html

I'm also wasted time and am a little disappointed with Summit Racing. After sending me $450 worth of wrong rod ends, they paid for the return shipping of the parts but advised me that I couldn't exchange them for the rod ends I wanted. It seems their supplier either can't or won't ship the new part numbers to Canada, and Summit won't act as an intermediate shipping destination. They only "drop ship" parts, meaning they only arrange their suppliers to ship directly to their customers. That's pretty pathetic service. They refunded my money but not the taxes nor duty, nor customs fees, nor shipping expenses I paid the first time around... all of which I now have to apply for on my own time because of a fault on their website. Anyways, Jegs was more than happy to sell me the correct part numbers for $5 more apiece adding $100 to the total cost. They should be here in 2 weeks.

Of course not having all the parts didn't stop me from progressing with the fabrication of the suspension mounts. I started with the mounts for the lower lateral links by making a template from my drawings and cutting the 8 mounting ears from 3/16" thick steel plate:



Here I just temporarily sat them on a spare length of 2"X3" tubing similar to the cradle side rail to mock them up and make sure they were identical in all respects. Once properly shaped, I carefully measured the location of the mounting hole, center-punched them, drilled a pilot hole, then finished up with the 1/2" bit in the drill press:



Next, I wanted to build a jig that would ensure the four mounting ears on each side would be at the right distance from each other and also have all the holes line up on the same axis. To build the jig, I found a cheap pair of female rod ends that measured the same width as the ones I've ordered from Jegs. Here are the parts that go into each side, just don't mistake the long bolts that I temporarily screwed into the rod ends as the lateral links... they're just there to help me mock up the installation:



Then, I slipped all the parts onto a foot long 1/2" fine threaded rod using jam nuts to locate the mounting ears at the right distances from each other and to make tack welding them to the cradle side rails easier. The threaded rod will be removed and replaced by two bolts (one for each pair of mounting ears) once welded to the cradle, but for now it serves to keep the holes concentric. From my earlier drawings, the center line of the rod ends must be 145 mm's apart.



Here's the completed jig sitting on a section of square tubing mimicking the cradle side rail:

I would add .003-.005 shim into the stack with each rod end... If you weld it like that, the rod end and spacer stacks will be extremely difficult to R&R.

Thanks for the tip Will. There's another way to make sure there's enough room between the mounting ears. By welding the mounts along the bottom outside edges, the mounting ears will spring ever so slightly apart at the tops when the weld cools and contracts. Tightening the mounting bolts when assembling the lateral links later on will close up the gaps.

Here I've tack-welded the mounting ears for the lower lateral links to the cradle side rail using the alignment jig. I'll finish welding them properly the next time I remove the cradle from the car:



As expected, when I removed the 1/2" threaded rod, the tops of each pair of mounting ears sprung apart slightly by about a 1/2 mm giving a little slack to remove and reinstall the rod ends and spacers. (You can't actually see it in the photo... but what you do see is the distortion from the macro camera lens I used to take the picture).



With the mounts tacked in place on the driver's side, I mocked up my "stand-in" rod ends along with the spacers using the 1/2" dia grade 8 bolts, nuts, and hardened washers that I intend to use in the final assembly. I threaded the bolts so they are head-to-head to give me the maximum possible clearance for the axle shaft to pass between them.



And here's the passenger side tacked in place as well (I only have two stand-in rod ends while I await delivery of the proper ones, so there aren't any in this photo).



With the lower lateral link mounts basically completed, I turned my focus to where the new upper link mounts would be installed. I started with the aft upper mount since I knew it would be the most difficult and I wanted to get it done. If you go back to my drawings earlier on, you'll notice that the upper mounts get welded directly to the top of the lower frame rail. After studying the rail in that area, I realized that the sheet metal from the strut tower was sitting in the way on top of the frame rail acting as a sort of doubler. I marked up the area with a red marker so that once removed, I would have access to the frame rail:



Apart from the surrounding sheet metal, that section of the strut tower metal was also being held to the frame rail with two big spot welds, so the first thing I did was drill them out:



Once they were gone, the zip wheel in the angle grinder made short work of removing the hashed area leaving full view of the underlying frame rail:



That then allowed me to take accurate measurements to draw up a cardboard template for one of the aft upper mount ears. I used my drawings to guide me in making the correct shape for the template and used the chart of suspension coordinates I created earlier for the Lotus Suspension Analyzer program to locate the hole in the template in exactly the right place.



Unlike for the lower mounts, the contour of the frame rail changes so the two ears for the aft upper mount will have to be slightly different shapes, making it more challenging to keep the pivot axis (the bolt passing through the ears) aligned in three dimensions. Creating the template for the second mounting ear is next.

[This message has been edited by Bloozberry (edited 08-25-2013).]

After lots of fooling around with the laser level and a pair of rulers, I finally got repeatable measurements to trace out the template for the second mounting ear. If you look carefully, there are subtle differences between them to accommodate the changes in profile of the lower frame rail:



These are the parts that go into making the upper aft lateral link mount (once again I used my female rod end as a stand-in for mock up purposes):



This is what it looks like once it's assembled... this photo also gives a better idea of the size of the mount:



And here it is mocked up onto the lower frame rail (the red thing is just a magnet to hold it in place for the photo). I'll tack weld the ears to the frame rail while it's mocked up like this to ensure the alignment stays true:



And a close up:

looks great but are you going to put 1/8 plate in the area for extra strength that upper metal is thin and should be reinforced

Thanks for your observation Bubbajoe. I don't believe the upper mounts will see much load considering the geometry. When you consider that in the stock configuration only a single point locates the top of the knuckle (ie the strut pushrod in a bushing), the bulk of the side loads are resisted by the lower lateral link mounts. (Accelerative and decelerative forces are transmitted through the trailing link.)

Nevertheless, a quick look at the forces applied to the suspension of the outside rear wheel in hard cornering shows that that lateral forces exerted by the road onto the tire (red arrow) transform into a moment (pink arrow) about the bearing, which is then applied to the upper and lower link mounts (blue arrows) by the links.



The leverage from the tall knuckle favors the upper link mounts and reduces the load considerably compared to the lower lateral links which take the brunt of the load. If you bear in mind the total lateral load on each of the two outside tires won't exceed half of 1G (or approximately 1500 lbs), then that means the bearing will see about a 1970 lbft moment that is countered by the upper and lower link mounts. Solving for the forces at each mount, the lower link mounts will need to absorb around 630 lbs each and the uppers will need to absorb about 260 lbs each at max lateral G's, which isn't very much. Normal driving probably won't generate half of those forces.

Even still, when you look closely at the cross section of the lower frame rail where the aft upper link mount is attached, the frame is already doubled up in thickness due to the left-over strut tower material (except for the very top surface of the rail). I'll have to weld that second layer to the frame rail properly to gain any strength though. Then, when you consider that this area of the rail is framed by two vertical structures (the remnants of the strut tower) that connect it to the upper rail, I believe there's sufficient strength to handle the anticipated loads. But I invite others to express their views as well.

(edit: error in drawing)

[This message has been edited by Bloozberry (edited 08-31-2013).]

Don't forget to consider the inverse load as well. That would wind up pushing the upper mounts toward the center of the car. The extra reinforcement might be warranted factoring the leverage of the mount arm to the frame rail.

True, but the load direction you suggest will only ever occur on the side of the car that's on the inside while going around a corner, and given the weight transfer the loads will be considerably less than those generated by the outside tire.

I'm also trying to argue my way out of reinforcements because I have precious little room for them between the inside edge of the frame rail and the transmission in that area.

the reinforcement is only needed where the upper brackets are welded in and will not affect the trans space it is just to prevent tearing of the base metal and increase the load area

OK, I see what you mean. I actually show flanges on these mounting ears in my drawings to do as you say... spread the load over a greater surface area of the rail. That was back when I thought I'd be able to "bend" these ears to have flanges. The trouble is the parts are just way too small and made of steel that is way too thick to bend with any accuracy given the tools I have on hand. I did have a closer look though to see what I could do about giving the mounts a greater area where they meet the rail and think it will be worthwhile to weld some flanges onto the ears. That'll follow after I mock up all the parts to be sure everything fits and aligns.

I've made some progress on the forward upper link mounts over the last couple days. I needed to locate these mounts 252 mm further forward of the centerline of the aft rod end so I measured along the sheet metal and made an access hole in the sheet metal to expose the top of the frame rail:



I also needed to make a small slit in the weld flange to gain some clearance for the aft mounting ear which overhangs the inside edge of the frame rail by a couple mm's:



Creating the templates for these mounts was a little more difficult that I expected. They have to position the rod end so that when the link is installed and the rod end is centered, the link will sit at 42 degrees to aft upper link, AND a line drawn through the centers of both the front and rear upper rod ends has to be parallel with the car's longitudinal axis. To make matters more complicated, the frame rail runs at 7 degrees from the longitudinal axis of the car (when viewed from the top). I have to admit there was a little head scratching but I got the templates figured out.

Actually fabricating the mounting ears went quickly because all I had to do was trim up some ears I had screwed up earlier while making the aft link mounts.



I use my belt and disk sander to square up all the edges and fine tune the final dimensions of the mounts:



And once built up, you can see why it wasn't a straight forward task to imagine what they would look like.



This is the top view of the driver's side frame rail with both upper link mounts mocked up. It's a nice clean installation.



And this is the view from the wheel well. I'll refine the size and shape of the window in the sheet metal once I get the proper rod ends. I've gotten an email from Jegs saying they should arrive by Friday... Yay!

Well... this project seems to be about taking one step forward and two steps back. I ran into a rather significant snag yesterday after making the templates for the upper links at the top of the knuckle. The rod end on the forward upper link doesn't clear the wheel. I could've sworn there was plenty of clearance in my drawings so I had to go back and see what went wrong. It didn't take long to realize that I hadn't drawn the inside diameter of the wheel but rather the outside diameter of the wheel lip, to which I made the suspension components fit. After doctoring up the drawing with the correct ID of the wheel (red circle), the interference became apparent. To make matters worse, the drawing doesn't include the head of the bolt running through the rod end, which would dig even further into the rim. Drawing all this stuff out was supposed to eliminate these kinds of errors!



So ever since then, I've been trying to find a solution that minimizes having to go back to the drawing board. I tried every conceivable way to package the rod end differently and keep the same configuration of the links but it doesn't look like it's possible. So the next thing I tried was to swap the angled link to the back and the true lateral link to the front. This would work since the upright part of the knuckle is offset towards the front of the car giving me the room I need for the angled link towards the back, like this:



That looked very promising until I realized that it would adversely impact the direction of toe gain under jounce, effectively making the car oversteer. I didn't want that after all the effort to make this car handle correctly.

At the moment I believe the easiest way to fix the problem is to make both upper links parallel to each other and make them both true lateral links, like the lower ones. I'll keep them the same length as the original upper aft link so no other parameters except toe gain should change. I'll lose toe gain throughout the suspension's travel, but that's better than having the toe go negative. Also, having one upper link angled was a way to triangulate the upper portion of the knuckle over a larger area, making it less susceptible to unwanted movement at the top of the knuckle. Having the upper links parallel to each other will impact that characteristic somewhat, although I don't think it's that critical since the top of the knuckle in the stock Fiero only has the single strut mounting point, plus whatever side to side resistance there is in the spring to keep it from moving or twisting. Anyone see things differently?

Tomorrow I should get my rod ends in the mail... that'll help me mock things up so much more easily. I'll work up a new drawing showing my latest concept and post it tomorrow.

why not lower both links 3/4 of an inch using 2 plates bolted to the upper part of the spindle upper mount and pick up the spring rod at the same time

Thanks for your suggestion Bubbajoe, but lowering them 3/4" would have a significant impact on the roll center movement and a smaller, but important impact on camber change throughout the suspension travel. I need to keep all of the pivot axes in the same locations and orientations to keep my nearly perfect theoretical performance characteristics. All I'm willing to do is slide the rod ends along their current axes to find better packaging otherwise I'll end up throwing all that work out the window.

quote Originally posted by Bloozberry: So ever since then, I've been trying to find a solution that minimizes having to go back to the drawing board. I tried every conceivable way to package the rod end differently and keep the same configuration of the links but it doesn't look like it's possible. So the next thing I tried was to swap the angled link to the back and the true lateral link to the front. This would work since the upright part of the knuckle is offset towards the front of the car giving me the room I need for the angled link towards the back, like this: That looked very promising until I realized that it would adversely impact the direction of toe gain under jounce, effectively making the car oversteer. I didn't want that after all the effort to make this car handle correctly. At the moment I believe the easiest way to fix the problem is to make both upper links parallel to each other and make them both true lateral links, like the lower ones. I'll keep them the same length as the original upper aft link so no other parameters except toe gain should change. I'll lose toe gain throughout the suspension's travel, but that's better than having the toe go negative. Also, having one upper link angled was a way to triangulate the upper portion of the knuckle over a larger area, making it less susceptible to unwanted movement at the top of the knuckle. Having the upper links parallel to each other will impact that characteristic somewhat, although I don't think it's that critical since the top of the knuckle in the stock Fiero only has the single strut mounting point, plus whatever side to side resistance there is in the spring to keep it from moving or twisting. Anyone see things differently? Tomorrow I should get my rod ends in the mail... that'll help me mock things up so much more easily. I'll work up a new drawing showing my latest concept and post it tomorrow.

A) Lower the knuckle end of the problem link so that it bolts to the knuckle via the lower bolt instead of the upper. Can you keep sufficient anti-squat with that configuration?

B) Having the upper links AND lower links set the toe complicates adjustment. Are you sure that the upper link can affect toe in jounce while the lower links remain rigid? VAG uses a 5 link front suspension on the B5 and C5 (and maybe newer, I don't know) bodies. The configuration results in enormous caster change over the range of steering travel. Look up info on that design, as it's conceptually similar to what you're doing. Also, here's some Honda discussion regarding a similar rear suspension: http://world.honda.com/news/1997/t970702b.html

C) Having the upper link behind the axle as drawn will result in poor anti-squat at ride height and divergent (meaning it gets worse) anti-squat as the suspension compresses.

D) With the two upper links parallel, the knuckle will be free to flop fore and aft around the aft pivot of the lower trailing arm.

I suppose a bigger wheel is out of the question...

Bob

Have you thought about just swapping left and right knuckles? It would move the strut centerline back and give you more room for the upper fore link.

------------------
yellow 88 GT, not stock
white 88 notchie, 4 banger

Sorry I meant to speak to you about this issue earlier, I hit exactly the same issues as you though I have different width and offset wheels. I had to use 15mm concentric wheel spacers to get round this problem.
Though in my case because I don't have a specified body for the car so it does not matter if the wheels stick out a bit further. It is not a perfect solution but it was a solution.

Thanks for your input guys...

For RCR: I take it your comment was tongue-in-cheek... new wheels & tire$$$

For ccfiero350: The thought had occurred to me to flip the knuckles side to side but that then relocates two of the three outboard pivot points behind the wheel centerline... I'm not sure what the impact would be, but it's worth looking into further if nothing simpler comes up.

For Will: Thanks for the link to the Honda system... it's amazing how many similarities there are as you said. As for the rest, I understand some of what you've said but not all of it:

quote Originally posted by Will: B) Having the upper links AND lower links set the toe complicates adjustment. Are you sure that the upper link can affect toe in jounce while the lower links remain rigid?

You're right, the toe can't change with lower links being rigid. I misspoke since I had an earlier configuration in mind where I had planned to use poly mounts in the lowers, but now I plan to use spherical rod ends which don't have any compliance.

quote Originally posted by Will: D) With the two upper links parallel, the knuckle will be free to flop fore and aft around the aft pivot of the lower trailing arm.

I agree now that I've had a chance to look at this option with a clearer mind.

quote Originally posted by Will: A) Lower the knuckle end of the problem link so that it bolts to the knuckle via the lower bolt instead of the upper. Can you keep sufficient anti-squat with that configuration?

If I lower only the outboard end of the problematic link, the system will bind as the two upper links try to scribe different, non-concentric arcs. I played around with some stick diagrams and the newly lowered forward link would become too long in jounce and too short in rebound as compared to the aft link, which would try to twist the knuckle in the steering axis but which would be resisted by the lower links. However, if I lower both the outboard and inboard pivot points of the forward link by an equal amount (in the range of 25mm), both links scribe nearly the same arc (within full jounce and rebound limits). I think that might do it, though I would like to examine the alternative a bit more ie, having the angled link at the back instead of the front.

quote Originally posted by Will: C) Having the upper link behind the axle as drawn will result in poor anti-squat at ride height and divergent (meaning it gets worse) anti-squat as the suspension compresses.

I'm not sure I understand why that is. My (limited) understanding of calculating anti-squat doesn't take into account the location of the pivot points relative to the centerline of the wheel. For example, in this case, wouldn't the anti-squat solely be a function of the height of the instant center, which is found by the intersection of the angle of the trailing link axis (angled upwards to the front) and the axis created by the upper inboard link mounts (horizontal)? I need to understand this because this configuration seems like a cleaner looking solution if it doesn't adversely affect anti-squat (or other parameters).

quote Originally posted by ccfiero350: Have you thought about just swapping left and right knuckles? It would move the strut centerline back and give you more room for the upper fore link.

X2

The inboard lateral link brackets will need to be moved as well as the inboard upper link brackets and the trailing link would need to be longer as well, but those are all fairly minor changes that should have minimal impact to the geometry you have worked so hard to obtain.

Another option is to move the upper outboard pivots inboard about 25mm along the same angle as the upper a-arm. This will likely give you the needed clearance, while only shortening the upper link. It will have some impact on the geometry, but probably far less than lowering the upper outboard mount.

Or bolt the rod ends to the upright directly through the top upright hole, then angle the links as they go inboard (equally about the upright centerline) to get about 6-8" of separation between them by the time you get to the frame rail.

quote Originally posted byBloozberry: Drawing all this stuff out was supposed to eliminate these kinds of errors!

EVERYTHING works on paper! .................but in the real world..somebody had to say for the first time somewhere: "Back to the drawing board."

You gotta have a plan...you had a plan. The best anybody can ever do is to have a plan and implement it to the best of their ability, make changes when and where necessarry, and stick to the plan till it proves itself unworkable...in which case, you then come up with a new plan! I don't think you'll have to go that route.

Wish I could shoot an equation to you or give you an altered drawing that'd fix it "just like that", but I'm no draftsman or engineer, just a backyard craftsman that likes to "tinker", so I can't really offer any constructive ideas, only moral support and the faith that you will work it out, as you have with anything/everything else you've ever done that had to be changed a little here or there. I'd almost bet that you'll figure out something that not only fixes the error, but improves the design in the long run.

Anyway, still enjoying seeing your work and how things are progressing.

HAGO!

What about changing from two upper links to a true A arm? Retain your existing inboard mount locations and the rear outboard location that clears.

These are all great suggestions (and a boost to my sour mood), so thanks Fieroguru and Zac. I also appreciate your words of kindness there Sage. You're always there giving positive comments and encouraging members to do their best.

I'm glad you chimed in there Zac because simply "looking" at what might be great solutions is only a first step... any decision is going to be best made with the support from another Lotus analysis to see the effects on the kinematics. Hopefully you'll be able to crunch a few more numbers for me once I get a new table (or two) of coordinates put together.

From a subjective point of view, I think the solutions with the best potential so far are flipping the knuckles side to side or flipping the arms. Fieroguru, your idea of moving the pivots inboard by 25 mm would increase camber gain and move the roll center around among other things so it's not ideal. Your third option to simply use the available misalignment range of the rod ends is also an interesting idea, though the particular ends I bought only have a 10 degree range. As for your idea Zac, I'm not sure how I would go about attaching an A arm to the top of the knuckle.

Flipping the knuckles has a few other advantages:
a. it keeps most of the geometry intact, though I'd like to get a simulation done to see actual changes (if any). Although Will hasn't commented specifically about this approach, he has led me to believe there may be hidden problems.
b. it moves the shock bell crank further backwards giving me more room for the front shock mount;
c. it moves the rear calipers closer to the cabin making it potentially easier to find cables that are long enough;
d. it would be dirt cheap to implement.

On another note, I finally got my rod ends delivered today... yay! At $26 a piece (before taxes, duty, shipping, and brokerage fees) there's a chunk of change in this photo:

Can the upper links share the same bolt, and the forward link utilize a high misalignment rod end?
Aurora (my rod end of choice) makes rod ends that can tolerate up 22 Deg misalignment.
McMaster-Carr sells units rated for up to 32 Deg.
http://www.mcmaster.com/#rod-ends/=odsjhp

EDIT: McMaster measures total angularity, unlike Aurora, whom measures off bolt axis angularity.

[This message has been edited by FieroWannaBe (edited 09-05-2013).]

quote Originally posted by FieroWannaBe: Can the upper links share the same bolt, and the forward link utilize a high misalignment rod end?

Thanks for your input FieroWannaBe. What you suggest is certainly a possibility, that's essentially what Fieroguru's last suggestion was. One problem with using high misalignment rod ends at their limits is that a greater component of the load acts axially though the rod end, essentially pushing the ball out of the side. Most companies only state the radial load capacity (along the axis of the pushrod) but a general rule of thumb is that a rod end's axial load capacity is about 10% of the radial load capacity. If I went this way, I'd have to be certain that the loads wouldn't be too great in the axial direction.

quote Originally posted by Bloozberry:

Another alternative is to swap locations of the upper a-arm tie in point to the lower OEM strut hole and move your vertical transfer link tie up a little. You will get more camber gain out of it to boot.

------------------
yellow 88 GT, not stock
white 88 notchie, 4 banger

quote Originally posted by Bloozberry: I'm not sure I understand why that is. My (limited) understanding of calculating anti-squat doesn't take into account the location of the pivot points relative to the centerline of the wheel. For example, in this case, wouldn't the anti-squat solely be a function of the height of the instant center, which is found by the intersection of the angle of the trailing link axis (angled upwards to the front) and the axis created by the upper inboard link mounts (horizontal)? I need to understand this because this configuration seems like a cleaner looking solution if it doesn't adversely affect anti-squat (or other parameters).

Two separate links should not be analyzed like an A-arm.
In side view, your lower longitudinal link (stock '88 trailing arm) and upper longitudinal link form half of a dragster 4 link rear suspension. It should be analyzed as such. With the upper link behind the axle, you have an asymmetric Watts' linkage. When the upper link is inclined more steeply than the lower link, the instant center will be behind the axle. As the suspension compresses further, the side-view instant center rises and gets closer, decreasing anti-squat.

Can you lower BOTH pivots of BOTH links? You should be able to do that while preserving your camber and forward view instant center behavior. That would also make you build a pocket into the frame rail for the inner pivots. If you do that, you dramatically reduce the twisting load on the frame rail that you have now, replacing it with a pure bending load, and come up with adequate reinforcements right off.

quote Originally posted by Bloozberry: One problem with using high misalignment rod ends at their limits is that a greater component of the load acts axially though the rod end, essentially pushing the ball out of the side. Most companies only state the radial load capacity (along the axis of the pushrod) but a general rule of thumb is that a rod end's axial load capacity is about 10% of the radial load capacity. If I went this way, I'd have to be certain that the loads wouldn't be too great in the axial direction.

With separate links, like you have, only pure axial loads can be supported through the link. The rod ends will only have radial loads (unless they bind). If you change to an rigid A arm then you will have to consider the axial load rating of the rod ends.

Dare I say custom knuckle?


ccfiero350 has done something of the sort with laser cutting if I remember right.
https://www.fiero.nl/forum/F.../000094-10.html#p385

I know it might add quite a bit of cost to it, but you should be able to do all the assembly work, and you are really only wanting to change the relative position of the "strut" mount in relation to your axle centerline to not negatively effect the rest of your suspension points.

Chris

quote Originally posted by Will: Flipping the knuckles will make your lower links into a parallelogram

You're assuming that he wouldn't shift the inboard locations.

Keep up the good work blooz. Remember that if this was easy everyone would do it!

[This message has been edited by Jefrysuko (edited 09-06-2013).]

quote Originally posted by ccfiero350: Another alternative is to swap locations of the upper a-arm tie in point to the lower OEM strut hole and move your vertical transfer link tie up a little. You will get more camber gain out of it to boot.

quote Originally posted by Will: Can you lower BOTH pivots of BOTH links? You should be able to do that while preserving your camber and forward view instant center behavior.

Somewhere back around page 12 or so I had originally considered using the lower hole in the knuckle for the upper control links, but it was impossible to make the roll center behave in that configuration. I played around a LOT trying to make it work exhausting a dozen or so ways to salvage the idea back then, but it just falls flat. I'm nearly certain that using the lower hole would mean major concessions in the kinematics.

quote Originally posted by Will: That would also make you build a pocket into the frame rail for the inner pivots. If you do that, you dramatically reduce the twisting load on the frame rail that you have now, replacing it with a pure bending load

I've decided to strengthen the frame rail in that area with 2" angle over 10 or so inches in length. It will also restore the decreased cross section in that area due to the bite taken out for the stock spring clearance), returning it to a rectangular shape. As for the magnitude of the twisting load on the frame, you also have to consider that the center of the rod end is only 38mm above the top of the rail... so the moment arm isn't very long.

Thanks also for the explanation of the anti-squat behavior... I'll still need to go over it in my head when I have more time. For now it seems the best alternative is the one suggested by ccfiero350 to swap the knuckles side to side. I'll put together a set of coordinates for Zac to (pretty please) analyze this scenario. For the record, as Jefysuko mentioned, I will move the inboard lower link mounts to line up with the lower knuckle mounts.

Here's a quickie modified drawing (I've shifted the lower inboard mounts and upper inboard mounts, but haven't changed the trailing link nor the forward shock mount. Rather than lengthening the trailing link, I'll probably just move the mount backwards and keep the same angle):

There....... that wasn't so hard now was it.....

Great job Blooz. Nice to see so many knowledgeable PFF members sharing their wealth of knowledge as well. All the more reason to post our build thread on this forum.

[This message has been edited by Yarmouth Fiero (edited 09-06-2013).]

quote Originally posted by Will: Two separate links should not be analyzed like an A-arm.

This. What you have assembled resembles a 5 link suspension. None of the links are fixed relative to each other. They only provide the suspension the control of one degree of freedom each.

Yep... understood.

I've just fired off the suspension coordinates with the flipped knuckle to Zac88GT to run on his Lotus Suspension Analyzer program. With any luck, he'll see my email and have a chance to run them before too long. :fingers crossed:

Blooze,

Does your latest proposal shorten the wheel base, or are you relocating the forward trailing link pivot to the rear to compensate for switching the uprights? If I understand correctly, you wanted to maintain the stock length of the trailing links. The discussion you have opened seems very productive. It's good to see so many well thought out ideas and suggestions.

Ken

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'88 Formula V6
'88 GT TPI V8