Could you use the C5 axle shafts, then? Or at least the outer stub? Or is that what you're already planning?

 

The oddball 26sp of the S10/trailblazer front diff is the determining factor for CVs. If it's not S10, S10 ZR2, Trailblazer or Astro, then the CV must be custom. I'd like to keep an off the shelf axle for this build

Those CVs all have 27sp outer sections, so to keep 5x4.75" bolt pattern, only S10 hubs fit the bill

Keeping this CVs constrains overall track width to a few options. The shortest being pretty darn close to stock 3rd gen
Modifying for S10 hubs was an unforeseen obstacle, but not a difficult job either. I had less than 2 hrs buzzing both sides

 

Makes sense. I was thinking that w/all of the custom fab that you've done, CAN do, why not build a S10/C5 axle...but you just explained that.

 

I would really like to do something like this in the future as well. This thread is awesome

What about grafting a bmw awd front subframe to the third gen chassis?
Ive done similar with a friend when we put a bmw x5 front subframe under his older 7 series bmw to make all wheel drive. Worked really well
Just find one with the right track width and modify the chassis to fit
Then you can keep the stock geometry of whatever subframe you choose, and set ride height with coilovers and caster camber plates
Maybe I am overlooking something large like the compatibility of bmw front differential with gm transfer case....

 

I'd think that you could "fix" that in the front DS.

I think that^ is an innovative way to solve the problem....everything in and about this thread is innovative, which is why *I* love reading it and the updates, so much. It's situations like this, and your (wlink) suggestion, where it can pay off big time to take a few rough measurements and have a pretty good 3D concept in your head....then go walk around a junk yard for a couple hours and measure some candidates, stare at things....sometimes magic happens w/unlikely donor parts.

 

With the friends project I helped with, he went the route it seems the OP is taking, he got knuckles that could accept a CV axle and had to hack and chop and make custom control arms and his geometry was all effed up. To where when put put it in reverse the car would sink down in the front, and raise when in drive

So I gave him the idea to just snag a front AWD subframe from another vehicle and adjust the chassis the chassis of car to fit the new subframe, and within 100hours we had the car back on the road again driving perfectly. This way all the geometry is kept as long as you can clear the oil pan, which could be solved with an external wet or dry sump if it’s too tight
Ride height could to taken care of with coilovers as I mentioned above, and then the strut towers could get chopped up to make the camber and caster correct.

The trouble I see with subframe swap with steering racks is many of them are rear steer which doesn’t work well with traditional rear sump LS stuff
external oiling could solve all this though
I know from reading OP’s previous threads he is knowledgeable with wiring and electrical, etc, there could be a possibility to use steer by wire… or hydraulic steering so steering shaft clearance would be less of an issue

Another thing I am thinking of as I’m typing this is Dodge awd(think charger, magnum) front subframes. V8, and bit it all under a hood…

Best of luck to OP! I want to see this nearly as much as you do running

 

Have there been any road-going cars with full hydro steering?

Everything I've ever driven or been around with full hydro steering has zero road feel and the steering wheel never returns to the same spot. Tractors and big offroad trucks. Yes, I realize I just brought tractors into this discussion, lol. But I have a lot of seat time in tractors with hydro assisted mechanical steering that will drive 43+ mph down the road and they drive like a sports car compared to the more common tractors with full hydro steering.

 

Eventually, a design must be chosen if just to move on with a project. I'm sure there's plenty more to optimize on this design, but I don't see any glaring failures
The scrub rule of thumb was nixed.I found examples of successful road course cars having 2-4" on some seriously wide tires. We'll give this a try and see
Should it be a bust, swapping to high offset wheels and remaking the A-arms is a relatively minor change. That can be done after the car is completed

I laid out the hubs using the two different CV lengths min/max as a constraint. For CVs, short means base S10, long ZR2. I was able to get a track width pretty close to stock 3rd gen. From there, rough roll center was assigned and the control arm geometry basically filled itself in. Steering will have to be offset plate style because there is zero chance a centrally mounted rack like that clears anything engine/diff related


The CAD dimensions were input into VSusp for some dynamic testing. This link should save all of my data into one giant url
default values

Roll center is acceptable. L/R roll oscillation is meh, but not terrible. Camber gain curve is nice and flat
Expecting +/- 2" of tire travel and +/- 3* body roll
Both variables can allow for another +/- 1 without the metrics going crazy. This should allow some adjustment later on like ride height


Time for a full scale mock-up. While I'm building that, I'll draft a side view to start planning the anti-dive/squat mechanics
I'm matching C5 for caster (6*) and anti-dive (5* on UCA)
Anti-squat will take some planning because AWD incorporates the torque split at the t-case. I'll map it out for 50/50, 60/40 and 70/30 and probably average it. We'll see if common Fbody LCARBs are enough and if the slightly shorter MM TA will change much
CG will become important there

 

Not surprising, I scrapped the above design after a long conversation with a retired roadracer. He illuminated several points I was unclear on. I also ran across an excellent tech heavy forum that is most up to date with custom suspension designs

This post is mostly an info dump on some of those points

KPI/Scrub radius
If using an existing knuckle, then KPI is already set. Scrub radius can be tweaked by changing wheel offset, adding spacers or changing tire diameters
Excellent reading
https://www.locostusa.com/forums/vie...116ed699b4a295
https://www.locostusa.com/forums/viewtopic.php?t=20885

Instant centers. Above I had a question about control arms that either crossed IC lines or did not
Turns out it doesn't matter. Crossed guide lines are most common for custom designs because small changes in control arm pivots/length can result in larger changes
Opposing lines are common on most OEM systems
The part that does matter is the length of the guide lines, called the virtual swing arm length (VSA)
Target 2-3x track width
Too short leads too erratic roll center and excessive jacking
Too long requires excessively stiff springs/sway bars
https://www.locostbuilders.co.uk/vie....php?tid=75181
https://www.pistonheads.com/gassing/...f=135&t=445503
https://www.locostusa.com/forums/viewtopic.php?t=21701

Roll center height (front)
There is alot of contention on this one
Dean in this thread has some good points for having a high roll center
https://www.thirdgen.org/forums/susp...do-i-make.html
Most corner carving forums shoot for a relatively low, but not below ground roll axis to reduce the corner jacking effect
What the actual value is seems to be secondary to the relationship of ground level, roll axis and center of gravity

Camber gain
<1* per inch
.6-.9* for the first inch of suspension travel seems to be ideal. UCA/LCA length ratio seems to have the greatest effect on this
https://www.pro-touring.com/threads/...in-is-too-much
https://www.locostusa.com/forums/viewtopic.php?t=12843
https://grassrootsmotorsports.com/fo...s/25771/page1/

Analyzer ranges
3* of body roll is pretty standard for sports cars. Racecars plan for less, but have very stiff spring/sway combos
+/-2" of tire travel is also standard
That's helpful when setting limits

Lastly, all this is best guess. As long as the design isn't obviously wrong from the start, minor deficiencies here or there will not cripple a car. Every relationship will benefit one thing and hamper another, so it's about compromising the design

Atleast it put some of my questions to bed and I'm confident enough in my design to proceed forward

 

I just got caught up on your build progress and feel bad that you have to totally redesign the front suspension. But like you said this gives opportunity to make it better.

In your spindle selection, you disregarded the 4th gen fbody spindle. I think you should reconsider. Yes it is tall, but that allows space for cv shafts and coilovers. With the DSE c5 bearing kit you can run c5 hubs. brakes, and many styles of 17 and 18 inch wheels. You can also use the 4th gen rack so rack travel and steering arm length match. There are lots of aftermarket options for upper and lower A arms to help give you the adjustability you need.

 

Last night I ordered some parts and then went down a much deeper rabbit hole than expected: Ball joints

Since I'm fabricating my own LCAs, I need a machined sleeve to hold the BJs

There seem to be 3 common sizes for press fit and 3 more for screw in. The screw in's are all the wrong taper, so press fit it is
K6117 2.198 OD 1.989 ID
K6145 2.37 OD 2.09 ID
K6141 2.495 OD 2.184 ID

Reading through more BJ specs than I care to go over, I settled on 3 candidates and ordered one of each to measure because the website specs are usually missing key dims or contradictory
K6145 3rd gens, most 70's cars 2.100 OD
K6345 C4 2.082 OD too loose for the 3rd gen sleeve
K6537 C5,6,7 1.935 No sleeve compatible

Once the parts were in my hand, I decided to scrap the sleeve idea in favor of a .25-.375 plate with a precise hole bored in the end. These will allow more surface area when welding to the A-arm tubes for a stronger bond. Most sleeves are ~1" tall, so joining to the tips of 1.5"sq tubing didnt see like the strongest joint

More parts from the machine shop... ugh

I decided on the C4 BJs. 3rd gens flat out didn't fit. C4 and C5 were identical on the pin, but the press-fit base was a different dimension for some reason. C4's were cheaper, so they went into the rockauto order






I pressed out the upper BJs because they needed to be replaced. Lots of guys on the corvetteforum were stating the C5 had proprietary pin tapers and replacement uppers damaged the UCAs. I then realized I was terrible at measuring tapers. CAD is great at precision like that, so I could overlay my measurements vs nominal tapers and see what matched up. Spoiler: none did. I assume that the bored are slightly mushroomed or I measured a burr etc. Instead, I grabbed up all the BJs and tie rod ends I had in the shop and dropped them into the C5 knuckle holes. C5's use the common GM 2" per 12" taper ~10*
The rub is how far up on that cone it fits. Nothing I had on hand was the correct depth, but all passed the sharpie test

I tried some MII parts and their 7* tapers were all floppy fits

Saving these for later
Tie rod end catalog. Not all dims are given, so trial and error method is expected. I'll probably just buy C4 and C5 ends to save time
https://www.moog-suspension-parts.co...e_rod_ends.asp
Inner catalog. This is more useful once I determine overall tie rod length
https://www.moog-suspension-parts.co...r_tie_rods.asp

The rest of the catalogs look super useful for the future. CV boots and tie rod links in particular

This popped up too so I had to include it
https://www.suspension.com/universal-dust-boots.asp

The tubing should be in shortly, so I can finish the frame stub

 

I had this problem when I was trying to find ball joints for the C4 suspension. I found a housing that would press into the LCA, but had the wrong pin taper/length. Found the correct pin taper, but the housing was too small. I finally had to go to Howe Racing and get modular ball joints and mix/match to fit (even their C4 ball joints weren’t right). In the end I used a 2.100 housing with a 3/4” extended C4 tapered pin (the Howe BJ’s use the same size ball in the housings).

 

Mocked up the oil pan

Big 2x4 frame rails should be permanent. The rest are temp. The silver rods are the LCA pivot axis. The UCA mounting plates are getting plasma cut because they're semi complex for a hand grinder. The rest of the fab parts should be in sometime next week






I dunno, it just looks... huge
CAD to metal always feels different, but this just looks out of place large. We'll see once the controls arms are tach'd and mocked up. Adding a mockup block and headers may help it look more normal. TBD
28.5" between the frame rails

I am lost on trying to accurately measure caster once the suspension is assembled. On CAD, it's easy because parts float in space until the user specifies where to mount. Imaginary lines are easy to draw through objects and measure to an unobtainable level of precision. Really drawing a blank on how to to check my work without going to an alignment shop. Or how to build in adjustment without skewing everything

 

Saving this to compare to actual

default values

 

Answer my own question

Basic answer is to turn the wheel a measured angle (20*) and compare camber gain

There are probably better videos on the subject, but these get the point across

 

I've been following along with great interest. I appreciate all the tech you're posting here... a little late, you've answered the question, but came in to say I use Longacre caster camber gauges to do my alignments and this is the method they preach. glad you got it!

 

I took a few quick measurements on my stock 91 TA and overlaid them in CAD vs the AWD suspension

Looks close enough to continue

Red 3rd gen
Teal C5 AWD

 

Made some progress on the mock-up stand

I built a LCA out of scrap 1" tubing. The only critical dim was the overall length


This is why I made the LCA from scrap metal first. I had no idea the BJ would be maxed out. Will need to bake in 15-20* for the final


I also found these high offset wheels are much less forgiving of LCA width than expected. the final will have to be VERY narrow for most of its length. With this width, the wheel can only turn 20-20* each way


I remembered to bring the CV axles and headers from home this time. Found another error in my measurements. I measured min/max lengths with the CV laid flat. At ride height, it's approx 12* which allows one of the tripod bearings to poke into the boot. Too short to run like that. On the bright side, I can compress it quite a bit. I'm going to try a trailblazer CV before declaring custom axles. I have approx 2" of compression where TB CVs are 2.3" longer(based on rock auto dims). TBD


More moving bars around and the DR header fits. I wasn't expecting issues with it



Despite my measurements, the PS did not fit directly
Since it was only one tube, I considered modifying the header, but ended up cutting the frame rail


I sliced it at an angle and offset it 1". I should still have tire clearance, but will have to wait and see. Alternative would be to totally disassemble the frame assembly and move the two rails outwards

 

One of the hardest parts of this mock up has been knowing when to temp attach a bar vs permanently. Since so many things are occupying the same space, permanence has been fleeting
I decided the rack had to take precedence, then the LCA from mounts. The t-bird rack fit the tightest to the pan/diff area of the racks I had, plus it's long travel will give the best shot at having a proper turning radius
A local machine shop is making extensions to turn the 15/16"x20 F to 1/2"x20 F so I can bolt on a rack end plate


Lots going on here
Blue is LCA pivot axis. Front mount only needs to clear the steering stuff. Rear can be anywhere that doesn't interfere with the diff/header
Red is the offset tie rod approx location and rough shape of the plate. Since the plate will travel with the rack, there needs to be a bunch of clearance
Green is guide rod so the plates can't rotate down
With the rack crossmember figured out, the front LCA mount can be fabricated. The rear has the most freedom


My next big quandary is a spring. With the current UCA, there is no chance a standard coilover fits. With the wheel being so tight, I don't think a custom UCA would grant enough clearance either

Current ideas, good and bad:
Push rod coil over. I can't fit it where it normally goes, so move it. The rocker geometry would be tough to solve
Transverse leaf spring. Between C4, C5,C6, C7 there are an absolute boatload of springs to try. Down side is it would go under the already low oil pan and droop further under the ball joints. Not very confident in this route
Finally, torsion bars. I tried S10 bars and they were simply too long. I've thumbed though a few threads about old streetrod guys using sprint car splined bars. Also considering VW/Porsche bars. Sprint bars have the largest range, since I don't have a clue where to start. The VW bars are more costly per set, but are also more compact

Something to think on

 

Wow Pocket, you've got quite the packaging problem going on and it looks like you'll need a Rube Goldberg solution to get it all to work. I don't have the depth of knowledge about different suspension and steering systems that you do, as most of my work has been with 70's, 80's, and 90's GM cars, but I really think you should look at the 1998-2002 fbody for your build. The tall spindle can accommodate the vette spliced hub assembly, and the lower control arm has the 20* lower ball joint angle. UMI makes a very strong road race lca. Add the 4th gen r&p and you've got the proper travel and pivot points. As for the shock and spring dilemma, I was thinking a a yoke style lower mount that would straddle the cv axle might be a solution. Just a couple of ideas to toss around.

 

It's definitely taking some patience to figure out how everything gets packaged together. I believe this will work with some refining. Both a push rod coilover and torsion bar setup can be solved after the suspension design is complete

I nixed the tall spindle design early on in the build with the trailblazer frame. It's chassis ended up too wide to use, but the height was another hold up. Fbody or other spindles may be slightly shorter, but will still crowd the engine like 4th gens do. The tiny UCAs also have a much smaller window of acceptable camper gain before the numbers go crazy. The 1953 at the beginning of this thread used that excessive camber gain with the air suspension to actually fit under the fenders

 

Just spit balling for the CV axle issue, I stretched the chassis 1" per side and changed nothing else. Roll center raised 1/8" and the camber curve actually improved
Trailblazer CVs are 2.4" longer than S10 ZR2. Rough measurements at the current angles have approx 2" of compression. I'll stick in a TB CV to make sure before making any changes. If the hub sticks out 1/2-1" then the frame stretch should be sufficient

https://www.vsusp.com/#0.8%26project...left_camber%7D

The CAD is basically the same



3rd gen overlay is even closer. Bottom has 12mm spacers added
Scrub radius increased from .23" to .73", wheel base nearly identical to stock 3rd gen




Looks better all around

The wider frame should accept trailblazer CVs
It should also clear the PS header without modification. That will make it easier to mount and adjust the UCA plates. I have one last piece of 2x4 tubing to replace the zig-zag chunk
Wider frame should be more accepting of the steering rack compromises, so bump steer should be easier to wrangle
It should also give more clearance for this big gorilla to service the drivetrain

Unfortunately, it means the mock-up assembly needs to be broken down almost completely to start over. Atleast it's all tach welded

 

I'm feeling more confident about sprint car torsion bars

Here's a calculator to convert bar diameter/arm length to effective spring rate
https://www.speedwaymotors.com/the-t...eet-rods/29351

Here's a rough calculator to estimate spring rates (for coil springs)
I plugged in 850lb frt corner weight, 125lbs unsprung, 13" : 16" LCA mount points. Not sure the shock angle really translates, but 75-90* had minimal effect on the calculated spring rates. 350-400 for an aggressive suspension came out. Right in the middle for the sprint car bar options
The numbers are complete guesses, just to see how the spring rate changed
https://ridetech.com/tech/spring-rate-calculator/

The torsion bar can be further tuned by drilling multiple holes on the arms. Changing the distance from pivot changes the effective spring rate without changing the bar. If the arm is attached via heim tube vs slapper bar, then fine adjustments can be done easily




I found a youtube pushrod build focusing on the bell crank aspect. That seems a little more strait forward. For my build, I'd position the shocks almost vertically between the engine and radiator
Really interesting build. Not sure why it didn't come up when I was scouring the web for AWD conversions. C5 suspension too

Another C5 based pushrod suspension

Still too early to choose a path, so I'm saving these for later

 

I got a day and a half to work on the frame stub, so progress pics were sporadic as I covered as much as I could cram into the few hrs

Old frame was broken down, cleaned up and reassembled 2" wider. The PS step frame rail was replaced with strait like it was originally
PS header clears, steering rack clears, AC+brkt clears. Mounts were fabricated and are removable. Headers slip in easily. For being a relatively narrow frame (30.5" inside) there's a ton amount of room






With everything fitting nicely, I stripped it down and finish welded everything. I gave it a quick paint in the hard to reach places while the frame was bare
Then I started on the LCAs from 1 1/2" tubing. Using my 18ga mockup plate with a BJ again, the suspension clears when turning and bump/droops






Getting close

Laser cutter should be done with the UCA plates soon. Steering rack ends and LCA BJ cups are still at the machine shop
Kicking myself for not trying stock C5/6 LCAs to skip most of the hassle of building my own. Originally, it was to allow 14" LCAs when I had the super narrow track width design. Now the LCAs are 16" with tons of clearance. C5's are 15.95". Big question would be front bushing to steering rack clearance. That may be a job for later after the car is completed

 

Great build I love the affection to detail. The progress feels steady and impressive

 

Found a video explaining torque steer from a design perspective. Justifies my decision to center the diff and go with equal length CV axles. He also goes over KPI vs hub CL offset which I really cant help and CV angle (which mine are semi-extreme)


It makes more sense why more and more modern cars are moving away from the standard LCA to use separate control arms and virtual BJs to move the pivot axis and thus, the KPI outward

Kind of funny how the 1953 truck at the start of this thread had zero though put into the suspension and it still launched like a rocket with zero torque steer. About the only thing going for it was the equal length CVs

 

UCA plates came in. Still need the LCA/BJ cups to finish out the bottom

I spent some time looking over things and believe I found another oopsie. I believe the two strait frame rails need to hook down in the rear
Perspective is working against the photos, but it seems the frame rail will run strait into the steering column if left as-is. If they somehow clear, then the connection to the current SFC/frame section will be a sharp "Z" and ruin the strength of the tubing. If the frame rails would angle down, then the splice should be much closer in angle, and thus a stronger joint

Green is rear of the block
Blue SFC frame
Red new frame





A little more fab work
Atleast I haven't welded the UCA plates on yet...


Shifting gears, here's a very unique corvair flat 6 engine I wired in with a holley terminator ECU. Seems at home with the craziness of this thread
Crank/cam inputs for sequential port fuel injection
Coil on plug ignition
Will go DBW when the turbo kit is built
The braided flex hoses will be replaced with AN4 SS hardlines with the turbo too

Incredible change from the old 4x 1bbl carb setup

 

If you are going to continue sprinkling little bits of that Corvair project in here, you certainly won't hear me complaining about it! That's slick!

 

I took a few extra hrs for the project this week knowing my time will be greatly diminished soon. Two large projects will be returning to the shop soon, so fun car will have to wait for a while

Anyhow, here's what I was able to accomplish

The frame assy was broken down and the "kinks" added to the frame rails. I rolled it around and fully welded everything that was finished




The UCA plates came in, but were 3/8" instead of 3/16". I'm not sure if I want to use them after all. They either need to be recessed into the frame rails or have pockets machined in them to allow ample camber adjustments
Or I could cut some out of 1/8" by hand and put gussets behind them. So much for the quick and easy solution




Steering ends and BJ cups came in too
That's a stock inner tie rod end with the ball/rod cut off. A plug was turned to press into the modified tie rod base. It has a basic 1/2" 20 thread cut into it


Here's a mockup piece showing how the offset steering arm will look approx centered. The offset plate will need to be substantially thick and have gussets pointing towards the wheels
I'm still kind of leery on this design



I forgot to take a pic of the BJ cups, but no matter. Just some 1/4" plate with a precise hole bored, then a 15* bend
I recessed them into the A-arm tubes, fully welded and then wrapped the perimeter with 1.5"x.120" strap. Hopefully that's strong enough
The spring below is literally the cheapest spring/sleeve I could find on amazon. I need something to mock-up width wise as I try to cram a spring into this contraption. It will NOT be a part of the finished build




Next up, check my work vs the CAD model and Vsusp numbers whenever I have the free time. It may be a little while before I update again

 

Awesome, Jon, just incredible.

Just got back from Utah wilderness on a BLM road that was washed out. Had to backtrack 100 miles with no internet. We were dejected until we ran into the Safari Party Rally! Mostly Porsches modified for Safari, but some others as well. Amazing what people are doing - car craft. Some cool pics in their gallery: https://www.pelicanparts.com/swapmee...25_2/Page1.htm

 

^Money pits^

You live in UT?

 

No, but visit often.

Out in the wild, miles from anywhere, you just never know what kind of fabrication and fun you're going to run in to.

 

Personally, I'd be inclined to use those 3/8" plates. You would need substantial gusseting for 1/8" and that may take up space needed for other things later on. Minimal gusseting needed for the 3/8" though.

 

What I've been working on recently for the 1941 project. Scott's hotrods chassis





Wish my welds looked that nice



Man, that 9" axle assembly kicked my butt trying to align the carrier studs while man handling the 74lb 3rd member

 

This short week before thanksgiving is going to be pretty light at work so I'm spending some time on the AWD build

First up, CV axles

I was basing the build around S10 ZR2 extended front axles. I know the inner tripod bearings were protruding past the guides, but not how much. I hypothesized that trailblazer CVs being longer would fit since I also widened the chassis 1" per side. This was based on advertised lengths posted on rock auto. It was semi-accurate

I took the boot off the S10 ZR2 CV for a visual (which I should have done from the beginning)
I couldn't believe it was completely out of the socket and unusable


Next up was the TB axle. It's basically bottomed out and a pain to cram in there



Spinning the hub, the three bearing cups can be felt bottoming out as it rotates. At full suspension droop, it's basically seized
So, it looks like the LCA pivot points need to move outward a little. I plan to redrill the rear LCA pockets and fab new tabs up front. That should solve the issue without reinventing the whole thing
Hopefully, the new width will still fit the fenders. The alternative is to move the control arm points inboard about 2" per side which will seriously crowd the front diff. Not impossible to do, but harder than widening things slightly

Next up, I measured caster. Design was 6*, actual 4.8*
I believe the missing caster was from an error in the rear LCA pocket hole locations. They're about 3/16" inboard compared to the fronts causing the whole LCA to rotate slightly. With the holes being redrilled, this should self correct

 

awesome build
very impressed

 

Only had a few hrs today, but was able to redo the DR side

Trailblazer CV axle fits, caster was measured at 5.8*. Close enough for me
In addition to moving the rear LCA pocket holes forward, the UCA plate was biased rearward .25"
L/R axle CLs will be slightly off, but that's normal, even for production cars





Measuring caster from a loose suspension like this takes forever
First, a zero plane must be identified. Thankfully the frame rails are parallel, so a plumb bob from reasonably strait was marked off from the frame legs. I used masking tape on the floor for this
Then estimate 20-30* of turn L/R using a long strait edge clamped to the hub. Mark distant points on the tape and use the strait edge to mark where they cross under the spindle. This is roughly the pivot axis CL
From the CL and zero, +/-20* can be calculated on the floor
Clamp a strait edge to the hub and use the plumb bob to accurately turn 20* each way. Record the camber values at L/R and the sign
Obv, the spindles must be accurately positioned at ride height. Small inaccuracies accrue so the whole process will be a waste

Caster = (180/3.1415)*(Camber1 - Camber2)/(Angle1-angle2)
For my DR suspension:
Caster = (180/3.1415)*(2.7- (-1.2)/(20-(-20))
Caster = (180/3.1415)*(3.9/40)
Caster = 5.8*

Target for the PS will be 6.3*, but anywhere close will do. It takes quite a while to adjust the UCA plate and then redo the tape measurements each time, so I will not be chasing each tenth of a degree

 

Had a good chunk of time today

PS suspension is redone



PS caster measured out to 6.8* which was closer to the 6.5* target. The DR UCA plate was cut free and moved slightly back again
DR 6.4*
PS 6.8*
That's close enough

I started on the rack offset plates. It ended up being a BIG job, so if you don't want to get too deep in the weeds, skip a post or two down

To begin with, I drilled a few holes in some scrap .100" plate just guessing where to mount the inner tie rod



Using a laser clamped to the hub, I attempted to measure bump steer but couldn't get anything near repeatable. The tie rod joint was so tight it was actually twisting the plate which would wind up then pop free and jog the rack over some



After quite a while, I ended up scrapping the thin mock-up plate. I tried clamps on the steering rack shaft, fail. Tack welding the PS of the rack shaft to the frame. Still some flex
I drug up some very hole-y 1/4" plate to get the 'plane' set. It was tack welded to the frame on 3 corners. Still had some walk
The final culprit was the hub slowly turning. I had a bar and C clamp holding it, but they were slipping. A piece of threaded rod was finally enough to jam the hub solid. With that, the laser test became repeatable
Finally


After a half dozen holes and few drill bit resharpens, a tie rod position finally gave good results so I transferred it to a fresh piece of plate. This is still a rough in, but gives proof of concept
No idea what possessed me to fully weld the angle bracket on, but what's a few more minutes to make a new one later
You can see the guide rod down below. It's a pretty hefty 16mm solid SS rod. Common 12mm would have been plenty, but that's what happens when you don't pay attention to drop downs when amazon shopping
About a foot will be trimmed off once the steering is finalized


With the DR side roughed in, the scrap metal tacked to the rack shaft was cut free. I wasn't expecting it to move so smoothly first try. I guess the rack's soft rubber mounts flex enough to not bind as the system travels
Full travel right


Full right looking how it threads through the very tight space


Full left. Should be just enough room for a perimeter strap to strengthen the 1/4" plate


Now bump steer is directly correlated to ride height which isn't set yet. I plan to have slots machined in the final pieces of plate for some adjustment later. It's kind of wild how much the laser would move with such minor adjustments. I debated running heims on the inside, but tie rods are so ridiculously cheap I decided to stay with the standard vette stuff. I will have to replace the tie rods though, they only go into the outer sleeves about 1/2" currently. Good thing they were like $5 ea on rock auto

I have suitable replacements picked out thanks to the moog catalog I linked above. Kind of funny, step up/dn a fraction from what you need and the part cost can plummet drastically. The difference in a $40ea current production model parts, or add .02" and now it's an obscure 80's car that's exiting production $5ea. I'll definately keep that in mind the next time I replace inners on any other vehicle

Anyways, happy Thanksgiving

 

A little late, but did you see these ones?

https://www.facebook.com/groups/6158...ser/681745664/

 

Putting in a C4 vet IRS is not as difficult as you would think,

 

Coming from someone who has done this, I would do a 5th or 6th gen Camaro drop out rear. The geometry is already set and it is far more stable under load. With Pocket’s fabrication skills it would be quite easy to do.

 

Compared to the effort required for this AWD conversion, IRS is relatively simple. That said, I am not pursuing IRS at this time. An 8.8" axle is already done

After this build is completed, I may visit IRS conversion, but not at this time. There is already an enormous amount on my plate with this build