S10 - Take Two

My stack of big honkin' washers showed up today.  A little test fitting is telling me they will require some reworking to be useful, so I am not %100 sure I'll use them. 

The center bore is a bit too small, which I knew ahead of time, and had planned on just removing a bit of rubber from the bushings to make it work.  The lip on the frame mounts is keeping them from centering properly, and that is a bit of a problem.  I could stack and weld them on top of the mount instead, but I think that may not be as strong.  Regardless, I'll keep them around, even if they don't get used for this.  I figure I can find another use for them.

I'm taking a little time to make sure I get the rear frame right, and that means figuring out the rear suspension.  Here's a really rough idea of how I intend to lay it out:

I'll try to mount the lower links on the outside of the chassis, and the third link will likely be offset to the right side of the differential.  Might see about building a bracket that runs over it to center it better, though.  The shocks will likely stay in the stock position on the axle, using the leaf spring mounting plate.  Depending on how much threading is on the u bolts, I may need to add some shims to replicate the thickness of the leaf spring.  There are spring pockets on the Trailblazer rear end that I can transfer over to the S10's axle, and then I can build some sort of adjustable mount on the frame for ride height/weight balance.  If we do find some appropriate coilovers, I can instead strengthen the shock mounts, and just use them.

In an effort to save some fab work (and money), I'm using a cheap 4 link kit, that I intend to convert to 3 link.  It also has provisions for a panhard bar, but all the links are 24" long(plus heim joint length), and I'd rather run a longer one, so will probably re-purpose the one from the Trailblazer.  It's about 39" long, and I can shorten it and make it adjustable with some large diameter allthread.  I could also use the one that came with the ZR2 rear axle, but it is shorter, and the curve in it is designed to go up higher around the upper part of the rear differential.  At the very least, I should be able to reuse its bracket, as it just bolts to the axle.

I may have overestimated the width of tire I can fit with the link on the outside, but 275 or 295 should still fit on the wheels I have, and we could go wider if we find the right offset.

In order to get the cut right, I want to know where the lower link mounts are going to be attached to the side of the frame.  Since I've been meaning to relearn CAD at some point, I downloaded FreeCAD today, and started stumbling around.  First step I wanted to do was replicate the four link brackets.  This is about as far as I got:

I'm running into issue with fillets screwing up other dimensions, and on the axle side, I appear to not have every line connected properly, as it won't let me convert it to 3D.  Again, if you have any suggestions as to a different program to use, let me know.  I was hoping not to have to set up an account to use Fusion, and didn't like the idea of using Solidworks in the browser, but maybe I have to reconsider.  I may just trace everything out on corrugated cardboard(including multiple link lengths), and figure it out on the truck as it is.

With the heim joints installed (and with 1.5x diameter thread engagement), it looks like my max link length bolt center to bolt center will be 30", which seems longer than will be necessary.  The bigger concern is adjustability.  Without reducing thread engagement, or getting thinner jam nuts, the most I can change the length by is 3/8".  Having never messed with this kind of setup, I have no idea if that is enough.

One minor issue I'll have is the kit is designed for a 3" diameter axle tube, not the 2.75" tube I have.  Since I only need the bottom half of the bracket (unless I set it up to be able to be converted to 4 link), I think I can get away with it, maybe with a little gusseting.  A not so minor issue is backup parts.  I was planning on buying some spare heim joints to use for testing, so I wouldn't risk damaging the ones in the kit, then swapping to them right before the challenge.  However, they are a metric approximation of a 5/8" joint, and it looks like I can get right hand threaded ones cheap, but left handers, not so much(Edit:  found lefties cheap, so problem solved).  Need to do a little more digging.  I will at least have a few spares if I stick with the three link idea, and stay with rubber bushings for the panhard bar.

ComputerAD was annoying me so I switched back to CardboardAD.

With a 26" tire the center of the frame bracket will need to be 13" off the ground, if the holes in the bracket will be level with each other.  This is my preference, so the lower links can be level, slight upwards or slightly downwards.  It'd be nice if the lowest hole was more than 3.5" below the axle centerline, but I don't want to spend money for more brackets.  I'll make sure the upper link is raised more off the axle centerline.

Next step was to take the axle bracket to the axle, and measure forward from the holes to see where the frame bracket would fall with different link lengths.  Marked it up on the side of the frame.

I am trying to go with a minimum link length of 24" mostly to fall in line with Ron Sutton's recommendations.  The frame mount would sit here at 24".

I plan on using 2" square tubing for the mount, and want it to be completely below the top of the frame.  At 24", I would need to z the rear frame a minimum of 1" to achieve this.  Moving forward from there, it goes 2" for 26" links, 3" for 28" links, and 3.5" for 30" links.  Additionally, the more I z the frame, the more travel the rear axle will have before hitting the bumpstops.  I'd also like at least half and inch or so margin, as the plan is to make a mounting plate that bolts to the frame, and has slotted holes for small adjustments to keep the bars aligned with each other.  Not the easiest to clearly describe in text, so I'll end up either making a model out of cardboard or dig back into a CAD program.  All in all, the assembly will stick out about 3" from the frame, so I will lose that much in backspacing.  I'll still have about 8" clearance to the mounting face of the discs.  The Z06 wheels have about 6.75" backspacing, giving another 1.25" for tire width and flex, and a little axle articulation.  There are some brackets on the frame, but none of them stick out by enough to reduce clearance further.

I intend to spend a little time with an instant center calculator, in order to figure out a compromise for the link length.  If I mount the upper link in the same vertical plane on the axle side as the lowers, its max length before intruding into the cab is about 22".  I could, and probably will increase the length a bit by mounting it a bit rearward of the lower link mounts.  Just moving to the axle centerline adds 2" to the max length.  Going back the the Ron Sutton reading I've done, he appears to prefer an equal length upper and lower link.  Other sources seem to say you are good with an upper link at least 70% as long as the lower.  Then there's the S197 Mustang, with a much worse ratio, and it still can handle.  I am also going to try not to get too into the weeds here, but it is too cold to work in the garage for extended periods right now, so might as well do some more calculating until I can start cutting, grinding and welding.

I am also regretting not buying that fabricated diff cover off the Summit discount section last fall.  Every other "prefab-ish" solution I am finding for the upper link mount is considerably more expensive.

Didn't like the IC calculators that I was finding online, so I threw together a spreadsheet where I can enter link locations and sizes, and iteratively find instant center.  I then added added a few other variables, and can now get an anti-squat percentage based on an estimated center of gravity.  Going to try to figure out the math so I don't have to iterate to find instant center, then update the sheet for that.  I'd like to be able to adjust from around 50% to 100% to find a good drag strip setting and a good autocross setting.  May also play around in java again and see about writing a program.

Messing with the spreadsheet showed me that most of my IC adjustments will need to come from the upper link, since I have very limited adjustability for the lower links in the brackets I have.  I may need to get a better drill press, as mine is probably not up to making 5/8" holes in 3/16" steel.  Also, to keep this a roller for as long as possible, I'm going to keep the leaf springs on when cutting up the rear frame.  The engine/transmission may go in to get camshaft height to estimate CG, and make sure my driveshaft length calculations were correct.  The leaf springs will also serve to keep the axle located when mocking up the rear suspension. 

Figured out the trig to make the spreadsheet do more of my work for me, as long as I don't violate a few assumptions.  Yellow boxes are inputs, and the green boxes are output data of interest.

I noticed changing the upper link front pivot height was causing some pretty radical changes in anti-squat, so I was worried I'd screwed something up.  Plugged the numbers into an online calculator, and it looks like my numbers are right.  Instant center was pretty much dead on, and anti-squat was off by a very small amount, but I had to guesstimate how their system works, as the online calculator asked for crankshaft height, and calculated a CG value from there.  It looks like they added about 5".

If I get bored, I may start working out how it changes under suspension compression and rebound.  Although at that point, I really should start writing a program vs continuing this way.  Would be neat to come up with a graphical display, too.

Dig the thought process sir.  Very excited to see how much progress you are making on it darn near solo!

In reply to 84FSP :

Not entirely solo, thanks to you and others!

There are two goals with this number crunching.  First, come up with decent configurations for both drag and autocross that won't cost much if any extra cash.  Second, to come up with an autocross setup that doesn't have any surprises.  That way, the pro driver can concentrate on getting faster, and not have to worry about fighting the car.

Couldn't stay away from the garage forever, and even though it is still only in the 40s, the wind has died down somewhat.  Yesterday, I ran out and picked up some more metal to use in the rear frame z and the lower suspension mounts.  Today, I shuffled the frame around a bit more, and cut off the remaining cab mounts, and a few bed mounts that were getting in the way.  It'll still need a decent amount of grinding and de-rusting before it can be cut.  And, I intend to re-weld the front cab mounts before that, as they will be a bit less accessible once the frame is shorter.

Today was supposed to be the day to add reinforcements to the front cab mounts, and weld them back on, but the wire wheel wasn't taking the rust off well enough, and the flap disc wouldn't fit in the nooks and crannys.  They are getting an Evaporust bath for now, and I hope they turn out alright tomorrow.

Since that was out of the question, I shifted the frame back, and cleaned up the spots where I will be cutting it. 

I'd like to make the cut further rearward, but this is about as far back as I can go and keep all the work on the straight section before it begins kicking up in the back.  I would like to avoid everything being as complicated as up front, and just plan on using 2.5" square tubing for reinforcements.  Due to the positioning, the center cab mounts will be a little bit more complicated, and the rear cab mounts will be a lot more complicated, but I am certain I can make it work.  Might have to sacrifice the ability to convert the three link to a four link, though.

Finally, snagged a $50 aluminum seat this evening.  The team will all have to try to sit in it to see if it fits, and if so, I'll try to come up with a way to mount it to the S10 seat rails, so we can move it back and forth to fit our widely varying heights.

With Jo-Ann going out of business, I may stop there to see if there are any deals to be had on upholstery fabric and foam.

Enjoying watching your progress. Both of my sons own multiple S trucks. And I had an 84 that I was originally Isuzu powered that I 4.3 swapped in the early 90s. We just finished notching and plating the front cross member of my youngest sons shortened to fit a F body pan LS. He also moved the cab mounts back 3/4 inch. Not nearly as radical of mods as yours but some parallels. Keep up the good work looking forward to seeing your future posts and the truck in person at the challenge next year. Pan notch.

In reply to eastsideTim :

If you were closer, I'd give you the bench seat out of my S10, the passengers side has good foam still, drivers side is falling apart though, after 360K miles.

In reply to 81cpcamaro :

I was actually thinking of sacrificing one of the bucket seats for its foam, and I think the seat covers that came with the truck have some vinyl panels, so that might be an ultra low budget option.  The main reason not to is I may want both normal seats back in it after the challenge,  2nd gen S10s are still fairly common in junkyards around here, though, so getting a replacement wouldn't be difficult.

In reply to madmrak351 :

Is he lowering it with springs?  I seem to recall reading 3/4" is how far you are supposed to move the cab back to get the front wheels re-centered in the wheel well when you do that.

It appears the Evaporust works.

They weren't perfect, but were good enough to tack some reinforcements onto them, and weld them back on the frame.

Hopefully, the next update will be the rear frame cut and re-welded, but I was doing some thinking today, and there may be some snags I'll have to deal with first.  I'll be taking a look at it tomorrow, as I want to be as ready to cut the frame as possible at the end of one work day, then get to work on it early the next day to give me as much time as possible to work on it, as the frame ends up hanging outside of the garage a bit when it is as far back as possible.

Today was a day of no visible progress.  Lots of measuring, lots of staring, and lots of thinking.  It turns out I really screwed myself over with how I have the cab supported.  Changing that at this point would be a ton of work, so I have come up with a rough list of things I need to do to work around it, and that's about another day's work.  Another concern is that there may be no way to take diagonal measurements, so it is possible I will weld the frame back together out of square.  I'll try to take multiple measurements between holes on the frame to limit that chance of that happening.  Finally, after 25 years and nearly 200K miles in the rust belt, the frame is no longer rectangular in the back, but is a bit of a parallelogram instead.  88 degree angles on the left rail, and 89 on the right rail.  I am trying to accept that any screwing up of the frame will have to be countered by suspension alignment.

On the positive side, someone bought the Trailblazer's transfer case, front differential, and oil pan, so that's a bit back in the budget and less stuff taking space in the garage.

In reply to eastsideTim :

Long ball joints on the lower control arms, 2" drop spindles, 1/2 coil cut on zq8 front springs. The move is mainly to allow the engine to be as far back as possible. If the aesthetics improve that would be a bonus.

I think I've come up with solutions for all the issues I saw.  The frame will get an approximately 2" z, as any more than that will force major floorpan surgery, and much less will significantly limit rear suspension travel.  There'll be 9.25" taken out, and I can remove a little more if need be, such as if I screw up the cut and have to square it up.

Here's the driver's side rail:

Yellow shows the marked cut lines, and red is where I have taken reference measurements.  There are actually 4 holes up front, just didn't get them all in the picture.  Measurements on each side either match or are off by 1/16".  I am hoping having 4 measurements per side will help me square it up properly for welding.  The frame is too tall for the portaband, so the cuts will be with a sawzall and/or an angle grinder.

To keep the rails from moving out of position, the front section should be kept in place by the carrier bearing crossmember.  For the rear section, I added a couple pieces of all thread.

Based on what I've seen online, the rails usually want to spread out, so this should handle it fine, and even allow me to fine tune it a bit.  If they want to bend inward, I may be in trouble, as the all thread is just as likely to get pretzeled as it is to hold everything in position.

Weather is supposed to be bad this weekend, and I need to do this with the garage door open and the frame sticking out, so it might be a few days before I get to it.

We think of cars as perfect, tight tolerance produced things, but they give a lot of clearance and slots in mounting holes for a reason.

One interesting thing I'd seen that put things into perspective is that the tolerance stackup on Fox body Mustangs when they'd weld the tubs together allowed for a full inch of difference in length from one car to the next.

Newer cars aren't much better.  There was a lot of consternation when trying to fit the rear subframe into "Colin" because the brackets and such were made to exact tolerances but the actual tub of the car was welded together straight as a banana.  

In reply to Pete. (l33t FS) :

I want to say I read 1/2" out of square was perfectly acceptable to GM on their full frame cars back in the 60s/70s, and 1/8"/3mm is the current standard.  I am aiming for 1/8" as a maximum, but I should allow for more, considering suspension adjustability and this thing being 25 years old now.  Heck, I might just eyeball it once it is together, and say "that looks good".

Keep rolling sir - I love the potential for turbski in the budget...  All the HP...

Rear frame is cut.  The sawzall kept walking when I tried to start the cut, so I ended up using a cut off disc on an angle grinder to cut the top and outer parts of the frame rails.  If I'd had the clearance, I'd have done the same with the rest, but I needed to just use those cuts as a guide for the sawzall.  Unfortunately, it wandered a bit, so I will likely need to be doing some grinding to fit everything together.  It should not be too much of a problem, as I was mostly worried about where I cut with the angle grinder, especially since the boxing plates may not be solid enough to weld back together, especially on the driver's side.  I've seen S10 frames without the boxing plates there (including extended cabs), so I am not sure if they are a ZQ8/Xtreme thing, or if maybe they were added late in the production run.

Also, I managed to vibrate and and scrape out at least 10 pounds of rust from the frame.

I think I have ground/cut away everything I need to, but getting everything positioned is proving impossible.  I'll either need multiple people to help, or maybe I can drop the axle and leaf springs, and then be able to adjust it on my own.  Only issue with that is there's not really anywhere to stash the axle, other than in the driveway, so I'd need to do the whole job in one sitting, then toss it back under the frame when I'm done.

Pete. (l33t FS) said:

We think of cars as perfect, tight tolerance produced things, but they give a lot of clearance and slots in mounting holes for a reason.

Coming back to this comment because it was especially relevant today.  I figured a way to fit the frame without any help, involving a few small floor jacks and a tiny bit of brute force.  After iterating through grinding and fitting, I got most of my measurement comparisons to somewhere around 1/32" from where they were different when measured before the cutting.  Stepping back, the frame also "looked" right for the most part when standing at the back of each rail and looking forward.  Some cut brackets screwed up the perspective a bit, though, and something seemed "off".  Decided to take a few quick measurements from each axle, and was getting worrying results.  Just in case, I made sure axle droop was the same on both sides.  Then I measured forward to the leaf spring mount.  The axle was 3/8" out of square, presumably from the factory.

Anyway, I had a jack on each side to adjust rear frame rail height.  I really need to invest in some 123 blocks, but I found that two stacked hockey pucks did the job for making sure height was the same on both sides.

Tacked both sides together, took another look from the rear of each frame rail, then went ahead and ran a bead on each side.

I need to clean up a bit more metal, then cut and weld braces in.  I will try to get as much of that done tonight and tomorrow.  The gang is also stopping by tomorrow, and I am hoping we can pull the old rear axle, and swap the one I got from Somebeach, especially since it has been sitting in the back of the minivan since I bought it, and it would be nice to have that space back.

I was able to cut and partially weld the upper reinforcements this evening.

At this point, there should be enough structure to start moving the frame around again, so that's what I'll do for the rest of the welding, to make it much easier.

tim, idk if this helps in time or not but when the cab mounts rotted on my 88 silverado we found a steel electrical receptacle cover for a 240v outlet on a 4" square box where the hole was the right size for the gm body bushings and thick enough to weld and feel confident it was supporting stuff. on the shelf at home depot too