Front Suspension Do-Over = Too much Positive Caster - Ideas?

Hey everyone,

In the midst of a front suspension do-over and I'm struggling with way too much positive caster.  Not sure how to get back to the +6 deg range.

Some Details:
03 S-10 RCSB ZQ8, 4.3, 5-spd
UMI 3832-1 LCA with 0.5 inch taller LBJ
UMI 3056-2 Adjustable UCA with 0.5 inch taller UBJ
oem Blazer 2WD Front Spindles with sealed bearings
Landrum 700 lb springs (12 inch free length) with 0.5 inch Belltech Spacer on top


Trying my best to REDUCE the positive caster, the lowest I can do is +12 degrees with the adjustable rod ends on the UCAs.  This is with about 2 degrees of neg camber.  I've got the rearmost UCA rod end adjusted out about as long as I'm comfortable with while still having 5/8-inch engagement with the control arm threads.  The front rod end is adjusted all the way in (short as possible).  So, effectively, the upper ball joint has been adjusted as far forward as I can get it... and I still have 12 degrees of caster in this condition.

I also checked to make sure I don't have the UCAs on the wrong side of the vehicle (LH and RH swapped).  I have them on the vehicle such that the upper ball joint plate is forward (in vehicle position) relative to the rest of the UCA geometry.  Swapping to the opposite hand UCA as a sense check, the caster value approaches a ridiculous 20 deg.


Any ideas why I am seeing so much positive caster?

I want to be around +6 degrees but I don't see any realistic way of getting the upper BJ forward enough to achieve this based on the UCA rod end adjustments on the UCAs.

At 12 deg as described, the steering arm portion of the spindle is rotated up quite far... likely going to have Tie Rod clearance problems to the sway bar (or something else) due to this.

For reference, alignment is being checked at ride height/suspension loaded with a Longacre Digital caster/camber gauge.

Appreciate any ideas you may have about what could be causing this.

Thx.

Darren

Sounds like you've checked all of the obvious things. Have you talked to UMI about it? Maybe there's a problem with the parts combo?

Do the UMI lowers put the LBJ forward farther? Are the uppers intended to be bolted on with no shims and adjusted entirely with the arm adjustment, or could you add shims and readjust? Are you 100% confident on the measurement you are getting with your camber/caster gauge? Given, I have a completely different setup than you, but I had to try really hard to get the 9 degrees of caster that I wanted with stock lowers and speedway uppers.

I've been wondering for a while if G-Body uppers are truly the same as the S-10.  With my SPC adjustable uppers I needed to get a longer rear sleeve to get the alignment where
I wanted (about 6* of caster & 1* of camber), otherwise I would have had the same issue with too much caster/camber.  I'm starting to think that UMI & SPC (and every other company) never actually looked at an S-10 upper control arm, and they just re-label the G-body stuff.

Anyone have a G body that they can measure?


FWIW, I also noticed the SPC lower arms were slightly shorter than OEM S-10.  With stock height ball joints & the same springs, camber went slightly positive with the SPC lower arms.

I'll second making sure you're using the gauge correctly. When I did the rough check on my front suspension with my camber/caster gauge setup I was doing the calculation/measurement wrong and thought I was positive caster, but was actually negative.

I'd say it would be worth the money to have a shop double check what you're seeing with a professional machine.

Hey everyone,

Thanks so much for the helpful feedback and suggestions.

I've been emailing back and forth with UMI support for a couple weeks.  They suggested that the UCA might be on the wrong side, which is typically what results in crazy positive caster values.  As described, I confirmed that I've got it on the correct side though, with the UBJ pad biased forward in vehicle, relative to the rest of the arm geometry.  Otherwise we're kind of stuck as to what the problem might be.  They asked for a few more measurements on my side... once I get them done I'll send off another note and see what they say.


The UMI Adjustable UCA is designed to dial in the caster and camber values using only the rod ends (no shims needed) so long as you're using relatively "common" components.  In my case, with the matched set of UMI LCA and UMI UCA, and a stock-type spindle that even the GBody guys use a lot, it's not like I'm throwing a bunch of confusing variables into this.  UMI support sent me a couple photos of their Green Machine GBody with about 8 degrees of caster and a couple degrees of negative camber, all dialed in using the Adjustable UCA Rods ends (with pretty minimal/balanced adjustment of the rod ends in the pictures too).  I wish my truck UCAs looked the way their photos do!


It's certainly possible that, in addition to the UMI UCA moving the UBJ rearward, the UMI LCA may move the LBJ forward.  The UMI support folks did not suggest that the lower changes the LBJ position though.  However, they were very upfront that the UCA BJ position is changed for additional caster relative to stock.

I laid the UMI LCA beside the stock stamped LCA and made some reference measurements.  The LBJ location doesn't appear to be that much different, relatively speaking, as compared to the stamped oem LCA.  Doing a similar exercise for the UCAs it's very obvious that the UMI UCA has the UBJ about an inch further rearward.


The Longacre Digital Caster/Camber gauge I'm using is pretty straightforward, so I'm pretty sure I've got it right.  In all honesty though, the caster angle is laid back so much in side view that it's fairly easy to see that it's more than 10 degrees off vertical, leaning rearward.

My original goal was just to get the alignment roughed in before taking the truck for a proper alignment.  The fact that it's off so much has me stumped though.  I don't feel comfortable reassembling everything and pretending it's ok, only to find out from the shop that the caster is likely way out.


I'll post back when I get some more feedback from UMI after I send them another note with additional info.

Thanks everyone for your ideas!

Darren

Do you have any pictures of your set up now and the pics of the UMI truck for comparison?

The pics that UMI provided to me, for reference, were of their GBody Monte Carlo... unfortunately, not specifically an S10.

What method do you guys suggest as the best for posting pics on the forum?  It's been a while since I've posted images on a forum so not sure what the current best method/service is to host them.

Thx.

I'm not super familiar with how picture posting works on this site.....but on many other forums, possibly this one if it applies, if you can find it on the tapatalk app, you can post right inline with text from you phone. Nice big pictures that are good quality.

The other option is webhosting. Flickr and postimages.org seem to be the current popular free services.

Trying an image from imgur... my current ride height with the new stuff installed, including the too-big positive caster:






Hooray, imgur works!


I will have to take some pictures of my suspension setup now, for reference relative to my described "problems".

Here's the G-Body/Monte Carlo reference pics UMI sent me.

These are supposed to show the adjustment of the UCA Rod ends to achieve 8 deg Positive Caster and some aggressive negative Camber.


Unfortunately, my rod end adjustment on my S-10 is way more aggressive than this on the UCA (rear rod end threaded out +15mm and front rod end threaded all the way in/shortest possible)... and I'm still waaay higher than the 8 degrees of caster captured in these G-Body images.











In the UMI reference photos here, it looks like their G-Body has the front rod end threaded out a little bit (maybe 4mm) for some additional positive caster and then an equal number of shims added to each cross-shaft attach location to get more negative camber.  Both of these adjustments are the complete opposite of what I need to do on my S-10!

There must be something awry with the lower control arm.....I have around 9 degrees of caster and my wheel is nowhere near that well centered in the wheel arch. Mine sits back a fair amount farther than that. Like when I turn, the tire very barely clears the rear of the inner fender. So I'd think for you to have 12+ degrees, the lower ball joint would have to be way farther forward than stock.

Hey autoxs10, that's an interesting observation.  I'm beginning to wonder about the lowers too.

In a recent email exchange with UMI support, they indicated the lowers move the LBJ forward about 1/8th of an inch, which is fairly minor compared to the magnitude of my problems.  I think I need to take the lowers off and make a solid effort at comparing them side-by-side with the stock stamped lowers.

I'm really running out of ideas now.  Also afraid that if I replace with other UCA/LCA combo, that I'll still be in a similar position since all these companies seem to be recycling G-Body stuff for the S10's.  I don't have much confidence that any of them have developed stuff specifically by looking at our trucks.

I know there are people out there successfully running the UMI parts, I am just not personally familiar with them to give specific advice. I would recommend maybe heading over to s10forum.com and doing a search there or asking questions there.....seems to be a lot more activity from users there and you might be able to find the answer you are looking for.

If you head over to S10forum chat with 98Sonosls. He's a sharp guy and from the Toronto area (I'm assuming you are too with your reference to Mosport). Wouldn't hurt to get an educated second opinion of the parts in person if he's willing.

Reading through the thread again it sounds like you have all the caster/camber concepts understood and it's hard to armchair quarterback across the internet, but we all get so caught up in our own projects sometimes that we miss that one important detail.

Have you tried doing some basic trigonometry to understand how big a change the 1/8" movement of the LBJ could make. Same goes for the UBJ movement too. The theoretical math doesn't always line up with what we actually see on the trucks, but I've used it to solve a few problems I've run into along the way.

I'd also like to think we could rule out your truck as the problem. I believe it is implied that you had no alignment issues before swapping parts. Would it be worth the time to swap the factory control arms back on without changing anything else to see where your alignment ends up? The springs wouldn't need to be installed if you set the ride height with a jack or a "calibrated" stack of 2x4's. I set my ride height with that last option when I was mocking up my Blazer 

Another thought, does UMI suggest/expect any UCA mount changes on the G-Body? I believe it is for many of the earlier platforms, like the 1G/2G Camaro, but the Gulstrand mod is a very popular UCA mount mod to improve handling performance on those chassis. Not sure if it is a thing on the G-Bodies that an aftermarket control arm company would be expecting to be used with their design.

Thanks for the advice guys.  I'm in the process of taking things apart and plan to reinstall one thing at a time to see if I can figure out what the main contributors are.

The UMI Upper and Lower are designed to work together (or separately per UMI) with stock components.  For the spindle height we're talking about (plus the 1/2 inch taller upper and lower ball joints), a 1 inch rearward movement of the UBJ should be around 5 degrees of extra positive caster.  Given that the Stock setup is spec'd at 3 degrees, the end result should be around the 8 degrees that UMI suggests.  Relative to this, a 1/8-inch forward movement of the LBJ shouldn't change it a whole lot... likely less than a degree.


Harley, I think I'll proceed with your suggestion and skip reinstalling the springs for now... will get creative with the 2x4's under the frame and the LCA to mock up the correct ride height with the stock components and then change one thing at a time after that.

As a sense check with my caster/camber gauge I went ahead and measured my DD Colorado.  Ended up with basically 0 deg camber and 3.1 deg positive caster... so, I know the gauge works, and I know I'm using it correctly.

If I'm still stuck after this next go round of parts swapping, I'll head over to S10forum and solicit some advice there.

I'm doing all of this in 20 minute increments here and there, so it may be a while... having fun in the garage has, unfortunately, moved down the list of priorities (responsibilities) in my old age - lol

Darren

Keep at it. Some of those popular guys on the youtubes suggest an hour/day in the garage will make more progress than you expect. It does suck to have all the right parts, but not having them work right, but hopefully it helps us all learn and help others going forward. I applaud you for pressing onward.

I just read a little blurb on s10forum...

"I know that this thread is a few months old. UMI offers a lower control arm that has the ball joint moved 3/4" forward...."

are these the arms that you have?

The UMI Lower I have is this one:
3832-1
http://umiperformance.com/catalog/index.php?main_page=product_info&cPath=256_284_460&products_id=961
According to UMI, it's only supposed to move the LBJ forward by about 1/8th of an inch.

They have a newer Lower now, with shear mounts specifically for a coilover.  I think they call it their "competition" arm.  I wonder if that's the one that moves the LBJ even further forward?
3057-1
http://umiperformance.com/catalog/index.php?main_page=product_info&cPath=256_284_461&products_id=1056