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4-link suspension (Satchel Link) Lots of pics!!!
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Old 07-12-2009, 04:42 PM
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Default 4-link suspension (Satchel Link) Lots of pics!!!

This forum seems to be geared more towards drag racing w/ an s-series. The modifications I have done to my rear suspension are designed for well-rounded performance handling, whether it’s drag racing, auto-cross, road course or daily driven on the streets. The Satchel Link is most definitely considered a racecar suspension.

Here is what I started with:

I installed the V8 back in 2001-2002. It has almost 30,000 miles on it with this setup.



General summary: A Satchel link , in simplest terms, is an upside-down triangulated 4-link. It has desirable characteristics for a certain set of user preferences. It enables you to have roll understeer w/ high anti squat and a low roll center. All without using a panhard, watts or other lateral locating device. The upper bars in PLAN VIEW are forward facing & parallel to eachother. These bars help determine the roll axis during travel ….unlike the common 3 or 4 link. The lower bars in plan view are attached to the outer edges of the axle tubes & angle equally inward toward the center of the vehicle. These bars share most of the duties with the 3-4 link but also help determine the roll center and keep the rear end centered beneath the vehicle. Why did I choose this design for my S-10? First & foremost … the leafs had to go… the V8 created entirely too much axle wrap and the truck handled like…. well… a truck… it wasn’t a safe controllable ride. A lot of people add a leaf, use cal-tracs, slapper bars, blah-blah…. I look at those solutions as more of a band-aid for a design deficiency .
I wanted to get the ride’s center of gravity lower without sacrificing ground clearance much beyond the frame rails. But I also want to be able to haul a few hundred pounds every so often. Solution? Adj. coil overs. I really wanted to be able to dial in some roll understeer throughout travel. I think understeer will help balance out the tendencies of oversteer w/ having a light ass end. I live in Washington State, where the roads can get suddenly quite wet. Having a rear end that behaves & doesn’t want to kick out going around curves is a safety factor that appeals to me. Besides doing a test & tune or 3, I really have no “intention” of racing this truck. It will see mostly street driving & I intend to have fun (safely) when I drive it. Plus… I just like being different… hahaha.

Here is a mock up of the suspension:


Here’s a rear suspension parts list:
DR5855B QA1 coilover adjustable shocks
130/250 lb. QA1 Progressive rate springs
Bars are made from both 1.5” & 1” diameter X 1/4” thick DOM tubing (FYI…using this material is overkill)
SD Super pivot adjustable rod ends w/ delrin bushings (not poly) on one end of all the bars. 1-1/8” threaded stud and jam nut.
On the other end of all the bars are currently solid ends w/ poly bushings. I’m not even gonna bother w/ the delrin into these ends, as it won’t be optimal. I plan on getting some solid spherical rod ends after I get the truck road worthy. I really need a way to let the bars rotate while maintaining their axis without creating bind thru-out travel. Sphericals on both ends of all the bars appear to be the ideal way to accomplish that quest and not put any undue loads on the bars or mounts. Plus, bushing compliance will no longer be of concern.
Most of my 10 gauge to 1/4" plate mounting brackets were designed in Autocad or Opus drawing programs and plasma cut from MAP CNC cutting software on a Lockformer plasma table.
Here's some of the hardware:


I did some frame moidifications prior to installing the 4-link:
I notched the frame:

And I also boxed the frame rails:


I raised the bed floor 4" to clear the notch and give me additional gas tank clearance. The existing bed floor was dented to hell, so I just decided to fab one from scratch:





I used an s-10 blazer gas tank mounted behind the axle. This mod put more weight on the ass end (a good thing) and gives me the space needed for the 4-link bars.





I’ve designed all of the control arm mounts w/ full adjustability. Since there is plenty of room under the bed… why not? Everything I’ve read says the challenging part about running a 4-link, is tuning it.

All 4 of the bars are right around 25+” long. I’m getting around 2.3 degrees per inch of understeer from the UCAs w/ this length. Bar length is definitely an issue w/ a Satchell link. Terry Satchell, when commenting about this config in a Lotus forum, made it a point to stress the importance of having the lower links as close to 45 degrees plan view as possible (to retain axle lateral constraint). This limits the forward mounting point of the LCAs to be no more than half the width of the rear end (minus the width of the brakes). But even then, you have a driveline to clear, so take away that allowance from the total length as well. Those bars are getting shorter & shorter eh? As a rule of thumb w/ any 3 or 4-link design… the longer the bar, the better. This rule primarily applies for roll steer purposes. So in a Satchell link, shortening the SVSA for the lower bars does not effect the roll steer. Problem solved you’d think………….

3 & 4-link design basics dictate that to achieve fairly consistent Anti-Squat thru travel that the upper bars should be approx. 70% the length of the lowers. If I followed this concept, I’d be looking at 14” long uppers…… which would create a shit-ton of roll steer. I decided a flat AS curve was not as important as having low roll steer numbers, so I lengthened the UCAs to give Roll Steer amounts I’d be happy with.
I’ve ended up with a 22% AS decrease for every 1” of bump. I think I ‘ll be okay w/ this. I am inclined to think that my variable rate springs will start compensating for squat. I also don’t mind getting some of the load off the bars during articulation.
Quite frankly, I’m not sure where I stand on the whole “Squat vs. Anti-Squat” debate and how it applies to a V8 S10 under various driving conditions. Both sides bring up good points for the performance handling-minded driver.

Here is the calculator I used to help find the best mounting points of my bars. These are the actual settings of my suspension:


Besides designing a Satchell link, another choice I’ve made that seems to be very rarely discussed, is using progressive rate springs. In my case, I chose the 130/250 from QA1. I’ve read that most people seem to be happy running 100# to 150# linear spring rates in their rear coil over S10 application. I decided to fab a bracket that will locate the mounting angles from 85 to 65 degrees in 5 degree increments. This will give my spring rates some adjustability. If the whole variable spring rate gamble does not pay off…. I’ll at least be able to drive the truck to a scale and calculate what I want for linears instead. Right now, I’m sorta skeptical about these progressives. I think it will be too hard of a ride a little ways into compression due to a high spring rate limiting the travel. We shall see.

The Roll Center Height sits @ 11” & goes down 1/4” for every 1” of compression. This seems to lie within acceptable tolerances.

I have nothing in mind for designing in a rear sway bar right now. I don’t think it would be a good idea to use one until I get the suspension tuned to my liking first.

This is how it looks as of Friday July 10th 2009 (pardon the mess!!! I was reorganizing). I expect the truck to be hitting the road within the next few weeks:




This build is all about the "performance".... It's nothing I'd plan on taking to a show to win a prize. That will be a different project.

I'll always welcome any questions, comments, criticisms, advice and general feedback.
Hopefully no one fell asleep reading this.
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Old 07-12-2009, 11:43 PM
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Nice work...
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Old 07-13-2009, 12:14 AM
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very nice work, i really like the gas tank mod, can't wait to see more progress
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Old 07-13-2009, 12:46 AM
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i would like some more info on how you did the bed?
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Old 07-13-2009, 06:32 AM
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Excellent job journeyman!!
Nice write up as well.. Keep the info coming..
I like your style.. Nice welds too!!

Mike
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Old 08-25-2009, 08:58 PM
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Thank you all for your kind words.
The truck has been roadworthy for about 3-4 weeks. I still need to finish off the bed. It's still looks the same since the last update. I have all the materials and resources to finish it, but just need the time & motivation!

Here is where I ended up locating the filler neck:
---------------------

Had to modify the neck w/ a 90 degree bend. here it is all prepped to paint.
---------------


Here is the new stance:
-------------------





As far as handling goes..... What a huge difference. I've been able to put the suspension thru it's paces pretty thoroughly now . Some curvey roads. Bumpy roads. A few good launches. Some hard breaking. The suspension performed great. Nice articulation. No noticeable bump steer. Even the coilovers seem to have a good setting w/ the progressive rate springs. The ride is firm, but not harsh. I went over some railroad tracks and was pleasantly surprised (my wifes SUV hates these tracks). I thought for sure the springs would be too stiff, but so far I'm really happy w/ my choice.
Having understeer is a very noticable difference!!! When I would gas it midway thru a corner.... the ass end would've normally wanted to kick out.... NOPE!!! The rear tires now feel like they are following the same track as the fronts... almost like it's pushing itself into the corner.... a very different feel than what I'm used to. I like.

Got an all aluminum 3 throw corvette radiator w/ two 1400 cfm e-fans to replace my neglected v6 stock s-10 radiator that decided to prove itself unworthy during some of my more spirited test drives.





Got a new grill & bumper that I waited to install until after the truck was out of the garage and all tuned in.


==============

Next phase will be working on the front end geometry, steering, and some better braking capabilities. Now it might get spendy!
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Old 08-25-2009, 09:03 PM
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Nice job man! The truck is coming along and looks awesome!
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Old 08-25-2009, 09:29 PM
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Looks killer!
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Old 08-26-2009, 11:47 PM
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Nice work
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