rear suspension

im starting to plan again. i hav a whole winter coming, and along with it my slow season.

im seriously still debating 3 linking the back of the drivabeater. my thoughts were to go with the bolt in thorbecke brothers 3 link kit, put some mounts for regular coils on top of the axle, and let it eat. reason im not up to designing my own is that i quite frankly dont trust my welding in thios application. for general stuff, its fine. for my safety's sake? no.

my questions are a few.
1. any idea if it will clear the bedfloor? i dont wanna cut it.
2. how bad will the geometry be?
3. is it worth the time, money, and headache to do it over my current setup plus panhard bar?
4. any SIMPLE, non welding tweaks to make it work better for the autocross/open track truck?
5. someone wanna build me a better option for the same price?

thanks in advance, guys.
\Michael

1.   I think itÂ’s designed to fit with no floor cutting. IÂ’m not sure of clearances, but  I think youÂ’d need a pretty short coil to fit between top of axle and bed floor (?) Is there some sort of bolt on kit for rear coils?
2.   IÂ’m not sure of bar angles, and have only seen a couple different views in pics, but I can give you some thoughts on the rear geometry. The bars are not very long. I canÂ’t really tell, but IÂ’m assuming 18-20” upper and lowers. This will probably create a quite noticeable amount of Roll Steer. How the bars are angled will determine whether you get over or under steer.
 Having the upper and lower bars the same length will create a pretty drastic decline of Anti-Squat during suspension compression.
 Using the optional Spherical Bar Ends would be crucial in reducing bind during articulation.
I guess IÂ’m a little confused about the use of a panhard bar in this set-up? IsnÂ’t the wishbone link intended to provide the lateral constraint? I guess you could use a panhard with this design, but then why use the wishbone? Just a single upper bar would work. If the intention of the wish bone IS to provide lateral constraint, it is also determining the Roll Center. The forward upper mount does not appear to be centerline of vehicle, therefore, neither is the roll center. How far off center will determine how noticeable that is.
 3. IMO your money is best spent on upgrading the current suspensionÂ…Â…not a bagger bolt-on. No offense to anyone.

Will all the things I brought up be noticeable while driving hard? I can't say for sure, but I'd be inclined to say YES.

the SD kit will not fit without cutting the bed floor.
the front wishbone mount alone cuts into the floor, with the wishbone and rear end bracket probably going higher depending on ride height


i 'modified' the SD kit to be all bolt-on.

if i were to do it again id never buy a kit that wasnt designed for it and go from scratch.

its more a headache than anything

so, this ofiicially wontwork for me. especially with the bed floor.

so what are my options? i think i have gone about as far as i can go with the leaf spring rear suspension. it works, but it could definately work better in my opinion.

For the money you would save on buying a kit you could pay someone to weld in any brackets you would need. Not sure if you remember this thread but it may give you some ideas.
http://www.pro-touring.com/forum/showthread.php?t=37235

I'm designing my own "bolt-in" 3-link for the Blazer.  Anti-squat figures to be between 50-60% depending on my upper bar length and mounting points.  I'll have 1.17* roll-understeer.  I haven't really starting messing with the panhard mounting points yet.

With coilovers, I'm calculating about $1000-1200 total.  I'll fabricate everything and have someone do the final welding.  I'm not completely done designing it, but it's getting there.  

Later, Doug

I'm designing my own "bolt-in" 3-link for the Blazer.  Anti-squat figures to be between 50-60% depending on my upper bar length and mounting points.  I'll have 1.17* roll-understeer.  I haven't really starting messing with the panhard mounting points yet.


Later, Doug

Nice design Doug.
 I just want to point out what I believe might be a misconception about the 3 and 4 link calculator. The Anti-Squat % and Roll Steer angle that you see above is where the suspension sits at static ride height. Those factors will change when the suspension travels. What needs to be looked at for roll steer is what the angle changes to after you compress the suspension an inch. This will determine the amount of roll steer during articulation. I read that you want to keep within 3 degrees of change for every 1" of bump to not have extreme amounts of noticeable roll steer. For Anti-Squat you want to keep as linear of a curve as possible during travel. This will create a more consistent feel of your rear suspension.

the way your design is looking os to use the stock leaf spring hanger on the front and axle pad on the rear. 24.5 long links, with all the availible adjustment at the rear point of the leaf. am i right so far?

also, it appears that the upper link is designed to mount to the gas tank crossmember. again, am i correct? if so, i could oprobebly do teh fabricating and have someone else do the welding.

so, please alaborate on the design a little. if you mind me copying your design, let me know. im not trying to take buisness form someone else, just looking for a way that i can save money.

really, the only parts that look like theyll need welded are the center link mount and the lower able ends if im understanding things right.

Michael

the way your design is looking os to use the stock leaf spring hanger on the front and axle pad on the rear. 24.5 long links, with all the availible adjustment at the rear point of the leaf. am i right so far?

Correct.  The plan is to use the front spring hangers as mounts for the LCA's.  The rear mounts are going to be located using a combo of leaf spring pads and trailing arm mounts from a stock car part supplier. Depending on what trailing arm mount I decide I can get either 3 or 6 holes for adjustment.

also, it appears that the upper link is designed to mount to the gas tank crossmember. again, am i correct?

Sorta correct. There is a crossmember on the Blazers in front of the axle that doesn't look like it serves a purpose other than being a crossmember that I'm going to try and use.

The rear UCA mount still needs some work as there is a lot of force going into the plate.  I was thinking of some sort of backbone that is tied into the diff cover.

if you mind me copying your design, let me know. im not trying to take buisness form someone else, just looking for a way that i can save money.

Feel free to steal my design.  I've been using some ideas from the airbag guys anyways so it's not like the ideas are 100% original to me.   

the only parts that look like they'll need welded are the center link mount and the lower able ends if im understanding things right.

Pretty much.   The LCA's and UCA is pretty much a screw together affair so no welding there.  There will be some welding for the LCA axle mounts but nothing radical.  The front UCA mount looks like it's going to be fairly straightforward.  The only big hurdle is the rear UCA mount and how to make it strong yet still bolt-on.

I just want to point out what I believe might be a misconception about the 3 and 4 link calculator. The Anti-Squat % and Roll Steer angle that you see above is where the suspension sits at static ride height. Those factors will change when the suspension travels. What needs to be looked at for roll steer is what the angle changes to after you compress the suspension an inch. This will determine the amount of roll steer during articulation. I read that you want to keep within 3 degrees of change for every 1" of bump to not have extreme amounts of noticeable roll steer. For Anti-Squat you want to keep as linear of a curve as possible during travel. This will create a more consistent feel of your rear suspension.

I downloaded a demo version for a 4-link software and I could change settings but it always defaulted back to a standard setting.  If anyone can suggest a good FREE 3 or 4-link calculator that can calculate at different amounts of suspension travel that would be great.

Later, Doug

now, couple of questions.
so far, looks pretty straightforward. pretty easy with the lower link bars, as well. hell, i could even make the lower mounting "tubes" with the adjustment holes, given the proper steel.

as far as the upper mount goes, (remember, were just talking hypothetically for a guy that can weld)

could you weld a pair of tabs to the Pass side axle tube for the upper mount, and then a pair to the gas tank x-member? ive read somewhere that the upper link should be offset due to torque.

also, what would this do to the geometry?

thanks
Michael

could you weld a pair of tabs to the Pass side axle tube for the upper mount, and then a pair to the gas tank x-member? ive read somewhere that the upper link should be offset due to torque.

Sure, there is a guy not too far from me that has a project thread on Pro-Touring that is doing that on his Nova.  He is using the front spring leaf perches for the LCA, like I plan, but using an offset UCA bracket.  I don't know what calculations he used to figure out how far offset it should be though.  His thread is here.

also, what would this do to the geometry?

I have no idea.  I haven't gotten that far in my calculations.

Later, Doug

the SD kit will not fit without cutting the bed floor.
the front wishbone mount alone cuts into the floor, with the wishbone and rear end bracket probably going higher depending on ride height

Hmmm... greencactus is definitely the expert with using this setup. The first paragraph mentions the kit is not made for longbeds. This might be a welded kit in the below link I provided, but the gas tank cross member appears to be a bolt on. The bed floor looks cut out only for the frame notch, but appears uncut where the gas x-member is. Perhaps I'm not seeing it correctly?
Anyhow, here is a link from where I based some of my assumptions from.
http://www.s10forum.com/suicidedoors_3_link_5_link_install

Offsetting the upper link has no effect on geometry. It can help cancel torque. Basically you want to mount it as far out as possible as long as it's in the frame rails. The link I posted earlier is an offset 3 link using the gas tank cross member.
http://www.pro-touring.com/forum/showthread.php?t=37235
 Here is Billy Shope's calculator though I find it hard to use.
http://www.racetec.cc/shope/tim.39.htm
Looks like he has two up now.
http://www.racetec.cc/shope/tim.17.htm

Oh, I helped Ryo with his setup too  

If you do use the gas tank x member you may want to gusset it. Here is a pic I stole from that link.

ok, so i looked at the BUNCH of stuff i dont understand. which means i missed some of the basics. probably starting at measurements and research. anyone have a link to where i can start learning, preferrably written at knuckle dragger level, as i flunked algebra. hell i flunked geometry in high school and had to take remedial math in college....

so, heres what i think i know.

i like my ride height now. i would like to retain it. is set at a 5 inch rear drop, and rollining on 245/50/16's.
i can use the factory front leaf hangers to make the fabricating easier.
if i use the stock leaf/shock plates, i could theoretically reuse my stock shocks and shock mounting poits. again, easier fabbing.
gas tank crossmember is a viable option to mount my upper link to. would need to be welded, and probably need to weld the member into the frame.
i should be able to clear the uncut floor if i offset the link, and keep it low.


now, how do i determine things like the mount heights and such? i want to do a set it and forget it suspension. adjustment is cool, but not needed in my application. at least thats my belief.

the bed floor looks cut out only for the frame notch, but appears uncut where the gas x-member is. Perhaps I'm not seeing it correctly?
Anyhow, here is a link from where I based some of my assumptions from.
http://www.s10forum.com/suicidedoors_3_link_5_link_install

Terribly sorry... not sure where i got mistaken.
i dug around a little and came up with this...
again, sorry!
http://www.s10forum.com/forum/f207/cutting-into-the-bed-question-335273/

Since you are using the front leaf hanger you have to start the design there. Also, since the bars will be parallel you want the lower bars level at ride height to help with roll steer. If the were to pint up you would end up with roll over steer and that is considered by most as being undesirable. Pointed down and you will have a hard time getting a decent anti squat number and a lot of roll understeer. If they were converging you could get away with a lot more but that is more fab work.

I don't know if you want to adapt the spring plate. It's going to see a lot of bending and twisting forces. I would make some using at least 1/4" or thicker.

Get the measurement to the center of the leaf hanger bolt to ground and to the axle center line. I'll mess around with some numbers.

for mine, i had a hard time getting the lower frame side pivot point to work using the stock leaf hanger locations, which is why i had to do a 'drop-down' on the SD bolt- on brackets.

Yeah but with the spring perches in the stock location they are farther forward and lower.

Did you get the measurement of the front leaf bolt yet? I'm bored. Could be working on you 3 link.....