independant rear suspension idea

geoff

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For a senior mechanical engineering design project, one of my classmates and I had planned on building a 4 link suspension.

The shop behind mine does a ton of muscle car fab as well as some rails, and has quite a bit of rears laying around. After stopping by and looking for a 65" 9" they offered to trade some of my welder's TIG welding skills for an independant aluminum rear and CV axles out of a 2002 navigator.

The rear is an 8.8, the axle is 17" for the main shaft and each CV gets 27 degrees of misalignment each way.

Now obviously hard mounting the rear in a subframe would be easy, and i wouldnt have to compensate for driveshaft plunge. However, doing this would limit rear travel to about 22" (rough measurements), so the other option would be to make the center section "floating" to move with the axles.

Im not dead set on going with this, but it might be kidn of cool. The hubs, axles and rear were all free so i may as well set it up like a RC10T hehe. Any ideas? Kritter/ntsqd?

also roll centers are far easier to calculate with IRS vs SRA.

"We are the music makers, and we are the dreamers of the dreams." -- Willy Wonka
 

ntsqd

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If you're into this for the project aspect of it, and not just doing it instead of fangling about with linkage or leaves for the LA, I'd go for it. Make your adjustments easy to to do and don't forget that one of those adjustments is toe-in which you will now need.

TS

I used swerve around my halucinations, now I drive right thru them.
 

geoff

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thanks for the input

definately upon bump/squat there will be some toe in, that will be easy to control with the front link.

Im thinking about doing something with really long A arms that arent center mounted, rather from opposite frame rail to opposite frame rail, like a kind of I beam mounting, but still an A arm... not sure. I gotta look into more paris-dakar setups i think.

Do you have any pics of something like this??

If the A arm doesnt work (i dont see why it wouldnt) i can always just cut it off after our project is over and put a trussed, linked 9", it isnt gonna cost me anything. I just really dont understand why no one does this?? Is it becuase everyone has the 4 link idea so dialed and they are so comofortable with that? Or is it jsut that a CV setup is usually more expensive? This stuff has discs too... seems awfully appealing. Also there wouldnt be the binding that is inherent to a 4link/3link setup in this.



"We are the music makers, and we are the dreamers of the dreams." -- Willy Wonka
 

ntsqd

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Treat it like you're designing a front suspension, because in a lot of ways you are. You will likely encounter bump/droop toe change. Herb Adams has a very good section on bump steer that should help with this aspect.

I think most don't bother with IRS because of the limitations of most CV's mostly in plunge but to some degree, also in angularity. It's also more parts to fail.

If you're coming up short on things to make your supervising Prof happy, investigate going to inboard rear brakes. After all the whole point is to reduce unsprung weight.

TS

I used swerve around my halucinations, now I drive right thru them.
 

geoff

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well the face that i am funding the project makes the factory lincoln discs a mandatory thing =)

i think that (quite obviously) the only way to know how well it will work is by getting a rough design and then cycling it, changing it, cycling it etc. if the angles get too bad, hopefully i wojnt have to use limit straps and air bumps for all of it :\



"We are the music makers, and we are the dreamers of the dreams." -- Willy Wonka
 

hoeker

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where do i find this herb adams book, you guys refer to it regularly, i think i should read/study it? what is the name of it?

i am in the process of evaluating the CORR Pro-2 spec chassis, and while i can't deviate from it, i would like to understand it. it sounds as though walker designed it more for desert racing than short course. CORR allows us 3 front pivot locations for the rear suspension, my spec chassis pro-2 is going to be the first one on the track to have the adjustability as an option.

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hoeker

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just a thought. in sportsman 2 we are required to run 15" wheels. many of the guys complain about poor braking with the 12" rotor. the other night i considered adding a pinion brake. we always run more rear bias, all others being equal this would automatically add that, instead of taking away front brake with the balance bar, add more rear.

FYI- i am planning on running 6 piston CNC calipers front and rear, a balance bar on one brake pedal, and a second brake pedal for rear brakes only. as resident brake expert your thoughts are appreciated.

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ntsqd

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Adams' book is called "Chassis Engineering". You can find it on amazon, or it's ISBN is 1-55788-055-7

Largest rotor you're likely to get in a 15" wheel is a 12.19"' OD, & that may take some fangling to do. Have you tried different pad compounds on the front and rear ? My guess is that you want some wilwood D or T pads on the rear and maybe some E's or Q's on the front. You can also get more static rear bias by going up one bore size for the front m/c.

Some Cup cars use pads with the friction material at different radial centroids. This effectively increases or decreases the lever arm length. Might be worth looking into.

TS

I used swerve around my halucinations, now I drive right thru them.
 

MNotary

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We got blocked on camera shots. Really. No pics allowed.

Later the truck was changed due to rule changes.
 

ntsqd

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What do you mean by "floating 9in" ? I can picture a couple of different layouts that could be explained this way.

TS

I used swerve around my halucinations, now I drive right thru them.
 

geoff

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a couple ideas for making the center section "floating" come to mind.

one involves attaching two trailing arms from the front to the center section and then some sort of arm from the housing to the hubs, that might work... i have searched high and low, finding pics of this stuff is pretty difficult.

"We are the music makers, and we are the dreamers of the dreams." -- Willy Wonka
 

John Bitting

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Didnt the AWD hedgehog car that Riviera racing owned had 9" center sections using u joints and axles. I am sure someone can come up with pics of that thing.
 

MNotary

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The center section moved up and down along with the tires. It had 930 CVs and pretty long axles. Only had a quick look and couldn't get a good idea of how it worked.
 

FABRICATOR

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Are you talking about this this car John (see attachment)?? If so, it did not have anything that moved.



<font color=orange>The best ideas are the ones that look obvious to the casual observer.</font color=orange>
 

FABRICATOR

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Oops, pics in wrong order...

<font color=orange>The best ideas are the ones that look obvious to the casual observer.</font color=orange>
 

FABRICATOR

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#3

<font color=orange>The best ideas are the ones that look obvious to the casual observer.</font color=orange>
 

FABRICATOR

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#4

<font color=orange>The best ideas are the ones that look obvious to the casual observer.</font color=orange>
 
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