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Discussion Starter #1 (Edited)
So I have my car in the shop and the Watts linkage just got installed today, its not completely finished yet but this is the majority of it.
Also, later in the week, the rear beam will be converted to a 3-link suspension. The trailing arms are going to be cut off and replaced with two 18"-20" swagged tubing with 5/8" rod ends on each side and the third link will go to the back where the spare tire well was.
On with the pictures!

The Before


The Scott-Russel Linkage laying where it belongs...


The rear beam


This was a 3/4" bolt at one point, but the head was cut off and inserted into a hole that was drilled into the bottom of the torsion bar, then welded in, then the plate was put over top of that and welded again. Its pretty fuckin sturdy and I would be really surprised if it sheared off cuz its grade 12 steel.


The watts link installed for the most part, still have a few things left and that part is done.


The 3-link suspension will be added as soon as it gets done and I get pics of it. In the meantime, the control arms are being fitted so those should be the next thing done. Look for those in the appropriate thread in the F-IR sub-forum.

Update 16 August 11
Watts linkage and 3-link suspension are done.










This shows the free play that the 3-link gives. The passenger side only was lifted 10" higher than the drivers side. The front passenger tire is off the ground and you can clearly see that the rear axle stays on the ground.
 

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I see what you doing now :d keep up the good work wahaha we need someone to figure out how to make our cars become to AWD lol
 

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Discussion Starter #4
Watts linkage and 3-link suspension are done.










This shows the free play that the 3-link gives. The passenger side only was lifted 10" higher than the drivers side. The front passenger tire is off the ground and you can clearly see that the rear axle stays on the ground.
 

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Totally badass and original. Thanks for spending the time and money to do this. I just bought rod ends and brackets for a panhard but now I've got a lot to think about, lol.
 

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Nice!
 

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Looks like you get some dynamic toe in/out from the 3rd link. Which would cause heavy toe out in cornering based on the current rod angle. Running coilovers you'll get maybe 2" of droop, unless this car is being set up for RallyX.
 

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This shows the free play that the 3-link gives. The passenger side only was lifted 10" higher than the drivers side. The front passenger tire is off the ground and you can clearly see that the rear axle stays on the ground.
You will only have as much articulation as is allowed by your suspension travel. So if you run a high rate spring and only have 1" of compression on the loaded suspension, then you will only have one inch of downward movement before the inside tire comes up. You could gain more by running helper springs but because traction is a function of tire load, once the main spring unseated the load would go to almost 0 and so would traction. The main benefit to keeping the inside tire down even if unloaded would be that the outside tire wouldn't end up with positive camber. I suspect you are running a spring rate in the 500-600lb range, which means the rear suspension probably only compresses 1/2-3/4 of an inch. I'll tie this in in a second.

The rear beam is designed with built in roll resistance, with the way it was modified the built in resistance is gone. So one of two things needs to happen, or both... spring rates need to go up to control body roll (which will exacerbate the lack of compression and droop), or a LARGE sway bar needs to go back in to control body roll. Body roll, combined with a lack of suspension droop travel is what picks up the inside tire. When it happens is a function of track width, suspension travel, and degrees of body roll.

With a front sway bar the more roll a FWD car sees, the more the inside front tire unloads, and the outside tire loads/overloads. Roll doesn't contribute but a very small amount of to weight transfer in and of itself, typically 3 percent give or take. Roll in combination with a stiff roll bar will keep the car flat by borrowing rate and weight from the inside tire. Once you exceed a certain load, traction begins to drop off. If you can keep the tires more evenly loaded by limiting transfer, the max traction available at each tire will go up and given no other changes, the car will grip better. Transfer is a function of CoG height, track width, and cornering forces.

Most of the great books written on suspension and chassis were written years ago when FWD was a non-factor and a gimmick, so not a lot of directly applies. I could go on and on. Under braking the forces are dealt with at the ends of the axle near the wheels, which lessens the moment (leverage) acting on the beam. With the added articulation and removal of the fixed trailing arms the torsion is now resisted by the 3rd link around the center of the beam with may cause toe out under braking and possible stability issues. There is the potential to end up with hop or oscillation under braking also.

The horizontal watt's link is pretty good, the rest.... it'd be great if it was a RWD late model roundy round car or a Mustang.

The key to getting a FWD car to handle, especially the B15, is to do your work at the rear of the car, but it has to be the right work.
 

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Discussion Starter #14
I did notice the toe out, however, it doesnt seem too excessive. The car feels pretty stable and the rear squats under breaking. I think the 3rd link will be upgraded with bigger hardware and a thicker tube to account for the breaking forces that it will see. I think 3/4" hardware will be enough. The car also feels like the rear is helping to steer the car around corners almost like it has 4-wheel steering. I like it. I wont be able to fully experience the changes this setup will make til it hots the track, but from making some runs down the nearby curvy rural road, it seems very promising.

Sent from my phone. Who cares what it is. They all do it now-a-days.
 

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Toe out under braking would make the car nervous and pitch side to side. You should be able to drop gear changes while braking to stop, which also means you only have one hand on the wheel during hard braking. The car should track true and straight near full lockup.
 

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I have been following this thread for a few days now, I may not be a mechanical engineer, but wouldnt two links in the front and one link in the rear, under suspension travel, tend to twist the axel front to rear? while if you have zero toe or camber, this wouldnt have much of an effect, but with any camber or toe change, it seems to me as if it would make it too squirrley to drive with the rear changing so much, also, when you reach the limits of the suspension travel, wouldnt the 3 link effectivly 'lock" the suspension at extreme travel? Also, it would seem as if lowering or raising your rear suspension would affect this, if you had gotten the "bent beam" to change your rear camber for handling. The last thing I am wondering about, since the rear shocks/coilovers are an active part of the suspension, would limit the front to rear twisting on the rear beam, it just seems to me that the two shock mounts, two front links, and one rear, would seriously limit suspension travel up and down, but would have no effect on side to side, basically negating any roll resistance you may have, and creating a very harsh ride every time the rear tires hit a bump?

or... I could have quoted Justins post.....
 

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Discussion Starter #19
Ok, so the dynamic toe out issue has been addressed with some camber and toe shims. The rear wheels now sit straight so there will be no changes in wheel angle. The third link was disconnected and the axle was rotated fore and aft so that we could measure any changes in the wheel's angle under cornering and braking. Its gonna see some track time on Sunday so we will see how this works out. Im gonna mount the go pro back there so I can get some video of this thing working. Im hoping for good results. If not then Im gonna have to figure something else out.
 
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