The G body shuffle.

[Rt Jam]

This is at the mock up stage. I was planning on using a poly bushing, which is what is on a long F body torque arm. I have a link to connect it to another poly bushing but there is not much room or ground clearance for this idea. I might use one bushing only. Open to ideas, this is just an idea. I have no numbers or driving experience to report back yet but I am sure side to side will be more solid than any G body with 4 control arms. Driveshaft diameter and where the front gets mounted to is still to be sorted out. The arm is very close to the floor with the suspension compressed.

We will make a 1x2 bar for a 4L80E transmission crossmember and torque arm mount to reach the frame. Again, only at mock up stage. Provision for an exhaust pipe still to be fabricated in.

There is no binding. The droop travel is limited by my brake line. I might add a limiting strap.

There is no previous 60 to compare to and do not think I will have enough room to make an adjustable the front pivot point. If it doesn't work I'll weld it some later but no room is a factor.
My rear lower control arm brackets have adjustability and so does the pinion angle.

The rear is a G body with a 12 bolt center for an F body.

 

[Supercharged111]

Sweet, fabricated from day 1 for this exact purpose.

 

[Zelnak Zilla]

Some things to consider:

1) Torque arm length affects ant-squat - the shorter the arm the more anti-squat. If you've ever seen a GNX on sticky tires you will have seen the jacking effect of its really short torque arm. The 3rd & 4th gen F body cars have quite long torque arms and do have some squat on sticky tires. The ideal anti-squat depends on the intended use and the tires.

2) Roll center is affected by the height of the panhard bar. It's best to fabricate adjustable height mounts on both ends of the bar. Roll center height affects the effectiveness of the anti-roll bar. A stock G body has a pretty high roll center and it likes a pretty big rear anti-roll bar. Lowering the roll-center will allow the use of a smaller anti-roll bar.

3) The forward link of the torque arm should NOT be constrained fore & aft. The lower trailing arms are what will constrain the axle fore and aft. If there are two members trying to constrain the axle (in any plane) bind is introduced. With rubber bushings this MAY be acceptable but I wouldn't do it. The 3rd & 4th gen F body cars had a rubber sandwich at the front of the torque arm that allowed it to float in the fore/aft direction. The GNX design got this wrong.

4) One thing the GNX design got right is mounting the torque arm on the right/passenger side of the drive shaft. The asymmetric lift from a torque arm is better used on the right/passenger side than the left/driver side.

I love seeing someone take this project on! I've been meaning to do it for ages but never got around to it. The G body rear suspension (not to mention the front) was never a great design for handling purposes. It was designed primarily for cost and packaging considerations.

Years ago I came across an aftermarket G body torque arm on eBay. I bought it out of curiosity. It turns out it must have been a prototype from ATR (sadly gone now). It used a modified F body arm and an interesting diff girdle instead of a cast rear cover. It got same things wrong I described above. Never got around to trying it on a car. I'll probably try selling it at some point. It's probably worth more as a collectable or curiosity than a useful piece. Pix below. I have the instruction sheet that came with it somewhere. I really need to find it again. Too much stuff. Sigh...

 

[Supercharged111]

Some things to consider:

1) Torque arm length affects ant-squat - the shorter the arm the more anti-squat. If you've ever seen a GNX on sticky tires you will have seen the jacking effect of its really short torque arm. The 3rd & 4th gen F body cars have quite long torque arms and do have some squat on sticky tires. The ideal anti-squat depends on the intended use and the tires.

2) Roll center is affected by the height of the panhard bar. It's best to fabricate adjustable height mounts on both ends of the bar. Roll center height affects the effectiveness of the anti-roll bar. A stock G body has a pretty high roll center and it likes a pretty big rear anti-roll bar. Lowering the roll-center will allow the use of a smaller anti-roll bar.

1) Ride height and the angle of those lower control arms has a huge role here too.

2) Roll center is typically below CG, and the distance between those 2 points represents your mechanical anti-roll, i.e. the car's natural resistance to body roll. When you lower the roll center more than the CG, you increase the length of that moment arm which gives the car more leverage against the roll center and decreases mechanical anti roll. When it's inherently easier for the car to roll, you need MORE spring/bar to prevent this, not less. Having said all that, lowering the front of the car without drop spindles will have this effect. Out back? I'm not sure how roll center and CG react to a drop spring, but I do know it's very simple to correct the geometry of those lower arms.

 

[Zelnak Zilla]

1) Ride height and the angle of those lower control arms has a huge role here too.

2) Roll center is typically below CG, and the distance between those 2 points represents your mechanical anti-roll, i.e. the car's natural resistance to body roll. When you lower the roll center more than the CG, you increase the length of that moment arm which gives the car more leverage against the roll center and decreases mechanical anti roll. When it's inherently easier for the car to roll, you need MORE spring/bar to prevent this, not less. Having said all that, lowering the front of the car without drop spindles will have this effect. Out back? I'm not sure how roll center and CG react to a drop spring, but I do know it's very simple to correct the geometry of those lower arms.

I stand corrected! It's been a while since I read Herb Adams' Chassis Engineering book. I need to dig it out and read it again.

Way back when I bought his front and rear anti-roll bars. They were monstrous - 1 5/16" front (with huge Heim joint end links) and a whopping 1 1/2" rear bar. The problem with the G body rear bars is that they are attached to the lower trailing arms, which causes major bind. I wound up using a two wheel drive Blazer rear bar with some home-made adjustable end links. Some day I should take some pics and post them.

Those Herb Adams bars are yet more old stuff collecting dust. Hi, my name is Chris and I'm a G body hoarder. The first step is acknowledging the problem...

 

[melloelky]

I stand corrected! It's been a while since I read Herb Adams' Chassis Engineering book. I need to dig it out and read it again.

Way back when I bought his front and rear anti-roll bars. They were monstrous - 1 5/16" front (with huge Heim joint end links) and a whopping 1 1/2" rear bar. The problem with the G body rear bars is that they are attached to the lower trailing arms, which causes major bind. I wound up using a two wheel drive Blazer rear bar with some home-made adjustable end links. Some day I should take some pics and post them.

Those Herb Adams bars are yet more old stuff collecting dust. Hi, my name is Chris and I'm a G body hoarder. The first step is acknowledging the problem...

no worries Chris,that hoarding club has a lot of members..

 

[565bbchevy]

I remember reading about this set up years ago.

Hotrods to Hell

 

[Clone TIE Pilot]

I stand corrected! It's been a while since I read Herb Adams' Chassis Engineering book. I need to dig it out and read it again.

Way back when I bought his front and rear anti-roll bars. They were monstrous - 1 5/16" front (with huge Heim joint end links) and a whopping 1 1/2" rear bar. The problem with the G body rear bars is that they are attached to the lower trailing arms, which causes major bind. I wound up using a two wheel drive Blazer rear bar with some home-made adjustable end links. Some day I should take some pics and post them.

Those Herb Adams bars are yet more old stuff collecting dust. Hi, my name is Chris and I'm a G body hoarder. The first step is acknowledging the problem...

Also have to be carefull of not going too thick with the anti sway bars or you lose tire grip, especially on the street. Generally you use either stiff springs or stiff sway bars, not both. For example my CVPI has thinner sway bars than regular Crown Vics because the cop springs in it are much stiffer.

 

[Supercharged111]

Also have to be carefull of not going too thick with the anti sway bars or you use tire grip, especially on the street. Generally you use either stiff springs or stiff sway bars, not both. For example my CVPI has thinner sway bars than regular Crown Vics because the cop springs in it are much stiffer.

You can have both, it all depends on your objective. If you want it to handle well, you'll most definitely want both stiffer springs AND bars. If you're trying to lift the front end on a launch, maybe not so much.

 

[melloelky]

this is a decent read on spring rate/sway bar,shock theroy,pivot points etc.Mark's got a big head about himself but but the info is sound.