Sunday, December 27, 2009

Ok, finally got the pics from Ben. Not a lot, unfortunately. This session involved installing the rear end into the 3-link rear suspension. Here's a shot of roughly the parts involved:

The big bracket in the upper right is referred to as the banana bracket. Its other half is roughly in the center of the shot. These two parts clamp around the right side of the axle and play a part in locating the axle relative to the body, particularly providing anti-squat. The bulk of the work involved deburring the inside of the bolt holes, without which they simply couldn't bolt the banana bracket around the axle. It seriously look over an hour to line things up and drill out the crappy flash. A similar complaint can be lodged against all the spacers. When it comes to accurately placing anything, the kit uses spacers around a joint, like so:

Notice how neither spacer is quite cut flush, with the skinny one just not looking like it belongs on any serious build. Kit cars... Ben and Marc are gonna take the remaining spacers and grind them a little nicer at work.

After all that cutting and drilling was over, lining up the axle with the frame and bolting stuff on wasn't so bad. After I did some research on it, they ended up not swapping the caliper mounting plates, which one place online had recommended as a way to gain some leeway with running the brake lines. So this is a completely default setup:

Note the leftover brackets from the Mustang's stock 4-link mounting setup. A better side shot from FFR:

From the back:

Note how the banana bracket is clamped just to the right of the diff.

I guess I should take some time to explain why the 3-link suspension is an upgrade. The factory Mustang rear suspension is a 4-link system:

When the body rolls or the axle pivots about the diff, the links will push or pull hard on their bushings, thanks to their triangulated arrangement. Despite Ford's using soft rubber bushings, the forces on them can still cause them to bind up, locking out suspension travel at that point. Furthermore, because of the softness, the axle can wander side to side under the body, which defeats the point of triangulating the 4 links in the first place! Even so, the base option in the FFR kit is to keep the 4-link setup.

The 3-link suspension upgrade kit tosses all that stuff out in favor of a different system. 2 trailing arm links are used along with a panhard bar. The benefits of the kit:
- the panhard bar lowers the roll center of the car, which on a stock Mustang is high for track use.
- a lot of Heim joints are used instead of rubber bushings, which leads to less slop in the suspension
- everything is adjustable, which is highly desirable on a track car that needs to be tuned

Just for reference, the parts again:

And how the suspension is set up:

The blue lines are the 2 trailing arms. The red lines are the coilovers. These do most of the work in locating and suspending the rear axle (or rather, the body over the axle). The yellow lines are the banana bracket and a pivoting link to the body, acting as an upper control arm. As you can see, that limits the pinion angle (how much the diff can pitch up and down about the axle). We're using it in the <400hp setting. The >400hp setting is intended to give the most anti-squat to have the best hookup at the dragstrip.
The green lines are the ends of the panhard bar. On the right, the panhard bar is attached to the suspension, swiveling about the endpoint formed by the control arm and the coilover. On the left, however, the panhard bar is attached to the frame of the car, indicated by the pink lines. Thanks to the bad side shot posted above, it's easy to mistakenly see the panhard bar as rigidly connected to the other coilover, but it isn't. If it were, then it'd just be a really shitty sway bar.

Anyways, the left end of the panhard bar is fixed to the body, and the bar swivels up and down as the axle moves up and down relative to the body. Because the bar is long, the motion at the middle of the bar approximates a vertical line. This means the axle will also stay approximately centered to the body as it bounces up and down. You advanced math nerds will observe that if the suspension is stiff and doesn't travel much, then the approximation is very good. Panhard bars are a pretty good solution for solid axle race cars, and it's what the Spec Factory Five Roadster cars use. I sperged on this part mostly to dispell the idea that if it has a solid axle, then it necessarily cannot be made to handle well. You can have a spergin good time by reading more on the Mustang suspension here:

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