thewarmachine

The rear suspension of our stangs and the change in geometry after lowering is a big topic on the forum.
Many adjustable parts are recommended by many members, and I'm sure they work.
The problem is that I, for one, would like to know exactly how the geometry changes and how these adjustable suspension parts (LCA's,....etc) correct this change in geometry.
Please don't dismiss this as nitpicking.
I think that having a picture of the geometry in our heads will help us to see what parts are needed and why they are needed.

Before I ask my specific questions, I'd like for you to watch this video I found. This person is trying to illustrate different types of rear suspension and the effects of raising or lowering the axle.

http://www.youtube.com/watch?v=YoAu-gPPktQ

It would be nice if someone who knows exactly the layout of our stangs' 3-point suspension would make a similar video or at least a drawing that shows the exact position of all pivot points and lengths or LCA's and UCA, as well as the driveshaft's length and pivot positions.

For instance: I assume that the UCA is shorter than the LCA's, but, at ride height, at what angle do they sit relative to the ground, and at what angle to the ground are the front pivot points and the rear pivot points? Also, how is the differential housing angled? Does the driveshaft intersect it perpendicularly? Does the differential housing tilt backward to match the angle of the driveshaft?
Also, the lengths and pivot positions of the UCA and LCA's will make a huge difference in which way and how much the differential tilts when the car has been lowered.

One thing I've heard is that LCA relocation brackets help correct the pinion angle. The only way this seems plausible is for the new, lower holes in the brackets to force the differential to tilt backward or forward because the LCA (nonadj) will be the same length as stock. Something seems fishy about that to me. I would think relocation brackets would not do much of anything to correct pinion angle. What would help is adjustable LCA's. Now, you can move the differential angle forward or backward by lengthening or shortening the adj LCA's.

Could someone please explain the geometry in detail, preferably with drawings like a cutaway of our cars. Thanks.

thewarmachine

http://www.cherod.com/mustang/HowTo/LCA%20_adj.htm

Ok, someone gave me this link, which explains what each part of the suspension does and how to measure the pinion angle, but it does not give a sketch of the complete suspension so we can see how things move relative to each other. That's really what I'm looking for. Perhaps someone has a mustang mechanics manual with a cutaway of our rear suspension.

Or....maybe someone who knows can just explain, in detail, which way things tilt when lowering. Thanks in advance.

howarmat

pm f1fan

Norm Peterson

What you're asking for could fill a chapter in a book. But the Cliff's Notes version is that the S197 rear suspension is essentially the same as the "Forward 4-link with shorter upper bar" in that video. My guess at this point is that in the OE positions and stock ride height, the upper is slightly downhill going from the axle to the chassis and the LCAs are slightly uphill.

The point of relo brackets is not particularly to correct pinion angle. If anything, relo brackets more strongly suggest adjustable LCAs, as it is very easy to end up with the axle slightly crooked for any number of reasons. Normally, relo brackets revise the geometry to give more anti-squat and improve the launch(which is something that lowering gives away), but it also changes the amount the rear axle steers as the car rolls in a corner (rear axle roll steer).

What relo brackets tend to alter as far as pinion angle is concerned is how rapidly it changes as the suspension rises and falls - a consequence of having a shorter side view swing arm (more rearward Side View Instant Center).




Norm

timothyrw

here's another link:

http://forums.bradbarnett.net/showthread.php?t=60937