mustang 5.0 front suspension?

[gchandler]

I am in the planning stages of a mustang 5.0 build. I will be acquiring a 1991 fox in very good condition. My plan for the car is to remove as much weight as possible, convert the front suspension to coil over, and do either a truckarm or 3-link in the rear. I am building a daily driver so the engine will be mostly stock with perhaps some weight savings such as aluminum heads and water pump. This car MUST be 100% smog legal.



In my research it has come to my attention that the front roll center on the mustang becomes unreasonably low when the cars are lowered. I plan on changing the rear suspension and installing an adjustable panhard, so I will be able to adjust the rear roll center, but I want to get the front into the ballpark.

Does anyone have a diagram of a stock mustang front suspension? I am going to the bookstore later and will be looking for something, but thought that I would ask here first.

[Norm Peterson]

William Mathis' "Mustang Performance Handbook 2" is probably the most common Fox reference in print. Although there are a couple of errors that escaped proofing (at least in my copy), it's worth the $20. Some dimensional information is provided, though not enough to put together a suspension analysis file of any sort without having to estimate a few things. Then again, you're probably best off measuring up your own 14 y/o car.

Online, there's very little about cornering/handling relative to the Fox/SN95 Mustang chassis that hasn't been discussed over on corner-carvers.com, including Evolution Motorsport's "Tri Link" (aka 3 link). But be forewarned that CC.com expects people* to

(a) search first
(b) get down to business and write as professionally as you have demonstrated above when asking a question

and has a reputation for being rather less than patient and polite at times.

Re: strut front suspensions, the geometric roll center drops about twice as fast as the suspension does, as this is a function of LCA length and the chassis pivot distance off centerline. At least equally bad as far as dropping strut front suspensions goes is that you put the suspension into a region where the rate of -camber gain in bump is less and falling more rapidly. So you end up with a larger roll moment and less desireable camber with which to cope with it. The usual bandaids are stiffer springs/bars, and more static -camber and +caster than you'd use for an otherwise similar car with front SLA suspension. Competitively driven Fox/SN95's typically run 800 lb/in or higher conventional springs where a (possibly heavier) 4th gen F-body might only be using 600's.

Re: the rear suspension, I'd favor the 3-link over the truckarm in what is apparently intended as a relatively lightweight vehicle. It's my opinion that the greater unsprung weight and potential for bind associated with truckarms become smaller considerations as vehicle weight goes up.

* a search over at CC.com on "gchandler" returned no hits, so I'm assuming that you aren't a member there.

Norm

[gchandler]

I have read up on that board quite extensivly, but I am not interested in the new member politics that go on. They rag on people for repeat posts, but their raggin is the biggest repeat post on there.

On CC.com there is extensive discussion of different manufacturers offerings, but I am looking at doing a little of my own work or at the very least having a better understanding of how the strut system works so I can make an educated buying decision.

The reason for the request of a front end diagram is due to the fact that I don't yet own a 5.0, hopefully in a few weeks.

I will take a trip to the bone yard next week with a tape in hand. What dimensions do I need to measure?

I came up with some of the same conclusions that you stated about lower control arm length, but I am not sure how to draw out the roll center for a mcstrut on paper even once I have the measurements.

[gchandler]

After a little more reading it seems as though I can extend the lower a-frames and pull in the upper mount of the strut (towards engine). Does this make sense?

Now it seems that I simply need to make measurements and determine where I want my final ride height.

[Norm Peterson]

After a little more reading it seems as though I can extend the lower a-frames and pull in the upper mount of the strut (towards engine). Does this make sense?

Now it seems that I simply need to make measurements and determine where I want my final ride height.

The roll center construction is fairly simple. One construction line goes through the lower arm's balljoint and its chassis pivot axis (this may be between the control arm bushings, at one of them, or even outside them). A second is at right angles to the strut as seen in front view (if you consider this second line to be a "virtual" upper arm it may make this easier to understand this by comparison to SLA RC diagrams). Where they intersect is the FVIC. The third line goes from the FVIC to the center of the contact patch as in a SLA suspension. Repeat for the other side, and the intersection of the two "third" lines is your geometric roll center. You need to know front view strut inclination (which incidentally is NOT the same as the SAI/KPI), the coordinates of the strut top about which the front view strut inclination varies, and the coordinates of the lower arm bushings and ball joint.

Altering a McStrut's front view inclination will drag your SAI and camber along with it, and too much of either is, ummm, too much. I suppose that the knuckles and/or the strut attachments to them could be modified to get camber back to a reasonable value, but that still leaves the SAI out of whack. So you're rather limited in how much strut top movement is feasible just from a suspension point of view. Never mind the additional encroachment on header space.

Longer control arms with the chassis pivots moved in closer to the chassis centerline is the better solution, space permitting (oil pan, starter, headers, etc.). In fact, that was the solution used by Mazda/Ford on their 626/MX-6/Probe lines (shared platform) for the strut rear suspension relative to the front strut arrangement. Vertical RC migration at the rear in bump (with 23" arms) is in the vicinity of 55% of that up front (13" arms).

Norm

[gchandler]

One question SAI?

And thanks for the great feedback.

[Norm Peterson]

Steering Axis Inclination, aka KingPin Inclination. Runs from the [lower] balljoint to the strut's centerline at the strut top chassis attachment and is not necessarily along the strut axis itself (usually isn't).

Norm

[gchandler]

Thanks

[bobbaganoosh]

The Mathis book shows how to relocate the control arm pivot points inward, and you can run t-bird or sn-95 control arms which are longer.