Chapter 5 - The Cobra Pile

[nolastyankee]

Dave,
A couple things...Wheel hop has nothing to do with pinion angle on an IRS car. Misalignment between the rear end and tranny may cause you some driveline vibration depending on the angles, but not wheel hop. All Mustangs (except - I believe - the '03 Cobra R) have been solid axle suspension where the angle may make a difference. The center section on your car is bolted to the frame solid - any wheel hopping is happening outboard of that. You need to be looking for wheel balance, suspension geometry, suspension setup, etc, etc. on your car.

Do NOT take for granted even basic things like the fact that the entire rear suspension in your car is square to the chassis. While it may have been straight leaving Unique, even the slop in the holes attaching the rear end to the chassis can cause the rear end to be out of square to the car. (Trust me on this one, we took an entire build day to square our car front to back) Start with the basics and check everything.

As for driveshaft angle, the pinion in the differential case is offset to the passenger side and you will always have some lateral angle. To line out the vertical plane you will need to work with the tranny and rear end. We ended up fabbing a full size shim plate to change the angle of our rear end to better align.

Finally, there is an instruction manual for the Unique cars, I have even heard of a CD version. However, this is mostly limited to things like interior, finishing out the aluminum work, and a few helpful hints. For anything mechanical your best bet is the internet - this forum, Jag sites, Ford sites, etc. The most important thing to remember - almost every car is different and there are very few questions for which there is one "right answer".

[davids2toys]

Dave,
A couple things...Wheel hop has nothing to do with pinion angle on an IRS car. Misalignment between the rear end and tranny may cause you some driveline vibration depending on the angles, but not wheel hop. All Mustangs (except - I believe - the '03 Cobra R) have been solid axle suspension where the angle may make a difference. The center section on your car is bolted to the frame solid - any wheel hopping is happening outboard of that. You need to be looking for wheel balance, suspension geometry, suspension setup, etc, etc. on your car.

Do NOT take for granted even basic things like the fact that the entire rear suspension in your car is square to the chassis. While it may have been straight leaving Unique, even the slop in the holes attaching the rear end to the chassis can cause the rear end to be out of square to the car. (Trust me on this one, we took an entire build day to square our car front to back) Start with the basics and check everything.

As for driveshaft angle, the pinion in the differential case is offset to the passenger side and you will always have some lateral angle. To line out the vertical plane you will need to work with the tranny and rear end. We ended up fabbing a full size shim plate to change the angle of our rear end to better align.

Finally, there is an instruction manual for the Unique cars, I have even heard of a CD version. However, this is mostly limited to things like interior, finishing out the aluminum work, and a few helpful hints. For anything mechanical your best bet is the internet - this forum, Jag sites, Ford sites, etc. The most important thing to remember - almost every car is different and there are very few questions for which there is one "right answer".

I'm glad you clarified about the wheel hop. Those were my thoughts exactly. I have regular, NON adjustable coilovers in the back. I was thinking this was the weak link especially since to me it sits low in the back, I even rub on th passenger side more often than I like. Really pronounced since I put the 295,s out back!
What would you recommend for adjustable coilovers for our cars?
Dave

[nolastyankee]

As for adjustable coilovers I know that a few on this site have gone to Bilstein with good results, Unique spec'd Carrera for a while until they went out, now I think it's QA1. SPAX makes dampers for Jag rears and is quite successful. However, keep in mind that the shock controls the rate at which the suspension is compliant (soft suspension or hard suspension) but the spring controls the ride height and the pressure with which the tire is pushed into the road by the vehicle. Shocks themselves will not change the stance of the car, the springs do that. You can swap springs on your stock shocks and change the ride height and perhaps impact your wheel hop issue.

When you talk adjustable coil overs it should have multiple damping settings for compression, spend big bucks and you'll get adjustable compression and rebound. All will have threaded bodies to adjust spring preload as well.

Suspension is a bit of an art. Go with a proven setup like something from Unique or the Bilsteins that Rick (eliminator) had developed for these cars or be prepared for a lot of testing and a box of left over springs until you get the right rates! Whatever you do it's not going to be cheap since you are talking four shocks and four springs.

[davids2toys]

As for adjustable coilovers I know that a few on this site have gone to Bilstein with good results, Unique spec'd Carrera for a while until they went out, now I think it's QA1. SPAX makes dampers for Jag rears and is quite successful. However, keep in mind that the shock controls the rate at which the suspension is compliant (soft suspension or hard suspension) but the spring controls the ride height and the pressure with which the tire is pushed into the road by the vehicle. Shocks themselves will not change the stance of the car, the springs do that. You can swap springs on your stock shocks and change the ride height and perhaps impact your wheel hop issue.

When you talk adjustable coil overs it should have multiple damping settings for compression, spend big bucks and you'll get adjustable compression and rebound. All will have threaded bodies to adjust spring preload as well.

Suspension is a bit of an art. Go with a proven setup like something from Unique or the Bilsteins that Rick (eliminator) had developed for these cars or be prepared for a lot of testing and a box of left over springs until you get the right rates! Whatever you do it's not going to be cheap since you are talking four shocks and four springs.

Exactly what I dont want, so where do I get the correct info and pricing for the tried and true system for our cars. As I said, right now i have NO adjustment on my coilovers at all!
I do realize that is the spring that controls ride height and not the shock itself.
Thanks Brian...Dave

[Jerry Cowing]

Dave,

Sounds like you have a couple of different problems in the rear of your car, tire rub and tire hop.

Tire rubbing. You didn't say where your back tires are rubbing. Three possibilities come to mind. 1) If the outside of the tires are rubbing on the wheel wells, it could be your wheels do not have enough set back. The 295 width tires are standard size for these cars, so maybe your wheels are not the correct design for your setup and you need more set back. 2) If the tires are rubbing on the inside top of the wheel wells, the springs could be too weak. Adjustable coilover springs could help, some increase the front springs 200# and each back spring 100# which makes the ride stiffer. 3) Another possibility is the lower control arm bracket may have broken loose from the pumpkin (3rd member) on the passenger side and when you corner the top of the tire leans out too much. This is a common Jaguar rear end problem that can be re-enforced with a plate that attaches to the lower control arm brackets. Unique sells these plates.

Wheel hop. I'm not familiar with the 1993 cars, but maybe yours doesn't have the four rear torsion bars: two attach to the bottom of the pumpkin and one each attach to the lower control arms near each wheel and then to the rear bumper frame. These really help to keep your rear end from twisting during hard acceleration which can cause terrible tire hop. Also you could install sway bars on the back. Most Uniques come with sway bars installed on the front, but not on the back. The sway bar will help keep both tires on the ground and not let one rise too much higher than the other. The sway bar will also help eliminate wheel hop as will the torsion bars and stiffer springs. Unique sells the torsion bars and sway bars that are correctly sized for the Unique. The diameter of the sway bar must be matched to the car, too large or too small bar diameter is not good.

Why don't you call Alan or Maurice at Unique and explain to them what is happening. There have been many changes to the Uniques since yours was built in 1993. I'm sure they can tell you exactly what to do to fix your problems.

[nolastyankee]

Dave,
For the tried and true systems shock/spring combos contact Unique (Alan or Maurice) or Rick Bagley (Eliminator).

Jerry has some great advice on things to start looking at. My suggestion is to start at the differential and work outboard to validate that your Jag rear end is operating properly - correct geometrys, correct installation, correct torque specs, correct tire inflation, correct wheel balance, correct wheel alignment, etc. In a word, validate that what you have is working 100% before trying to change anything. Lots of Uniques have been built with stock Jag shocks and given that wheel hop is not discussed on this board I would venture a guess that it is not very common and should be fixable without changing many parts.

[Naumoff]

Wheel hop is a problem with IRS and big horse power.

I have an '05 kit, adjustable coil over and a sway bar. With the upgrade to the stroker it is more frequent.

It sounds like you have the stock Jag shocks.
I have done some research on the net and found very little help even in the Corvette and late model Mustangs w/ IRS forums.

Going to heavier spring rate helps.

All the things Brian suggested is good.
Stuffer bushings new shocks and springs check wheel alignment etc., etc.

Bottom line is that IRS design was not intended for big torque, smoky burn outs and hole shots.
I am working on a solution but I need to set up some high speed cameras to see exactly what is going on.