Chapter 5 - The Cobra Pile

[nolastyankee]

I knew that it was time to post another update to the site last week. If my own instincts were not enough motivation, family, friends, and now site members have been prodding me for information. While I love to write, the call of the Cobra has been much stronger these past weeks. But something tells me that if you are reading this, you already know what I am talking about.

With the deep Wisconsin winter upon us there is plenty of time to stay inside, which is just what our Rescue Cobra needed at this time. Since my last words hit the forum, the Spence car has undergone a radical transformation. In the last episode my father and I (along with all the neighbors we could find on Christmas eve) separated the body and frame. With the two halves of the car by side in the garage, the serious disassembly could begin...And begin it did. What was once a somewhat functional, running automobile is now a tremendous heap of parts that I like to call the "Cobra pile". It is amazing that a car just over 90" in length can spread itself to all corners of a nicely sized home...In the garage we have the engine:

http://www.uniquecobra.com/uploaded/nolastyankee/Pile2.jpg

But then down in the basement are body parts, the electrical system, suspension, brakes, etc.

http://www.uniquecobra.com/uploaded/nolastyankee/Pile.jpg

The journey to this state was an intense three week thrash of component removal and engine disassembly. Once the body was off, we started innocently enough. Dad and I peered at the drive shaft that we knew was misaligned from the onset. We removed it to take some measurements for a frame modification that we have planned and set it to the side.

http://www.uniquecobra.com/uploaded/nolastyankee/Driveshaft.jpg

With merely those four tiny bolts bagged and labelled, the socket set started to sing, and the open end wrenches whispered to me in my sleep. The Cobra was calling and the pull was unmistakable, and my darling wife encouraged me to the garage.

Next the brake and fuel lines came off. Then it was the front brake calipers, shocks, and springs. Since our car is (currently) equipped with an MG front end, we consulted a restoration manual for disassembly tips. The most important one I found when taking apart the front end is as follows:

:) It is important to consider the sprung force of the coil spring in the MG front end. Loosen but do not remove the upper and lower pivot bolts on the kingpin. Use a cable to secure the spring to the lower pan and a jack to compress the suspension while you free the lower pivot bolt. Pivot away the kingpin and drop out the lower arm and be careful as you lower the jack. Once the spring is at resting length, "ease" it out of the perch with a rubber mallet.

The rest of the front suspension came apart with alarming ease and speed. In fact I am quite thankful that nobody ever drove this car...Despite 10 years of corrosion and sitting, there is only a handful of bolts that required more force than a standard 3/8" drive socket could muster. In fact more than a few of the front suspension bolts were removed by hand. Locktite was obviously not a priority for the original owner.

On a squeaky, borrowed engine hoist the 351W came out of the frame without incident. With the mill on an engine stand I dug into the power plant to see if the old girl was going to be salvageable. My first surprise came just after all the head bolts were removed. The builder had used the wrong head gaskets and there was improper coolant circulation to the heads. This explained the mysterious fluid in the oil and the ugly stains running down the block. While this baffled me initially, I was only mildly surprised as I peered down the bores to find evidence of valves which had been hitting the pistons despite deep reliefs. Even with these minor [?] problems the core looks really nice and still appears to be a candidate for rebuild. A trip to the machine shop this week will tell me for sure.

http://www.uniquecobra.com/uploaded/nolastyankee/Hoist.jpg

With the front end of the car void of parts, I found that the weigh

[brfutbrian]

brian, i cant tell what misalignement problem youve got. from your picture it looks fine. the trannny looks alittle low, but other than that, i didnt see whats wrong. the offset from the centerline on the rear end is normal. is that what youre referring to? and now that youve got the hardwork out of the way, the rest is pure fun. keep those pics coming. later brian

[excelguru]

Don't forget that the driveshaft will indeed have some angle to it because the rear pinion isn't on center. Boy, that engine was destined for doom. You guys are making great progress! And the story makes for great reading. Keep it up!

Keith :)
Unique Motorcars (http://www.uniquecobrareplicas.com)
Southern Automotive (http://www.southernautomotiveengines.com)
Bruce Bunn (the painter) (http://www.jodecoautobody.com)

My Photo Album (http://members5.clubphoto.com/keith355593/owner-429c-1.phtml)

[nolastyankee]

brfut,
The tranny was about an inch too low at the rear mount. We are lining up on the same horizontal plane and allowing the side-to-side offset to provide the angle needed to avoid harmonics. The picture does not show that the drive shaft was hitting the frame. Our fix will be shown in Chapter 6...

Unique 9122 - 289 FIA Cobra - The Legendary "Spence" Car

[pgermond]

Great chapter. Just out of curiosity.... how many chapters are you planning? This isn't going to be a Gone With The Wind sort of novel is it and, if so, which summer cruise are you referring to? :D

Keep'um coming, and good look!

Phil

427 Roadster, #4279436
Southern Automotive FE
3:31 and Toploader

Roseville (N.Cal)

[clayfoushee]

.......another masterpiece, thanks!

Clay

'98 Unique #9299, 427FE side oiler, top-loader (close), 3.31 rear

Annapolis, MD

[Jim Harding]

Brian,

Do you have a close up shot of the upper rear shock mounts? My older car came with series II springs/shocks, and I had to replace them with what Unique installs on their present cars. I have an interference fit between the forward spring and the stub axal universal joint..... it just touches the spring. I need to make a modification to relieve this problem, and don't want to re-invent the wheel... hence the request for the photo. Also could use the measurement of the distance between the two shocks (upper mount dimentions). Feel free to e-mail direct. Thanks in advance.

- Jim -

Jim Harding
La Plata, Maryland

1982 #3004
http://www.capitalareacobraclub.com/albums/album26/1aLeftside.thumb.jpg

[brfutbrian]

brian, the tranny should line up level with the rear end. possibly the problem your having could just be that the automatic tranny that was in the car uses a different crossmember than a standard transmisssion. you should call unique and see if thats the situation you have before tearing into a frame modification. it could be if youre going to switch to a four speed, the problem may cure itself. just a thought . later, brian

[excelguru]

I just noticed something... your crossmember just beneath the driveshaft isn't "notched" like mine...

http://a0.cpimg.com/image/44/6D/11542340-df3f-02000155-.jpg

I can see that your misalignment is vertical, now that you mention it.

Keith :)
Unique Motorcars (http://www.uniquecobrareplicas.com)
Southern Automotive (http://www.southernautomotiveengines.com)
Bruce Bunn (the painter) (http://www.jodecoautobody.com)

My Photo Album (http://members5.clubphoto.com/keith355593/owner-429c-1.phtml)

[Poorboy]

The earlier cars did not have a notch in the rear crossmember. The pinon of the rear end had to be raised hence the angle of the drive shaft. I can see in the picture of your bare frame that it looks like you have notched yours now. You will need to lower the pinon instead of raising the transmission. If you raise the transmission you will have trouble with header & side pipe fit.

Poorboy

[davids2toys]

BUMP:
I found this thread in a search for driveshaft/pinion angle. I have a wheel hop problem and one of our members suggested to me correct pinion angle, so I have started doing some research. I have a 93 kit, and I am not the original owner or builder of the car, I have only had it since last year.
I do have the notch in trhe rear crossmember. My configuration looks much the same as the third picture down. The rear is pointed 5 deg going up hill, and the driveshaft is pointed down towards the tranny 5 deg, that is a differance of 10 deg total, that certainly does not seem right, or does it! Also have the slight driveshaft angle to the drivers side. I know in my late model Stang, it is -3 deg at the pinion to the driveshaft, thats it,period.
Can anyone tell me if my angles seem correct.
Also, is there any such thing as detailed work instructions to assemble a UniqueCobra , I am constantly seeing refererances to all different assy recomendations and instructions...where do I find this info?
Thanks...Dave

[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.

[weaver]

You need to upgrade to adjustable coil overs.

Alan

[davids2toys]

As far as the tire rubbing, it is a gentle rubbing outside of top of tire to top of wheel well, pass side. Only in left hand sweeping turns while driving
I am going to post some pics, I tried but it would only let me do three because the others had already been posted to another thread, it is post #8 in this thread http://www.uniquecobra.com/forums/showthread.php?t=7404

The pics I will attach here show cars squat at take off, passenger side just cruising, and a shot of the driveshaft angle.

The pics in the link above show the components of my rear suspension. One of the pictures actually shows the wear on the fiberglass from the pass side strut going from the back of the car to the bottom shock mount.
I do get a clunk noise sometimes backing up, or taking a turn...I think it is that strut hitting the fiberglass floor underneath the fuel cell on the pass side.
You guys forgot more than I am ever going to know aboutthese cars...lol. So please look at these pics and don't hesitate to comment or point out something wrong or missing.
I was thinking new adjustable coilovers myself, I dont know how they could have got worn out after just 9000 miles. I would hate to waste money on parts I do not need!

[Justin Upchurch]

My car hops really bad, with sticky tires, even worse. I am almost certain it is due to not having enough pre load on the springs and rear end still needing to be shimed. I hope to have the car back at the end of the month to start playing with it again, just in time for winter.

Justin

[Naumoff]

I read an article in Car Craft about improving traction off the line.
When the car squats down it takes weight off of the tires.
This will make wheel hop more likely.
heavier springs will help.
You want the car to lift up not squat. This transfers weight down on the rear wheels.
Traction bars are the easy fix but with an IRS this presents some obvious design problems.

Watch the cars set up for drag racing. If they are set up properly you will see that the cars don't squat. It looks like a hand is lifting the car up from the center which puts weight down on the wheels.

New adjustable coil over shocks will also take car of the tire rubbing.

Eliminator has done a lot of research on suspension set up for these cars.
If he has no wheel hop then I would go with what he has.

[davids2toys]

Makes sense to me, so where is this famous Eliminator?
LOL