Complete MM IRS Fix It Kit or Built Live Axel???

[Serpentor]

MM has Delrin IRS control arm bushings now that include EVERYTHING: shims to allow for tolerances, tools to remove the old bushing, tool to straighten the mounting tab, and even gloves:


http://www.maximummotorsports.com/irsdelrinarmbushings.asp

 

[grnenvy]

hmmm

My IRS and rear is completly stock axle's and all. I do have with a set of adjustable shocks though. I also had my rims cut and widened to 11 inches with 315 bfg drag radials and have O hop. I have ran a best of 10.88. So for all these guys with a solid axle swap I just don't understand it.

 

[Fresh Cobra]

All...thanks for the info and advice!!! I've decided to just beef up the IRS and have the Nicks IRS Kit in hand and ready to go on soon.

One last question...is the DSS LvL 5 Half-shafts worth the $1900.00+++ or should I look at another option like LvL 2 or something else?

I'm leaning on making the Cobra Autocross ready and keeping my 96 for the 1/4 mile so any info/help is greatly appreciated.

~ Fresh

 

[jackers]

Let me correct myself from my last post. Change out the IRS. After doing some more research on it, I found that our cars were never designed for IRS. The bolts use the same holes as the solid axle from the mach's and gt's. It doesnt matter how good of a halfshaft or bushings or shocks you have. All it takes is one time to break a half shaft. In addition, you will be paying alot of money to build it up. Bushings cost me $350, halfshafts $650 amazon racing's, MJ's IRS brace $210. That is $1210. Now add the installation of bushings ($500-600) and halfshafts ($200) and IRS brace ($50) you are looking at about $800 dollars more. I think for $2000 I will have a pretty mean solid axle that weighs 130 lbs less, absolutly no worry of wheel hop, and no more clunk/pop.

just my $.02

 

[Fuerza]

I was reading about maximum motorsports box kits. They have an starter box a sport box, and a road and track box for the 03/04 cobras. Does anyone use these box kits? What do you'll think of them?

 

[toofast4u]

Here we go again. The greatest reason of wheel hop is uncontrolled suspension movement under load. Wheel hop does "not" only affect vehicles with IRS rear suspension solid axle cars also have significant wheel hop issues depending on the suspension configuration. There are several situations which increase the likelihood and severity of wheel hop with the IRS this including running tires over inflated, traction coefficient of the tire which is affected by weather, wrong size bolts stock in the torque box location, rear IRS bracket movement, and alignment mainly toe and thrust angle. There have been some people who have discovered there thrust angle being off as much as .25".

The best way to minimize wheel hop is to resolve these issues. This includes.
-Remove the compliant stock bushings the most significant being the rear LCA, IRS assembly, and pinion bushings. The most appropriate material currently for these bushings is Delrin for the rear LCA, urethane for the IRS assembly, and aluminum for the differential pinion location.
-Install the Mathis brace on the rear IRS assembly mounting location. Steeda currently makes a version of this brace which they call the IRS subframe bracket.
-Install a good set of full-length weld-in subframe connectors. You can not expect your suspension to perform optimally if the unifying structure is not stable.
-Replace the incorrect, I don't care what Ford says, 12mm bolts in the torque box location for the correct Ford 14mm bolts for this location. This issue is present in all IRS equipted Cobras that I am aware of.
-Replace the stock shocks with a higher dampening shock especially if a higher rate spring or Delrin LCA bushings are being used. The Delrin LCA bushings from our experience dramatically increase the spring efficiency which substantially increases the wheel spring rate. With the stock 600 Ibs/in springs the 00R shocks are great, but for higher spring rates above 700 Ibs/in conventional or 600 Ibs/in coil-over you might experience under dampening with the 00R shocks.
-Check your tire pressure. Just because Ford recommends 32 psi for the stock tires does not mean it is correct. For one considering our cars have a ~57%/43% weight distribution there is no way the front and rear tires should have the same pressure to distribute load present on that tire. In my experience the front tires need substantially more then 32 psi to provide optimum traction, tread life, and gas mileage. And the rears require significantly less. The best way to determine if your tires are optimally inflated is to draw a line across the tread face of all four tires and drive around and monitor the wear rate of the chalk. If the chalk wears evenly from shoulder to shoulder then the tire pressure is probably within it optimum range. If it doesn't it is an indication of a problem. If the chalk wears faster from the center you are over-inflated. If the chalk wears faster on the shoulders evenly then you are under-inflated. If the chalk wears faster on the outside corner you have to much positive camber. You should have a little more wear on the inside shoulder depending on your alignment, but if it is substantial then you probably have to much negative camber. Another quick way is to drive through a puddle and then over dry concrete and examine the tread pattern. If it is even from shoulder to shoulder the most significant locations are the shoulders and center you are good if not then you have an issue. Again if the center is lighter then the shoulders you are under-inflated. If the shoulders are lighter then the center then you are over-inflated.
-Have a 4-wheel thrust alignment performed and make sure the thrust angle is 0.00" and have the toe set to toe-in 1/16" per side and 1/8" total in the front and rear.

 

[ShelbyGuy]

ive seen solid axle cars hop bad enough to bend the trailing arms. i've also seen a real cobra dragonsnake run high 9s with a weberized 289 and (gasp!) independant rear suspension with (double gasp!) transverse leaf springs.

the drag racers begged ford to build a quad cam mustang with an automatic and a solid axle. sell your cobra and go buy the mach 1 you wanted ford to build anyway. the price difference will get you the forged bottom end.

 

[Snake Eyes]

Here are my thoughts on the IRS. This is based on all information I have been able to collect on the 99+ Cobra IRS.

The main problem is traction. Thus good tires are a must, and those tires must to be properly inflated to perform properly. But you also need to keep those tires on the ground (not bouncing) so a good set of shocks and springs are very important. Coil-overs are best but standard springs are still better than stock. Adjustable shocks are great for those who like to open track or drag, and they can be dialed in to combat wheel hop. I have a Griggs coil-over kit with Koni adjustable shocks myself and I recommend them over MMs IRS coil over kits because Griggs installs spherical joints into the eyelets of their shocks where as MM uses polyurethane bushings which over time will fail. Nick ([email protected]) makes Delrin replacement bushings which will solve this problem and Billetflow has recently released an adaptor kit to use Strange Engineering adjustable shocks with the IRS, http://www.svtperformance.com/forums/showthread.php?t=144341.

Needless to say subframe connectors are an absolute must, Griggs and Maximum Motorsports sell the best. For those wanting the strongest frame possible go with Griggs through floor frame kit, also recommended for high horse power convertibles.

Also the IRS comes with soft rubber bushings (even the 03s still use rubber though harder than 99/01s). The subframe bushings must be replaced with polyurethane bushings. You can find them at Maximum Motorsports here http://www.maximummotorsports.com/mmirsu.asp or Steeda here http://www.steeda.com/store/-catalog/Cobra_rear_bushings.htm. The Steeda bushings come with new nuts and bolts, the Maximum Motorsports does not but you can purchase them as extras. This is important because some 03 Cobras came with 12mm bolts in the forward IRS mounts instead of 14mm bolts. This allows the IRS to shift which of course is not good. You can also order the correct bolts and nuts from Ford. The part numbers are W704939-S426 Bolt M14x109 H and W520215-S427 Nut M14 HEX FL. I recommend the Steeda kit because of the lower cost (when including the bolts), they include 4 (grade 10.9) bolts front and rear, and the rear bolts are a pan head design which allow bigger tires to be used without spacers or grindingon the OE bolt.

For those who need additional wheel clearance with replica style wheels (AFS etc.) I recommend these billet wheel spacer from Lightning Force Performance http://www.lightningforceperformance.com/catalog/productDetails.php?productID=1168 with these lugs http://www.gorilla-auto.com/product.../ULTRA+STYLE+CONICAL+SEAT+LONG&image=5384.jpg and locks http://www.gorilla-auto.com/product...&productName=E-T+/+ULTRA+STYLE&image=5803.jpg by Gorilla (you will need the 1/2" threads).

The control arms and differential mounts are also rubber and must be replaced with delrin and aluminum. This will keep the IRS components from moving relative to the subframe which now will not move relative to the car giving it a very sure footed feel (like a torque arm and pan hard rod does vs. the 4 link solid). The guy to get them from is Nick [email protected]. You can look at the bushings he sells here http://www.aossguns.com/images/bushing/index.htm. Maximum Motorsports has released delrin control arm bushings, and an aluminum differential mount kit that allows slightly better adjustment of the pinion angle but Nick's kit will cost you considerably less. The Maximum Mororsports IRS parts list can be found here http://www.maximummotorsports.com/irs-asp.asp. 1999 and 2001 cobras owners will need to purchase an IRS pinion brace to be used with these bushings. I recommend the stock 03 brace, the cheapest place to pick one up is Ford Parts Network http://www.fordpartsnetwork.com/03Cobra.htm. For optimum performance I would replace the swaybar bushings with polyurethane units from Maximum Motorsports and install their new end links http://www.maximummotorsports.com/irs-asp.asp.

The rear IRS subframe mounting point attaches to the car using a cantilevered bracket that is prone to flexing under load because the outer half of this bracket is completely unsupported. This flexing causes unwanted alignment changes and contributes to the IRS feeling like it is moving under the car. Steeda's Cobra IRS Subframe Bracket Kit http://www.steeda.com/store/-catalog/IRSsubframebracket.htm keeps the rear mounts from flexing and improves corning stability.

A shock tower brace improves rigidity and prevents chassis flex over the IRS (highly recommended if you run coil-overs). It is also advisable to weld the brace rather than bolt it in to add strength to the shock towers. If you are running coil overs with a stiff shock (to reduce wheel hop) the increased loads will cause significant stress on the mounts. Braces can be purchased from Hans RaceCraft http://www.hansracecraft.com/product/ford/mustang.htm and Kenny Brown http://www.mustangweekly.com/2002/june/newproducts/n6-7-6th.asp.

For cobras that have been lowered Maximum Motorsports makes adjustable IRS tie-rod ends that allow you to move the joint of the tie rod end back in to correct alignment. This is the equivalent of a bump steer kit for the IRS, http://www.maximummotorsports.com/irstr.asp.

Finally it is necessary to have your IRS aligned. A good alignment shop should be able to get you -1.3 degrees camber and .10 degrees toe with 0.0 thrust angle.

http://corner-carvers.com/forums/showthread.php?threadid=12350&highlight=irs*]
Many have reported problems not being able to get enough negative camber on the IRS. Rotating the bolt is how it's normally adjusted, but some people get much less than -1.5 and here's why... pretty simple actually, but if you look at how most alignment shops do things, it makes sense.

When the wheel is off the ground, and the upper knuckle is loose, the weight of it tends to rotate the wheel towards positive camber of course. Adjusting the eccentric to the max negative camber by rotating the bolt, only goes so far... the upper arm end is slotted on both sides to allow the bolt to adjust, and to get max camber out of it, it needs to be pushed back in the slot further on both sides of the bolt (The bolt will torque down at an angle if you let it, as the eccentric is on the opposite side). It's sort of sloppy. I'm at about 80% of the camber adjustment on one side, and about 70% on the other side (meaning I can get somewhat more negative if I choose to)...

Now that you can plant your rear tires with confidence you may snap you half shafts, GKN and Raxles did make shafts for the 99/01 guys (I am unsure if they still do) but a set of used 03s are a cheap upgrade for 01 guys who are near stock power levels. Remember they will not fit the 99s because 99s came with 28 spline shafts where as 01s and 03s use 31 splines. If you want the best the Driveshaft shop makes near indestructible half-shafts, check em out here http://www.driveshaftshop.com/MUSTANGC.V..ivnu. Razors Edge Motorsports http://www.razorsedgemotorsports.com/ currently have half shafts in development as well. And finally you may want to pick up a IRS girdle from Zone 5 or Billetflow, http://www.mafterburner.com/irs_girdle.htm.

If you follow this list of upgrades you will have an IRS that plants like a solid, handles like a Porsche, rides like a cloud (compared to a similar level 8.8) and is as close to bullet proof as possible.

 

[mustarrosa]

A sollid axel...

 

[mblgjr]

Ok, any opinions on using the Polyurethan vs, Delrin for street use? I am leaning towards the poly, as I know how hard the Delrin is. I will be using those, as well as a BF brace, and HD toe rods, already have pinion bushings. T

Think that will be good enough to handle 550-600 on street tires?

 

[Snake Eyes]

No, Polly will not hold up. Check out this thread on this exact subject over on Corner Carvers.
http://corner-carvers.com/forums/showthread.php?t=14618

 

[Jpjr]

No, Polly will not hold up. Check out this thread on this exact subject over on Corner Carvers.
http://corner-carvers.com/forums/showthread.php?t=14618

That's why I bought Delrin. Do it right the first time.. this install is such a PITA that you won't want to upgrade later. I'm gonna get some coil-overs eventually so that should help compensate for the stiffer ride.

 

[Jpjr]

For the Mathis/Steeda bracket.. do you need to order two??

 

[Snake Eyes]

No you only need to order one kit, unless you want to make it, then you will need to make two.

 

[mblgjr]

I don't plan on beating my car that hard, as to need the Delrin, and don't plan on coil overs. As my car will be close to 99% street, you still suggest the Delrin? Thats a lot more money and effort....think I better do some thinking.

 

[Snake Eyes]

The entire kit from Nick is only $350. That is dirt cheep for Delrin. I have Delrin and yes it will raise noise more than Polly. How much, I don't know, probably not significantly more but it will perform much better.

 

[Tide612]

solid

You will never make an solid axle ride like a IRS car but you can not hardly break a solid axle. I broke 5 IRS setups. I basically taking the thing to FORD and getting them to fix it. I went with a fully built solid axle. I am in the process now of making the thing ride better. Besides what did MUSTANG's have all the way back to the 60's? They had solid axle's, not IRS. I think that ford made the IRS in the 99-04 cobra's an after thought, just something to make it ride like a vette. THis is just my .02.

 

[mblgjr]

The IRS is an adaptation into an old platform that wasn't meant to have one, so they did make compromises. So, it's heavy, has limited travel, and the body can't handle the added stress of it. Also, the IRS unit itself is relatively new to Ford, much less making it handle high HP.

 

[BLWN03]

Damn all that efffort and money......guess my solid axle build will go ahead as planned. I could probably swap out the rears in less time than it takes to install all these bushings...and the rear can still break.

 

[Mrcobraguy]

Well i just welded up MM full length subframe connectors. Its been raining out so i haven't really tested it out yet but i can still fell the diffrence. It seems to handle alot better and it just feels alot better.