Best suspension for 03/04 Cobra??

i know steeda sells a kit for the irs to stop wheel hop,as for spinning the tires,its gonna happen unless you get a drag radial like nitto's.

The only 100% fix for wheel hop on an IRS equipped Cobra is to swap it for a SRA. Since that defeats one of the many benefits the Cobra has over a standard GT there are some things you can do to beef up the rear and eliminate the majority of the hop. The following info is courtesy of PostBan over on the SVTPerf forums...

http://www.svtperformance.com/forums/suspension-modifications-211/231900-level-5-irs-red-pill.html

The only cure for wheelhop is the system approach. The stock car has many flaws in the rear suspension system. Soft rubber bushings, flexible body structure, unsupported IRS mounts, soft springs in the vert, slippery tires, weak halfshafts and a fragile diff cover.

The basic premise is firm up the points of contact for each of the major components.

Below is a list of relationships so you understand where hop comes from;

*Differential case is mounted with soft bushings, allows it to rotate side to side and front to back, MM bushings cure this.

*IRS Cradle is mounted with flexible bushings, allows it to move in relation to cars chassis mounting points, MM polyurethane bushings cure this.

*Upper and lower countrol arms are mounted with flexible bushings, this allows the wheel to move forward/back when you only really want it to move up/down, MM delrin bushings, aluminum sleeves cure this.

*Toe link bars are very small diameter and flexible, weakest point of support for the wheel, allows wheel to turn in/out and move forward/back, using PHP toe link bars cures this.

*Rear IRS subframe mounts are cantilevered 3+" from the rear subframe, allows for up/down flex in the IRS cradle mounting point, using Billetflow IRS Mount brackets with backer plates cures this.

*Convertible springs are too low of a rate to work with us to reduce hop, using coupe rate springs helps.

All these parts moving and flexing and rotating...... it has no choice but to hop.

Luckily now, after several years of suffering, a replacment or improvement exists for everyone of those components.

Follow this proven mod path to a hard hooking but smooth riding/handling Cobra IRS.

The below mods are carefully arranged to help you out.

You should start at #1 and go straight to #6 for any car from stock up to 500rwhp.

All those mods compliment each other and will dramatically reduce wheelhop on all surfaces. Do not ask me which of the first 6 you can skip, the answer is NONE.

FOR WHEELHOP
Listed in order of necessity/priority.
Stock to CPIE wheelhop mods

1)Billetflow Diff Cover Brace $160
2)MM Diff bushings $50 or $250
3)MMFLSFC's installed $250-300 installed
4)MM IRS Bushings $50 with 14mm bolts/nuts $15
5)Billetflow IRS Mount Brackets $50
6)Used coupe springs $50 (est) (only for verts)
7)Nitto DR $375-$425 installed

500rwhp and up
8)PHP toe link bars $410
9)Maximum Motorsports UCA/LCA Bushings $550
10)Level 5 shafts $1500


11)Strange ADJ Shocks $59ea from HBH Billetflow mount bushings $50
Any shocks other than stock coupe ones or Cobra R Bilsteins are to be used with this caution, It gives you a rougher ride on the settings which actually reduce hop, basically destroys the feel of IRS. And you get to crawl under there and adjust the valve between hop and comfort. Also please realize the possibility of the shocks actually breaking the eyelets. EDIT 8-23-06 Mine actually just broke. This is a seriously dubious mod. My advice is don't do it.

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1)Billetflow Rear Diff cover brace.
Numerous stock Cobras have grenaded the flimsy diff cover. The damage only gets worse as you mod these cars. Get a Billetflow Diff brace ASAP on any IRS Cobra and you will thank me later. They are guaranteed to never break or full refund. This is not a bull***** advertisement, this is a critical reinforcing mod to keep your diff/driveshaft/trans safe from breakage. BF IRS BRACELINK HERE

2)Firmer Differential Bushings like the ones offered by Maximum Motorsports. They sell a Urethane kit for $50 and a fancy adjustable Aluminum set for $250. There have been other companies that offer low quality urethane bushings that melt and deform in this location (diff gets pretty warm) but I have not seen a report of these MM Urethane ones yet. They may be able to take the heat, I cannot say for sure so no endorsement for their urethane ones yet. Their aluminum ones will work fine. Also any other source for aluminum bushings for here could be used as well. One last thing to consider is the noise of the diff (gear whine) will be transferred more and be audible in the interior depending on how loud your car is. I use aluminum here and have a loud exhaust and can still hear the gears. The front two are the ones susceptible to heat, the rear bushings can be delrin, UMHW, nylatron, urethane..... just reuse the aluminum sleeve from the stock bushing or something like it and it will work fine.
MM Differential Bushings LINK HERE

3)Quality Subframe connectors like MM Full lengths. Have them properly welded in by an experienced installer on a drive on lift. The drive on lift is absolutely critical, if the weight is not on the wheels you are unknowingly permanently warping and binding your chassis. Other brands like Global West, Laurel Mountain Mustangs and UMI Performance have shown good results. I currently have HANS Force subframes and do not like them, way too much flex, pass on them.

4)IRS Subframe bushings
from Maximum Motorsports. Others sell them but I have used three sets of these now (3 different cars) with excellent results. Be CERTAIN to order the 14mm bolts and nuts when you buy your bushings. MM Sells only the OEM strength ones so no need to worry.MM IRS Bushings LINK HERE

5)Billetflow IRS Mount Brackets,
3-hole design with backing plates, available now from Billetflow. Sometimes called Mathis Brackets these are an important part of the system. The outer portion of the rear IRS mount bracket is cantilevered out away from any support and free to flex under load. William Mathis originally developed them. I was making a set of my own and cut out a simple cardboard template. While marking the holes to drill I tapped through the template using a hammer and phillips screwdriver. A very mild tap resulted in me piercing the inner wheelhouse metal. Further research showed this metal to be less than 1mm thick and very weak. I did not trust such thin metal to withstand the stress so I then developed a backing plate to make it a robust modification. Billetflow IRS Mount bracketsLINK HERE

6)Coupe rate springs or heavier (especially in verts). Coupe rear springs are 600 lb/in, verts are 470lb/in. 650lb/in Cobra R springs have been reported as giving excellent results. I experimented with cutting stock springs and found 1/2 coil cut circumferentially will approximate most commonly available lowering springs. Drop will be 1"-1.25" with 1/2 coil cut. 1/2 coil = one "C" shape.

7)Drag Radial Tires M/T DR or BFG DR. Nitto DR are an intermediate traction DR, no where near the traction from an M/T or BFG. Nittos will last 3-4x longer and not kill you in rain though. M/T and BFG are dry only tires, you will not be able to drive your car at all in rain/snow with either. Just know how dangerous DR can be in wet conditions, extreme caution is what I urge before depending on DR an a daily driver, very bad idea. One of the benefits of the mods above this point is it reduces the need for sticky tires to fight hop. You can skip tires if you have done all the above mods, the only negative is you will have more wheel spin.

8)Pauls High Performance Toe Link bars
The stock Toe Link Bar is the weakest link in the support of the spindle from forward/reverse axis vibration. Our stock ones are very thin. Compared to the other two points of support for the rear spindle (aluminum LCA and steel UCA) these are very flexible, like noodles! PHP did a test where they actually mounted a remote camera under the car and observed the TL bending 1" during a wheelhop incident. I also have seen a friends set of damaged TL bars warped 1.5". Common sense that these bars help with hop because they keep the spindle from unloading by twisting in the Z rotational axis. PHP Toe Link BarsLINK HERE

9)Maximum Motorsports Control Arm Bushings.
Get the rubber out of the IRS, all of it. The factory IRS bushings are all of seemingly different durometer setting up an unpredictable harmonic nightmare unless you replace it with proper bushings. Best source for all the bushings UCA, LCA, Front and rear Diff is Maximum MotorsportsLINK HERE

10)DSS Level 5 halfshafts
Yep, they cost $1500 bucks. Nope, there is is currently no alternative. The only setup proven to handle the power of a turbo, twinscrew or heavily sprayed Eaton are these Level 5's I do not suggest Level 2's as 3 that I know of have broken at the stock outer hubs Bearing stub. They are only good for a teeny bit more power than the stockers will hold. Instead of breaking the bars like the stocker they break at the bearing stub potentially allowing wheel separation! If you have the power you need the full Level 5's with the stronger bars and larger outer hub assemblies. DSS LEVEL 5 LINK HERE


WARNING! To be used only in extreme cases due to rough ride, basically destroys the feel of IRS. Also please realize the possibility of the shocks actually breaking the eyelets. This is the last mod you want to make to the IRS. Do everything else first.

11)Strange Adjustable Shocks and Billetflow custom Bushings. Billetflow has made these bushings available machined from Nylatron stock, a super strong synthetic bushing material. They are designed to be a compression fit in the Strange eyelet.
CLUNK POTENTIAL!!! You will need to cannibalize parts of your stock Bilstein upper shock mount bushings to prevent a very annoying clunk condition. The Strange shock come with non-locating flat rubber mount washers. The hole left in the shock tower is way larger than the shock stem, under load it moves around and clunks against the shock tower. The old Bilstein plug/stem will not fit because the stem of the Strange shock is too short. It will fit if you follow the below modifications.
B-1. Seperate the top nut/washer from the centering rubber plug/steel sleeve.
B-2. Seperate the steel sleeve (pictured here) from the rubber plug on the top washer, shorten it to 5/8".
B-3. Cut the center hole of the provided Strange rubber mount washer to 1" (big enough to allow the bilstein plug to mate with it. Put the shortened steel sleeve back in the rubber plug, make sure the modified Strange rubber mount washer will fit it and install.
B-4. Sleeve and plug go on the bottom (through the shock tower, rubber mount washer goes on top with one metal washer Strange provided. That will prevent this specific clunk.

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Step by step IRS drop instructions:

STEP 0 ziploc baggies and sharpie marker for every piece, label them as you remove them.

1)Get car up on 4 jackstands with the tires about 8-10" off the ground
in the rear and 4-6" in the front. A little angle is important to keep
the trans from leaking when you pull out the driveshaft.

2)Remove catback. Soap or spray lube on the hangers ease insertion/removal.

3)Remove Driveshaft use 12pt 12mm socket. Pull it out of the trans.

4)Remove tires 13/16" socket.

5)Remove lower shock bolt. 18mm socket, disconnect bottom only, leave them hanging.

6)Remove ABS sensors from differential and pull/pry the fasteners off
the IRS subframe. Get it completely off the IRS. They detach under the
rear seats. You can pull up through the floor if you pull the big
rubber grommet up.

7)Remove Emergency brake cables. There are little c-clips mounting them
to the calipers. DO NOT remove the spring, way harder to get it back
together. Just push on the little arm holding the cable end till you
can work it out. I use vice grips to compress it. Make sure e-brake is
off, of course. Also have a helper pull all the slack to the side you
are working on.

8)Remove brake calipers, two 15mm bolts. Put jack underneath bottom of
spindle, just support it. Mark the position of the eccentric washer
where the UCA mounts to the top of the spindle. Remove upper
spindle/UCA bolt 18mm. Pull back on top of spindle and slip the brake line
out from under the UCA. Remove brake line bracket, 7mm bolt, which mounts to UCA. Replace the upper spindle bolt momentarily.

9)Remove rear IRS subframe bolts, 18mm. Support IRS at the center of the main
rear beam, directly rear of the pinion mount bracket (back of the
diff). Take both bolts out once it is supported. Use some 4x4's or
jackstands to support it a few inches under its normal position (you
don't want to lower it to ground till the front is loose.) You just
want to lower it enough so the springs will come out.

10)With the rear supported on 4x4's or jackstands, put the jack under
the front differential brace. Remove the front IRS subframe bolts.
Lower the front down. It may stick, both the ones I have done needed a
few smacks with a mallet. Once loose lower to the 4x4's then reposition
the jack, lift a bit, remove 4x4's and lower to ground or pull out from
under the car on top of the jack.

11)Reinstall in reverse order. Be sure to get it up close again on
4x4's, too much angle and the front bushings will not go in.
*CRITICAL that you install the FRONT first because those bolts have to go through fixed holes. The REAR bushing nuts (which are movable) and can be positioned to line up with the hole in the bushing. After the fronts are installed (and still a bit loose) swing up the rear, look through the hole, line up the nut behind it and insert the bolt.
Remember to swap out the stock 12mm front IRS bolts for the new 14mm bolts from
MM.



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STEP by STEP Differential removal (w/o removing IRS)

STEP 0 ziploc baggies and sharpie marker for every piece, label them as you remove them.

1)Get car up on 4 jackstands with the tires about 8-10" off the ground
in the rear and 4-6" in the front. A little angle is important to keep
the trans from leaking when you pull out the driveshaft.

2)Remove catback. Soap or spray lube on the hangers ease insertion/removal.

3)Remove Driveshaft use 12pt 12mm socket. Pull it out of the trans.

4)Remove tires 13/16" socket.

5)Remove lower shock bolt. 18mm socket, disconnect bottom only, leave them hanging.

6)Remove Emergency brake cables. There are little c-clips mounting them to the calipers. Make sure e-brake is
off, of course. Also have a helper pull all the slack to the side you are working on. DO NOT remove the spring, way harder to get it back together. Just push on the little arm holding the cable end till you can work it out. I use vice grips to compress it.

7)Disconnect ABS sensors from diff T40 torx or 1/2" wrench.

8)Remove brake calipers, two 15mm bolts. Use some coat hanger wire or zip ties and hang them from the IRS mount bracket or anywhere out of the way.

9)Disconnect Toe Link Bar from spindle. Pull out cotter pin. Remove castle nut 18mm. DO NOT HIT the taper bolt with a hammer, you will crush it because of the cotter pin hole. You can either use a tie rod puller (Autozone 25202 3.5") or the pry bar way. Spray taper bolt with penetrating oil, use long screwdriver or prybar and apply downward force on the cast end of the bar while striking the rearmost point on the spindle. Pry downward and hit it hard, it will come out.

10)Remove halfshaft/spindle assy.
Put jack underneath bottom of spindle where it meets LCA, just support it. Mark the position of the eccentric washer on the Camber Bolt where the UCA mounts to the top of the spindle. You will realign these marks during reassembly to maintain current suspension setting. Forgetting to do this will mess up your tires and ride feel.
Remove upper spindle/UCA bolt 18mm.
Lower jack all the way down allowing the springs to stretch out. Remove jack.
Remove lower spindle/LCA bolt 18mm.
Pull halfshaft out about 1/2"
Use flat screwdriver/prybar between diff and inner hub to make sure it is coming out of the diff. Pull halfshaft all the way out.

Repeat other side.

11)Remove two 18mm bolts from diff cover-to-rear bushing. Leaves the rear diff bushing bracket hanging momentarily while we proceed to get the diff out.

12)Remove Front Differential bushing bolts 15mm

13) Remove nuts off front (only) LCA pivot bolts 24mm. Leave the bolts in place though. This allows the front differential support brace to be removed.

14)Remove Diff. Support rear of diff with a jack, remove front support brace and diff will move forward and down and out of the car. It is about 70lbs so be careful. Do not tip it or you will spill "fish guts" the nastiest smelling oil there is.

15)Remove Rear Differential bushing bracket bolt. 15mm and lots of extensions from the drivers side. Very tough to get to initially. Easier if you also remove drivers side toe link bar from its inner mounting point 13mm bolt on bottom, 15mm nut above.

Good time to reseal the diff with Permatex Ultra Grey ($4 Autozone) or Ford TA31 Diesel Sealant ($15 dealer only)

Reassemble in reverse order.

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IRS TORQUE SPECS
Subframe-to-body bolts 76 lb-ft
Subframe-to-rear bracket bolts 76 lb-ft
Subframe rear bracket-to-body bolts 59 lb-ft
Shock absorber-to-lower arm and bushing bolts 98 lb-ft
Shock absorber-to-body nuts 30 lb-ft
Upper arm and bushing-to-subframe nuts 66 lb-ft
Upper arm bushing-to-knuckle nut 66 lb-ft
Lower arm and bushing-to-subframe bolts 184 lb-ft
Lower arm and bushing-to-knuckle nut 85 lb-ft
Toe link-to-subframe nut 35 lb-ft
Toe link-to-knuckle nut 35 lb-ft
Stabilizer bar bracket bolt 41 lb-ft
Stabilizer bar link nuts 35 lb-ft
Rear axle diff rear insulator-to-axle housing bolts 76 lb-ft
Rear brake disc dust sheild-to-knuckle bolts 89 lb-in
Brake line-to-rear brake caliper bolt 30 lb-ft
Parking brake cable bracket-to-lower arm bushing bolt 11 lb-ft
ABS sensor bolt 17 lb-ft
Axle shaft-to-hub retainer 240 lb-ft
Driveshaft to pinion flange 83 lb-ft
Wheel nuts 95 lb-ft

Dude, you forgot something....Oh wait, no you didn't...lol

This is a very informative writeup, can anyone give me any ideas for installing the same IRS in a classic Mustang? I have a '69 with a weak rear axle. I would like to hear from experienced people if I would need to perform any of the same mods before installing it.