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 shocks (and springs in the vert), slippery tires, weak halfshafts and a fragile diff cover. Luckily now after several years of suffering a replacment or improvement exists for everyone of those flaws.
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)MMFLSFC's installed $250-300 installed
3)MM IRS Bushings $50 with 14mm bolts/nuts $15
4)Billetflow IRS Mount Brackets $50
5)Used coupe springs $50 (est) (only for verts)
6)Nitto DR $375-$425 installed
500rwhp and up
7)PHP toe link bars $410
8)Maximum Motorsports UCA/LCA Bushings $550
9)Strange ADJ Shocks $59ea from HBH Billetflow mount bushings $50
10)Level 5 shafts $1500
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 bullsh*t advertisement, this is a critical reinforcing mod to keep your diff/driveshaft/trans safe from breakage. They are also the best looking and strongest available. BF IRS BRACE
2)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.
3)IRS Subframe bushings
from Maximum Motorsports. Others sell them but I have used three sets of these now (3 different cars) with excellent results, no reason to look elsewhere. 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
4)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 brackets
5)Coupe rate springs or heavier (especially in verts). Coupe 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 avalable lowering springs. Drop will be 1"-1.25" with 1/2 coil cut.
6)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.
7)Pauls High Performance Toe Link bars
The Toe Link Bar is the weak 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 Bars
8)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 Motorsports
9)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. You can have full control over the ride of your car after this mod. Cruise in total comfort at #3 or launch hard on slicks at #10. BE CERTAIN to do UPPER BUSHING MOD to prevent clunk or negative NVH problems.
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 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
Step by step IRS drop instructions:
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. Pull it out of the trans.
4)Remove tires.
5)Remove shocks, disconnect from top and bottom.
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 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. Pull back on top of spindle and slip the brake line
out fromo under the UCA. Remove brake line bracket which mounts to UCA.
Replace the upper spindle bolt.
9)Remove rear IRS subframe bolts. 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. Remember
to swap out the stock 12mm front IRS bolts for the new 14mm bolts from
MM.
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
FRONT END TORQUE SPECS
Front shock absorber upper nut - 74 ft/lbs
Front shock absorber-to-spindle nuts - 148 ft/lbs
Shock absorber upper mount-to-body nuts - 30 ft/lbs
Shock absorber upper mount-to-body bolt - 30 ft/lbs
Wheel hub and bearing retainer nut - 258 ft/lbs
Stabilizer bar bracket nuts - 52 ft/lbs
Stabilizer bar link nuts - 14 ft/lbs
Anti-lock brake sensor bolt - 53 in/lbs
Anti-lock brake sensor wire bracket nut - 21 ft/lbs
Ball joint-to-front wheel spindle nut - 129 ft/lbs
Front suspension lower arm-to-body nuts - 148 ft/lbs
Tie-rod-to-spindle nuts - 41 ft/lbs
Steering gear-to-crossmember nuts - 52 ft/lbs
Wheel nuts - 95 ft/lbs
postban's trans removal writeup
1)Disconnect Battery
2)Get car up on jackstands, tall ones, need 12" under the tires airspace
3)Remove Shifter handle, bezel/plate and then shifter.
4)Remove mid pipe
5)Remove driveshaft (trans plug to keep from leaking or wrap tailshaft with towel/ziploc "diaper") Drain it works too.
6)Remove Trans mount
7)Unplug all electrical connections from the trans
8)Remove clutch inspection cover
9)Detach clutch cable
10)Remove lower 4 trans bolts
11)Support with trans jack
12)Remove remaining upper trans bolts
13)Slide trans back and lower trans jack down
14)Remove Starter 13mm socket, tons of extensions
15)Remove Bellhousing bolts (remember there are two on the front face holding the bellhousing shield on)
16)Remove Bellhousing
17)Remove pressure plate bolts and pressure plate/clutch
18)Remove flywheel bolts and flywheel
Do LDC cooling mod!
INSTALL
19)Be sure bellhousing shield is in place on dowels
20)Install new flywheel and bolts 60ftlb
21)Hold clutch plate in place with alignment tool
22)Attach pressure plate and bolts, 35ftlb (BE SURE clutch alignment tool appears to be sticking straight out before you tighten too hard.)
22)Remove alignment tool
22)Install Bellhousing and bolts, remember the two that face forward attaching the bellhousing shield. The two top bellhousing bolts also hold a bracket that supports some wiring. 60ftlbs
23)Install starter 30ftlbs
21)Put trans in any gear (with your finger)
22)Raise trans up with trans jack, insert input shaft into clutch slowly while slowly turning tailshaft (aids alignment)
23)Push trans all the way forward, install trans bolts 40ftlbs
24)Install trans mount and bolts 40ftlbs
25)Reinstall all electrical connections on trans.
26)Install Clutch cable
27)Install clutch inspection cover
28)Reinstall driveshaft and bolts 100ftlbs
29)Reinstall midpipe 30ftlbs
30)Reinstall shifter/plate and bezel
31)Lower car
32)Reconnect Battery
