Frequently Asked Questions
I'd like to post a few quick comments here. I seem to be answering a lot of the same questions regarding the kit so I'm going to try and address a few of them here.
Q: "Why does my car wheel hop?"
Q: "Why does the ass end of my car feel so squirrelly when I mash on the fun pedal?"
Q: "Do I need subframe connectors?"
Q: "Are shocks and springs important?"
Q: "What does SN-95 and NVH stand for?"
Q: "How much increase in NVH will I see with this kit?"
Q: "How bad will the noise level be with 4:10's?"
Q: "My rear cover is leaking. (again) Why does this keep happening?"
Q: "How much stiffer will the ride be with these new bushings?"
Q: "Do I need level 5 halfshafts?"
Q: "I see that you offer a 36mm socket. What's it for?"
Q: "How important are the adjustable sway bar end links?"
Q: "Why do I need the 9/16" bolts and where do they go?"
Q: "Where is the bolt that rubs on the wide rear tires?"
Q: "What components am I NOT getting with your kit compared to the kits of your competitors?"
Q: "What does your kit offer that I'm NOT getting from your competitor's kit?"
Q: "How hard is this job?" " I'm comfortable doing a clutch job."
Q: "How long will the job take?"
Q: "I hear the terms polyurethane, urethane and poly. What's the difference?"
Q: "How important is bumpsteering the IRS?"
Q: "I'm still having trouble grasping the concept of bumpsteer!" "Help me!!"
Q: "Are there any other benefits to bumpsteering the IRS?"
Q: "Do I really need the bumpsteer/upgraded toe link kit and how necessary is it?"
Q: I drag race. How important is bumpsteering the car?
Q: "You offer two bumpsteer kits, what's the difference between the two?"
Q: "Why do I hear a clunk in my drive train?"
Q: "Do I need a rear cover brace?"
Q: "Are there instructions included?"
Q: "How can I be assured you sell a good product and can be trusted?"
Q: "What if any surprises might I expect installing the kit?"
Q: "What would you suggest if I wanted to do this in steps?"
Q: "Lastly on your bushings and I know you don't recommend this, but it is too costly for me in one shot to buy the whole kit from you, so is there a set you recommend that I could do while the IRS is still out of the car and purchase the other bushings at a later time that won't be to difficult to install when is in the vehicle?"
Q: "Is there anything else I should do while I have the IRS assembly out of the car?"
Q: Do I really need the removal tools you offer to remove the OEM bushings?
Q: "Can I expect this kit to cure my wheel hop like waving a magic wand over the car?"
Q: "How does the kit perform?"
Bruce's reply to Jack Hidley's (Maximum Motorsports Tech) internet message board post.
Link to original post on SVTPerformance.com........post # 26
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Q: "Why does my car wheel hop?"
A: There are a few reasons your car wheel hops. The biggest offender is all of the rubber in the differential mounts, control arm bushings and the subframe mounts. A secondary reason is sidewall stiffness of a hard street tire. It oscillates between traction and slip when it hops. The rubber compresses, then rebounds and repeats. If you remove the "give" (suspension rubber) it can no longer do that. Some tires can increase and or decrease hop to a certain extent. For the smooth application of power, you need a rigid structure (stiffer IRS assembly) and tires that will absorb some of the 'shock' of a launch. For instance an Eagle F1 will wheel hop on almost any car. Chassis flex is also a contributor to wheel hop. See subframe connector info below.
Q: "Why does the ass end of my car feel so squirrelly when I mash on the fun pedal?"
A: Mainly from all of the rubber in the entire IRS assembly. Your wheels are mounted to the rear knuckles and the knuckles are mounted to the subframe via control arms with rubber bushings in four places. (two places on the upper control arm and two places on the lower control arm) When you mash the gas, this pushes the lower control arms forward, compressing the rubber bushings which in turn, increases rear toe-in. How much the control arm moves is directly dependent on your rear tires, how much RWHP you are putting down and how much traction you are able to get. The upper control arms are along for the ride. Keep in mind the whole subframe assembly is also mounted to the chassis in rubber and who knows what direction the tires are actually traveling at this point. This uncontrollable wandering of the rear tires translates into a vehicle that is hard to control in a particular direction. By removing the all of the rubber, your rear tires will gain control of their direction and you will feel the ass end plant and increase traction in a much more controlled manner.
Q: "When I get on the gas hard, the rear end of my car wants to dart to one side and when I let off the gas, it goes back the other way. What's causing this?"
A: This is somewhat of a common Cobra IRS problem. The first thing I would check would be the 36mm halfshaft retaining nut that holds the rear hub to the halfshaft. It needs to be torqued to 240-250#. If it was loose, you most likely destroyed your knuckle bearing. If it was run long enough in that loose condition, you may have also destroyed your rear hub as well. If you find the nut keeps loosening up, you're going to want to replace the nut. Even if you found the nut was tight, you're going to want to jack up the rear end of the car and feel the rear wheel for looseness in all directions. If the nut is tight and you have play in the hub/bearing, the bearing and/or the hub needs to be replaced. The torque on the 36mm nut should be checked every time you change your oil or before you head to the track. Sometimes people find a loose attaching bolt on the toe link but that's not real common unless that's been worked on recently.
Q: "Do I need subframe connectors?"
A: Yes absolutely, any SN-95 chassis needs a good Full Length Sub Frame Connector. There are many subframe connectors available on the market today. You can get them from Steeda, Meier Racing, Paul's High Performance and a few other places as well. Stifflers and Global West also make an excellent set. They are however a little more pricey and a little more hard core. You just won't be able to do a side exhaust if you ever want to. If you have a convertible, I like to refer to these cars as "special needs vehicles". These are POSITIVELY necessary with a convertible. In fact, if you have a convertible you are going to want to consider the Stiffler or Global West systems that would include their matrix/spider bracing. With a convertible you need the best chassis stiffening you can get your hands on period. Be sure the subframe connectors are being welded on the car with the suspension "LOADED" as it would be on a drive on lift and not with the tires suspended.
Q: "Are shocks and springs important?"
A: Yes, factory shocks are going to give you minimal help in the effort to reduce wheel hop. You want a good aftermarket shock. If you have a convertible you have a 'special needs' vehicle. You are going to want to at least switch your springs to the coupe version which are slightly stiffer. Or better yet a lowering spring, race spring or coil-overs will be even more help.
Q: "Everyone is talking about a solid axle swap and I'm thinking about doing it, what is your opinion?"
A: Hogwash I say! If you don't care about handling or ride, then you won't miss your IRS. My advice to you would be give the IRS a chance. The IRS is a FAR superior suspension component than the archaic stick axle. There is a reason why every sports car from every major manufacturer comes from the factory with an IRS. How many true sports cars have SRA's in them? Well none actually! Unfortunately for Cobra owners, they have a sour taste in their mouth regarding the IRS. The IRS was delivered from the factory in a very poor state. You really need to remove ALL of the rubber (and or aftermarket poly) from the entire assembly including the subframe. The only way I would recommend a stick axle would be if you had a dedicated drag car that you trailered to the drag strip.
Q: There has been a lot of talk regarding solid rear axle (SRA) conversions, I'm undecided on what to do, what's your opinion?
A: Well the simple answer is this: If you're more concerned about drag racing and going fast in a straight line and you're less concerned about quality of ride and handling, then a SRA conversion will serve you fairly well. But you need to remember, a Cobra is a more expensive vehicle than a Mustang GT because it has upgraded components on it that cost additional money. And an IRS is considered one of those upgraded components. But.......................
The more complicated answer is this: If you're a very sharp mechanical engineer, and you've spent many years researching, designing, developing, testing, racing and executing the production of motor vehicles and suspension systems, there is still a very slim chance you'd be more knowledgeable than a team of SVT engineers. SVT engineers came to the ultimate conclusion that the SVT product line would be better served with an IRS under it. It unfortunately came quite compromised due to NVH requirements which has led to many of it's issues and unpopularity, particularly as the rubber suspension bushings age and wear.
Numerous centuries ago when wagons were built to be pulled behind oxen and horses, the SRA was axle of choice. Roman's put SRA's on chariots. The first motor vehicle produced back in the late 1800's had solid axles on it as well. Both front and rear. As you may have guessed suspension systems, just like anything else have improved in design over the years. Almost every vehicle on the road now has an independent FRONT suspension on it with the exception of four wheel drive vehicles. Independent REAR suspension systems have become so popular due to improved ride and handling that they don't just come on high performance sports cars any more. They also come on pony cars, two and four door sedans, sport utility vehicles, mini vans and many other vehicles as well. There is a reason that every high performance sports car manufactured today, comes from the factory equipped with an IRS. The SVT Cobra Mustang, considered a pony car, is one of many high performance cars that came with an IRS. The Corvette, which is without a doubt one of America's most successful sports cars, came with an IRS starting in 1963. That's more than forty six years! These cars all came with an IRS for a reason. Their manufacturers decided these car would be better served with an IRS under them for improved ride quality and superior handling.
Yes, handling can be improved to a SRA adding things like a torque arm, panhard bar or a watts link. But they will never be an IRS. Some people like the idea of swapping to an SRA because they will reduce their vehicle's weight by about 150#. This is fine for drag racing but for street manners you are making a vehicle that already has a lopsided F/R weight distribution of 57/43 (for an '03-'04 Cobra Mustang for example) even MORE unbalanced. One other thing to keep in mind is a SRA will add a substantial amount of unsprung weight to the rear suspension. Some people run these GT axles with GT rear brakes. Brakes are a safety item and for people that are making their cars faster with aftermarket parts should not be downgrading their brakes. They should be upgrading them.
Cobras are more sophisticated vehicles than a Mustang GT for numerous reasons, making them considerably more expensive . They have a higher performance engine, sometimes equipped with a supercharger, better transmission, improved brakes, wheels and SUSPENSION including the IRS. These cars are already depreciating fast enough without downgrading the rear suspension to that of a Mustang GT. Be certain what you are deciding to do with your car.
In closing I'd like to say the ultimate decision is in your hands. It's your car, do with it what you want.
Q: "What does SN-95 and NVH stand for?"
A: SN-95 is Ford's code name for the Mustang and Cobra platform covering the years 1994 through 2004.
NVH is Noise, Vibration and Harshness. It's a key design criteria for new cars these days. Americans like nice cushy quiet rides. But us "Car Guys" want our power to get to the pavement in the most efficient manner possible. So, bye-bye rubber!!!
Q: "How much increase in NVH will I see with this kit?"
A: The change in NVH will hardly be noticeable with the exception of the aluminum front differential mounts. They can be a bit on the noisy side in some cars. The NVH will be worse if you have 3:90 or 4:10 gears. If you have an aftermarket exhaust that's loud, it will help mask the noise from the diff mounts. Some have used the sound deadening matting available at car stereo shops to minimize the sound. It's a self adhesive matting you put down on the floor pan right above the differential. It's called Dynamat and it's also available at Eastwood.
Q: "How bad will the noise level be with 4:10's?"
A: 4:10's are definitely going to raise the noise level particularly with the Aluminum front diff mounts. As mentioned above, if you have loud aftermarket exhaust, that will help. Some people put down Dynamat on the floorpan directly above the differential and that seems to help a lot. Some say it's noisy, and others have said it's not bad. It's like asking what the best beer is. You won't get the same answer from any two people.
Q: "My rear cover is leaking. (again) Why does this keep happening?"
A: The rear cover leaks or keeps leaking because the differential housing is not stabilized. It's impossible to stabilize the differential in OEM rubber (even if new) or aftermarket poly. Once the differential is stabilized, the rear cover will stop leaking. In extreme power level cases, (550 RWHP and up) you are going to want either a rear cover brace (at the minimum) or the Ford Racing upgraded rear differential cover (best option) we offer. With higher RWHP levels in the 600 to 700 range you may need to upgrade the rear cover with larger fasteners. When you reseal the rear cover, use the gray Ford silicone sealant in generous amounts. Make sure you're starting with a very clean surface. Don't put lube in for 24 hours allowing the silicone to cure. Be sure the pinion seal and halfshaft seals are not leaking as well.
Q: I was going to buy one of your rear differential mounts and was wondering if using a urethane front diff mount will have a negative effect. "
Your plan for the diff mounts is a bad one. You never want to have the rear of the differential housing stabilized with our mount and try to have the front stabilized with that lousy poly. You'd run the risk of cracking the rear cover with that combination. No different than replacing the front with aluminum and leaving the rear rubber or poly. That would run the risk of cracking the front mounting ears. Always replace the front and rear differential mounts at the same time stabilizing both ends of the differential housing.
"I see that you offer a Delrin isolated lowering rear differential mount FT 1401. How's that different from your FT 1300 Delrin rear diff support?"
A: The FT 1300 Delrin rear diff support bushing set replaces the rubber bushing in the OEM mounting bracket. Used in conjunction with our front diff mounting bushing set FT 1200, you will be able to improve your driveline angle as it came from the factory but you will not be able to completely optimize it. In order to be able to completely optimize the driveline angle you'd need the lowering rear diff mount. If you currently have a driveline vibe I would highly recommend the lowering rear mount. If not, you most likely don't need it. The FT 1401 comes complete with the Delrin bushing installed in it. The FT 1401 is modified to work with the Ford Racing rear diff cover we now offer. However, if you're using the FT 1401 combined with the Ford Racing diff cover you will run into some clearance issues with the inner toe link mounting brackets on the subframe. We are currently working on some specs to modify the Ford cover and mill it so it fits in the subframe without any clearance issues.
Q: How much stiffer will the ride be with these new bushings?
A: The ride ironically enough, will improve and be less harsh. Unless you are changing springs and shocks at the same time, you will actually see an improvement in the ride. This is because the control arms are now articulating freely as opposed to being bound up like they are with the OEM rubber bushings. Many customers have commented on this as a matter of fact.
Q: "I have a cobra with wheel hop. My car is a daily driver, but I want to fix the wheel hop problem and keep a smooth, quiet ride. Is this possible? I want the IRS to be as sturdy as possible, but still have a smooth, quiet ride for the most part. What would you suggest?"
A: I get this question a lot. If you want a (and I quote) "smooth and quiet ride" you're going to have to put up with wheel hop. Simple as that. Or get a Lexus to drive as a daily driver. You can't have your cake and eat it too! We are dealing with a Mustang here! Here is what I suggest: Put the complete kit in your car. If you have aftermarket exhaust and stock gears you will hardly hear the front diff mounts. If you hear them a little bit and it bugs you, put down some Dynamatting on the floor pan above the differential. (on the inside of the car underneath the rear seat) The complete transformation your car will make with this kit will rapidly make you forget how much you miss the nice quiet cushy ride! That is about the best answer I can give you!
Q: "Do I need level 5 halfshafts?"
A: Most likely not. The 1999 halfshafts are really not sufficient for mildly to highly modded cars drag racing with slicks or DR's even after you remove all of the rubber in the IRS assembly preventing wheel hop. Your best bet at that point would be to upgrade to a 31 spline gear carrier and install '03 halfshafts. If you then break one of the '03 Ford halfshafts, AND you have removed ALL of the rubber from your IRS assembly, you may need to look to the aftermarket. We have customers that have proven once you remove all of the rubber in the entire IRS assembly, you can successfully run well over 600 RWHP with OEM Terminator halfshafts. The '01 Cobras have a 31 spline halfshaft but they are not quite as stout as the '03 style.
If you have an '03 - '04 you have a pretty stout halfshaft already. Have you broken any of these Ford halfshafts? If you answered yes, then possibly? But ONLY if you've removed all of the rubber in your IRS assembly and still broke a halfshaft. IMHO more halfshafts have been broken due to the flopping of components mounted in rubber, than broken because of sheer power. This includes L-5's. Also, as previously mentioned, a tire with a very stiff sidewall like a Good-Year Eagle F1 will not absorb a lot of the shock of a launch and will contribute to halfshaft failures. Once all rubber is removed from the IRS assembly and you break a halfshaft, then by all means you're a candidate for looking into the aftermarket.
Q: "I see that you offer a 36mm socket. What's it for?"
A: The 36mm socket is a tool that EVERY Cobra owner should own. This socket will allow you to check the torque (240-250#) of your rear halfshaft nuts. This should be done at every oil change if you're a street driven car or before every racing event. (1/4 mile or road course) It is also the correct socket for when your non-serviceable front hubs need replacing. This socket, along with a 1/2" drive torque wrench that goes to 250#, belongs in the tool box of EVERY single person that owns a Cobra and works on it themselves. This socket will also fit the retaining nut on your front hubs and allow you to change those yourself. The socket we offer is priced below what you can buy it for at your local Auto-Zone or O'Reilly's.
Q: "I see you are now offering cross axis joints. What can you tell me about them and do I need them?"
A: We are offering the cross axis joints for several reasons. The first reason is because they are not available from Ford unless you buy them in a complete knuckle assembly. The list price of a knuckle assembly from Ford as of May, 2010 is over $600.00. The second reason is because our competitors only sell them in a set of four and you normally only need to replace them one at a time.
Replacing the joint with our unit is not an 'upgrade' in performance. The OEM joints are just fine unless they get play in them and then they need to be replaced. It's very common for the OEM boot seals to tear or rip on these joints from mis-handling, but that in itself does not mean the joint is bad or needs to be replaced. If you have torn boots and the joint is still tight you can clean the boot up and repair it with some black Permatex RTV. You can check the joint for play by jacking up the car and wiggling the wheel from the 12 and 6 o-clock positions.
Two things that typically destroy these joints are: #1 road racers that run race slicks will typically wear out these joints, the left lower in particular. #2 would be impact with a curb after losing control of the vehicle.
Q: A few years ago I installed Maximum Motorsports IRS bushings in my car and now I am
experiencing a LOT of play in my upper control arm. What's causing this?
A: This is a VERY common problem that many users of MM Delrin IRS bushing kits have experienced. There are a few inherent design issues with these parts and it will not take long for this excessive play to manifest itself as an ill handling car.
Once you replace those with our parts, your problems will be gone.
Here is some video footage showing the play in a set of MM upper control arm bushings:
Loose MM UCA Bushings (Tire Wiggle)
Loose MM UCA Bushings (UCA Slop)
Loose MM UCA Bushings (UCA Slop, Close-up)
Loose MM UCA Inner Sleeve
Q: "How important are the adjustable sway bar end links?"
The adjustable sway bar end links are necessary to properly set up and balance your suspension if you are on coil-overs.
They are also a lot easier to install and remove compared to the Ford OEM parts even if you're not on coil-overs.
Q: "Why do I need the 9/16" bolts and where do they go?"
A: Your car came from the factory with a 12mm bolt holding the front portion of the subframe into the chassis. This attachment point has the capability of accepting a 14mm bolt or a 9/16" bolt. The 14mm bolts are insanely expensive from Ford and that is why I have substituted the 9/16" grade 8 bolt in it's place. This kit is all about getting the job done as economically as possible without sacrificing quality or integrity in any way shape or form.
Q: "Where is the bolt that rubs on the wide rear tires?"
A: Those are the rear subframe mounting bolts. I don't like the aftermarket "button head" bolts because they have soft heads and they tend to strip out when you try to remove them after a few years. I prefer to grind about half the head of the bolt off. This will leave plenty of head to remove with a six point socket when necessary.
Q: "What components am I NOT getting with your kit compared to the kits of your competitors?"
A: There is NOTHING you're not getting with this kit. A bumpsteer kit is included in some of the more expensive 'packages' from our competitors. Ours is sold separately.
Q: "What does your kit offer that I'm not getting from your competitor's kit?"
A: Our kit has an anti-wear Hardcoat on the aluminum inner sleeves for the control arm bushings. You don't get that with the our competitor's kits. Many people have worn out the steel inner sleeves for the control arm on our competitor's kits. One competitor in particular only offers a polyurethane (poly) subframe bushing. Poly is only marginally better than the OEM rubber that originally came in the car from the factory. The UHMW pieces you get with this kit will hold your subframe infinitely more firmly than a poly bushing. This is important for the elimination of wheel hop. We also offer grease fitting kits for a long trouble free life of silent operation of your kit. Our competitor's rely on their assembly lube to lubricate the bushings for life.
A: UHMW is Ultra High Molecular Weight Polyethylene. It's a great material and there is a specific reason we chose it for the subframe bushings.
Q: "How hard is this job?" " I'm comfortable doing a clutch job."
A: If you can do a clutch, you can do this. The more tools you have at your disposal the better. Get a competent friend to help. Supply the food and beer. It will be worth it.
Q: "How long will the job take?"
A: This job is a considerable undertaking. It requires some car wrenching skills and an assistant. An assistant will make the job go much easier. Two heads are always better than one. If you start on a Friday after work, you should have the IRS out of the car in a couple of hours. You can finish the night taking apart the IRS for the bushing install. Saturday you will spend installing the bushings, reassembling the IRS and hopefully getting the IRS assembly back in the car. Speed depends a LOT on the people doing the job and the amount of tools/equipment at your disposal. You always have Sunday to finish up in case you run into some snags. If you can locate someone that's done the job once or twice before you might be able to knock the job out in 6-8 hours with two people. If you have a couple of knowledgeable people that are good wrenches, a lift, air tools, a trans jack and a well equipped shop you could knock this job out in four or five hours.
Q: "I'm not comfortable doing this job, how much should I expect to pay for installation of the kit?"
A: If you are not comfortable doing this job yourself, installation cost varies on the shop. I would say the low end for labor would be in the $700.00 range. But to be honest, don't expect a lot of shops to do it for that. On the higher end, you're looking at possibly as high as $1,000.00 for the basic kit. Installation of the bumpsteer kit and bumpsteering the IRS would be additional.
Q: "I've done a bit of work on my car in the past. Do you think this is a job that can be tackled at home?
A: Take a look at the installation video we shot recently. It shows all of the preparation steps involved in the project, the removal of the subframe from the chassis and the subframe prep and bushing install. This will give you a much better idea if you feel comfortable doing the job yourself.
Prep and IRS removal from chassis:
http://www.fulltiltboogieracing.com/Videos/FTBR_IRS_REMOVAL.wmv
Subframe disassembly and prep Part 1:
http://www.fulltiltboogieracing.com/Videos/FTBR_Subframe_prep_part_one.wmv
Subframe disassembly and prep Part 2:
http://www.fulltiltboogieracing.com/Videos/FTBR_Subframe_prep_part_two.wmv
Subframe Install:
http://www.fulltiltboogieracing.com/Videos/FTBR_subframe_install.wmv
More videos on this project coming in the very near future.
Stay tuned!!
Q: "I hear the terms polyurethane, urethane and poly. What's the difference?"
A: The terms poly and urethane are simply shortened versions of polyurethane. And there is no place for them anywhere in your IRS assembly.
A: Definition; Bump Steer is when your wheels steer themselves as they travel up and down in their suspension range. The undesirable steering is caused by bumps in the road or track interacting with improper angle of your IRS toe links. When your tires move up and down in their normal suspension travel, your rear toe setting changes which scrubs speed.
Most car builders design their cars to push (understeer) when taken to the limit. A push is infinitely safer than oversteer. It warns the driver much sooner and is easier to recover from. But a push is not fast, nor is it efficient. You can optimize the IRS by installing a rear bumpsteer kit and increase cornering efficiency. This is of particular importance if you've lowered your car with aftermarket lowering springs or coil-overs.
Q: "How important is bumpsteering the IRS?"
A: Bumpsteering the IRS after this bushing install is like putting icing on a cake. It's not critical for drag racing unless you're looking for ways to shave some extra tenths off of your ET. For guys that like to hound Corvettes in the turns you will really appreciate the optimization of a bumpsteer operation. It's a lot more critical if your car has been lowered. Adjusting bumpsteer is more for the efficiency of cornering and feeling the rear end of the car firmly planted.
Q: "I'm still having trouble grasping the concept of bumpsteer!" "Help me!!"
Lately I've received LOTS of inquiries regarding questions about bumpsteer from potential customers, purchasing customers and past customers of our Aluminum, UHMW and Delrin bushing kits that I'm selling on this site.
Explaining this with a keyboard is difficult at best. So I figured I'd do a video which is infinitely more informative than a few pics and notes!
So hopefully this will make bumpsteer a little easier to understand.
If anyone has any questions regarding bumpsteer or chassis set-up we'd be happy to explain it.
Q: "Are there any other benefits to bumpsteering the IRS?"
A: Yes, by going with one of our new bumpsteer kits you get the very much needed upgraded toe links. These help hold your rear tires more stable. Drag racers and road racers alike need to be concerned with these components if they have upgraded the power output of their car!
Q: "Do I really need the bumpsteer/upgraded toe link kit and how necessary is it?"
A: Well it depends. The OEM toe link is a weak spot in the IRS. So if you have upgraded the power level you need to strengthen this weak link. If your car is lowered on lowering springs or coil-overs, you will need to optimize the bumpsteer because it will have been thrown off quite a bit from lowering the suspension. So this kit is a double bonus.
Q: I drag race. How important is bumpsteering the car?
A: In my opinion, bumpsteering a road race car is much more important. But having said that, bumpsteering a drag car can also be very important for someone that is concerned with tenths. When your car squats during a launch or right after every shift, the rear of the car's suspension compresses and the rear tires are in bump. Leading up to the point where you shift, the car is no longer in bump. (well, not completely) So by bumpsteering the car, you are insuring your rear tires are pointed in a forward direction no matter what position they are in. If bumpsteer is not optimized your rear tires may be pointing in a direction that is actually scrubbing speed (toeing-out or in) going down the 1,320'. This obviously is not efficient as it could be if the bumpsteer was optimized.
Q: "You offer two bumpsteer kits, what's the difference between the two?"
A: The FT 1800 is our standard bumpsteer kit. It gives you the ability to adjust bumpsteer from the inner mounting location and it also gives you an upgraded toe link compared to the OEM toe link. This kit reuses the Ford outer tie rod and is more economically priced.
Our FT 1860 deluxe bumpsteer kit replaces all of the parts in the toe link assembly and no OEM parts are reused. You get an upgraded toe link and have the ability of adjusting bumpsteer from both the inner and the outer mounting locations.
Q: "Why do I hear a clunk in my drive train?"
A: There are a few reasons for this. Your transmission and differential can combine for quite a bit of play, but that usually is not the MAIN source of the "clunk".
A few things can contribute to the Cobra "clunk".
#1 would be the rear differential support bushing. The rubber OEM differential bushings are designed to handle about 390 RWHP driven in a moderate fashion. That eliminates about 98% of Cobra owners right there. This is what a rear differential bushing looks like after a few years of driving:
(click image to enlarge)
# 2 would be the front subframe mounting bolts that can contribute to the "clunk". The 12mm bolts that were originally installed at the factory allow play when applying torque and decelerating. This location is capable of accepting a larger bolt which will hold the front subframe mount more firmly in the chassis and prevent movement. See info above for the 9/16" bolt upgrade.
#3 would be a front diff support brace if you're running a 1999-2001 Cobra. The photo below shows three types of front diff support braces. The top brace is what came on Cobras from 1999-2001 and this brace does not incorporate attachment to the front differential mounts like the other braces do. These should be replaced with either of the other two. The center brace is what came on 2003-2004 Cobras and these are fine. The bottom brace is an aftermarket piece typically available from vendors such as Kenny Brown or Paul's High Performance.
(click image to enlarge)
Q: "Are there instructions included?"
A: Yes. The kit comes with EIGHT pages of VERY comprehensive detailed installation instructions. In addition to the detailed instructions included with the kit we also have many detailed photos on our site to assist in the installation procedure. These photos can be found under the link on our site titled Installation Photos and Tips.
Q: "How can I be assured you sell a good product and can be trusted?"
A: You need to look no further than our Testimonials link on our main page.
Q: "What if any surprises might I expect installing the kit?"
A: Because there is no "exact" location or position to weld the full length subframe connector to the rear unibody frame members, sometimes there can be a certain amount of interference depending on the location it was welded. One installer had to grind about 1/16" of off each side to get the subframe back in with the new UHMW bushings in place. Another installer had interference of nearly 1/4" on each side. This required a sawzall and a reweld patch afterwards. Those were the only two instances so far, so I think it's a pretty rare occurrence to have this issue on your install. But I did want to bring it to everyone's attention.
Q: "What would you suggest if I wanted to do this in steps?"
A: This project is a considerable undertaking. It's not an easy job. There is quite a bit of labor involved to drop your IRS assembly, replace all of the bushings and re-install it. There really is no good way to do the job in stages. You REALLY want to do it all at once and get it over with in one fell swoop! If you can't afford the kit, I suggest you wait until you can buy the entire kit. It's sort of like the question "All of the tires on my car are bald, I can only afford two, which two should I replace first, the fronts or rears?" All of the components in this package work in conjunction with each other. The key to the kit is the removal of ALL the rubber. Removing some or most of the rubber is only going to give you a marginal result.
Q: "I'm thinking of just doing the subframe bushings and diff bushings for now and probably the UCA/LCA bushings later on.
Will that be ok? Will I notice a big difference when I do the control arm bushings after the subframe and diff bushings?"
A: I don't like your bushing installation plan for a couple of reasons. Both the subframe AND UCA bushings require the removal of the subframe from the chassis. You really don't want to remove the subframe from the chassis any more times than you absolutely have to. But if you are on a crazy tight budget you're just going to have to do double labor. There really is no way around it.
In order of importance, this is how you should do it if you absolutely HAVE to do it in stages:
1st - Front and Rear Diff mounts
2nd - UCA and LCA control arm bushings
3rd - Subframe bushings
4th - Bumpsteer kit with upgraded toe links
Q: "Lastly on your bushings and I know you don't recommend this, but it is too costly for me in one shot to buy the whole kit from you, so is there a set you recommend that I could do while the IRS is still out of the car and purchase the other bushings at a later time that won't be to difficult to install when is in the vehicle?"
A: If you're on a crazy tight budget you need to do the front and rear diff supports as a first priority. Then the UCA bushings and the subframe bushings would be next on the list because they BOTH require the removal of the subframe from the chassis. Trust me, you don't want to do this job anymore times than you have to. Then at a later date you can do the LCA's which BTW are the most expensive of all the bushings. So you'd need F&R diff mounts, UCA set, subframe set, a grease fitting kit and upgraded front subframe bolts. But keep in mind the LCA's do a majority of the work in the IRS.
Q: "Is there anything else I should do while I have the IRS assembly out of the car?"
A: Yes. Because the fuel filter is very difficult to get at with the IRS assembly in the car, as long as it's out, now would be an excellent time to change your fuel filter while you have full unrestricted access to it. Another thing would be to torque your rear halfshaft to hub nuts at the conclusion of this job. Many have had these nuts come loose and once they come lose they can damage the hub AND knuckle bearing. You're going to need a deep 36mm socket and a torque wrench. Torque those bad boys to 250#. BTW, these nuts should be torqued every 2-3 months for street cars and before every event for track and race cars.
Q: Do I really need the removal tools you offer to remove the OEM bushings?
A: In a word, ABSOLUTELY!! Many people have commented on how much time they have saved and how efficient the removal tools are. They cost you a little bit up front but there is a nice deposit you will receive upon their return.
Q: Can I expect this kit to cure my wheel hop like waving a magic wand over the car?"
A: No. Although this kit eliminates ALL of the rubber in the IRS assembly and raises it's efficiency to a completely new level, it's not a cure all in every single instance. About 2-5% of our customers still have some minor lingering wheel hop issues after installing the kit. Usually they have a convertible, are on Good-Year Eagle F-1 tires and don't have subframe connectors. All of the information contained in this FAQ has been compiled to inform everyone of the things that need to be done to the car to make it rigid enough to be hop free.
Q: "How does the kit perform?"
A: It is state of the art on track. You won't believe how the car handles. The car drives like it's on rails.
Here are a few examples of Bruce's favorite pastime.
Passing Z06's at the track:
Here is Kyle's (aka Snake Eyes) review of the kit:
http://www.svtperformance.com/forums/showthread.php?t=424884
For drag racing and street performance, this kit also increases the efficiency of the IRS to keep the wheels pointed in a forward direction. Rubber in the IRS is your enemy and the more power you have, the more you need to upgrade your IRS assembly.
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