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Old 12-16-2004, 10:29 PM   #1
RheacerDave
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Hopping Cobra

I've seen several posts about severe (DOH) wheel hop with the IRS.
Diff bushings seem to help (ok), sticky tires (??) too. Anyone know for sure what is happening when the wheels hop?
I have a Grigg's on the LX and get hop if I don't get braking, shift just right, but can accelerate just fine.
Are the Arms moving around, shocks not controlling bounce, both??
I bought car with 23,000 on the odometer, so I don't know what fresh shocks feel like on it.
Any definitive scientific answers?
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Old 12-17-2004, 03:41 AM   #2
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Quote:
Originally Posted by RheacerDave
I've seen several posts about severe (DOH) wheel hop with the IRS.
Diff bushings seem to help (ok), sticky tires (??) too. Anyone know for sure what is happening when the wheels hop?
I have a Grigg's on the LX and get hop if I don't get braking, shift just right, but can accelerate just fine.
Are the Arms moving around, shocks not controlling bounce, both??
I bought car with 23,000 on the odometer, so I don't know what fresh shocks feel like on it.
Any definitive scientific answers?
Are you going to drag race or Open Track? 2 different totally complete animals.
Read all the posts on both subjects. After you have figured out which route your taking, please ask away, this post contradicts itself in the end run


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Old 12-17-2004, 11:43 AM   #3
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Sorry, track days. 03 Cobra Conv

Hops in 1st,2nd, and 3rd. 2.8 pulley, Bassani long tube c X-pipe, dyno tuned chip.
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Old 12-17-2004, 11:56 AM   #4
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RheacerDave, there are a few post about how to fight off wheel hop.

Wheel hop is just that, the wheels bouncing up and down, oscillating, usually alterating from left side to right.

Causes:

  1. Not enough rate on the spring -- get stiffer springs <--great start
  2. Not enought dampening rate -- get better dampening shocks/struts <--great start, the 03/04 bilsteins are nice, but no where as good as aftermarket bilsteins
  3. Rubber bushing in the IRS, which are inherent to "play" and "warping of the rear suspension geometry -- get stiffer bushings, Urethane or Delrin for IRS, Differential, Upper/Lower control arms.
  4. IRS pumpkin not planted and moving -- get IRS brace, which 03/04's have, so not for you
  5. Differential Posi is inferior - the posi-track does not distribute 50/50 power to both sides 100% of the time. What that leads to is pulsed power from right to left, which cause the right to left oscillation, which leads to hop. -- get a better rear end, either a nice spool for drag racing, or a Torsen for open track.
just my experience and opinion, other will have a different viewpoint I'm sure.
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Old 12-17-2004, 01:03 PM   #5
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Bushing and shocks have always worked beforeon Fox bodies, which I'm fimiliar with.
Bummer this is on a 23,000 mile car, though. I guess shocks have worn.
I was concerned of a design flaw, or just worn out components.
We'll try replacing bushing with urethane and new shocks.
Is the differential actually moving around under there (stuttering) or is it the control arms, or a combination of both?
As for damping, I've used Bilsteins on racecars before, and like them.
Is the Diff the TracLoc with plates? I've rebuilt them before, no problem.
Thanks
Dave
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Old 12-17-2004, 01:43 PM   #6
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Quote:
Originally Posted by RheacerDave
Bushing and shocks have always worked beforeon Fox bodies, which I'm fimiliar with.
Bummer this is on a 23,000 mile car, though. I guess shocks have worn.
I was concerned of a design flaw, or just worn out components.
We'll try replacing bushing with urethane and new shocks.
Is the differential actually moving around under there (stuttering) or is it the control arms, or a combination of both?
As for damping, I've used Bilsteins on racecars before, and like them.
Is the Diff the TracLoc with plates? I've rebuilt them before, no problem.
Thanks
Dave
I don't think its 23k on the car as much as the stock items being on the threshold.

I guess you can kinda call it a design flaw, but basically,IMO, the "comfort'" items like the rubber bushings, make the IRS more cushy, but that also causes the linkages to not be stiff like they would with urethane or delrin, so basically, the fact that rubber gives, causes the IRS to shift under real heavy load. The control arms themselves are not the problem, and the aftermarket ones offered at this time (like Kenny Brown) only offer weight saving as their advantage.

Before urethane bushing, doing Open track, when I would throw her into a turn, I had to compensate because once the car went under load into a turn, the characteristics would change and the rear was sloppy and unpredictable. I think, IMO, not only was it shifting, but the shifting was changing dimensions of the suspension and the alignment in the turn.

Now with Urethane, it just sticks and goes. It is night and day on predictability. (even moreso on the delrin cars) Be forewarned, the bushings, especially 4 main IRS bushings, are very time consuming, and require a certain approach unless you want to spend all day on em.

I know that is Road Racing vs Drag racing, but the same "Give" applies under both conditions.

Also, as far as the different rear ends. I think that is a last item to look when all else is done. The stock trac lock does use the plates, but basically, the statement of not being 50/50, 100% time, is just in that design. A spool would be better for drag, and Some have used superior Torsen for road racing, such as this one http://www.globalwest.net/torsen_tra...fferential.htm . If you read the description, it kinda touches on how it is a better design than the stock one.

For dampners, the Cobra R rear Bilstein are much better for the rear than the stock 03/04 shocks. The best ones would probably be the Maximum Motorsports Race valved rear Bilsteins, but those are only made for live axle cars, not IRS. Lastly, you could always ship your stock Bilstein back to Bilstein, and for a fee they can revalve them for you to your liking.
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Old 12-17-2004, 04:55 PM   #7
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All makes sense.
Thanks
Dave
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Old 12-28-2004, 08:39 PM   #8
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Firme and others,
I already have the urethane IRS bushings (to be installed) and will be
ordering the urethane front and rear control arm bushings. Having said
that, do the aftermarket Bilstein shocks and struts make that big a
difference? I'm still running the stock dampners at 15k miles on a lowered
vehicle. Please let me know so that I can order everything at one time.
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Old 12-29-2004, 03:03 AM   #9
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I've had my H&R springs, Full-Length subs, Differential bushings, Rear Sub-frame bushings installed and I still have a bit of wheel hop. I was just wondering if I installed a Heavy Duty Cross Bar would it make any difference?
Any input would be greatly appreciated!
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Old 12-29-2004, 08:02 AM   #10
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my bushings and H&R's are going on soon, i'll let you know if this cures my wheel hop issue...but then again it doesnt really affect me too much right now as I havent been doggin the piss out of it yet..
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Old 12-29-2004, 09:25 AM   #11
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Hop is still uncontrolled movement, the best shock you can get should make a difference. I've raced on Bilsteins before and like them. Currently use Koni's on the A/Sedan car.
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Old 12-29-2004, 12:44 PM   #12
Firme
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Quote:
Originally Posted by Lumpydogs
Firme and others,
I already have the urethane IRS bushings (to be installed) and will be
ordering the urethane front and rear control arm bushings. Having said
that, do the aftermarket Bilstein shocks and struts make that big a
difference? I'm still running the stock dampners at 15k miles on a lowered
vehicle. Please let me know so that I can order everything at one time.
Yes, they make a good bit of difference. The best idea is alway to match the springs with the shocks/struts as far as rates go, but for wheel hop, you need a good, stiff spring, and a set of shocks/struts to match.

What kind of eibach springs do you have? The Pro-Kit might not be the way to go to remedy wheel hop since they are progressive rate and will alway be soft during the initial force back.

Quote:
Originally Posted by InfamousSVT
I've had my H&R springs, Full-Length subs, Differential bushings, Rear Sub-frame bushings installed and I still have a bit of wheel hop. I was just wondering if I installed a Heavy Duty Cross Bar would it make any difference?
Any input would be greatly appreciated!
If its was me, I would get the Cobra R bilsteins for the back for starters.
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Old 12-29-2004, 06:12 PM   #13
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Thanks Firme, I was looking at those a few weeks ago and I figure that will help out, so I'll be purchasing those sometime soon. Thanks for the info!
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Old 12-29-2004, 08:38 PM   #14
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Firme

One more question for you. I'm not really familiar with the bushings and stuff, but I've got the Differential bushings and the Rear Sub-frame bushings changed out to Urethane. I should also get the rear Control Arm bushings replaced as well right, these bushings are different from the ones I've already changed?
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Old 12-30-2004, 01:11 AM   #15
Firme
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Quote:
Originally Posted by InfamousSVT
One more question for you. I'm not really familiar with the bushings and stuff, but I've got the Differential bushings and the Rear Sub-frame bushings changed out to Urethane. I should also get the rear Control Arm bushings replaced as well right, these bushings are different from the ones I've already changed?
yup, they help from changing your toe under stress...amongst other things.

to sum it up there is:
Differential bushings (the pumpkin)
IRS Bushing ( the whole IRS 4 bushing for the 4 locations it bolts to the body)
Upper Rear Control arm
Lower Rear Control arm

The uppers are easier than the lowers..We torched and pressed the rubber bushing out, it was fairly quick
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- Magnaflow Catback, Magnaflow X-pipe, 03 Bilstein Shocks/Struts, MM front Coil-Over kit, MM STB, H&R rear Race Springs, MM IRS bushing, MM upper and lower rear Control arm bushings, Custom SFC. MGW shifter(replaced the p.o.s Tri-Ax), a whole slew of MGW pieces
 

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