I am just going to copy and paste this over from a thread that i created. Hopefully some of you will have an idea or two:

Info:

Turbo LSx Rx7 with a Grannys solid rear end conversion. (Tourque arm setup) Double adjustable shocks in the rear, lakewood 90/10 shocks in the front. NO ANTIROLL BAR and NO swaybars. Ford 8.8 with a Trac Loc LSD.


As of last year the car worked great with no issues. Over the winter i installed a 10 point roll cage. I did nothing to the drive line components. Last weekend was my first trip to the track for a test and tune. Things didn't go so well. I couldnt get it to hook at all with slicks on the car. Out of frustration, i threw on the drag radials i had since i did well with them last year. The drag radials worked, and allowed the car to hook. However now i have a crazy bad wobble or wag from side to side.

I relate the Wag to going downhill on a skate board and it starts getting a high speed wobble before you get bucked off. I made two passes at the track this way and it had the wobble both times. I can go out on the street, and go any mph and it will not wobble. Anything from 10 mile an hour to 120 mph. If you maintain speed, or accelerate slowly it does not do it. Now if you roll into the power or really give it the loud pedal, it will do the wobble while accelerating.

All of this being said, i did get the car in the air and i noticed the watts linkage was way close to the bracing around the torque arm. It appeared that when the car would launch the watts link would rotate into the diff and not allow it to move. I adjusted it out farther by shortining the bottom link, and extending the top to re center it in the car. Took it out tonight, and under hard acceleration, it still has that same wobble.
Does anyone have any ideas of what could be going on here? This is definitely not normal and not safe. Its really throwing me off because only the cage was added over the winter.

Any help or ideas would be greatly appreciated.
Thanks.

Oh, and the video as stated. Watch from about the 60 ft on. You can really see it on a large screen instead of a phone.

Video:

 

These are the only think of:

1. Are wheels equally torqued down?
2. Are wheel/tires balanced?
3. Is the front suspension adjustable?
4. Is front suspension torqued down?
5. Re-check rear suspension while being loaded.
5. If your running radials out back, make sure your running radials up front.


I have often heard people experience a high speed wobble when they run bias ply out back and radials up front. Just make sure you run bias ply with bias ply and run radials with radials.

I hope you get this figured soon. This is all I could think of. Good Luck!

 

A couple days ago i went out on the interstate to get a few more symptoms. It is not speed based. I can do 20 or 100 mph and maintain speed, and the car will not shake or wonder.

I can do about ahalf throttle acceleration and it will not wobble.

However, if i go full throttle and accelerate hard, it will wag back and forth the entire time im in it. And its not a slight wag like how the sidewall of slicks feel, its more of a hard wag that goes out pretty far. More intense then how a set of slicks feel on the rear.

 

What tires you running up front?

Are they the same as the slicks in the rear?

 

This video and all testing has been on a drag radial. Radial in the front, radial in the back .

 

What rear shocks/spring rate and length are you running? What is the length of your shock at ride height? On the launch the car is dipping to the right rear.

 

Have you checked the inner and outer tie rods? Did you make sure the car was perfectly level, before, during, and after you welded in the cage? Did you go get a 4 wheel alignment after the install?

 

The reason I asked these questions are, you have bumpsteer going on. And that and the change in traction can all be contributed to the cage install. If the car is not tweeked to bad from the install. Then the 4 wheel alignment should take care of it. And he will tell you if you tie rod ends are bad, if you cant tell.

 

Rear shock is double adjustable. Spring rate is 150#. The shock is damn near fully extended at ride height. The car dips to the right on lauch due to no anti roll bar. The car has always twisted on launch.

Here is the car with the exact same setup before the cage went in the car.


I went over this with the cage builder. He claims that all was well when the cage was welded in. No, there was no official alignment done after the install. Just some tape measure work in the garage. However if it was an alignment issue, i dont believe it would do the wobble ONLY under hard acceleration. It wont do it when cruising at any speed and it wont do it on normal acceleration.




I purchased a Tru Trac to throw in it last night. One of the theories was that the car was over powering the LSD that was in the rear transferring power from one tire to the other and back and forth causing it to drive side to side trying to walk over itself as it switched back and forth. Not sure if it will help, but its a decent upgrade that was most likely needed in the long run.



Any other thoughts guys?

 

Now you have more weight in the car, the shocks may be topping out as the car settles or not enough travel for separation. Tighten up the rebound on the the rear shocks and see if it affects the wobble. Remove the rear shocks and measure the compressed and extended length.

 

I actually had 140#s of sand in the back of the car last year on the second video i posted. The cage went in, and the sand came out of the rear. I bet the car is lighter now then it was last year. Obviously the weight is now in different places though.

I do have the rebound quite loose and the compression quite stiff....

 

What rear spring rate are you running?

 

" Ford 8.8 with a Trac Loc LSD."

Betting the traction loc has **** the bed.

 

150# springs in the rear.



This was my thoughts as well. I pulled it out, checked the clutches and all of them look brand new. Barely any wear on them at all, dont look like they got hot or anything. However, i figure i may be just over powering it. I purchased a Tru Trac to go in it. When it arrives i will get it all together and see if it helped the issue any or if i/we were all wrong in thinking rear end.

 

[QUOTE=Phish806;19596037]Rear shock is double adjustable. Spring rate is 150#. The shock is damn near fully extended at ride height. The car dips to the right on lauch due to no anti roll bar. The car has always twisted on launch.
However if it was an alignment issue, i dont believe it would do the wobble ONLY under hard acceleration. It wont do it when cruising at any speed and it wont do it on normal acceleration.

You need to get an arb. Now that you have th cage in the car, the chassis won't twist anymore. Now the whole car will be rolling over. Being you have a small amount of extention left on your shocks, your probably lifting the rear on hard accel. Causing loss of traction. And on hard accel, your car transfers the weight and the front comes up and stays at close to or even full extention. This can cause the steering geometry to change. And if your car is setting low enough that your tie rods are going up hill to the hubs you will need a set of bump steer eliminators. Take it to get a 4 wheel alignment where they know how to do drag cars. But first put on an arb. It will make all the difference in the world.

 

No wishbone or any kind of rear locating device?

 

Its running a watts link setup to locate the rear end left to right in the car.

 

[QUOTE=TTur1996;19597260]


So how do i get more extension out of the shocks while maintaining the same ride height? Would it be stepping up to a longer extension shock?

Also i agree totally that it needs an ARB.

 

Need to more about the shocks. What is the stroke of the current shocks and what is the free length of your current springs?

 

The shock right now is a viking double adjustable with a coil over style bottom.

13.61" Compressed - 21" extended

I have a 14" 150# spring on them


They do have one step longer which puts it at 23" extended.