Well first off Hi, been lurking for awhile but now I have a question I couldn't find an answer to. Ok so I have an '87 Iroc-Z, 350 TPI, mostly stock with bolt-ons. Headers and 3" exhaust, that sorta thing. So after buying it I realized the rear suspension was gone. Replaced the shocks with KYB GR-2's. Replaced the slightly bent LCA's with non adj tubulars from BMR. The panhard bar was bent upwards (like someone tried to jack the car up there), sideways like a Z, the whole thing was twisted, and it was cracked. Replaced it with a non adj from BMR. I thought for sure my problems were caused by the panhard. The problem being that on hard throttle lefts and when it was wet out, the rear end came around real quick, and a few times uncorrectably so. Right turns just result in a good roasting of the tires no matter what i do. The sway bar is still stock as are the springs. Oh and I'm also running BfGoodrich G-force sports 245-50zr r16, the left rear has good tread, while the right rear is getting near the tread indicators. (was like that when I bought it) So any input as to what is causing a severe imbalance in oversteering would be greatly appreciated. Thanks Tyler

Get an alignment and I'd be looking for other damage if the LCA's and PHB were bent.

I hate the be the bearer of bad news but you have a tweaked chassis most highly caused from a bad accident or hit on a curb. Tell-tell signs of bent componants you replaced.

What is happening is you have low cross weights, not neutral (negative cross weights meaning: the LF and RR tires are supporting more of the chassis weight than the RF and LR.)

On left turns you are loading only the RR tire and driving the cg (center of gravity) hard to the left. The LR tire is not loaded as much and thus not driving the left side of the cg balancing thrust.

on right turns the RR tire is thrusting on the inside of the cg and helps keep the car stable.

You have a tweaked chassis. You will have to try and get the car onto scales and have an expert shim the corner weights for you- then you have to worry how level the car sits visually once the car is 50/50 diagonal x-weights.

Dean

I understand the first part of your post, but would the part I quoted be necessary for a street only vehicle? I can see why it would be needed in a race car but corner weighting a street vehicle seems to be overkill. Maybe I'm just having a brain fart... its been a long day.

Mike

I believe he means this:
LF weight+RR weight = X
RF weight+LR weight = X

Not this:
LF = RR
RF = LR

Yeah, I know... but why would that be needed on a street vehicle? Like I said, I can understand why it should be done on a dedicated race vehicle.

it doesnt need to be perfect, just close.
if currently its:
LF+RR= 2000lb
RF+LR= 1500lb

then clearly there is a problem.
if he can get it close, such as:
LF+RR= 1700
RF+LR= 1800
then i'd say call it a day.
now thats a hundred pounds off of equal, and would still handle funny, but its better than before.

think about it like this,
right now, he is driving a pringle, one front wheel is putting less pressure on the ground than the other, causing the opposite rear to do the same.

i agree that it must have hit a curb or something though.
get the cross weights equal, or close, and come back

Thanks for the replies.

That certainly sounds like the problem. It hasn't been in any major accidents, but knowing the previous owners I could see them smashing the rear end into a curb or something similar. Note to self don't check over a car when its getting dark.

On another note, where would I find such a specialist, and what would the approximate cost be? Any chance at all that through trial and error it could be done yourself?

Thanks

No, you can't do it yourself. Take it to a body shop. When my brother had his fox fixed after he twisted the car, (DS door to fender gap was about 3/4", PS door to fender had no gap, door wouldn't open) it cost about $500 + an alignment.

I would suggest calling around a few suspension shops and/or alignment shops asking if they have scales to check x-weights. If they they jumble around the question then move on to the next call. Some performance shops will do race care setups for local circle track and road course racing. Here in So Cal we have numerous shops llike this. Most of the time this is pointless on a street car without adjustments, but tell them your problem and you need to check the car's corner weights to see if that is the confirmed trouble you are suffering from. One quick scale reading will tell you your x-weight percentage. It really should not be worse than the range from 45% to 55%. Scales will give you this reading. It will be the calculated percentage of weight on the RF and LR tires combined.

*50% is neutral and ideal.

* Lower than 50% will tighten the car on right turns and loosen it on left turns.

*Higher than 50% will tighten the car to the left and loosen it on right turns

You are probably sitting about 40-45% xweights so you are way loose left and tight right.

Dean

ps- scale the car with a full tank of fuel and you IN the drivers seat with both hands on the steering wheel.

What about a bad, worn, or damaged when hitting a curb limited slip? Spinning tires when turning right with out sliding seems like the inside tire is spinning and oversteer when turning left seems like your overpowering the outside tire. How does it turn when not hard on the throttle?

With the spider gear setup a posi will just go towards an open diff rearend when the cone clutches wear. That would mean the inside tire always spinning (one tire fire) when load is transfered on the heavier tire the lighter tire is driven. this is not his case.His remains one sided, this would only happen with a spool having one side splines broken- no way that internal sidegear cone clutch individually broke or wore from a side hit- I just do not see it happening- But stranger things have happened.

If the spider gears broke, he would be hearing some terrible noise and I am pretty certain he would also be feeling some terrible clanks when the assembly rotates. He has no mention of this.

the first thing to break from a side hit would be the c-clips or the spider gears on the pinion shaft or something in there bending or breaking- but again, it would make one hell of a noise when rotating and grinding- disc brakes would hold the alxe in place but the axle still spins. If the axle broke? again, one hell of a noise.

Surprisingly, he has not come back in here with any followup???

Dean

sorry i haven't replied, I just started school and have been pretty busy. I haven't talked to any specialists nor will I probably get to it soon. At low speed, say idling to 1/4 throttle, it behaves the same left and right. 1/4 throttle to breaking loose the tires, the rear end almost hops through the turn. I dont know how else to describe it. I'll have to pay a bit more attention next time. But it feels like the LR (on a left turn obviously) unloads or something, because the rpms will jump a bit at the part of the turn where its the sharpest, and I get the hopping sensation.

And a note on the posi...its pretty beat. For the most part its basically just open. However now and then the posi does actually work.

What if one cone in the 9 bolt were worn, or the other were sticking or galled? My old worn 9bolt had a split personality. Either way he'll have to spend money and time to fix the problem. Just another hypothesis.