Colt

Hey guys,

I do a lot of road racing with my car and have never been able to power out of right hand turns because the car always lights the right rear tire. I have always thought it was a problem with the diff so I finally got a auburn racers unit installed.

I just took the car to a place to test it out and I was utterly disappointed that there is virtually no improvement with the new diff.

I'm thinking it has to be something with the rear suspension. Anyone have any thoughts?

SlickTrackGod

I would suggest checking the condition of the right rear shock be the first thing I'd look at. See what the compression stroke feels like if there is anything there ciompared to the left side shock. If that is the culprit then the chassis is leaning on the LR wheel coming off corners. Left corners it would still lean in the LR tire weighting it and keeping the car tight off corners- the other way would be a mess with right turns standing on the outside tire only(left rear)and overweighting/overpowering it

My question is how do you know its spinning- By feel? or is someone video taping it?

sofakingdom

iTrader: (1)

The cause might be completely contained in one word:

AlkyIROC

A posi should provide power to the wheel with the best traction. That doesn't mean you'll still get power to both wheels.

Under hard acceleration, a lot of things are happening to the driveline and suspension. The driveshaft and diff pinion are rotating counterclockwise. The pinion is trying to climb the ring gear and force it out the back of the diff. This rotational force is transfered to the diff housing.

When you launch hard, the torque of the engine is trying to lift the left front of the car. At the same time, the rotating diff is trying to lift the right rear of the car. Unless the suspension can equalize the torque, the right rear wheel will have less weight pushing down on it which means less traction or a one wheel burnout.

There are different things you can do. The simplest is to install an air bag in the right rear side to add more stiffness that the diff needs to force against. Although it will work, it's not a great solution since it's only adding resistance and not extra weight.

The best way to keep both rear wheels on the ground and also keep the car from twisting during a hard launch is to install a rear sway bar (anti roll bar). Even an open diff will have better traction with a rear sway bar. When the diff twists against the roll bar, weight is transfered back to that side to keep the wheel in contact with the ground.

For road racing a large front sway bar should also be used for the same thing. It reduces body roll in the corners and keeps more weight on the inside tires.

Colt

I understand the effects of torque, but i think my issue is beyond this. I believe my corner weights are horribly off which is most likely the main factor of this problem.
There is very few shops around here that have corner weight scales so its hard to get this checked.

GCrites80s

Do you have SFCs?

Colt

I have SFC's and a cage...

GCrites80s

Look here then:

https://www.thirdgen.org/forums/susp...less-grip.html

SlickTrackGod

Hi Colt, corner weights seems to me to be your isue also. HOWEVER, there is staitc corner weight and then there is dynamic corner weight. There is really a very slim chance you have any kind of substantial static corner weight issues with a conventional non-weightjack sping setup. The obvious thing to do is quickly measure fenderlip heights from side to side. If those don't vary more than a 1/4" then chances are the spring cups aren't much off either.

Now dynamic corner weights can and generally do cause havoc on an intended symmetrical setup road race car. That is cause by worn or faulty shocks. You need to check the shocks like I first started above and disregard any of these othe gose chased until that is ruled out.

Colt

I think its a corner weight issue as well. The car does have weight jacks on all 4 corners. I haven't been able to get the car corner weighted since scales seem pretty rare and people are asking an arm and a leg for doing it; also, i have just been busy getting the car running right. I will hopefully put it on scales soon enough.

sofakingdom

iTrader: (1)

Did I correctly just read that you have jacks on all 4 corners but no way to set them? That makes no sense at all.

You can AT LEAST get them close side-to-side by parking the car on a level surface, jacking up the front by the exact center of the K-member, then setting the rears to level the car; then jack the rear up by the pumpkin, and set the fronts level. Tweeek and tune from there. Won't be "exact" of course, but should be close enough to at least drive. Then you can adjust the ride height at each end of the car by turning the jacks on both sides an equal amount.

A set of scales costs less than 1 set of shocks or 1 set of tires. Well under $1000 for some fairly basic but at least functionable ones. Sounds like, given what you're trying to do, that would be considered indispensable. Right up there with a timing light, a DMM, a set of sockets, etc.

GCrites80s

Yeah yeah, I was just talking to Axoid about this kinda stuff on Sunday and he said his car was a total mess after he put on weight jacks but before he did what sofakingdom suggested in post #11.

plum92_camaro

I set my weight jacks with a digital caliper. They are within .003".

SlickTrackGod

What Sofa has suggested on trying to set a cars corner weights via jacking under the kmember is about as naive a statement I have read on the issue. (Now I understand my comment may be interpeted as rude- but it is not- it is just STRAIGHT FORWAD fact, that is what this tech forum is about.)

You can not set 50/50 x-weight of a car via that method- not even close.

Colt is better off puitting a half turn in one front and taking a half turn out on the other each way to see how each will effect the way his car handles. He will first hand learn from this and keep adjusting in a manor that will progress a better feel to him of how the car responds both ways in turns.

How a car handles on the street is a far cry from a balanced car on a track at high speed with race tires. This eyebaling level method will be fine for the novice street car driver, but is a far cry from a sorted competition car with a title on the line.

When you are all finished, check your alignment and then do it one again to make sure any alignment changes didn't just render what you did inaccurate...because it probably will...

Sofa- for the record so you understand what you are saying is not corrrect- when you turn both jacks on one side of the car equal. Whether it is both fronts, or both rears, the left side weight is differnet then the right side and thus will respond silghtly different building or dminishing x-weight. Ride height is tricky to learn- knowing which jack to turn and how much is whether any of you will believe it or not AN ART. You want to bet me on it then I will buy you a plane ticket out here to So Cal and I will make you a $500 bet + airfare that you can not get it correct setting a chassis where I will give you chassis heights in 8 jackings or less- otherwise you owe me the airfare + plane ticket. I do this stuff weekly, I am what is call an expert on this subject and am a paid professional on a race team because of this. and I would have a hard time in 5 jackings or less with all my knowledge.

Now setting a car on scales to set corner weights is no joke either. you may think you can get this set real easy, but never use scales much? then you will be taking up a lot of time rolling on and off them, jacking and resetting...repeat...repeat repeat- I guess I made my point- its not as easy as any one would assume. Now try it wil different spring rates on all four corners and guess which to turn while maintaining chassis ride height AND chassis rake...and then come talk to me...it is an art.

Now you know why scaling a car is very expensive. Most shops want $1000 to set up a racecar.

Now when you still read this and say it's easy- then let me measure your changes that most will consider two opposing corners of the car to be 1/16" off what the last setup was in rake. but close enough right? wrong. Consistancy is the name of the game..... A little rake change will change alignment specs and dynamic articulation of the suspension geometry. Ever so slight yes,but it still is a change that will take out that .10 of a second that may make the difference on winning or loosing.

Now, you wear out a set of tires, the next tires you buy are off in diameters because you did not record the previous set nor the new set, you then AND now have staggar issues you had no idea you were overcoming in setup tweaks. You baseline your car again and its just not working like it did...what next? most people blame the crappy tire company saying they must be changing the quality of these tires because this set is not gripping as good as the last (..because OF COURSE I "know" my setup is good)...not having any clue on unwanted tire stagger issues...etc. I could go on all day, but that give a little experience to any greennecks that there is almost always a lot more to this game as you think you have learned enough to be an expert.

Colt

look what i just scored:

SlickTrackGod

Very nice. Now you will need 4- 2"x12"x12' boards to lay behind them so you can roll the car back off then and do your adjustments- then all the way back to the end of the boards, then settle the chassis and roll it 10 feet forward onto the scales again to keep consistant with readings. Make sure the ground is laser leveled, if not them shim the pad underneath with a thin metal plate to get the pads all leveled..and then box outline the spot of each scale on the garage floor so you can later duplicate the working area.

edit to add. I would also suggest you always scale the car with a half tank of fuel exactly each time, and if you are not in the drivers seat them weigh yourself and be creative on weight placment in the drivers seat and floorbard to duplicate your weight- including helmet and safety gear if worn (ie Hans, extinguisher, radio, etc).

If you are road racing, then scale with a full tank (you are using more fuel than autox. The ruel load drop with a full to half is less percentage of rear weight ratio to front in drop than from half to empty drop. The car will stay just a tad more consistant- every tad in the right direction is good.

Colt

Heres the weights of the car as it sits with no driver. There is clearly something wrong with the rear suspension. I believe the issue has to deal with the swaybar mounts.

I just got these scales and haven't had enough time to corner balance the car, but I will when i get the chance.

sofakingdom

iTrader: (1)

I don't see anything wrong with that at all. Looks just about what you'd expect.

Definitely try tuning on it, and see what you can get; but don't expect miracles at this point.

Looks like you might be back to that magic "auburn" word. Too bad those thieves are still in "business" (I use the word loosely), scamming the unsuspecting public out of their hard-earned money.

SlickTrackGod

50.3 cross

you have a shock problem like I have been stating