I have a '91 RS. Last winter I rebuilt most of the suspension as it was worn out, and a prior owner had lowered the car by cutting the stock springs.

I feplaced the tie rod ends, adjustment sleeves, center link, idler arm and ball joints with TRW components.

I installed new Energy Suspension poly bushings in the control arms, and KYB GR-2 struts in front and Gas-A-Just shocks in the rear. I replaced the springs with Eibach Sportlines. I also boxed the rear lower control arms and installed Energy Suspensoin poly bushings.

I then put new Kumho Ecsta 711 tires in a 245-50-16 size on factory 16" flat spokes.

I had the car aligned at a reputable shop. The car seemed really "darty" at highway speeds and seems to "grab" grooves in the pavement at all speeds. I took it in and the re checked the alignment- they said it was fine, and gave me the printout (stock specs)

I have been doing some reading here and have realized the rear is probably not centered due to a stock panhard bar still in place.

If I install an adjustable model, where do I measure to center the rear?

I had a 1990 Ford Probe that handled like this- after front alignments didn't chage it and it still wore rear tires on the inner edges, I had a four wheel alignment done. The rear was toed in. After that it drove much better.

 

try going over to fl-thirdgen.org and looking up a guy named mrr23, He's the alignment guru over there. I know there's guys on this page that could also answer your questions, but he might be faster.

 

Drop a plumb bob (or any weight tied to the end of a string) over the rear fender opening when the car is sitting someplace flat (use a level, you’d be surprised) and measure from the string to the edge of the rim, adjust till you get the same measurement on both sides.

Lowing the car shouldn’t really effect this though, do the math, you’ll find that 2” change in ride height will effect the axle placement roughly .05”, way less then the factory tolerance (something like 3/16”)

 

If you can get a little more caster in the front alignment it will help. I see you have a V6, they tend to be much more responsive to slight steering movements than the V8's. It is very improtant to have the alignment done with a person in the drivers seat and best to try and get about +5* L/ + 5.5* R caster and the car will track better at speed and not be as twitchy.

The rear thust angle is best to be set on an alignment rack (4wheel align- but you need aftermarket adj provisions). Too hard to set this by yourself in your garage- its very hard to measure that exact.

Most of your wandering is most likely the result of tire quality and/or charateristics, and bumpsteer. You need to check the horizonal geometry of the suspension "mid" travel points and verify that you are not suffering from bumpsteer under suspension travel

I see you are lowered slightly with the Eibachs. If you have added relocation brackets, you might want to try raisding the rear mount position of the LCA's up a notch or two. Rear mount being too low on a V6 will really induce roll oversteer feel causing the nose to be "darty"

Lastly, centering the rear axle (as long as the car has not been in an accident) is preety much as simple as measuring the distance of the tire to the fender on each side making the offset fender reveal equal. Then the alignment shop can set the thrust if you have adj LCA's (This is not your problem with being "darty")The addition of a lowered axle panhard mount (lowering the rear roll center) will aid in taking the twitchiness out of the "darty" V6 and will create a little more push on the nose when the wheel is turned slightly -or- jsut the addition of an aftermarket panhard rod with urethane or rodend bushings will tighten up the rear and make the nose feel better underneath you also.

Hope that helps you with some ammo
Dean- Vsix

 

Thanks for the plumb bob idea 83
crossfire!

RTFC- I will install an adjustable PHB, I will go with poly bushings and align it right. I will talk with the shop that did the alignment, and get them to re set the caster per your suggestion with my wieght in the front seat. They do all our fleet vehicles so I know them pretty well.

Should I NOT get LCA relocation brackets? Will they make it worse?

As far as tire type etc. I still have to experiement with pressure, I'll use the chalk method on the tread to see what the contact patch is.

I'll take this one step at a time until I get the car to do what I want it to.

 

The LCA won't help alignment issues if they're straight. You could "string" the car.
You need to measure the wheel base to make sure it's the same from side to side. (make sure the diameter of the tires are accounted for)Take 2 step ladders and find the center of the vehicle. (take a LOT of measurements) run a string from both of the step ladders down the exact center of the car. Use a large square or the plumb bob to extend those measurements to ground level. Now, with the car straight, use 4 jack stands and run string down the side of the car just touching the outside of the rear tires. (both front and rear sidewalls of the rear tires)The measurement from the plumb bob hanging off of the step ladder should measure equally to both of the side strings, if not, then you need to center the rear end in the car. (adjustable panhard bar). consider yourself lucky that you don't have an IRS, you could be setting the rear toe as well. Now to the front, using the string extending from the now centerred rearend, and just touching the rear side walls. These side strings should be equal distance from the centerline of the front plumb bob as well as the rear. (not the same as the rear, but rather same from side to side). You then measure off of these strings to check the toe-in and adjust the same. You can also measure camber this way with a angle finder or even a level.
Basically, with the steering wheel centerred, everything should measure (as close as possible) the same side to side.
The really trick hi-zoot guys use a chassis plate and lazers, the rest of us use string and a concrete floor.

 

FWIW, and this is coming from someone way too **** retentive for my own good (IE, someone that, if anyone, something like this would work for), there are way too many places to introduce inaccuracies while “stringing” for most people to get any meaningful results out of it. I’ve tried it a few times, and after getting inconsistent results I tried it again, a few times in a row (probably 5x in one night with the same car) and found that no matter how hard we tried we could not get repeatable results more accurate then about 3/16” of an inch toe. You’d be shocked how much variation there is with a tire sidewall (especially skinnies) and even wheels. To get accurate, repeatable numbers you really have to eliminate that all the runout at whatever point on the wheel or tire you’re measuring to, which is next to impossible. In addition, slight breezes and lighting differences easily make a couple of 16ths difference in measurements.

If you really want to try it, I’d suggest jacking the car and marking the tire tread with something sharp while spinning the tire, to have a fairly well defined point to measure to on all 4 corners that should not show more then a few thousandths run out.

 

You're correct, that is also a good way to do it. The problem with that, (and you shouldn't have this problem on a street car,I'll admit) is that if you're running a different wheelbase from side to side, like an oval track car, then you have to measure toe from the right rear.

 

I'm having a similar problem, but my car will grab grooves on the highway and toss me around like a ragdoll...

also my car has FLAWLESS alignment, according to two different shops using computer alignment systems...

even so, somehow no matter what road I'm on, the car will pull sharply the direction the road is angled to... think circle race track, my car would swerve towards the inside of the curve and I would die... if I tried to follow the circle (or in normal terms, drive straight on the highway,) my tires wear weird...

if I am on a PERFECTLY flat surface, my car goes very straight, and brakes very straight... as soon as I go on an angle, or hit some grooved pavement... who knows what lane I'll end up in...

 

I havnt driven a thirdgen yet that wasnt darty specially on uneven roads its because of the tire width from what i can figure?Keeps the adrenalin flowin though

 

yeah I can't even count the number of times I've almost died becaue of crappy suspension

can we not adjust camber? i know there is something that we cannot change for some reason...

 

Its all suspension componants and adjustments- My car does NOT under any circumstance dart side to side from any kind of road imperfections or tire width. I run 245/50-16's.

Darting is generally alignment, bumpsteer, & worn componants.

I can drive my car down any road with just a thumb & finger grip at all times at any speed

 

Hmm, it seems that alot of people here have problems with the car drifting due to road conditions ie. grooves, slant, etc. But why do the majority of people blame it on the width of the tires? I don't think that this is completely true. I think that it has more to do with the sidewall height than anything else. I will give an example. My 94 Pontiac Sunbird, yeah it FWD but I built up the suspension. I have 16 inch wheels with P205/55/ZR16 tires. It has the Eibach Pro kit lowering springs, front strut tower brace, lower subframe brace, KYB GR2 front struts and rear shocks. I also put poly bushings in the front lower control arms as well as a 28mm front swaybar with poly endlinks. I added a rear 19mm swaybar too. Now I have the same problem as you guys do with the car 'grabbing' grooves in the road, and the car drifting with uneven road surfaces. BUT, look at my tire width, 205! Even the third gens have what a 245 width tire! That is a 1 inch wider tire than I am running right now! Your alignment could be perfect and still have this problem. But why you say? It is a mixture of the sidewall height and alignment. The shorter your sidewall height, the less deflection the tire has from side to side. Yeah that's great for increased steering response. Plus, most people don't have the equipment/tools/ability to do their own alignments so they take it somewhere else to have it done. This is OK, but most techs who perform the alignment only put it to stock specs, and make everything even from side to side. That gives you a problem with cross camber and cross caster. Here in FL we have terrible road crown. Road crown is the slope of the road(usually to the right) to allow water to run off the road. If the camber was set to the same in the front(-.5 and -.5 for example) the car would drift to the right because of the cross camber. So you have to take into account the crown and offset the camber to something like this(-.4 and -.6) This offset will want to make the car pull left slightly, but the road crown will keep it going straight. To give you another example with my car, the sunbird, I put my weight into the driver's seat and aligned it myself. My specs right now are

Camber -.7 -.9
Caster 3.0 3.2
Toe 0.05 0.05

And the rear which is at

Camber -.5 -.5
Toe 0.05 0.05
Thrust angle 0.01

I like the way my car handles. I can take a 90 degree turn at upwards of 60 MPH if I want and I have done it before. Like dean said, adding some more caster up front will reduce the amount of road feedback at higher speeds.It will also reduce the amount of steering effort to turn the wheel at 45+MPH but make it a little bit harder to turn at lower speeds. With my alignment setup now, I don't have as many problems with pulling unless the road is really bad/uneven. Try checking your old alignment printouts and see if your front camber/caster numbers are the same or really close to each other. If so, next time you have an alignment doen, ask the person to adjust it with a little bit more cross camber/caster and see if it helps. Damn, sorry for the long post!

 

Paulmore,

Caster is what affects the crown in the road, not camber.

 

I'm not sure that I understand that. The caster does not affect the crown in the road, the car is affected BY the crown of the road. I'm not trying to argue about who is right or wrong. I'm just telling what I 'see' by dong alignments on our Lexus cars. Also, being here in FL is very different. The crown of the roads is actually visible down here, you can literallystand in the road and see it slope to the right. What I was talking about above were things I know from my previous experiences. All roads are different, and all cars are different. Hell, 2 f bodies withthe same alignment specs will handle differently on the same stretch of road. I should clarify one thing. If camber and caster and toe were all adjust tobe equal on both sides, there is a very good chance that the car will drive straight on a road without a heavy crown. Under braking, however, you sill see some type of pull or drift. It will usually occur in the direction of the crown. This is due to the shifting of weight to the front of the car, and the rear of the car unloading. This causes a dramatic camber changes and makes it more susceptible to be influenced by the irregular road surface. But it doesn't make it any easier that our customs are kinda lazy and like to drive without their hands onthe steering wheel. So many of out customers complain about it, and when I go on a road test they take their hands off the wheel, and after about 300 feet the car starts to drift and they are like see, it pulls. I tell them that once they take their hands off the wheel the alignment is basically rendered useless. it's funny cause they don't understand.

 

yup my car pulls to the crown, and when I brake its very dramatic... I can never take my hand off the wheel ever... it sucks... I like having to not pay attention when I drive

 

"If the caster is out of adjustment, it can cause problems in straight line tracking. If the caster is different from side to side, the vehicle will pull to the side with the less positive caster. If the caster is equal but too negative, the steering will be light and the vehicle will wander and be difficult to keep in a straight line. If the caster is equal but too positive, the steering will be heavy and the steering wheel may kick when you hit a bump. "

+0.5*caster on the passenger side will puh the nose of the car slightly to the left and keep the car straight on a crowned road- most roads in the U.S. are crowned no matter where you live.

Camber has abosolutely nothing to do with straight line tracking, only cornering contact patch, and tire edge wear.

More caster (more as in +5* rather than +3*) will make a car track straighter and harder to turn.

 

This is like listening to a bunch of crackheads argue…



BULL****. Just because a computer tells a monkey it’s right doesn’t mean squat. If you’ve had it aligned 2x then you should have print outs. Tell us what they say and I’d bet that we won’t have to go any further to figure out what is going on. That is assuming that you actually had a proper thrust angle alignment and that they properly checked out the suspension and steering linkages for wear before doing it. (If you didn’t then it wasn’t done right anyway and we could be looking for anything)

If your steering changes significantly under braking then you know that something in the suspension or the brakes is wrong and you need to fix that first before wasting time on this.

Wider tires do make a car more susceptible to road imperfections, but to a large extent they can be compensated for. A 245 is not a wide tire. Not enough caster, too much camber, too much or too little toe in, worn out suspension/steering components… will all do it also. Sway bars that are too heavy will also cause those problems

I own 3 f-bodies that have front tires ranging from 235 to 275, and they’re all very nice and stable. None of them require an excessive amount of attention to keep going straight.



Exactly… .5* is usually a good cross camber difference, but make sure that this is with the car normally loaded (ie, driver in the seat).



Wrong. Camber can make a car darty if you’ve got too much negative camber or if your cross camber is too great. The thing is that you can’t really use camber to correct for it if it’s something reasonable. For most street going f-bodies, something in the -.5 to maybe about as much as -1 range is about optimum. More then -1 will wear tires fast. More then about -1.5 to -2 will cause the car to be darty and start showing braking problems. More then somewhere in the -2 to -2.5 range, well, if your car runs faster in that range that only means that you don’t have enough roll stiffness for whatever you’re doing to it; fix that and start over.

Most performance cars are happiest with something in the 4 to 6 range. Drag cars can be setup for as much as >10*. Be aware that caster effects ackerman angle, bump steer and anti-dive…, so if you insist on running large amounts make sure that you know how to fix those or only intend to go in a straight line.

 

when I said flawless... I was being sarcastic... since I know that shops don't know much... I actually went into an NTB and told them it was pulling around like an SOB and they went in to check the aligment, and entire suspension system... only to tell me that nothing was wrong at all

they have also replaced any warn linkages and what not.
my brakes are brand new, front and rear as well as two new rotors... fluid is new and the master cylinder is brand spankin' new... I used a mighty-vac to assure that no air was trapped in the MC.

I wish I could find that printout... it's been almost 2 years though.

and in Texas the highways are crowned, but the peak is in the very middle of the road, so the left lane side leans to the left, and the right lane leans to the right... if at all possible I will stay in the center lane... but its so severe that on some roads, if I were to let go of the wheel for more than 1 second, the car was completely swerve off the road... normal highways, I'd say if I was in the left lane at about 80... I'd have about 3 seconds before my front driver tire ran off into the dirt...

at least it makes me pay more attention--but it's tiring as hell to keep constantly correcting my position in the lane... I bet I look like a drunk driver sometimes to other people.... it's especially bad because my steering wheel has a slight bit of "play" in it, so I have to move the wheel about 3-5^ in the opposite direction before it does anything.