: Alignment specs?
Does anyone have the alignment specs for a few cars for me?
Specific on these years, as I have a book that notes some of these and I want to confirm:
(these cars share our front suspension)
1975 Grand Prix
1980 Firebird base and Formula/Trans AM (with and without WS6)
And as a large car comparo, 2000-2007 S-430/500 Mercedes, 1995-2001 and 2002-up BMW 740/750iL, and 1997 Bentley Turbo R/RT, and 2006 Bentley Azure. This should give some good indication on what alignments we SHOULD have....
I am working on revising the alignment of my car (94 Fleetwood) and seeing if I can come up with a more robust alignment. The stock specs suck, and even with some of my variations, didn't prevent nasty tire wear, so time to get far more agressive.
The tentative plan so far is:
Camber: -0.75 degrees
Caster: +5.5 degrees
Toe: 1/16" toe OUT
And before you tell me this will quickly destroy my tires, I can give the specs that DID destroy my tires and why I want to go with these.
Camber: 0 degrees
Caster: +5.5 degrees
Toe: 0 toe
I do drive enough to exceed good tire wear on these specs. Don't use if you drive like me! I did get 30K out of my set of 40K mile warranty tires, but the alignment is what did them in. Severe wear on the outsides due to too much positive camber (0 degrees is what it is set at).
I want MORE caster, but I think I am going to have to sacrifice caster for more negative camber, as I can't get enough camber gain (caster) in corners. So we just have to up the ante.
I do my own alignments if I can, but probably go have the shop set this up with my specs after I have them toss in another set of control arms that I am setting up with new bushings and ball joints. Hopefully 5/8" ball joints if the set I have is a late 9C1 car (1995)....
Some additional reading on our cars... http://www.9c1.com/technical/info/alignment.htm
The Ape Man
08-17-07, 08:36 PM
I've been driving cars with the same chassis as yours since 1984. Always ran 0 camber, slight toe in sometimes reset by eye sighting the rims in line with the rear rims and about factory spec for caster. 35 PSI. My tires always come off for new ones because they are old enough to have dried out and start cracking. Wet traction gets bad and I junk the treads. Wear simply isn't an issue. Dunno why you are having wear troubles. Negative camber is for people who really want to wail around turns. Throw out the comparison to Mercedes. That brand is miles ahead. You can do a full lock circle in sand with one then go out and see every tire tread imprinted in the sand with no scrubbing. They actually change camber a lot as the car steers. The mid to late '90s S class drives a lot like an American car. Much less road feedback than most Mercedes cars. Maybe it has a lot less caster.
All season tires stink. Highway tread rules.
The tires I have are the Kuhmo's. I don't push corners that hard, that is what is puzzling me for the wear. Unless Cadillac ran excessively soft control arm bushings and they just are deflecting like crazy.
The 2000-up S500's are around 10 degrees caster. Not sure on the other alignments. BMW probably close. The 75 Grand Prix is supposed to be 5.5 degrees caster in my handling book, the 71 Z28 is -0.75 camber. The 80 Firebird is 1/16" toe out. All same identical suspension. Very close front sway bar dimensions. But I want to see what other specs they have.
I am looking at a doing the upper ball joint relocate kit (raises it up higher) to improve the handling. But overall the heavy weight of these cars and lack of strong sway bars doesn't help.
The crutch for poor suspension design is stiff springs, which help limit the travel of the suspension which often gets it out of the proper camber location. Also stiff springs helps keeps the weight transfer from end to end to keep it from losing traction on the other end of the car in a hard handling maneuver. The stock springs I do feel are a bit soft (Mine are FE2 springs, same RATE as Impala SS, but taller), I have some 9C1 springs that likely will go in with 1 coil cut off.
08-21-07, 01:02 AM
Hey guys, I hear spring rate comparison term thrown around a lot, but no real values. How do we find the actual spring rates of the various model and options, FE1, FE2, Imp-SS, V4P options etc. I'm always leary of making modifications and buying parts without actual specs to know what I'm getting.
I found something once. The Impala SS and Fleetwood FE2 have the same RATE, but different heights. I'll see what I can find, it was on the Impala SS forum that Bill Harper (Navylifer) posted, but it was a quote and I haven't found the original post.
I'll let you know! Should I post it in the tech pages possibly?
08-22-07, 12:02 AM
I would look at the rim width vs tire tread width. I would look at the center link also. Caster causes tire wear unless you are taking a test and then it does not.
I like a lot of caster. It makes the car feel heavy and centers the wheels. Over 3° to 4° of caster will cause tire wear on the outside edges. I hate 2° cars they drive like crap. I remember Radial tuned suspension from the 70's. It was more caster! I think I have 7° in my RX7.
I would look at the tire section, Center link, You are changing the control arms, Make sure the wheel bearing are set to spec (tight), and I would run an IMP SS shock.
The specs you listed look good. I have talked to you so I am sure that the center link and ball joints should be good. If you can just get the car to suck down to the road instead of being up. I don't mean ride height, but the rebound. If it sucks down you will add camber and less outside tire wear. Heavy shocks
Rim width/Tread width are factory sizes. Factory wheels. Center link is newer (probably got 40K on it by now), tie rods tight, ball joints the alignment guy said all was good, although they do creak in tight slow turns, but they didn't show any alignment issues. Idler arm is unknown, will have to check, but that shouldn't cause tire wear per se, but should make it wander, which it doesn't. It has a pull I am working on dialing out, I think from camber lean (both tire leaning the same way, like both to the left, or to the right, it will pull that way too). Summitracing has a caster/camber gauge for $49 in the circle track pages of the catalog. That is what I would like to get, 2 of them would be ideal. I use 2 7 foot straight edges to set toe, which I need to reconfirm too, as I just changed camber.
How can high caster cause tire wear on the edges? I actually am seeing wear on the outsides, but inside ok, just not enough camber for the suspension design, so either stiffen it to eliminate the suspension getting that far out, or add negative camber so it will help, but when straight has tracking and other issues too on tire wear. The tire is perfectly flat on the ground with 0 camber and any caster. But it IS leaned back, so the contact patch is behind the pivot centerline of the suspension (yes, I have been studying front suspensions a lot lately...). I have 4.5 degrees caster now, 0 camber, 0 toe. I dial in as much as I can.
High caster provides harder to turn wheels, but better stability and better steering returnability. I haven't really found a drawback yet of high caster except slow speed steering can be a tad slower. I look at it as negative camber gain in corners.
I will check wheelbearings, they are past due for routine maint of greasing anyway. I just did brakes, but I didn't have time to do it then. But I need it. When I got the car it had a bad front wheel bearing (left front) do I swapped it out.
The Ape Man
08-22-07, 10:25 PM
Bad idler arm will eat both tire edges.
Won't it wander? Not just wear on the outsides? When I did the drag link, I couldn't get any play in it moving the wheels back and forth. Any other ways to check it?
And alignment guy said all was good.
08-23-07, 12:06 PM
High caster will cause tire wear on turns. The tires not only lean over, but depending on the steering axis of inclination it can cause major toe change on turns.
You need the toe to change on turns because the radius of the turn is different from the rear to both front tires. The inner tire of the circle needs to turn sharper.
Caster can help this, but if the SAI and ackerman angle is not right it will eat tires.
Actually positive caster the tire has negative camber gain the farther the wheel turns. Properly setup, it has less wear. Negative caster the tire will lean over. Not positive.
I wish I could do a CAD model of our front suspensions and play with it....
08-23-07, 01:59 PM
Turn the wheel all the way to the left and then back of 1/2 turn. Then look at the camber in the Right front. If you had turn plates you can watch the degree variance of toe from side to side as you turn the wheel. quick list of specs in °
IMP-SS, Caprice, Fleetwood
Toe 0.0° except Fleetwood and it is .16°
Toe .8° ?.
Camber .8° + or -?
S500's are in the 10 degree range. Highest I have seen.
The Ape Man
08-24-07, 08:27 PM
Look at SL and S series from the 80s. Those are even higher.
The one I looked at was a 2000-2002ish S430/S500. I was very surprised at how high the caster is.
I have been playing a small amount with mine, trying to add more negative camber on the right to eliminate a pull the right. I first started to add come caster in to one side, but the car went to handling goofy, so I went back to what it was, and then started to try to visually make sure the camber is equal from side to side. If it is both leaning one way, say, -1 degree camber and 1 degree positive camber, the car will lean towards the wheel with the most positive camber. So I started looking carefully at my front wheels, and the right seemed more positive than the left, so I started dialing in more negative on that side. The pull is not near as bad, and today, I noticed in the parking lots maneuvers, the ball joint creak is much reduced. Maybe coincidence, but definitely seemed less binding in tight slow turns. I used to get some "Ackerman squeal", or squeal because the Ackerman angles were off. Even after an alignment on the rack it squealed. I read the numbers personally, unless it was setup wrong, it read correctly what I had asked for (4.5 degrees caster, add a tad for road crown on one side, 0 camber, 0 toe).
I will dial in a bit more negative camber on the pass side more and see how it does, I have to get that pull out. I will then have to reset toe, as anytime you do camber or caster changes, more so camber, toe MUST be reset.
How do you set or check the Ackerman angles? Can an alignment rack actually do it? Or it is just trusting the GM suspension engineers that those specs are correct?
I think it IS key to follow closely the limitations and notes in the FSM need to be followed, like the max thickness of the shim stack, and the max difference between the shim stack front/rear and left/right. I will have to dig up the details in the FSM. Mine to do what specs above was no shift front right bolt, one 1/32 shim right rear bolt, and then 2 around 1/8" shim stacks on the 2 left sides bolts. Interesting that only those few shims were needed to dial it in like that.
Being out 77-96 cars share the front suspension with the 70-81 F cars and the 73-77 A/G cars, Dick Guildstrand has some alignment specs that are worthy at looking at for our cars.
The only thing he does that is different is toe in a tad more than I did. It does help tire wear and keep some twitchyness down, but the overall handling of toe out is a tad faster.... But tire wear can hurt if too much. Which is why I keep towards zero, and try hard to preload the tires in the toe out position manually to ensure it is as close to a preloaded toe condition and shoot for 0.
I finally have my 95-96 9C1/Limo lower control arms with the HD 5/8" ball joints, they will be getting rebuilt very soon and installed and a fresh alignment then. The joints are worn, and the bushings are gonna get replaced anyway. Anyone have any comments on bushings to install? I was planning on 9C1 bushings if available, but not sure on aftermarket.