SparkyJJO

iTrader: (11)

Hi guys,

Last weekend I replaced all the bushings and ball joints on the front end, new non-adjustable LCAs and relocation brackets on the rear, an adjustable panhard, Bilsteins, and Strano springs. I have the LCAs in the upper holes and adjusted the panhard to get the axle centered again.

When I took it to the shop this morning to get aligned the thrust angle was off. I forget how much, I don't have the printout in front of me at the moment, but I want to say it was just under half a degree. Adjusting the panhard gets it to a 0 thrust angle but that makes the axle kicked to the driver side a decent amount and looks really stupid.

Obviously adjustable LCAs would allow for fixing the thrust angle while still being able to keep the axle centered under the car. But I thought that you only needed adjustable LCAs with aftermarket rear ends, or when running a tall tire to perfectly center the wheels? Or is that half degree thrust angle a non-issue?

LILWS6

Makes me want to check mine. I just centered my rear when i put the phb on and didn't have it checked on a rack. Maybe i should do that at work one of these days. I haven't had any problems driving mine with the rear centered and i have non adj. lca's with a 12bolt.

SparkyJJO

iTrader: (11)

I just checked, the thrust angle with the rear end centered was 0.39.

SS SLP2

iTrader: (8)

"...the thrust angle with the rear end centered was 0.39."
__________________
with 0.39 ( I suppose to be +) car MAY push to the left under hard hit, I like to run my car @ + 0.03 and pull stright, each car may react different, If I remember correctly thrust angle should be
within +/- 0.13
when money allows I sugest adjustable LCA, AND adj.TA,
just my .02'

Johnny

SparkyJJO

iTrader: (11)

Yes, +0.39. Allowed range according to the sheet is +/- 0.15. Hm, maybe that would counteract the desire of the rear to swing right when breaking traction under hard throttle lol

Makes me think that with stock everything back there it was still a positive thrust angle as the rear was visually pretty centered before. I had set the adjustable panhard to the same length as the stock arm, then only had to tweak it a little bit from there to recenter. The adjustable arm was longer than the stock bar to make it 0.

I wonder if I could shim the LCA relocation brackets at all to adjust it closer to 0 without having to buy new LCAs (again)? Also I wonder how much variance these LCA relocation brackets add. All it would take is to have the hole drilled ever so slightly forward or backward to tweak the angles and change that thrust angle.

LILWS6

mine also swings right under traction loss. Not that that ever happens

SuperSport01

Have you tried swapping the left and right LCA's to see if it helps the thrust angle? Also check the rear end centering and thrust angle with driver weight in the car... it does make a difference.

UMI Sales

iTrader: (1)

The Panhard adjustment should have a negligible effect on thrust angle I'd think. Thrust angle is more dependent on trailing arm length.

-- Ramey

leadfoot4

iTrader: (1)

I agree!

SparkyJJO

iTrader: (11)

I agree as well, but it does make 0.38 degrees worth apparently. I guess after thinking about how it all works together it does make sense that it can play a part.

I haven't tried swapping LCAs back and forth, but even if I did I'd have to have them put it back on the rack to check after the fact. I don't have an alignment rack, nor any idea how to measure the thrust angle without one.

It seems to drive fine with it centered, and while I haven't done any WOT runs due to serious tire traction issues I have opened it up some and haven't felt like I've had to fight it to hold it straight.

Flubyux2

Do these cars normally step the the right when the tires spin??

Mine steps left, even when I had the stock rear lca's. I know for a fact that my left lca is adjusted longer than my right so my axle is def thrusting to the left now. But on stock lca?

Also, would the thrust also be a cause for a "pull" to the right when on flat ground? I have to drive with holding it to the left just a hair. I don't recall my alignment being off on the stock lca but it seems to be now.

LILWS6

Depending how bad the trust was off i would say yes it could pull. What the thrust angle is is basically the degree of straightness the rear follows the front. so if its off .50 its off center about a half a degree while driving straight. so the rear is sort of turning the car a little bit all the time.

SparkyJJO

iTrader: (11)

Mine seems to have a slight pull, if I let go of the wheel it'll start to drift left. Thrust angle or due to the caster setting in the front being slightly more positive on the right wheel? Not sure there.

Is there any way to DIY measure thrust angle? The shop probably wouldn't let me put my car on their alignment rack and mess with stuff I want to try tweaking my arms/brackets/etc to see if it is just something like a slight left/right arm difference or whatever.

I may be taking it back to have the alignment in the front tweaked a little (put half a degree negative camber back in, even out the caster). I might want to wait until I get good tires before I do that however, as maybe the drifting might be caused by these crappy worn out tires.

LILWS6

car will usually drift to the side of the car with less caster so that might be your pull if you have more pos. on the right

Rare96LT1Formula

iTrader: (32)

Not to thread jack, but I also recently installed UMI 2 pt. bolt in subframes, Founders 3 piece poly joint LCA's, relocation brackets, and their adjustable PHB. I installed the LCA's in the lowest hole off the relocation bracket. How will this setup perform on the street? Should I move the control arms up to the next spot?

Subscribed!

z28bryan

iTrader: (7)

Maybe it will shave off a few seconds the next time you head to the grocery store

SparkyJJO

iTrader: (11)

But you just did

Really don't know exactly. Try it and find out

BMR Sales2

iTrader: (40)

Do you have the factory 10 bolt in the car or do you have an aftermarket rear end like a 12 bolt. 9", or Dana 60? If you still have the 10 bolt the thrust angle issue is going to more than likely be with either the lower control arms or relocation brackets since those are the parts that really determine what your thrust angle is.

If you have lowered the car at all I would start off in the very bottom hole if not start one hole up from the bottom and see how the car acts.

SS SLP2

iTrader: (8)

"I don't know but I been told"...look at tne angle of the LCA , it needs to be a few degrees ( 5-7 ) lower on the rear than on the front, on the street I suggest one hole lower than level, if too much angle is possible to get some crow hop on the rear at very hard braking.
just I been told, now u been told, Johnny

SparkyJJO

iTrader: (11)

Factory 10 bolt. This car has killed a few 10 bolts in its life, but this one has taken a beating and still lives. It'll stay until it blows.

Is there a good way to check the thrust angle in the driveway? I suspect the most likely source of thrust angle being off would be from the relocation brackets not being bolted in quite straight. If I could measure thrust angle then I could easily make some adjustments to how the relocation bracket sits.