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What's "Thrust Angle" wheel alignment mean?


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#1 MANGO

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Posted 03 December 2003 - 11:51 PM

Ok, I'm gearing up to get an alignment done for the car so I'm looking at shop ads and I saw two things that were advertized by just about any of the ads, "thrust angle alignment" and "four wheel alignment."

Now, "four wheel alignment" is pretty self explanatory, I assume they align all four wheels but what is "thrust angle alignment"?  Is that correction of camber?  

Or is that the type of alignment process that they do?  If so, but why call it separate of the "four wheel alignment process?

If they do four (or two wheel) alignment, do they check for camber automatically or do I have to request that separately and also charged for it separately as well?

Thanks
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#2 artinist

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Posted 04 December 2003 - 05:35 PM

i am not a 100% sure but sounds like a gimmic phrase. if the car has an adjustment for camber, they will do it while doing 4 wheel alignment.
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#3 MANGO

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Posted 05 December 2003 - 04:30 PM

This is the info I got off of the Technical Terms Glossary on the Web.  I get the whole thing about the crooked steering wheel but all the other details its talking about I vaguely have an idea about.



THRUST ANGLE

The angle between the thrust line and centerline. If the thrust line is to the right of the centerline, the angle is said to be positive. If the thrust line is to the left of center, the angle is negative. It is caused by rear wheel or axle misalignment and causes the steering to pull or lead to one side or the other. It is the primary cause of an off-center or crooked steering wheel. Correcting rear axle or toe alignment is necessary to eliminate the thrust angle. If that is not possible, using the thrust angle as a reference line for aligning front toe can restore center steering.



THRUST ANGLE ALIGNMENT

Aligning front toe to the rear thrust angle instead of the vehicle’s centerline to compensate for rear axle steer.
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#4 Dcrasta

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Posted 04 January 2004 - 10:05 PM

From what I understand Thrust Angle alignment is what they do when you have a solid rear axle.  They align the car (front suspension) to the angle that is created by the drive axle (rear).  This is done so you car will track in a straight line with the wheel centered.  4 Wheel alignment is when the alignment is down with all 4 wheels pointed in the same direction.  Since Camber, caster and toe cannot be adjusted with a solid rear axle car it has to be done using the existing 'Angle' that is created from the orientation of the rear axle.  Hope this helped (somewhat).  Our cars should have 4 wheel alignment done to compensate for stuff like the camber change in the rear with weight for example.(like when the car squats when u leave from the line, you want the tire to be square with the ground for good / better contact).
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#5 long4boost

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Posted 09 January 2004 - 10:57 PM

thurst line...


thurst line is a line drawn from the middle of the rear tires (axle) down the geometric center line of the vehicle.  this aligenmet angle is use to project which way the viechel is going to pull or not.  it is the combanation of the rear right and left toe numbers.  acctable thurst line for a fwd vichel is .05 degrees, for a rwd car is .25 this is one of the main angles that causes dificult driectional stablity of the vichle or pull as it were.


not a gimmic at all..  uh and if you have any questions or dis belifes i have my ase test results in my room saying i passed steering and suspension. thanks thats alli have for to night
peace
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#6 TMeitz

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Posted 27 January 2004 - 10:30 PM

In the most simplest term. they are going to set the rear toe-in.   If you have both the left and right wheels toe-in or out and they are evan. Then you have a thrust angle of 0.  Which in theory the rear is tracking Squarely with the front.  If you have the left rear toe-in .10 and the right rear toe-out-.10. You then have a positive thrust angle of .20  a** end of car wants to drift to the right which in turn makes the car drift to the left. Provide the front end is in align.   some Chrysler mini vans call for a thrust angle of .47. that is about 1/4 inch out of square.  TMeitz

#7 Ernie88TSi

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Posted 06 February 2004 - 12:50 AM

When doing a 4 wheel alignment, you can do a center line, or a thrust angle alignment.  With a center line, it does just that... aligns the front end to the center line of the car.  A thrust angle alignment will compensate for the rear end pulling the car in one direction or another.  

Every car has a thrust angle, solid rear axle or independent.  But with an independent rear suspension that has adjustments, you can compensate it, and set it to the centerline of the car.  

Our cars have no camber adjustment on the front, and only a small amount in the rear, although they will know what the camber reading is when they do a swing on the car.  Correct spring height and no bad parts (like say the strut tops) will keep the camber in spec.  

One thing to keep in mind is that when doing an alignment the front end must be tight.    That means no loose tierod ends, ball joints, etc.  Instead of a $49.95 alignment, you may be looking at a $200 bill to get everything correct.  Of course, the shop will tell you before they do any work like that.  

Another thing to watch for is tires, they can cause a drift or a pull.  While on other cars you can just rotate them to the back,  not so on ours, obviously.  A tire pull is pretty obvious, you just cross-switch the tires, and it'll either drive straight, or pull in the opposite direction.  

Ted, when did you take your ASE test?  Didn't know you were that far along in your classes.   Man I hate some of those questions, at first they look easy, and then you reread something that'll trip you up.  
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#8 MANGO

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Posted 06 February 2004 - 08:28 AM

The steering wheel was a bit crooked when I got the car, like the very top center of the steering wheel is pointing a bit at 11 o' clock.

I told the shop to straighten the steering wheel when they do the four wheel alignment.  I was told that they couldn't adjust the steering wheel anymore than where it is already, like it's already absolute.  Do I need to take the car to a different type of alignment to get the steering wheel corrected?

Even when I adjust the steering wheel, like remove it from the stalk on the steering column, the splines don't really get it straight but rather it gets it pointing this time at 1 o' clock.  It's either 11 or 1 o' clock when I try to take the steering wheel off and do a correction but never dead center at 12 o' clock.

Any solution to this?

Thanks
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#9 Ernie88TSi

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Posted 09 February 2004 - 11:45 AM

Take it to a different shop.  Part of doing a CORRECT alignment is making sure the wheel is centered.  That's by far the #1 complaint for a customer, is they pay for an alignment and the damn wheel isn't centered.  Will the customer notice a slight drift?  Probably not.  Will a customer know that they have a little too much camber, and their tires are going to wear badly?  Nope... but that steering off a little bit, and you better believe they'll be back in 5 minutes, raising hell.  

You're steering wheel being offcenter is directly related to what your toe is set at.  Everything can be set where it needs to be, but if your toe is off center, the steering wheel WILL be off.  When doing a thrust angle alignment, when you get done it *should* be straight.  Sometimes when doing a centerline or 2 wheel align, the steering wheel will be off, even though the two is set even.  One thing to keep in mind is that the rear end will steer the car... Kind of hard to expain, but if you visualize it, it'll become clear.  

In the centerline/2 wheel align, to center the steering wheel after you've set everything is really simple.  Say your wheel is low on the left, about 11 o'clock, just like you're saying yours is.  Probably a 1/4 turn on tierod ends will be enough to correct it.  Basically what you're doing is turning the wheels just like you were doing earlier with the steering wheel.  a 1/4 turn pushing the wheel out on the left side, a 1/4 turn pulling the wheel in on the right side, should bring the wheel back on center.  

That shop you took it to is either a) lazy or cool.gif doesn't know what the hell they're doing.  Stay away.  My advice would be to find a small shop in your town that does nothing but alignments, and is well established.  They'll do it right, and do it right the first time.  
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#10 MANGO

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Posted 10 February 2004 - 12:07 PM

Thanks Ernie.
There's no way they'll just do a "just straigthen my steering wheel" right, and leave the camber the way it is?  When they do an alignment, they go through the whole process right?

If they try to correct the tie rods/steering wheel, that will affect the alignment I just had done right which means they really DO have to do the whole thing over?

Or more so, they'll just do the steering wheel straightening like I'd request but probably still charge me the whole alignment fee right?

So I guess I might as well grin and bear it and pay for another 4 wheel alignment.

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#11 Ernie88TSi

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Posted 24 February 2004 - 06:46 PM

QUOTE
There's no way they'll just do a "just straigthen my steering wheel" right, and leave the camber the way it is?  When they do an alignment, they go through the whole process right?

If they try to correct the tie rods/steering wheel, that will affect the alignment I just had done right which means they really DO have to do the whole thing over?

Or more so, they'll just do the steering wheel straightening like I'd request but probably still charge me the whole alignment fee right?


Well, because of the lack of camber adjustment, they basically will just "skip" over that step.  If the camber is so out of adjustment that it's causing a bad pull, you've got something bent/broke anyway.  Caster still needs to be adjusted properly.  The reason I went the route I did to get my camber in spec is because my car is lowered about 1.5inches (ground control coil-overs), plus I went with a rather aggressive setup.... although doing that will decrease tire life.  I doubt most shops will be willing to do something like that, plus you chance them not knowing what to do.  

I do not recommend that you go in and ask them to just adjust the steering wheel.  While you can ask, I doubt any shop will do just that without atleast checking it... making sure the steering wheel is straight is the last step in an alignment.  Without making sure everything else is right, you're risking tire wear, increased fuel milage, and you're not getting the best handling out of your car.  

Do you have a phone number, and a good time I can call?  It'd be tons easier to explain over the phone.  You can just PM me with it.  
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#12 MANGO

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Posted 12 March 2004 - 04:27 PM

Thanks for the info everybody.  I do agree, I might as well replace every worn rubber bushing that needs to be replaced that involves the suspension, steering, tranny and engine mount.

Been eyeballing the Stedebani complete bushing package but oh man, the price tag on that package stings!!!!  I'm sure it's cost effective but just don't have that much dough squared away right now.  

What difference those will make I'm sure.

Ernie, thanks for the phone call offer, one of these days I'll take you up on your offer once I'm really stuck!

Thanks
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#13 bang4thebuck

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Posted 25 May 2004 - 04:39 PM

question...... Ive got way too much positive camber on my driver side front wheel !!!! Is there really no way to adjust the camber ???? It is making my car pull to the left, any help????

#14 mikec

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Posted 30 May 2004 - 09:48 AM

If you've got out-of-limit readings on front suspension alignment you've got something bent in the front of the car:
control arm tweaked
spindle bent on base of strut
bodywork damage causing strut to be tipped
track control arm bushing totally fried
track control arm mounting bolt bent
upper strut isolators that are worn so bad they're unsafe.  

I wouldn't be surprised to hear somebody whacked a curb with that wheel sometime in the car's life.

If you want to, there are a few tests you can do for just a few bucks.  Go to one of the chain auto parts stores and see if you can rent McPherson Strut spring compressors - quite a few places will rent them for free.  You have to provide a security deposit but that's generally 100% refunded when you return the tools.  Get two sets: so you can jack up the front of the car and compress BOTH front springs a bit.  The idea is to take ALL spring loads out of the suspension - compress the springs enough that they rattle in the mounts a little.  Now you can wiggle the control arms and compare slop/motion.  Especially see if you can PUSH/PULL the arm in/out - that's a sure sign of worn bearings, slop in the mounting bolt holes, or something else in that area.  Get a good tape measure and compare the distance between the track control arm mounting bolt to some reference point near the wheel hub to see if the arm is bent slightly.  The engine mount cradle (crossmember) is a fairly high precision part actually.  You can use that as a reference point to take bodywork measurements side to side.  

If  you see cracks in the rubber insert, replace them now!  Then, site along the top of the metal collar portion of the isolator and look at the center cap... if it sticks more than half an inch above the metal collars the struts are way too old.  The caps are supposed to be below the lip of the metal; as they wear the caps start climbing upwards.  Most cars are sagged about a quarter inch... that's about as much wear as I'd allow before replacing the isolators.  Avoid the Monroe ones; they seem weak and will sag within a few weeks.  Then grab the top of the strut and try to rattle it; if the rubber (or the bearing in the isolator rubber) has failed you'll get a tiny motion in the strut.

If you've never messed with suspension springs before, talk to the store supplying the spring compressors.  You have to be careful useing these things; springs can store a LOT of energy.  If the compressor slips off, or even just slides around the coils (which it wants to do) you can easily pinch off a couple fingers.  Use 2 compressors per spring and turn the big screw about half a turn on each compressor, then do half a turn on it's twin.  Walk the compressors evenly in other words.  Also, take a look at the compressor tools when you rent them.  You'll see they are basically two big hooks on a single big bolt.  Those hooks had better have safety snaps/bars on them; if not, don't rent them - find some other ones.  When removing the tools, again walk them out slowly and evenly.  Make sure the ends of the springs end up in their "pockets" on the two end plates.  When you look at the plates ("spring perches") you'll see they're not flat; they actually have a notch to catch the end of the springs.

mike c.




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