Home alignment, what about thrust angle?

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ValiantOne

ValiantOne

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Hey All,

I read some really great threads on fabo about doing home alignments. I am tempted to try it.

My question is about the relationship between the front and rear wheels though. When I used to do alignments at Merchants Tire back in the day, we aligned the front end off the rear wheels (we called it a thrust angle alignment) so that if the rear was cocked at a slight angle, the front wheels were in unison with them. Basically the wheels would all be facing the same direction, and the body of the car would be ever so slightly cocked.

Can this be done in a home alignment? Is it usually necessary? As we did all alignments that way, I don't know if it ever becomes much of an issue or not.

Thanks CE
 
Yes. With home alignment, you use the rear as a reference for the front.
 
Please 'splain how this is done? And start with the assumption that your audience is clueless..
 
Ok. Take 4 jack stands. Set them up in such a way so that they are at each outside corner of each tire, about 6" or so to the outside of the sidewall and a foot or so behind the rear tires and in front of the front tires.

Get some twine and tie a section to each side jack stands so that it is tight enough to not droop any. You will have a right side string and a left.

Now, position each side string so that it divides the rear tires exactly in half horizontally. Then position the string so that it will be equidistant from both the rear half and front half of the rear tires. I usually use 6". This is not critical as long as both sides are the same. you will of course need to re position the jack stands to accomplish this.

Repeat the same for the front, making sure not to disturb the rear. If you do, simply readjust so that the string cuts all four tires in half horizontally.

Once this is done, Center the steering wheel and find a way to lock it in the center. I have a steering wheel holder from when I did alignments.

Now, adjust each side's tie rod sleeve to put the front tires an equidistant amount from the strings both on the front half and rear half of the front tires. Once that is done, adjust so that the front half of each front tire is 1/16" MORE on the front side. This will give you a total toe in of 1/8" which is just right. Lock the tie rod sleeves down. Done.

Of course if you have camber/caster gauges, now is the time to break them out, too.
 
Good description of how to do it at home. We also called that "stringing" the cars, when we circle track raced...
 
So you are measuring from the string to the sidewall of the tire?
Very cool.
To me it seems like just aligning the front end without regard to the rear would be whizzing into the wind, no?

RustyRatRod said:
Ok. Take 4 jack stands. Set them up in such a way so that they are at each outside corner of each tire, about 6" or so to the outside of the sidewall and a foot or so behind the rear tires and in front of the front tires.

Get some twine and tie a section to each side jack stands so that it is tight enough to not droop any. You will have a right side string and a left.

Now, position each side string so that it divides the rear tires exactly in half horizontally. Then position the string so that it will be equidistant from both the rear half and front half of the rear tires. I usually use 6". This is not critical as long as both sides are the same. you will of course need to re position the jack stands to accomplish this.

Repeat the same for the front, making sure not to disturb the rear. If you do, simply readjust so that the string cuts all four tires in half horizontally.

Once this is done, Center the steering wheel and find a way to lock it in the center. I have a steering wheel holder from when I did alignments.

Now, adjust each side's tie rod sleeve to put the front tires an equidistant amount from the strings both on the front half and rear half of the front tires. Once that is done, adjust so that the front half of each front tire is 1/16" MORE on the front side. This will give you a total toe in of 1/8" which is just right. Lock the tie rod sleeves down. Done.

Of course if you have camber/caster gauges, now is the time to break them out, too.
Click to expand...
 
RustyRatRod said:
Ok. Take 4 jack stands. Set them up in such a way so that they are at each outside corner of each tire, about 6" or so to the outside of the sidewall and a foot or so behind the rear tires and in front of the front tires.

Get some twine and tie a section to each side jack stands so that it is tight enough to not droop any. You will have a right side string and a left.

Now, position each side string so that it divides the rear tires exactly in half horizontally. Then position the string so that it will be equidistant from both the rear half and front half of the rear tires. I usually use 6". This is not critical as long as both sides are the same. you will of course need to re position the jack stands to accomplish this.

Repeat the same for the front, making sure not to disturb the rear. If you do, simply readjust so that the string cuts all four tires in half horizontally.

Once this is done, Center the steering wheel and find a way to lock it in the center. I have a steering wheel holder from when I did alignments.

Now, adjust each side's tie rod sleeve to put the front tires an equidistant amount from the strings both on the front half and rear half of the front tires. Once that is done, adjust so that the front half of each front tire is 1/16" MORE on the front side. This will give you a total toe in of 1/8" which is just right. Lock the tie rod sleeves down. Done.

Of course if you have camber/caster gauges, now is the time to break them out, too.
Click to expand...

rusty, come on up and do mine !--LOL I `ve got an aftermarket front end, and coming up on the time for an alignment. will be a pain in the --- w/ all heim joints-looks to me like.
 
If you guys do a google search there is TONS of info on the net about various ways to check chassis / front end alignment, including lasers, and home built caster / camber gauges.

I did mine sort of "backwards." That is, the car has never been wrecked so I aligned the front end and "see how it drove". It drives great, so I'm not worrying about thrust angle. I MAY rethink that with more power in the car
 
ValiantOne said:
Hey All,

I read some really great threads on fabo about doing home alignments. I am tempted to try it.

My question is about the relationship between the front and rear wheels though. When I used to do alignments at Merchants Tire back in the day, we aligned the front end off the rear wheels (we called it a thrust angle alignment) so that if the rear was cocked at a slight angle, the front wheels were in unison with them. Basically the wheels would all be facing the same direction, and the body of the car would be ever so slightly cocked.

Can this be done in a home alignment? Is it usually necessary? As we did all alignments that way, I don't know if it ever becomes much of an issue or not.

Thanks CE
Click to expand...
What RustyRatRod said. You need to insure the strings are the same distance apart front and rear and that the car is centered between them and parallel. The distance from the wheels to the string may not be the same front to rear because the track width may be different but it needs to be equal left and right for both the front and the rear.

IMG_0770.JPG
IMG_0771.JPG
 
Great idea on the wheel dollies. I imagine you could you your 20* turns to check caster that way too.

Seeing it helps too. I've been watching a ton of videos on the process as well. It still seems like the strings could be canted one way or the other though. I get that you measure two points on the rear wheels, but even a small error there would be substantial up front. Maybe take a measurement off the body from the same point on either side up front to make sure the stings didn't drift one way or the other? Either way I'm going to try it. I'll likely buy a camber caster gauge too.

Thanks again!
 
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