GTM Alignment

[The Stig]

Hi Guys,

I know that there are quite a few of you that do your own alignment on your cars. So I have a question as to what your methods are to find your absolute center reference (front and rear) that you use to base your adjustments for toe-in / out? And once you find that, what are you doing to center the steering wheel and steering rack, prior to making any adjustments to the toe / camber / caster / bump-steer.

My first thought is to pull a string accross the car from each diagonal (for the front, and then again for the rear), and mark the intersection.


But what are you measuring from and to on each end?
I would assume that you would have to find measuring points on the frame, since the body in not necessarily centered on the frame.

I would really appreciate your input.

Thanks in advance!

Mike

[mikespms]

Hi Mike,

You set the rear wheels parallel to the front hub centers and then you set the fronts parallel to the rears, that should put all four wheels parallel to the center @ zero toe.

ps: Set your adjustments to zero on all four wheels before starting

[Presto51]

Mike see if this video made by DIY on the FFCars forum helps


https://www.youtube.com/watch?v=dDmGmCQ_mJQ

Also here is a link to his website

http://gator823-ls7gtm-primary.hgsitebuilder.com/chassis-and-electrical-buildup/suspension

Hope it helps

Ron

[crash]

Start by making a line down the center of the car. Work out on either side making sure both sides are symmetrical. Once you have a solid reference point on both sides of the car set up your strings. Then take measurements and make adjustments. Remember that the car needs to be at ride height and the tires need the correct air pressures in them. Also make sure you settle the suspension after each adjustment. For this reason it is much easier to make a string mount that secures to the frame instead of using jack stands. It can be done with jack stand, and if you are likely to only do the alignment once or twice then that is fine, but unless you set up a frame mounted reference, you will be doing a lot of extra measuring.

[VRaptor SpeedWorks, LLC]

I say do yourself a favor and take it to an alignment shop where the alignment tech knows what he's doing. It's not difficult to tell.....ask to talk to the tech and start asking questions about doing a custom alignment on a custom car that's not in his alignment machine data-base.......if he gets a confused look on his face and has no idea how to go about that, find another shop.

I've done a few string alignments in my shop myself. I've had a few cars in here that the owners have done a string alignment and thought they had it dead-nuts on. None of them have even been remotely close when put on an actual alignment machine. Honestly, I can stand back and eyeball the alignment and get it MUCH closer than taking actual "measurements". I did that as an experiment to see if I could just do the alignments myself instead of taking the car in to be aligned.....string aligned two cars and then took them to the alignment shop.....neither was even remotely close.....even using one of those fancy, expensive bubble-level camber gauges. The third car, I took ZERO measurements. I set the ride height by measuring, but that was the only thing I took measurements on. I adjusted the camber and toe on all four corners just by standing back and looking at the car and eyeballing it.....and took it in to the alignment shop and about 80% of the adjustments were already "in the green" on the machine....and the other adjustments were so close that they needed very little adjustment.

Just my $.02

[kabacj]

I agree with Shane. I think It's possible to get close enough without measuring if you have a good eye. although I would not recommend it , I have had the car at the track and driven 150 with an eyeball alignment. The car was fine. (I had set the caster at home already so that was in the ball park)

I also do the string/ caster plate caster guage alignment at home which makes me more confident that I have set the car up the same way as the last time out. Then I eyeball it to double check :)

I have center line marks on the chassis i hang strings with a weight from those points then shoot a laser line under the car to measure off of in order make the strings parallel on either side of the car.

Everybody here makes great points. You will not go wrong following any advice .

You are going to love driving the car. I can't wait to hear your reaction.

John

[mikespms]

Shane has good advice,It takes more than a fancy alignment machine to do a good alignment most tire shops wont be able to set up and do a good alignment on a gtm specially setting ride height or checking bump steer not to mention balancing the car on scales. I could not find an alignment shop in my area with scales or a bump steer gauge, the guy at tire kingdom didn't know what bump steer was. I started aligning my corvettes in the 70's back then independent rear cars were uncommon and the c3 vette rear alignment is tedious and time consuming and it was hard to find a shop that would do a good job. Same goes for the gtm you are going to find shops to align it but you may have to look for a race shop with scales and bump steer gauge willing to spend the time to set your car properly.I have all the alignment tools ,bump steer gauge and scales and it is a days work to set everything right. If you can't find a performance shop or race shop to do it, set the ride height do an eyeball alignment like Shane mention and take it to a good alignment shop. To set bump steer you have to remove or unload the springs so that you can check the toe runout while you raise and lower the front suspension.

[The Stig]

Shane has good advice,It takes more than a fancy alignment machine to do a good alignment most tire shops wont be able to set up and do a good alignment on a gtm specially setting ride height or checking bump steer not to mention balancing the car on scales. I could not find an alignment shop in my area with scales or a bump steer gauge, the guy at tire kingdom didn't know what bump steer was. I started aligning my corvettes in the 70's back then independent rear cars were uncommon and the c3 vette rear alignment is tedious and time consuming and it was hard to find a shop that would do a good job. Same goes for the gtm you are going to find shops to align it but you may have to look for a race shop with scales and bump steer gauge willing to spend the time to set your car properly.I have all the alignment tools ,bump steer gauge and scales and it is a days work to set everything right. If you can't find a performance shop or race shop to do it, set the ride height do an eyeball alignment like Shane mention and take it to a good alignment shop. To set bump steer you have to remove or unload the springs so that you can check the toe runout while you raise and lower the front suspension.

Mike you hit the nail dead on the head: twice!

First of all, I have huge respect for Shane and his wealth of knowledge. So when he offers advice, I tend to listen. Second, I have a contact at one of the race shops here in Charlotte (actually Denver, NC) who is going to do the set up on the car, and get it dialed in. He seems pretty excited about working on it, and actually did mention that you can't really set the alignment on a custom car the same way you can on a production car. They're just not the same. He equated doing a set up like this to doing a set up on his race cars. So I think he's at least thinking in the right direction. We'll see soon enough.

My question was more for my being able to maintain it after he has it set. In my mind, the starting point has to be finding a center line location on the front and rear of the chassis that can be used for reference. It's easy enough to set toe in at - 1/8". But unless you know where your center is, the two wheels may not be pointing straight ahead, (relatively speaking).

Maybe I'm missing something. And maybe whatever it is, isn't really that important. But it's the sort of thing that i need to understand before I can let it go. That's why I asked the question the way I did.

What I had planned to do, was take measurements, and document them, after the initial set-up, so I can use them as reference in the future. I guess if I had to, I could always take it back to him let him do what ever needs to be done. But really want to understand it in order to make sure it's set and maintained correctly.

I plan to buy a nice set of Longacre Scales (wired). I'll be able to use them to maintain the balance of this car as well as future builds. I don't understand all the ins and outs of setting and measuring bump-steer angles (yet), so I'm going to let the race shop handle that. They will also be installing a complete set of Pfadt Poly-Bushings in all of the control arms, and the alignment shims that I bought from Mike Holland a while back, to lock the alignment in.

It should be pretty well hooked up when he gets done with it. A lower HP (435 hp) LS2 engine with Michelin 335's on the rear to help a little with traction control, should keep me pointed straight most of the time. And that should keep Pam happy! :cool:

Mike

[eseethal]

On my GTM I did a string alignment (plus camber gauge) twice (once after adding Pfadt poly bushings). I borrowed scales and was able to set up ride height and corner weights as well. My GTM feels perfect and stable, even when accelerating hard with the LS-7 force in the back. I will have it checked by a race shop just to be sure somtimes in the future.
If you know what you are doing this method is quite precise. Many professional racecars are set up this way. I am pretty sure that you can set it up within the usual tolerances. The setup of the strings is important - the car has to be in a perfect rectangle, the lines have to be absolutely parallel. Talking about camber the floor has to be even (or corrected with the camber gauge). Camber is easy to measure with the gauge and the toe-settings with a thin string are also precise enough. I did not adress bump steer yet (will do this in a few weeks) - with a little laser level it should be easy to track the toe changes when moving through the suspension travel.

[Motohead]

Does anyone know of a good "race car" type shop in So California. I've driven my GTM up and down the street and it seems fine. The original builder had the alignment done, but I would like to make sure for myself that it's ready for the wide open road.