I am doing a frame up build and I will be installing the trailing arms next. I have read conflicting threads on setting this up with some doing an extensive wheel alignment to others saying it can't be done without the full body weight and vehicle ride height established - I read that on the NCRS site and they were arguing back and forth as well.

For now I just want to get a base setup as it will be sometime before I worry about going straight down the road and I am sure I will make other changes along the way. On the other hand I don't want to screw something up or not do something easy now that will be hard later.

So... how do I judge how many shims should go on each side of the arm? Do I just split it evenly for now?

Thank

 

Splitting them evenly will give you a good starting point. Put in as many shims as will fit.

 

Major consideration would be establish a ride height as most times suspensions will settle after the initial rebuild. You hear this a lot with rear fiberglass spring replacement.

The only thing to ponder is if you want to place a weight in the drivers seat equal to yours as that will give a true alignment. (If you drive alone mostly)

 

Establishing a ride height is at least a year away at this point. Thats what I mean as I am not even sure if I will use stock seats let alone put something in it.

I was thinking that it may make sense to set the shims so the wheel is the proper distance from the frame? I saw how to do that on a post in the general section by using a string and taking measurments. Again I don't want to waste time if it doesn't matter but I also don't want to pass up the chance to do something when it is all apart that will be harder later.

 

The shims in the T/A's control the toe. Nothing else. You won't be able to get it exact with no weight on the tires, but you can get daggone close. Set it with a tape measure- scribe a straight line around the diameter of the tire and measure the difference from front to back at the same height off the ground. Set it to whatever specs you are using (or want to use). Stuff shims in on both sides of the T/A until it's as tight as you can get it, then if you remove a shim on the inside, put it on the outside, or vice-versa. Torque the bolts to 50 ft/lb, tighten as needed to get the cotter pin holes lined up and it's done until you get it all together for a final 4 wheel alignment.

 

Iagree with the above, with the shims. What i do is to raise the trailing arm after installing the shims and place a 3/8 drive 5/8 socket under the trailing arm it will fit right on the lip there ,where the shims are ,this will get you close to ride height. it will also help when you go install the half shafts , as for camber i take a magnetic torpedo level and place that on the face of the rotor then adjust the strut rods .This shoud get you close until you get an alignment. I just finished the back half of my 79 ,now i'm working on the front end.

 

I have read and re-read this and I don't understand it at all

scribe a straight line around the diameter of the tire and measure the difference from front to back at the same height off the ground. Set it to whatever specs you are using (or want to use). Stuff shims in on both sides of the T/A until it's as tight as you can get it, then if you remove a shim on the inside, put it on the outside, or vice-versa.

This is what I don't get - the shims will move the arm on a horizontal plane either in or out right? So what does a vertical measurment tell me? Also, does this assume the car is level and the floor is level.

Believe me I am not trying to be a smart A I am more just showing my ignorance.

 

Not a problem. the line around the tire is a reference. If the back measures (ONLY an example here) 62-5/8 on the line, toward the rear of the car 3" off the floor and the front measures 62-3/8 at that same 3" off the floor, then you have a total difference of 2/8 (1/4). From that, you are 1/4" toe-in.

If you don't stay at the same height off the floor it could induce error into the measurements. If you have the body off, there's no reason you couldn't measure from the top. Just measure at the same relative point from the top center, but far enough from the center to get a good idea of the difference. 1" off top center will not show a big amount of change. 12" from top center will. look at it like a clock- measuring at 11:00 and 1:00 is not a big amount. But if you look at 10:00 and 2:00 that should show a bigger difference. It's a little confusing explaining it that way without being able to show a picture. Maybe this way- on the bottom, 6 is straight down, on the floor. Going to 5 and 7 is barely doable, but if you go to 4 and 8 you can get a tape easily to those points. So I suggested 3" off the floor- as long as you measure from the same point front to back your results should be easy to see and figure. that'll tell you what shims to move.

 

Again, first let me thank you for your help and tolerating my slow take on this.

I understand the positioning of the tape being at a point that shows a difference what I don't understand is simple -

what am I measuring from - I am standing there with tape in hand and I put one end on this line I have drawn - where do I put the other end to get this measurement?? What is at the other end of this tape that is 60 something inches away?

Also, I am a little confused by drawing a line around a diameter but I think I know what you are trying to say there.

Again, thanks for your patience.

 

What you are doing is measuring to see if your rear wheels are "pigeon toed" ( toed in). Put a reference line on each rear tire and measure between them at the same height off the floor in front and behind the tires, the difference is the toe in or toe out. That can be changed with the shims.

 

Got it.

I have read where you measure off from the frame to be sure it is in line that way so my mind never thought of tire to tire.

I do need to ask though doesn't this just tell you the tires are both headed at the same angle? Do you just assume it is the right angle as it is bolted in? And how do you know that they aren't to close together or far apart?

 

I think what has you confused is the difference between "THRUST ANGLE" and "TOE". Thrust angle is measured from the centerline of the frame to the centerline of the axles.
Toe is measured between the tires.

Thrust angle should be the same- frame centerline to center of the axles should be the same on both sides.
Toe is easily adjustable with the shims. Just measure from the difference on the tires only front to back, moving shims to get the correct toe-in.

 

I get it, thanks for your patience.

 

Not a problem. Figuring out alignment stuff makes me crazy- I usually end up setting in a pile of paper with lines drawn all over that make absolutly NO sense.

 

You should have saved your original shims and taped-labelled the location of these packs from which location they came out from. From there, its best to use new SS shims of the same set-up (such as 1 thick, 1 medium, and 2 thin for example) to re-eastablish your previous toe alignment set-up. From there you would have it pretty good to get you to the alignment shop. Only install thin shims in between the medium or thick shims in the pack. The last shim should be tight enough that you have to drive it in with a small maul (engineers hammer). If not, you'll get a wandering rear feel.

For ride height, set your new spring bolt to the approximate position of the old one and you'll have to wait until you get the car on the ground and settled to better dial in where you want it to be. Another way to do this would be to only bring the adjustment nut up until you have 2-3 threads exposed at the bolt end and adjust down from there once it settles-thats how Im doing it.

For camber adjustment, you can set a 9/16 impact socket under your trailing arm to get your arm to an approx ride height (Van Steel advice). From there, use a torpedo level with a magnet on your rotor face and crank out your adjuster to get a level indication. You can redo this if you have your ride height dialed in further.

If you dont want to go to an alignment shop, there are plenty of threads on DIY rear alignment also, although YMMV.

 

MN - I didn't say it so you would have no way of knowing but almost nothing is from the old car - different frame with all new and/or rebuilt suspension and I do mean everything down to the nuts and bolts. Did a coil over in the front with QA1 with new upper and lower A arms and all new power steering and tire rods ect. In the rear I have a new spring and bolts, strut rods, rebuilt diff and trailing arms, shocks.

The drive shafts are original as is the diff case

So yes I do actually have my old shims as I took them off but I don't think they could matter much unless it is shear luck.

I wasn't going to worry much about ride height until I at least have the body on as I will be using the newer rubber mounts and those alone will be up to 3/4 " different then the old solid ones.

Yes I am having fun but man what a lot to do!

 

In our shop we just split the shims up evenly on either side of the front bushings. Do not tighten up the shim bolt untill the arm is at the correct ride height. 50 ft pound is fine. You can eye ball the wheels after the car is on the ground and has been rolled back and forth ablut 20 feet to make any adjust ments. Full weight must be on the car when checking. We then move the car over to the all ALL four wheel alignment machine.

 

Here is a way to set up the trailing arms. If your car was together and on the ground you could have measured from the top back edge of the trailing arm up to the chassis at your ride height. If your car is apart get a measurement from another vette the same year as yours with the same spring and same length spring bolts. Now with the car on jack stands and the spring out of the car. Install the half shafts and strut rods. Put the rotor on and add three lug nuts to hold it on tight. Now jack the trailing arm up to the measurement that you had taken up to the chassis. Level the rotor up and down for the camber and adjust the strut rods. Now you need a level with a laser. Some are magnetic or you will need another person. If its small you might have to use something to space it off the rotor like another level to clear the chassis. Put the laser level on the rotor and let the laser shoot down the side of the chassis. You need the rocker molding off. Measure the distance of the laser to the flat side of the chassis at the rear and then at the front before it starts to curve in. The front measurement should be about a 1/32 to 1/16 less than at the rear. Add and remove shims until you can keep this measurement. I have done this on many vettes and it always came out great. After the cars were on the road and we went to get a front end alignment we never had to change the rear shims. I hope I explained this so everybody can understand it easily. Vinny

get something like this level.

 

Any attempt to set alignment without the car at final ride height is a waste of time. Split the shims 50/50 and move on to other projects.

The entire car will need to be aligned when it's ready to drive.