Rear Toe-in alignment with the body off the frame HELP!

[Patrick B.]

Re: Rear Toe-in alignment with the body off the frame HELP!

It certainly is NOT a waste of time to set the toe as I described in post #3. If fact it's the easiest way to set it up with simple tools prior to putting the body back on the frame.

The reward is when the car is finished, you put it on an alignment rack, and find that it needs no adjustment.

Duke

I used the same basic method that Duke described with a small variation that made it easier and more accurate. A friend of mine loaned me a laser with a magnetic base from a woodworking tool set that allowed me to do the alignment without the tire and to focus on points on the floor 4 feet ahead of and 4 feet behind the axle to expand the difference in measurements from 1/32" to 4/32" (1/8'') for ease of measurement. I attached the laser to a new GM rotor with negligible runout, but I do not think that matters if you rotate the rotor to focus the laser on the forward floor target and then rotate the rotor to focus it on the rear target without moving the laser block on the rotor.

The basic steps were:
1. level the frame fore-aft and side to side.
2. with the spring not connected, block the spindle support to the level ride height specified by dimension "D" in the assembly manual. This is simply putting some pieces of wood below the outer end of the strut rod so that the outer end is about 3 3/4" below the inner end of the strut rod. The assembly manual gives a precise number taking into account vehicle options, but the nominal 3 3/4" for a C2 will suffice. This step satisfies the issue in Dan's comment.
3. using a level on the rotor, adjust the camber to zero. THIS IS VERY IMPORTANT.
4. find the chassis centerline as described by Duke.
5. put pieces of masking tape on the floor 4 feet ahead of the axle and 4 feet behind the axle.
6. shim the trailing arm so that it looks more or less like zero toe-in by eye.
7. rotate the rotor so that the laser line shines on the forward tape target and mark the spot with a pencil.
8. rotate the rotor so that the laser shines on the rear tape and mark that spot.
9. measure the distance from the chassis centerline to the front and rear laser line marks. The average of the two distances is the nominal zero toe-in reference. Mark that reference dimension on both the forward and rearward tape targets.
10. shim the trailing arm so that the laser line falls 1/16" inside the front reference mark.
11. check that the laser line now falls 1/16" OUTSIDE the rear reference mark. You have now achieved 1/32" toe-in for a tire on that side of the car.
12. repeat on the other side.

I don't think an alignment shop could do it more accurately because they have to contend with the whole car. And most shops would not be very motivated to even try.

[Duke W.]

Re: Rear Toe-in alignment with the body off the frame HELP!

Not disputing your method, but without the rear spring installed how do you accurately measure the final correct position of the back of the T-Arm which will effect toe?

Read the fourth line in post #3. The back of the trailing arm has nothing to do with it. You're measuring between the tire tread and the centerline string.

Duke

[Duke W.]

Re: Rear Toe-in alignment with the body off the frame HELP!

For Argument sake I should see a total of one eighth of an inch difference measuring the OD of the back to the front of the tire when done correctly?

No, you want to see 1/32" toe-in per side. You put your chalk mark on any convenient groove of the tire tread. Then measure from the string to the mark with it facing the rear. Then rotate the tire 180 degrees so the chalk mark is facing forward and measure between the chalk mark and the string. Shim so that this measurement is 1/32" less than the measurement with the chalk mark facing to the rear.

It's best to pack the shim spaces about equal with both thick and thin shims. Then take a baseline measurement, and start swapping shims until you get 1/32" toe-in. It will take several interations to get that proper 1/32" toe-in.

I tried to explain how to do it as best as I can, but I don't think some are able to visualize the method from my description or you don't understand how to measure toe. Reread post #3 and think about it. Try sketching it out. Look at your CSM.

Duke

[Duke W.]

Re: Rear Toe-in alignment with the body off the frame HELP!

I used the same basic method that Duke described with a small variation that made it easier and more accurate. A friend of mine loaned me a laser with a magnetic base from a woodworking tool set that allowed me to do the alignment without the tire and to focus on points on the floor 4 feet ahead of and 4 feet behind the axle to expand the difference in measurements from 1/32" to 4/32" (1/8'') for ease of measurement. I attached the laser to a new GM rotor with negligible runout, but I do not think that matters if you rotate the rotor to focus the laser on the forward floor target and then rotate the rotor to focus it on the rear target without moving the laser block on the rotor.

The basic steps were:
1. level the frame fore-aft and side to side.
2. with the spring not connected, block the spindle support to the level ride height specified by dimension "D" in the assembly manual. This is simply putting some pieces of wood below the outer end of the strut rod so that the outer end is about 3 3/4" below the inner end of the strut rod. The assembly manual gives a precise number taking into account vehicle options, but the nominal 3 3/4" for a C2 will suffice. This step satisfies the issue in Dan's comment.
3. using a level on the rotor, adjust the camber to zero. THIS IS VERY IMPORTANT.
4. find the chassis centerline as described by Duke.
5. put pieces of masking tape on the floor 4 feet ahead of the axle and 4 feet behind the axle.
6. shim the trailing arm so that it looks more or less like zero toe-in by eye.
7. rotate the rotor so that the laser line shines on the forward tape target and mark the spot with a pencil.
8. rotate the rotor so that the laser shines on the rear tape and mark that spot.
9. measure the distance from the chassis centerline to the front and rear laser line marks. The average of the two distances is the nominal zero toe-in reference. Mark that reference dimension on both the forward and rearward tape targets.
10. shim the trailing arm so that the laser line falls 1/16" inside the front reference mark.
11. check that the laser line now falls 1/16" OUTSIDE the rear reference mark. You have now achieved 1/32" toe-in for a tire on that side of the car.
12. repeat on the other side.

I don't think an alignment shop could do it more accurately because they have to contend with the whole car. And most shops would not be very motivated to even try.

Toe is the difference in lateral measurements between centerline and a longitudinal plane about 13.5" from axle centerline, front and rear. If you are going to measure 48" from axle centerline then the difference you want is 48/13.5(1/32), which is equal to about 3.5/32".

IMO it's easier to just mount the wheels/tires and measure from a tread reference mark rather than trying to set up a lazer on the brake rotor.

Duke

[Patrick B.]

Re: Rear Toe-in alignment with the body off the frame HELP!

Toe is the difference in lateral measurements between centerline and a longitudinal plane about 13.5" from axle centerline, front and rear. If you are going to measure 48" from axle centerline then the difference you want is 48/13.5(1/32), which is equal to about 3.5/32".

IMO it's easier to just mount the wheels/tires and measure from a tread reference mark rather than trying to set up a lazer on the brake rotor.

Duke

Obviously, I was considering the tire as a nominal 2 foot diameter rather than 27". Rather than 48" ahead and behind the axle, 54" would provide an exact expansion by four of the toe-in measurement. However, I really doubt that anyone trying to measure the distance between a plumb bob and a string line with a tape measure could detect the difference between a 24" tire and a 27" tire. I think it would be difficult to make that measurement within 1/32" and nearly impossible to have a 1/32" difference between two such measurements be accurate.

[Louis C.]

Re: Rear Toe-in alignment with the body off the frame HELP!

OK, I was expecting to see a total of 1/8" toe-in by measuring the distance between the front and back of the tire. And that does not hold true. I will try again using the centerline method you described..

[Steve G.]

Re: Rear Toe-in alignment with the body off the frame HELP!

You're getting a lot of good advise on properly setting your toe, but they are missing out on dealing with your problem. True that measuring from the frt and rear edge of the rotor is giving you a false reading. The difference front to rear 8" from the centre of the wheel is not the same as 13.5 inches from the centre. You need to correct that. However, measuring to the centre line of the frame on each side vs measuring from centre of tire to centre of tire is not addressing your issue.

You weren't totally wrong with what you were doing. You can check total toe the way you are doing it. Total toe in will be correct, but the wheels may be pointing off to one side and the car dog tracking. Ie, if you set total toe to 0" by setting the left side 1" toed in (measured from the centre line) the right side 1" toed out (again from the centre line), the actual toe-in is correct at 0. The wheels are perfectly parallel to one another and won't be scrubbing, but the rear of the car will dog track to the right. This happens all the time with frt wheel alignment when the steering wheel spokes are not properly centred when frt toe in is set. Driving down the road the wheels are perfectly aligned, but the steering wheel must be turned off centre to get the wheels straight ahead. The total toe is correct but one side is too close to the centre line and the other side too far away when the steering wheel spokes are centred.

So knowing this, even if your method would leave the car dog tracking you still should have been able to get the actual total toe correct. And that's what seems to be missing here. You have both sides toed out as far as they will possibly go and you can not get anywhere close to correct total toe, regardless of relation to centreline. Something is way off here.

Once you've identified why you can't get total toe close I and dealt with that I would make up my shim pack for correct total shim thickness to ensure a tight bushing fit. I would then divide them in half ensuring an equal number of thin and thick shims on each side. Let the alignment shop with proper equipment set it up accurately. You can not provide the level of accuracy that today's equipment does with a crayon mark on a tire, strings and plumb lines. You might get it close enough that the alignment tech says "good enough", but I would prefer it was out enough so that he had to pull the bolt and instead got it right on.
Steve

Edit. And of course all this presetting is making the assumption that the actual riding height will be at the spec you blocked it up to. Setting it at actual riding height is going to give you a more accurate setting..

[Steve G.]

Re: Rear Toe-in alignment with the body off the frame HELP!

However, I really doubt that anyone trying to measure the distance between a plumb bob and a string line with a tape measure could detect the difference between a 24" tire and a 27" tire. I think it would be difficult to make that measurement within 1/32" and nearly impossible to have a 1/32" difference between two such measurements be accurate.

Additionally, for the tape measure method to be perfectly accurate the marks on the tire have to be exactly 180 degrees apart on a plane parallel to the ground, and that's seldom possible. Usually the points on the tires where the measurements are made is the highest point up from the ground that you can stretch the tape measure without running into the trailing arm. Same with on the rear. So the tape measure method is never at that correct distance from the axle centre line.

Steve

[Louis C.]

Re: Rear Toe-in alignment with the body off the frame HELP!

Initially I planned to address the crabbing issue by using a straight edge from the rotor to the outboard frame rail on each side making them equal. I have learned that using a centerline is the proper/better way. But thank you for understanding my question; I have removed all outboard shims and still have too much toe-in regardless of the direction they are pointing.

So i wondered if I was measuring toe-in correctly: measuring the difference between the centerline at the rear of the tires minus the distance between the front of the tires should be 1/16". One thirty second times two for each side. From the posts I am led to believe not.

[Steve G.]

Re: Rear Toe-in alignment with the body off the frame HELP!

Initially I planned to address the crabbing issue by using a straight edge from the rotor to the outboard frame rail on each side making them equal. I have learned that using a centerline is the proper/better way. But thank you for understanding my question; I have removed all outboard shims and still have too much toe-in regardless of the direction they are pointing.

So i wondered if I was measuring toe-in correctly: measuring the difference between the centerline at the rear of the tires minus the distance between the front of the tires should be 1/16". One thirty second times two for each side. From the posts I am led to believe not.

There is nothing wrong with your plan to to measure to the outboard frame rails at the same point to get the "straight ahead". In fact, I would say that would be more accurate than trying to establish the centre line and then maintain a perpendicular measurement to the front of the tire. Presumably the point on the outboard of the frame rails is the same distance to the centre line on each side.

The published specs for toe-in are actually for the way you are doing it and the way you describe it. Centre to centre (or same point anywhere on the face of the tire) on the front of the tire should be 1/16' less than the measurement from the same points at the rear for 1/16" toe in. The published spec presumes the equipment has established the theoretical centreline. So if you are measuring wheel to wheel, you use the published spec. If you are measuring from each side to the centre line you divide the published spec in half and apply half to each wheel for a total toe in of the published spec.

Further, using the front edge of the rotor instead of the tire will throw it off, but nowhere near what you have. Likewise with rotor runout.

So back to the issue at hand. I mentioned the spindle support because I know they are different rt to left and can cause that. If that is ok we need to think about what else can cause the issue. If the spindle support is right then the spindle to trailing arm is likely right unless something is bent or the support not fully seated in the arm. To change toe we move the inboard end of the arm in or out. Conversely, moving the outboard end in or out will change toe as well. If we can't get it to toe in enough the rear of one of the arms could be too far out from the centre line. This could happen if a u-joint weren't seated properly in the yoke. A place to start. I need to think about it further.
Steve

[Steve G.]

Re: Rear Toe-in alignment with the body off the frame HELP!

Using the measurement to centre line instead of wheel to wheel will tell you if the problem is on one wheel or both and if one, which one. If you can get one side to spec measured to the centre line you will be able to take a number of other measurements to locate the problem on the fault side, if it is just one side.

Steve

[Louis C.]

Re: Rear Toe-in alignment with the body off the frame HELP!

I am confident the spindle supports are correct both right and left. The shock mounts are inserted from front to rear with the flat slot in the spindle support to the rear on both sides. Both spindle to trailing arm assemblies are set correctly also. Not too much room for error there. Four bolts torqued equally pull/set the spindle in the trailing arm nicely.

Both trailing arm assemblies are shimmed tight at the front bushing area. However, when I grab the right trailing arm at the rear of the arm I do find some lateral play originating at the rear differential yoke. Minimal, but unlike the left side which is tight.


I will have to do the center line method or try to establish the fault side as 9/16" toe-in is obviously wrong.

[Louis C.]

Re: Rear Toe-in alignment with the body off the frame HELP!

I used the center line method, transferring all of my lines to the floor using a plumbob. Ride height established as in the AIM, frame leveled side to side. I took measurements from the center line to both front and back sides of the tires (tires are new with rib in center) and found 1/8" toe-in on the left and 1/4" toe-in on the right. A total of 3/8". That is with all outboard shims removed and a tight stack inboard on both sides. I looked over the spindle/trailing arm assembly for issues and see none. Camber is set at zero.

http://s186.photobucket.com/user/chip6565/library/

[Steve G.]

Re: Rear Toe-in alignment with the body off the frame HELP!

Are your camber adjusters near the outer limit of their adjustment? In the pic with the spirit level taped to the rotor it looks like the right hand side is close to the end and the left not as much, however the left side does not look like it has been set yet.

The relevance of this would be that if it takes most of the adjustment to 0 the camber the distance between the spindle and the centre may be off. If you take some measurements from the flange face at the spindle end to the edge of the casting adjacent to the inboard yoke I will compare it to the 67 in the shop.
Steve

[Michael W.]

Re: Rear Toe-in alignment with the body off the frame HELP!

You mentioned a large amount of axial play on the diff yokes. This is visible in one of the pics.

The wheel spindles, half shafts and yokes must loaded inwards while measuring toe and camber.