Setting rear toe

[fusion]

I have a 1976 280z that I am in the finishing stages of totally rebuilding from scratch.  I have stock rear control but custom hub mounts and needed a way to set the toe and camber so I am using adjustable rear control arm bushings that allow for toe and camber adjustment.  I understand how to adjust the bushings, but where I am struggling is a reference point to set the toe.  It's my understanding that usually the front toe is set with reference to the rear.  However, neither my front nor rear toe is set.  

 

Not sure the best way forward.  I guess I could find the centerline of the car?  The frame rails could be an option, however those have been replaced and might not be perfectly square.  

 

Any advice welcome. 

 

Thanks

 

Edited August 17 by fusion

[clarkspeed]

This very topic kept me up at night. Most set it to front spindles after removing dust cap. Probably fine for street use, even setting to front brake rotor is not bad.

 

If you want better you have to find a true Centerline for the car. A true thrust alignment. I set mine to a spot between the 2 inner front control arm pivots. Seemed to be the only spot I trusted to be true on a unibody that has seen many repairs. 

[fusion]

13 hours ago, clarkspeed said:

This very topic kept me up at night. Most set it to front spindles after removing dust cap. Probably fine for street use, even setting to front brake rotor is not bad.

 

If you want better you have to find a true Centerline for the car. A true thrust alignment. I set mine to a spot between the 2 inner front control arm pivots. Seemed to be the only spot I trusted to be true on a unibody that has seen many repairs. 

Thanks Clark.  Not sure how the rear toe can be set from the front spindles or rotors since my front toe is not set either.  Usually the front is set off the rear.  A real catch-22 if you need to set both the front and rear.  I think the only way is from the centerline of the car.    

[74_5.0L_Z]

Do you still have all the stock rear suspension attach points in reasonable condition?

 

If so, I would install the rear control arms so that they are symmetric.  If you are using aftermarket eccentric bushings, then make sure the left side and right side are mirror image of each other.  When I first set up my suspension after chassis mods this is what I did (using the eccentric bushing).

 

1.  I installed the front and rear bushings on the rear control arm such the the holes were outboard and up and one of the flats on the eccentric bushings was level to the floor.  I took a straight edge and laid it across the bottom flat of the bushing on either side of the car.  If the straight edge sat flush on the flat of both bushings, then I knew they were square to each other.  I did this for the bushings at the front and rear of the control arms.  This gave me a good starting point that was symmetric and square to the car.  This step above doesn't guarantee 0 toe, it just established symmetry and squareness to the rear attach points. The next step is to set the toe (at least roughly until you can get to an alignment shop)

 

2.  Scribe a line near the centerline of both rear tires.  I do this by jacking the tire so that it is a few inches off the ground.  I then support a scribe or small flat head screw driver near the middle of the tire and rotate the tire by hand to scribe a line around the circumference of the tire.

3. Set the tires back on the ground and settle the rear suspension.

4. Measure the distance between the scribe lines at the front of the tire and at the back of the tire.  Try to measure as high up on the tire as possible and measure at the same height front and back.

5. Subtract the front measurement from the back measurement.  If the front side is longer you'll get a negative sum and you have toe out.  If the rear side is longer, you'll have a positive sum and you have toe in.

 

You want to start with zero toe (front and rear measurement equal or slightly toe in (<1/8" total)

 

If you do need to adjust, do it equally on both sides by turn the eccentric bushing on opposing sides an equal amount but in opposite directions.  You want to try and maintain symmetry in your rear suspension set-up.

 

Edited September 8 by 74_5.0L_Z

[fusion]

On 9/7/2024 at 10:49 AM, 74_5.0L_Z said:

Do you still have all the stock rear suspension attach points in reasonable condition?

 

If so, I would install the rear control arms so that they are symmetric.  If you are using aftermarket eccentric bushings, then make sure the left side and right side are mirror image of each other.  When I first set up my suspension after chassis mods this is what I did (using the eccentric bushing).

 

1.  I installed the front and rear bushings on the rear control arm such the the holes were outboard and up and one of the flats on the eccentric bushings was level to the floor.  I took a straight edge and laid it across the bottom flat of the bushing on either side of the car.  If the straight edge sat flush on the flat of both bushings, then I knew they were square to each other.  I did this for the bushings at the front and rear of the control arms.  This gave me a good starting point that was symmetric and square to the car.  This step above doesn't guarantee 0 toe, it just established symmetry and squareness to the rear attach points. The next step is to set the toe (at least roughly until you can get to an alignment shop)

 

2.  Scribe a line near the centerline of both rear tires.  I do this by jacking the tire so that it is a few inches off the ground.  I then support a scribe or small flat head screw driver near the middle of the tire and rotate the tire by hand to scribe a line around the circumference of the tire.

3. Set the tires back on the ground and settle the rear suspension.

4. Measure the distance between the scribe lines at the front of the tire and at the back of the tire.  Try to measure as high up on the tire as possible and measure at the same height front and back.

5. Subtract the front measurement from the back measurement.  If the front side is longer you'll get a negative sum and you have toe out.  If the rear side is longer, you'll have a positive sum and you have toe in.

 

You want to start with zero toe (front and rear measurement equal or slightly toe in (<1/8" total)

 

If you do need to adjust, do it equally on both sides by turn the eccentric bushing on opposing sides an equal amount but in opposite directions.  You want to try and maintain symmetry in your rear suspension set-up.

 

Great info, thank you