Alignment Setback on 240Z

[jpc3006]

Does anyone know if Nissan designed the 240Z to have a setback (stagger) of the front wheels? I vaguely remember reading an article many years ago that it did but I have never seen a specification.

Some background for why I am asking this question. This past winter I removed the lowering springs on my 1973 240Z and installed stock Nissan OEM springs along with new Koni shocks and stock bushings. After doing this I took it to my local alignment shop (with whom I've been dealing with since I bought the car new in 1973) and they set the toe-in and gave me the printout from the alignment machine. The printout showed the left side having less caster (2.41 degrees) than the right side (3.61 degrees) but I was not concerned as the car always had this difference with the lowering springs and with the original stock springs. However, their new alignment machine also printed out the setback of the front wheels which I was surprised to see measured at -0.50 inches after the alignment. The setback was measured as -0.34 inches prior the toe-in adjustment. I am not sure how setting the toe changed the setback but those are the numbers. To confirm the setback values I measured the wheelbase on each side and the alignment shop is correct. Measurements in my garage verify the -0.50 inch setback as the RHS wheelbase measured 91 inches, the LHS wheelbase measured 90.5 inches. A 2305 mm wheelbase is 90.75 inches. So it seems that I have the passenger’s side 0.25 inches too long and the driver’s side 0.25 inches too short. After taking these measurements I put the car on jack stands and started looking for anything that could account for the difference and I found nothing. I measured the T/C rods, the front and rear suspension mounting points, checked the front LCA bushings, etc. I know I can shim the LHS T/C rod to get the LHS wheelbase to 90.75 inches and increase the caster angle but I can't shorten the RHS without adjustable T/C rods. Note that I am the original owner of this car, it has never been in an accident and is not rusty. The car tracks just fine and seems handle OK considering the increased ride height and the new, low performance 14 inch tires.

My question is whether I should try:  1) to get the wheelbase equal on each side, 2) adjust the LHS  to get equal caster angles on each side and leave the passenger side alone, or 3) not to undertake making any changes and just live with it?

Thanks,

John

[Zed Head]

They don't show any in the Body chapter dimensions, see below.  If caster is the same then it would have to show in the top strut mount area.

Those TC rod bushings are pretty squishy and tend to degrade over time. 1/4" one way on one side and 1/4" the other on the other side and you get 1/2".  I think that when you drive the car setback and caster move all over the place.

The rear end is suspended in rubber also.  

[jpc3006]

Zed,

I looked at the chassis dimensions before posting and, as you indicate, they do not show a difference side to side.

I don't think the T/C rod bushings are my problem as they are urethane and in good shape. When I was looking for problems under the car I measured the "gaps" between the washers and mounts on each side and they're the same.  As best I can tell the T/C rods themselves are straight. Since I removed and painted them there is a slight chance that I swapped left for right even though they were labeled. I am considering removing both and swapping them side to side just to see if it makes a difference but I suspect it won't.

Thanks for the feedback.

[Zed Head]

Did the guy's machine measure the direction and position of the rear tires to confirm that they were correct?  I know that today's machines can measure all kinds of things but if he saw that the rear wasn't adjustable he might have not measured it.  Maybe the rear wheels are set forward and/or back.  JMortensen has posted in the past about the early Z's having mis-drilled strut castings, causing the spindle pin to be misaligned, misaligning the transverse link (aka control arm).

The Z's were the poor man's sports car.  Not of BMW quality level.

A shot of the printout from the machine would be interesting.

[jpc3006]

I was in his garage an watched everything but I am not really sure exactly what he did but he did lift the rear when he installed the "fixtures" to the rear wheels and I did get rear toe, camber and thrust angle measurements. The thrust angle measured correlates with the RHS rear wheel toe-in of 3/16".  I plan to deal with this by shimming the inner front bushing.  I also manually checked the rears when I got under it to measure. I measured the leading edge of the spindle pins to a drain hole on their respective sides and got the same distance. Not very scientific but this may have shown something if there was a gross problem. So at this point I have no reason to believe the rear is the cause of the setback but then again I found nothing wrong with the front either. 

You may have something on your comment about build quality. In my readings I saw a comment that some automotive manufacturers consider a 1/4" wheelbase variance within manufacturing tolerance. I know that the alignment specs on my old Ford Explorer were so wide that you were "in spec" even though the car was eating tires every 8K miles!  Who knows what tolerances Nissan had for the 240Z back in the seventies.

Dave (the alignment shop owner) was most concerned with the camber of the LHS front wheel. He didn't seem to be concerned with the setback.  My thinking is that if I should first get the caster equal on both sides then address the camber issue as it will change with the caster change. See attached printout.