Shimming T/C rods for more caster?

[280Z Turbo]

Since I already have my compression rods off, I was thinking of shimming them a little for more caster.

 

How much can I shim it out? How much does shimming the compression rod change the caster?

[EMWHYR0HEN]

Your going to have to shim it out a lot to make worth while.

 

When I did my alignment (brand new hunter rack!) I noticed that 1 revolution on the turn buckle of my adjustable t/c rod gave me .1 degree of caster.

 

On my t/c rods 4 turns is about a 1/4 inch. So that's .4 degrees for a 1/4 shim.

 

I would shim the t/c rods for purposes of getting the caster even on both sides, but if you want more caster you might consider adjustable ones or moving the t/c mounting points forward.

[blueovalz]

When I did my alignment (brand new hunter rack!) I noticed that 1 revolution on the turn buckle of my adjustable t/c rod gave me .1 degree of caster.

 

On my t/c rods 4 turns is about a 1/4 inch. So that's .4 degrees for a 1/4 shim.

 

I've got to queston this measurement (and I may be overlooking something here). Assuming the installed strut is 20" long (corner weight has compressed the strut to normal ride height) from the tower mount down to the control arm mount (vertical distance), then moving either end 1" (arm forward, or tower rearward) should net roughly 2.9º of caster rather than 1.6º (not measured, but using trig). This is rough because the T/C rod is at an angle (which will reduce the extension by roughly 10%), the T/C rod is attached inboard of the strut's kingpin centerline (which would increase the extension by some amount offsetting the angle issue), and obviously, the length of the strut is generalized (but pretty close). The .1º for .1" extension appears to be too small a ratio.

 

You could compare this to the more common camber changes. I can use a 1" adjustment on my camber plates to effect almost 3º change in camber.

[EMWHYR0HEN]

 

You could compare this to the more common camber changes. I can use a 1" adjustment on my camber plates to effect almost 3º change in camber.

 

I forgot to mention that there are a lot of factors that determine wheel alignment.

 

For me, a 1/2'' change in my camber plate would give me about 5 degrees camber.

[JMortensen]

For me, a 1/2'' change in my camber plate would give me about 5 degrees camber.

That don't make no sense. It still has to work out via the geometry. Unless you had super short struts (like frame rails below ground level), I don't think this is possible.

[74_5.0L_Z]

Unless you have spherical bearings installed at the inner pivot of the lower control arm, you should not attempt to lengthen the T/C rod. If you still have rubber at the inner pivot, you can get away with it (sort of), but if you have the common aluminum delrin adjuster the DON'T DO IT.

[280Z Turbo]

Unless you have spherical bearings installed at the inner pivot of the lower control arm, you should not attempt to lengthen the T/C rod. If you still have rubber at the inner pivot, you can get away with it (sort of), but if you have the common aluminum delrin adjuster the DON'T DO IT.

 

I drive an RX-7 with that delrin/aluminum setup and stock control arms. It has as much caster as possible and I've noticed no ill effects from any binding.

[JMortensen]

I drive an RX-7 with that delrin/aluminum setup and stock control arms. It has as much caster as possible and I've noticed no ill effects from any binding.

I believe the RX7 is different in that the entire arm (the arm has both the LCA and TC rod all built into one) pivots when you change caster. On the Z it's different because the LCA moves independently of the TC rod, so lengthening the TC rod changes the of the LCA as it relates to the frame.

 

The delrin is in my opinion a bad idea even on a stock front control arm on the Z car because the caster sweep causes the control arm to move on an arc, and the delrin/aluminum doesn't allow for that range of motion.

[280Z Turbo]

I believe the RX7 is different in that the entire arm (the arm has both the LCA and TC rod all built into one) pivots when you change caster. On the Z it's different because the LCA moves independently of the TC rod, so lengthening the TC rod changes the of the LCA as it relates to the frame.

 

The delrin is in my opinion a bad idea even on a stock front control arm on the Z car because the caster sweep causes the control arm to move on an arc, and the delrin/aluminum doesn't allow for that range of motion.

 

You must be thinking of a second gen. I drive a first gen.

 

The front suspension seems very similar to ours except that the radius rods are in tension.

 

I haven't noticed any ill effects from all the caster. What would be the symptoms if it was binding?

[JMortensen]

I would expect damage at the crossmember as the most likely damage. It might take a while to actually show a crack, but that's what I'd look for.

 

If it were severely bound it might be difficult to move the control arm up and down with no strut attached.

[74_5.0L_Z]

My car has 6 degrees of caster. To achieve that, my lower ball joint is about 1" in front of the pivot for the lower control arm (in the side view). Looking down on the car from above, the control arm is angled forward ~ 5 degrees. If I were using the delrin aluminum bushings at the inner pivot, then I would not be able to push the control arm forward in that manner without applying a heck of a lot of force to the control arm, T/C rod, and the aluminum bushing. Additionally, the T/C rod is attached to the control arm with two bolts. As designed, the T/C is angled (~37 degrees) so that it is aligned with the holes in the frame and the holes in the control arm within a small range of suspension adjustment. As you push the control arm forward, the bolts at the control arm end will not line up properly. With a little effort, you would probably be able to force everything into alignment, but this creates strain on the control arm, T/C rod, and the attaching hardware.

 

My solution was to install spherical bearings at the lower control arm pivots, and to reengineer the T/C rod to allow angle change between the control arm and T/C rod.

 

 

 

When you get finished with that and can crank in some caster, the tire will be pushed forward in the wheelwell like this.

 

[EMWHYR0HEN]

Whatever it may be, shimming the t/c rods won't make much of a difference IMO. Your going to have to add over and inch to make a significant caster change and by then your going to bind your bushings and run out of thread on the t/c rod.

 

However, I do see sence in shimming the t/c rods to even out the caster on both sides.