Like your Z, this site is always underconstruction. :-)

Adjusting suspension ride height on a Z or Z-based car.

Front Suspension

1. Sectioning the struts really is essential. This involves cutting a section out of the body of the strut tube (usually about 1.5 inches) and welding the tube back together. Without it you simply can't lower the car enough without getting down to desired ride height and still have reasonable suspension travel.

2. With shorter strut tubes, you have to run a shorter cartridge. 300ZX (third gen) shocks are not only shorter by about 1.5", but they also have the same threaded piston rod (upper end) as the first gen cars. Therefore, you can use them without modifying the strut insulator (top hat). With the VW GTI struts (a common solution in the past) you have to drill out the insulators to accommodate the larger piston rod. It can be a pain to do so, plus it makes it more difficult to tighten or loosen the top nut. The GTI piston has a round threaded section, whereas the Z has a "D" shape that prevents the piston rod from rotating.

3. Coilovers are the way to go. I had some made locally but it was a pain; so much so that I'd recommend Ground Control in spite of the expense. I'd be interested to hear what others are using in this area. Coilovers will give you adjustability in ride height that will help you trim out the rake of the car just the way you want it. They will also allow for more clearance to the inside of the wheels, allowing you to fit a wider wheel and tire under the fender.

4. While you have everything apart, drop the cross member and relocate the inner pivot point per the JTR Z V8 book. This will eliminate the annoying bumpsteer that was built into the Z to help compensate for overly soft suspension. What's bumpsteer? The annoying tendency of the car to follow the ruts in the road or pull to the side of a bump if you only hit it on one side. It's due to the tie-rod arm and control arm not being parallel. Re-locating the pivot point will cure it.

If you have trouble visualizing why parallelism between these two components is important, try this simple exercise. With your car sitting on the ground and "rolled out" (roll it forward and backward a foot or two so the suspension can settle, making the last roll forward to simulate the car moving forward on the road) sight down the outer sides of the front tires toward the rear tires. If your toe-in is properly set in the front, you should be able to see a tiny bit of the back edge of the front tires. This would be a slight toe-in. Hopefully, the steering wheel is straight up and down when both front tires point in very slightly (a degree or so).

Now jack the car up and watch for the change in toe-in. This simulates full "droop." You get an opposite change when the car is bump loaded on one side like when running over an asymmetric (only on one side of the car) bump.

5. Install "bump steer spacers." Why the quotes? That's not really what they are, but it's what everyone calls them. They are spacers that go between the bottom of the strut and the ball joint. What are they really? "Camber curve correctors." My term. Copyrighted. Use it and you have to pay me:)

In essence, when the suspension height is stock the ball joint translates outboard with increasing bump load. This makes the camber more negative, i.e., the top of the wheel leans more toward the center of the car. The more negative the camber, the better the bite from the tire, which is exactly what you want when you load that side (the side on the outside of the turn).

As you apply increasing load to the suspension, the control arm goes from a normal drooping (toward the outboard side), to horizontal and eventually above horizontal. When this happens, the ball joint starts coming back toward the centerline of the car, decreasing camber and causing the front of the car to "wash out" (understeer) in hard corners and especially under braking (which transfers more load toward that critical outboard tire).

So, if you graph (I'm the self appointed king of analogies and visual aids) the camber versus loading, you see the camber start out at some negative value, go through zero (corresponding with horizontal control arm position) and start to become positive again.

When driving a stock Z under normal conditions you'd never get it loaded far enough to get the control arm significantly above horizontal. However, when the car has been lowered the entire "camber curve" from the above referenced graph is artificially shifted toward the positive camber area.

That is to say the closer you start out to horizontal on the control arm the easier it is to get into the wrong part of the curve. Imagine that if you started out with the control arm exactly horizontal, it would only take a minute amount of loading to start decreasing the camber.

The camber curve correcting spacers push the control arm back to something more like a stock location, and therefore depress the camber gain curve back into a more desirable region.

"How come I've never heard of this before, and why don't the racers do this?" I've heard that question, too. The answer is that most of them run such stiff springs and shocks that you don't have much movement on the camber curve. In essence the camber becomes fixed. The downside is loss of that all important suspension travel and its friend "ride quality." In a racecar, neither is that important.

I have some really nice billet CCCs that I never properly marketed. I sell them for $50/pair.

Another excellent question courtesy of Chris Larson: Do you need to do both the inner pivot relocation AND the camber curve correctors? Short answer: Yes. Long answer: The camber curve correctors move the ball joint down, in turn moving the control arm down. Unfortunately, they also move the outer tie rod end down which brings the tie rod down as well. This preserves the undesired un-parallel relationship between the tie rod and the control arm.

Here are some links to excellent discussions about this topic (when page opens, select Ctrl-F "bump"):
 

Rear Suspension. 

At the rear of the car, you will not experience the same bump steer phenomenon, because there is no steering. Technically, however, the camber curve displacement does occur. You normally would not notice it, though, because Zs seem fairly insensitive to camber change in the rear.

As for ride height, coilover suspension is the ideal way to acheive desired height. However, you can get the car down quite a bit with lowering springs (usually about 1 to 1.5 inches). If you are starting with a 280 Z (75-78) you can gain another inch or so by swapping the "top hats" or strut insulators at the top of the strut. On these cars they are about an inch taller in the rear than in the front. You can also use parts from front or rear of an earlier car (240), since they are the same as on front of the 280s.

Also: Some parenthetical comments: While you have everything apart, it's a good idea to do the suspension bushings. The steering rack in particular can cause irritating mystery problems that you won't figure out until you have a friend turn your steering wheel while you watch the rack move back and forth 1/4 inch relative to its mounts...or until you listen to me and just do it :wink:

You may as well change out the brakes at this time, too. The JTR-suggested Toyota 4-piston conversion is a pretty good one. I think I have one of those in a box here somewhere I'd make someone a deal on.

It's a little heavy compared to "real brakes." I hate to admit it and many of you probably hate to hear it, but our good friend at "the other Z place in Arizona" may have the best setup for that. If you just can't stand him so badly that you wouldn't buy a $20 bill from him for $10, let me know. I may have some inroads to some alternate sources, but don't have the time to invest in exploration without pretty promising prospects of selling some.

Be very conscious of the bottom of your car. There should be nothing hanging out below the "frame rails." This becomes even more critical with decreasing ground clearance (duh), but you'd be surprised how many aftermarket headers dump out an inch below the frame rails. I call these headers "speed bump feelers." Make sure whoever does your exhaust work from that point back understands the concept as well. This is especially important with V8 cars.

Not only will this stuff drag, scrape off that pretty JetHot coating, and tear up the exhaust, it will also loosen your exhaust manifold studs (or break them) and potentially ruin the gaskets. Also, I have had much better luck with graphite gaskets than anything else. They are a lot more expensive than paper, but it's a relative thing...relative to how CHEAP the paper stuff is.


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