Critique this setup pls!

[pparaska]

Jim, I like that - high tech and cheap!

[TimZ]

Originally posted by pparaska:

Tim, glad to hear someone else say the bumpsteer spacers don't help with bumpsteer. I've been saying that for years!

Me too. I thought I was the only one - maybe we should both respond at the same time more often.

 

I'd love to get comments on how to make a cheap but good bumpsteer gage. I have one dial indicator, and was thinking about using some plywood, some tight hinges (piano hinge), a weight to hold it steady, and have the dial indicator hit the rim edge at spindle height infront of the spinde, and a bolt through the vertical plywood piece hit the rim behind the spindle at the same height. Saw this somewhere. Any comments appreciated.

That's pretty much exactly the setup that I use - it's in the "How to Make Your Car Handle" book. To make it even simpler, I don't even use a dial indicator. I just have two 10-32 bolts placed where the dial indicators would have been, basically situated 17" apart, so they match my rims.

 

To make the measurement, I remove the springs from the suspension, disconnect the sway bar, and jack the car up until the suspension is at full droop. To allow travel to full compression, I place to 4x4s under the front tires, centered approximately on the kingpin axis, so that they offer as little resistance to change in toe as possible.

 

I then position my homemade 'gauge' such that the ends of both bolts are an equal distance (laterally) from the rim. The camber of the wheel changes as the suspension goes through its travel, so you don't want the bolts to actually touch the rim at any point during the measurement. I usually start with the bolts about 0.5" - 1" from the rim.

 

Then I just drop the suspension in approximately 0.5" increments, and use my caliper's depth gauge to measure the change in distance to the two bolts. As I mentioned, it's normal for the distance to change, but ideally, the distance to the front and rear bolts should change by the same amount. If they differ, then the toe is changing.

 

Make sense?

 

I hadn't thought of it, but the method Jim mentioned should work just fine, just substitute the laser pointer for the gauge.

 

One more thing - I use Heim-jointed tie rods, and do the adjustment with spacers to locate the rod end with respect to the steering knuckle. The nice thing about this is that it decouples the bump steer adjustment from the rest of your suspension geometry.

 

You should still be able to get to zero bump steer by relocating the inner pivot point (ala JTR), but now it's quite a bit trickier, since the inner pivot point also effects the static camber, camber gain, and roll center. It's generally preferable to have these parameters symmetrical for the left and right sides.

[TimZ]

Originally posted by Tomahawk Z:

.About 7 inches of threaded adjusting sleeve in rear I would not recomend to anyone to section 2 inches (I have this lightweight Tomahawk that requires it)..... We originally tried the no section approach on Nezzie 76's Vello Rossa but the 2 inch drop did not get the car low enough due to its lightweight.

I'm not sure I understand why the weight of the vehicle should effect the amount of sectioning needed. This is purely a function of getting the suspension in the middle of it's travel at your intended ride height. Weight should not enter into it.

 

If the vehicle sits too high, then you either have too stiff a spring, too long a spring, or your spring perch is too high. Or some combination of these factors.

[Guest Anonymous]

[TimZ]

Originally posted by Tomahawk Z:

Hey - I wasn't trying to make you feel bad - just trying to make sure that I hadn't missed something.

[Guest Anonymous]

Tim.. the problem as I see it there is about one area to place a lower spring perch for a 10 inch coilover on a 2 inch sectioned 280 Z strut with about two specfic donar strut cartridges just for the front and rear to obtain the "middle of travel" in the USA. We have a member in Austrailia with even more limited materials and it seems his modifacation scheme has some successful results in practice. The first that I have heard of a 300 zx strut cartridge in the front of a sectioned 280 Z. Only the 1985-92 Golf/Jetta seems to work and not the MR2 which works on a 240.I know of few people with the resources to stock up on differing springs to find what works.There are so many factors that go into what works in finding the "middle of travel" that I relied on the accumaltive experience of "what works" And this seemed to work for me and for nezzie 76's Vello Rossa.And the formula is very simple...for 10 inch coilovers rest the lower spring perch where Datsun placed their original lower spring perch weld bead.

[Guest Anonymous]

Yes Tim Z.. I want to hear the tech info...In "regretfully" sectioning my struts 2 full inches on my very light Tomahawk, I used a 5 inch or a threaded adjusting sleeve cut to approximately 5 inches to fit precisely under the gland nut and the bottom spring perch on the front strut tubes which will give all the possible amount of adjustment.About 7 inches of threaded adjusting sleeve in rear I would not recomend to anyone to section 2 inches (I have this lightweight Tomahawk that requires it).If your 300 ZX modification is a proven method based upon avaialibity- Go for it.. In my next strut sectioning for my 250 GTO project I will use camber plates and try your "300 ZX strut cartridge" (thanx) in the front and try to get away with something shorter than such a radical (2 inch ) section of the strut tube. We originally tried the no section approach on Nezzie 76's Vello Rossa but the 2 inch drop did not get the car low enough due to its lightweight.

[Pop N Wood]

First thing I thought of for measuring the change in toe in is a laser pointer (or two). Simply secure the laser pointer to the side of the wheels and mark a point on the front of the garage where it hits. Move the suspension through it's travel and note how far in and out the beam travels. Just make sure the car is on blocks under the chassis so nothing moves.

[TimZ]

Originally posted by Tomahawk Z:

We have a member in Austrailia with even more limited materials and it seems his modifacation scheme has some successful results in practice..... I know of few people with the resources to stock up on differing springs to find what works.There are so many factors that go into what works in finding the "middle of travel" that I relied on the accumaltive experience of "what works" And this seemed to work for me and for nezzie 76's Vello Rossa.And the formula is very simple...for 10 inch coilovers rest the lower spring perch where Datsun placed their original lower spring perch.

First off, the formula above is a bit too simple. The free length of the spring is only part of the picture. You also must know the spring rate before you can make a generalization like that. You should also know the weight that the spring is supporting, and the dimensions of the strut (including the installation ratio), but since those are known relatively well for this example (and the installation ratio for the Z's suspension is 1:1 for our purposes), I'll give you those two.

 

You don't need to stock up on a crapload of springs to come up with a workable setup, but you do need to do some basic engineering homework. For the sake of keeping this thread to a readable length, I'm going to skip most of the process of determining a spring rate (we already had a lengthy discussion of that here). Instead, let's assume that this work has already been done - the original poster's combo of 175 front and 225 rear are known to be in the ballpark of combos that work well on the street for the Z.

 

Again, for the sake of argument, let's just look at the 175#/in springs in the front. Also, let's say that this Zcar weighs 2600lbs with the driver, and it has a perfect 50/50 weight distribution. So, each front wheel is supporting about 650lbs. From this, you can see that the spring will compress by

 

(650lb/175lb/in) = 3.7 inches.

 

First, let's take a look at the travel of your strut insert. Let's say that it's range of motion is 6 inches (this is about normal). Notice that to get the shock in the middle of it's travel, you will need to compress it by 3", but the spring will compress by 3.7". No problem - this just means that the spring will have to be preloaded by 0.7" when you install it. The springs are almost always preloaded - this keeps them from jumping off the perch when the suspension droops.

 

Now, given the dimensions of your strut, you will have a range of positions where the lower spring perch can be located. The trick here is to pick a spring length that will allow the spring to be preloaded by 0.7", and still be in the adjustment range of your adjustable spring perch.

 

As an example, let's say that your perch has a 3" adjustment range, and it's placed 3" below the gland nut. This gives you 3" to 6" of adjustment range below the gland nut. Next, let's say that at the strut insert's full extension, the upper spring perch is 7" from the gland nut. This means that you need to pick a spring length of somewhere between

 

3" + 7" + 0.7" = 10.7"

and

6" + 7" + 0.7" = 13.7"

 

... to get the suspension to come out at the middle of it's travel at your static ride height.

 

One last caveat - you also need to pay attention to the spring's fully compressed length - if the spring binds before full compression, then you have lost that amount of suspension travel.

 

Also, please notice that these rules apply, regardless of the length of the strut (i.e., how much it was sectioned). Just to reitterate, you should determine the amount to section the strut by placing the center of the strut travel at your desired ride height. Of course, you will still be limited by the lengths of the strut inserts that are available.

 

Conversely, if you are 'stuck' with a specific spring, you should be able to use this same technique to figure out what ride heights are possible with your spring, and section the strut with this value in mind (i.e., you might not be able to go as low as you wanted, but you should still be able to determine the right amount to section the strut by).

[Guest Anonymous]

Tim.. why limit yourself to a small length of adjusting sleeve like 3 inches? (since the adjusting nut is basically the bottom of the spring perch and the "range of travel" can be found on the threaded adjusting sleeve).My 1985-92 Jetta/Golf strut cartridge fits my 2 inch sectioned 280 Z front strut without any spacers and fully secured by the gland nut. MY spring perch is approximately 5 inches under the gland nut with a threaded (5 inch) sleeve filling in the space between the gland nut and spring perch. My 165 # 10 inch Carrera spring is preloaded less than an inch with the SBC/2300 pound Z with 49/51 ratio. Now if I have any problems of bottoming out, why cannot I pull out my spanner wrench as soon as I can pull over and adjust the coil spring's lower perch/adjusting nut on that 5 inches of threaded sleeve. Since I have given the specifics of my coilover front , can we compare them to your modification specifications to your Z. I am awaiting Carrera camber plates so I can make my own and modify them with rubber cushions. I kinda suspect that magic range of travel location can be found about a little over 3 inches from the bottom of the adjusting sleeve which will place those big old front tires about an inch below the wide fender flare

[260DET]

On eccentric camber adjusters influencing bump steer, I have had no problems in that area, once the bump steer was eliminated at the outset. That is using the adjusters to provide from 1.5 to 2.5 degrees negative.

 

The only thing to be aware of when using eccentric adjusters and standard tie rod ends is the possibility of running out of a safe amount of thread on the rack ends when going for big negative camber. Up to 1.5 negative should be OK although I know of at least one car using 2.5 with that setup.

 

To eliminate bump steer initially, on my car anyway, the outer pivot point of the tie rod ends had to be lowered. Whichever way this is done, shims or washers have to be used so as to provide a fine enough adjustment.

[Guest macks]

There's some good posts flying around in here, keep it up

 

A few questions:

Slotting the pivot holes and making some measurements in different positions is all well and good, but what direction/dimensioned slot should I be making - basically, what's the ballpark solution?

 

Then, how are you fixing the pivot points for measurement when they're flopping around in a slot..? I can imagine a crafty mess of spacers, washers and clamps could go some of the way, but is there a trick to it?

 

Finally - given that early zeds have the same suspension, wouldn't there be an exact pivot point that solves all of our problems? If so, why hasn't someone found it already?

[TimZ]

Originally posted by Tomahawk Z:

Tim.. why limit yourself to a small length of adjusting sleeve like 3 inches? (since the adjusting nut is basically the bottom of the spring perch and the "range of travel" can be found on the threaded adjusting sleeve).

I tried to make it clear that this was an example. I picked numbers that I knew from memory would be in the ballpark. They at not based on any particular setup. The numbers that I picked are irrelevant, anyway. The important part was the procedure that I was trying to lay out for picking your spring size, and getting the ride height to come out at the middle of the suspension's range of travel.

 

That said, it won't hurt anything to have a 5" long adjusting sleeve, but when your range of travel is only 6", there is really no useful purpose for it. Once you have established the ride height at the center of your suspension's travel, you really don't want to adjust the ride height more than 1.5" up or down. If you do, you will be severely compromising your suspension travel in either compression or droop, which was the condition that you were trying to fix by going to all this work in the first place.

 

Also, remember the caveat that I mentioned about making sure that the spring doesn't bind before the suspension reaches full compression? If you put the perch less than 2" (probably more like 3", depending on what your upper perch looks like) from the gland nut, it will pretty much be impossible to find a spring with suitable travel that will not bind before the suspension compresses.

 

My 165 # 10 inch Carrera spring is preloaded less than an inch with the SBC/2300 pound Z with 49/51 ratio. Now if I have any problems of bottoming out, why cannot I pull out my spanner wrench as soon as I can pull over and adjust the coil spring's lower perch/adjusting nut on that 5 inches of threaded sleeve.

 

Yes you could do this, but as I have been trying to point out, the relatively small (+/-1.5" max, preferably +/-0.75") range of ride heights that will give you adequate suspension travel has already been set by the amount that you sectioned the strut. This is independent of which spring you chose, or how you adjusted the spring perch. You can probably adjust the spring perch to get you into this range, but I have no way of telling you whether this was the ride height that you wanted.

 

You first need to determine whether or not the ride height that results from the suspension being in the middle of it's travel is what you want. Pull the spring out, reassemble the suspension, use a jack to position the strut in the middle of it's travel, put the wheel on, see if it's what you wanted. If it is, then use the procedure that I outlined above to figure out if your spring will work. If not, then we can help you figure out how to fix it.

 

Originally posted by 260DET:

On eccentric camber adjusters influencing bump steer, I have had no problems in that area, once the bump steer was eliminated at the outset. That is using the adjusters to provide from 1.5 to 2.5 degrees negative.

 

The eccentric adjusters that I had seen for the Z were offset bushings, which essentially move the inner pivot point around in a circle to make the camber adjustment. If this is the type of adjuster that you were referring to, I fail to see how this type of adjuster could not effect the bump steer.

 

I have seen another type of adjuster that uses an eccentric washer which is held captive by the crossmember to allow adjustment back and forth in a lateral slot. If this is the type of adjuster that you are referring to, then I can see how this could work, assuming that you adjust the rack's toe setting out the same amount that the pivot point moved, so everything stays in the same orientation.

 

Originally posted by macks:

Slotting the pivot holes and making some measurements in different positions is all well and good, but what direction/dimensioned slot should I be making - basically, what's the ballpark solution?

 

Then, how are you fixing the pivot points for measurement when they're flopping around in a slot..? I can imagine a crafty mess of spacers, washers and clamps could go some of the way, but is there a trick to it?

 

If you take a look at your crossmember, you will notice that there are washers welded to it for the pivot bolt and nut to tighten against. To allow adjustment, you first need to remove these washers. Use a cutoff wheel to break the welds, then grind the remaining flash smooth. Then you can cut a vertical slot in the crossmember to allow the pivot bolt to be adjusted up and down. Start with a slot about 1" long, with it's bottom at the original hole's location. When you reassemble the suspension, use two new washers of dimensions similar to the originals. You can now move the pivot point where you want it, and tightening the bolt down will hold everything in place while you check the bump steer. Once you find the setting you like, tack weld the washers in place. Pull the suspension arm out, and finish welding the washers in place, and you are good to go.

 

Well, almost - once you find the position that you like, you should also make sure that the suspension arm does not interfere with the crossmember through it's range of travel. Usually you need to grind a bit of metal away behind the bushing when you move the pivot point up. Not a very good description, but you'll see what I mean when you look at it.

 

Finally - given that early zeds have the same suspension, wouldn't there be an exact pivot point that solves all of our problems? If so, why hasn't someone found it already?

 

The reason that there isn't just one ideal place to move the pivot point to is that production tolerances just wouldn't allow it. Each car is different enough to make this impossible. This is essentially why they didn't come from the factory that way in the first place.

 

Additionally, these cars are at a mimimum 25 years old. There's no telling what has changed on the car since it rolled off the factory floor. For instance, when one of these cars were damaged and the suspension was bent, it was common practice to move the inner pivot point in the manner that I described above to get the camber back in line. This was almost certainly done without any regard for the resulting bump steer characteristics, or anything else besides camber, for that matter.

[Guest macks]

Originally posted by TimZ:

Then you can cut a vertical slot in the crossmember to allow the pivot bolt to be adjusted up and down. Start with a slot about 1" long, with it's bottom at the original hole's location.

Good post, but I keep coming up with more questions

 

It seems many people are modifying their pivot points by moving them up and out - is there anything more to be gained by cutting the slot slightly off-vertical?

 

You mentioned that the common bumpsteer mod may not enhance bumpsteer characteristics but is still a good idea for many because it improves the camber gain characteristics - how are they affected by pivot point relocation?

[260DET]

The Fortuna camber adjusters use slotted plates which are welded to each side of the Xmember, which itself then has to be slotted to match of course.

 

On where to actually move the pivot point to, from memory up about 20mm very approx. If the Fortuna bits are going to be used, if you line up the inner part of the slotted hole to match the original pivot hole vertically, you will end up with an adjustment range from stock out to about 2.5 neg approx, on my car which has 15" wheels.

 

Don't forget that tyre size variations can be used to help get the ride height you want, too.

[TimZ]

Originally posted by macks:

It seems many people are modifying their pivot points by moving them up and out - is there anything more to be gained by cutting the slot slightly off-vertical?

 

You mentioned that the common bumpsteer mod may not enhance bumpsteer characteristics but is still a good idea for many because it improves the camber gain characteristics - how are they affected by pivot point relocation?

Camber gain is a measurement of how the camber changes as the suspension goes through its travel. Basically, the lower control arm forces the bottom of the strut to travel in an arc as it goes through its range of travel. Since the top of the strut does not travel in an arc, the camber changes as the suspension moves. In our case, the camber is at its maximum when the lower control arm is parallel to the ground.

 

When you lower a stock Z, you change the part of the arc that the control arm uses at the static ride height. Instead of angling downward, the control arm is usually pretty close to parallel to the ground. This means that since the maximum camber occurs near the static ride height, when the vehicle rolls in a turn and the outside suspension compresses, its camber actually decreases, which is not what you want for maximum handling.

 

Relocating the pivot point upward, as in the JTR mod, does put the lower control arm back in the proper orientation (angled downward slightly) such that for the first few degrees of roll, the camber increases.

 

The up/down relocation of the pivot point effects your camber gain and bumpsteer. In/out (lateral) relocation effects your static camber. The reason people move the poivot point out is to increase the amount of negative camber. I would shy away from trying to do them both at once, just because you really want to keep the static camber characteristics the same left to right. If you want more negative camber, move both slots outward by the same amount.

 

I touched on this before, but this the reason that I don't like using the inner pivot point to adjust bumpsteer. Unless you are lucky and both left and right sides come out close to the same amount higher than the stock pivot point, you will have fixed your bumpsteer, but your camber gain will be different left to right. This is why on my car, I did perform the relocation symmetrically to get the camber gain that I wanted, and then adjusted the bump steer at the tie rod end, where you can adjust bumpsteer without effecting camber gain, or static camber.

[Guest Anonymous]

Tim you have made some very good definitive guidelines concerning suspension and this thread will make an informative contribution to this Forum.

[Guest macks]

Originally posted by TimZ:

I touched on this before, but this the reason that I don't like using the inner pivot point to adjust bumpsteer. Unless you are lucky and both left and right sides come out close to the same amount higher than the stock pivot point, you will have fixed your bumpsteer, but your camber gain will be different left to right. This is why on my car, I did perform the relocation symmetrically to get the camber gain that I wanted, and then adjusted the bump steer at the tie rod end, where you can adjust bumpsteer without effecting camber gain, or static camber.

Thanks for your input to this thread, I'm sure many have learned as much as I have as a result. Just to round things off nicely, how are you changing the tie rod end, and what can be gained from this modification with regard to bumpsteer?

 

In short - could I re-locate the inner pivot points to improve the camber gain characteristics as you've described, then fine tune the bumpsteer with tie rod end modifications? I suspect it's not that simple

 

I was discussing the measuring of toe over the range of suspension motion with a friend of mine, a zed-specialist mechanic who unfortunately isn't internet enabled, and he showed me the toe measuring setup he's got, which consists of a 'frame' that attatches to each wheel, connected to a bar that sits flat on the ground parallel to the direction of the car. Mounted on this bar at an equal distance each side from the wheel vertical centreline are two self-retracting tape measures which go under the car and clip onto another bar on the other side. The difference in the distances they measure as the wheel moves can be graphed as the toe curve. I was impressed

[TimZ]

Originally posted by macks:

In short - could I re-locate the inner pivot points to improve the camber gain characteristics as you've described, then fine tune the bumpsteer with tie rod end modifications? I suspect it's not that simple

That's what I did.

 

If you don't what to fabricate heim-jointed tie rod ends, you could achieve the same thing by changing the steering rack height. This will also require some fabrication, though.

[johnc]

FYI... I seriously looked at moving the steering rack. Even had some drawings done up. It really involves a whole new crossmember and if you're going that far, there's a LOT of things you can do with a clean sheet crossmember design. It became this huge Pandora's box and I eventually put it away and got on with getting my car back together.

 

Maybe later this year...