1990 coupe suspension upgrades

[sushiplugger]

I own a 1990 240sx coupe that I have had since about 1998, and the shocks and struts are definitely not what they used to be. I've got 105K miles on the original suspension, and I figured why not replace it with more performance oriented equipment, since it's gotta go anyway. The overall goal of these upgrades is to have a better performing, even more fun to drive daily driver. I have already installed front and rear strut tower bars (easy and cheap!).

After some fairly extensive research, this is the what I am currently planning on;

- Replace cracked and leaking T/C bushings with Whiteline polyurethane bushings
- Replace dry and cracked front and rear suspension bushings with Whiteline polyurethane bushings
- Replace stock sways with Whiteline bars
- Replace struts and shocks with KYB AGX
- Replace cracked and disintegrated strut and shock tower mounts and boots (prob'ly with KYB replacements)
- Replace springs with ???? - (and this is my dilemma)

I am fairly certain that I would like to replace the stock springs with linear rate springs as it seems there is some contention about the real merits of progressive springs for both comfort and performance. So linear seems the safer route to go for me. I also do not want to drop the car more than 1-1.5 inches as the front air dam already scrapes on everything if I am not careful (that also seems to be the lowest recommended limit for good AGX performance/wear). Since the goal is for a fun daily driver (I would eventually like to get into competition driving, but I have to be realistic too), I am also not interested in really stiff springs. I have been looking at Suspension Techniques and Tein S-techs as they seem to have a decent amount more stiffness with a good amount of drop for me.

Unfortunately, I can only guess as to what the spring rate numbers are going to translate into on the road. My only point of reference (if anyone has ridden/driven one) is the 2003 SE-R Spec-V suspension feel. I would be very happy to have the same firmness of ride as that car with greatly increased handling at the end of my upgrades.

I am also planning to do these upgrades myself, as I have some mechanical knowledge and experience (I am currently restoring a 1956 Chrysler New Yorker).

So all of this (thank you for reading it) boils down to three questions...

1.) Does anyone have any suggestions for good, moderately comfortable linear springs (or reasons to reconsider using progressive springs)?

2.) Does it make sense to collect all of the parts first and spend a weekend putting them all on at once, or are some of these upgrades separate tasks that can be done without much redundant work?

3.) Have I missed anything?

Thanks again for your help, and sorry for the long post!

|>@T

[AKADriver]

It's not of much importance to do everything at once, though it might be wise to do all rear suspension bushings at the same time as the struts, since you have to remove the rear uprights. At the front the only bushings are at the LCAs and the TC rods, 4 total, the uprights can stay in place bolted to the front strut.

I'd check the condition of the rear subframe bushings, and the tie rod ends.

The rear subframe bushings don't leave you much of an option if they're shot, you can either replace (meaning drop the entire subframe) or you can shove in spacers to take up the slack.

Tie rod ends, easy choice, Moog ends are greaseable, the OEM ends aren't.

I think you'd get the closest feel to the Spec V from Whiteline or Tein springs. The Suspension Techniques springs are okay, but I question their spring rate choices... Having front spring rates much higher than the rear like that will tend to want to transfer weight rearward more easily than forward, which makes a RWD car nice and stable below the limit; but driven near the edge it might feel front-light and, terminally, understeer. I haven't used them myself, though, to see how that translates to the real car. People seem to be very happy with Whiteline and Tein springs though.

I've heard some negative opinions about the Whiteline sway bars, by the way, but it seems to be an issue specific to setup. The endlink design is a topic of a lot of debate. If you don't forsee yourself using the adjustability feature of the whiteline bars, suspension techniques bars are lighter, the same sizes (or thereabouts), and cheaper, and they use stock-type endlinks.

[sushiplugger]

I hadn't even thought about the subframe bushings. I'll check those out. My tie rod boots are cracked, so that does not bode well for road junk getting in the tie rod ends. I'll was thinking about replacing those with the Moog replacements as well. They're pretty inexpensive, anyway

As for replacing bushings, most people seem to burn them out with a torch. I don't plan on getting one just for this project. Are a drill, hacksaw, a bench vise, and appropriately sized sockets and pipes to push out the old bushings and sleeves and push in the new enough? Or should I find a shop to do it?

If I find a shop, my main concern is leaving one half of each front & rear suspension assembled to use as a reference for re-assembly while I take the other half to the shop to get the bushings installed. I am afraid I would be totally confused if I took everything off all at once, though I do own a FSM. I guess two trips to the bushing presser's is way better than a confused hack mechanic with a driveway full of suspension parts.

As for the springs, the Teins seem very close to the Suspension Techniques with just a little higher rear spring rate, so I actually had a concern with both of them about that. They are also a little on the stiffer side of what I am looking for.

I am also looking into the RS-R Down springs (3.0 kg/mm F&R?) but haven't been able to find concrete numbers for the drop on S13's. I am assuming they are very close to the F 1.5 and R 1.2 drop of the S14 model springs, which would be great for me.

After doing much research on the endlink issue with the Whiteline bars, it seems that it was mostly due to the improper installation procedure a lot of people used (installation at full droop). I am planning on putting the car on stands and then jacking up the L and R suspension assemblies to ride height with my two floor jacks. I liked the idea of the adjustability not because I would change it often, but that I could find a setting that I liked and then leave it.

Thanks again for your suggestions....very helpful!

|>@T

[AKADriver]

heh.. don't be intimidated by the rear suspension! It's only 4 links per side, and all the links are different shapes. The exploded diagram on pg. RA-19 of the FSM is pretty simple to understand when you're actually looking at the car.