I would appreciate any help in diagnosing these problems I'm having with my FD, or any suggestions for where to look. I've owned two FD's prior to this that didn't have anything like this in terms of handling/suspension issues, although I think 1 was on freshly replaced bushings. I'm currently thinking of replacing the front tie rods and control arms. I can get rebuilt OEM sets of suspension parts with fresh bushings for about $1k, then for the arms with non-serviceable ball-joints it's another $500-700 or so.

Symptoms:
1.) Appears to be tramlining pretty hard, but I don't get steering wheel jerk like I would expect with tramlining
2.) Even on new, perfectly smooth roads I get weird steering feel, kind of like when the force feedback system in an arcade game is broken (for example, you turn the wheel gradually left, and it works fine, then halfway through it randomly cuts out your input and the wheels don't go where you want them to, then the input comes back and it begins steering again). So turning the wheel left or right I get normal feedback, but it feels like the steering wheel loses connection with the wheels.
3.) Steering effort is different when turning left vs right. Turning right takes a bit more effort. Not a huge difference, but noticeable.
4.) Car feels like it's understeering the harder I turn into a corner, but the rear also feels light. It's weird and unsettling. Car seems to grip fine though, and I've never really broken traction with it. I can feel the diff working, and can hear it clunking on low-speed tight corners, so it might just be that to an extent. On my previous RX-7's I didn't feel this behavior at all, so I thought maybe the subframe or something was loose, but then it appears to grip ok, so maybe it's just the diff giving more feedback than I'm used to as I'm progressively loading up one side of the car in a turn?
No weird noises really. I thought I had ball-joint bearing failure noises, but it turned out to be just a loose bolt on a stiffening bar that was creaking.

Car specs:
Car was purchased last year and appeared to be a demo/show car for a nearby shop. I don't think it had been driven much over the past 5 or so years.
Differential: KAAZ 2 way clutch type (I broken it in by doing figure 8s forever)
1997 (automatic originally, converted to manual), not sure if this matters with regards to the steering ratio
Suspension: new Tein Flex Z coilovers (previously super high spring rate Cusco, something like 16kg)
Sway-bars: Unsure, but appear to be aftermarket
Bushings, Ball-joints: Checked at two different shocks and told they there were good at both. Car only has 36k miles, been driving it since 30k miles last year. Don't believe there are any noticeable wheel bearing issues either.
Tires/Wheels: One set of 225r17 Michelin PS4s (new) on new, lightweight SSR GT X04 wheels (17x8, roughly OEM offset IIRC), and another set of 215r17 Michelin winter tires (purchased new) on heavier, used 17" wheels.

 

Disconnect the swaybar end links, zip tie the bars up, and go for a test drive. I'm confident the car will feel better ( and think you should put stock bars back on), but that's only going to be a part of the issue. Have you had a four wheel alignment done recently?

 

Forgot to mention that, but yes. Car has had 1, I think two alignments since I got it. It previously had something ridiculous like 20 inch wheels with low-profile tires on it, and the alignment was way out of whack before I had it fixed. I didn't take a photo of the alignment after it was done, but it's basically a stock alignment.

 

How is your power steering pump? When parked with the car idling, are you able to turn the wheel back and forth without any change of effort or odd noises? Is the car equipped with the OEM power steering cooler? Are the symptoms present when car is hot and cold (goes back to question about power steering cooler line and condition of steering pump and the ATF lube in the pump)?

Normally, I'd say it sounds like an alignment problem but you said it has OE specs and been aligned twice and that you have good tires with stockish offset wheels. Here in the US, we often have difficulty getting an alignment shop to actually do a full alignment inclusive of caster, camber, toe, thrust angle etc. So you take in for an alignment and it's still ****. Is that a problem in Japan? If so, maybe find a good alignment shop to take another look before spending the money on a front end refresh. At ~30k miles, the bushings and ball joints should not have much wear.

 

Hmm.. that just made me think. The car has a pretty ghetto FMIC setup, so maybe they deleted the power steering cooler. I can look into that. I don't remember there being a difference between the car being hot vs cold, but I hadn't really tried to test that either. It definitely had overheating issues when I first got it though, just driving around town and it would overheat, so I had to install rx-8 radiator fans and work on improving airflow around the radiator & intercooler to fix that, but temps still aren't great (hard driving for a couple minutes gets it up to 99C on coolant temps or so, and driving in traffic will get air intake temps around 60-65C in spring weather, although intake temps drop to the 25-30C range when moving at highway speeds). So even if the cooler is there, it could be getting warmer than normal.
I'll mess with it at idle and parked, but I don't remember hearing any odd noises. Will check this out in a bit and report back.

 

What, pray tell, is a power steering cooler? Is it the trombone attached to the steering rack? I thought it was for variable assistance modulation. for different speeds.

I had the rear end clunk for a long time and we could not suss it out.

Finally, when i swapped in a 4.3:1 rear gear and replaced the driveshafts between the dif and rear wheels, the clunk went away.

We found one missing dif hanger bolt as well.

The 3.9 dif from an automatic has different flanges, and propeller shaft front end that connects to the transmission is of thicker diameter, than that for a manual. If someone has swapped in a 3.9, they likely would have had to modify the propeller shaft (which you are not supposed to do). They may have damaged the universal joint.

I would watch for some obstruction from the FMIC set up.

Friend had to modify the steering to accomodate a V8 swap and the bumpsteer nearly threw him in front of a semi.

 

It looks sort of like this thing circled in orange (this is an aftermarket kit). I literally just learned about its existence a few weeks ago. You can run the car without it, but I guess you risk damaging the power steering system without one. Short write-up on how they work here: https://www.apexdesignsusa.com/pages...teering-cooler

 

The trombone looks familiar but i'd pay a nickle if anyone can prove that accordian thing has an OEM equivalent.

Also check if your sway bar links are bent and binding as the pass through the lower wishbone.

 

It just looks like a standard, passive heatsink to me, so it should do well with keeping temps under control initially, but if you're constantly adding heat to the system it may not be able to deal with that (something like doing constant figure 8's or autocrossing at low speeds).
(Edit: Did some more research, and it looks like autocrossers do indeed sometimes have problems with their PS systems overheating on other car makes/models.)
Just had a thought, but a simple way to fix this problem might be to just run unidirectional heatpipes from the PS lines to the radiator. This would be dumping a small amount of additional heat into the radiator, but at least you can monitor that, and you also would no longer have a cap on the PS system's cooling capacity (you'd effectively have active cooling for the PS system). You'd also then be able to throw away the passive PS heatsink and probably save a bit on weight.

 

Since your alignment is recent and in OE spec I'd rule that out. I believe your issue due to a combination of the 2-way rear diff with the stiffer anti-roll bars. A 2-way diff is going to lock up, or begin to lock up in many load shift conditions. My theory- your sway bars and heavy springs are reducing body roll and changing the way the weight of the car shifts from an easy roll to more of a jolt as the car follows variations in the road crown/surface and that jolt is causing your diff to lock up the unloaded wheel which intensifies the tramlining effect.

I'll suggest again to try disconnecting the bars to see if the tramlining feeling changes, if it does go back to OEM bars or leave the current bars and put a less aggressive rear LSD in. A 1.5 or 2 way diff on the street is going to feel weird and you will fight it sometimes.

 

Yeah, FMIC make for hotter than desired coolant temps in city type driving, stop and go, idling. Running the fans help but doesn't really resolve the issue. V-mounts mostly solve that issue. Getting off topic though...

Some input for additional context, research and troubleshooting

This kinda symptom is often related to things like incorrect front toe settings or maybe play in the bushings, ball joints or wheel bearings

Stiffer springs and sway bars also affect this. As does wheel offset to a degree.

This kinda sounds like a potential issue with the power steering system where pump pressure varies due to wear, overheating PS/ATF oil etc. Spring rates or sway bars shouldn't impact this. Not sure if the diff would affect this at all... If you can reproduce this easily, try it with the clutch in so you can isolate the functioning of the diff from the steering inputs.

Caster setting can affect this.

Yeah, that sounds like the diff

 

Ok, thanks. Guess I have a lot to look into. I forgot to save the alignment results, but from what I remember some of the settings were way off stock when I first got it (like -7 degrees of something or other), so I could see that wearing components prematurely.

I've had an OEM torsen diff in one car and a 1.5 way OS Giken in another, and both felt fine. I think I can get used to the sensation, and in some ways it feels like it's giving me extra feedback as to how much I'm loading up one side of the car, but at first it felt like the tires were slipping even when they weren't. So for now I guess I can just discount that as a difference in how it works and focus on the other stuff.

 

Yeah, I installed an aftermarket LSD in my Miata's diff and it definitely feels different, more aggressive than an OEM Torsen.

 

There seems to be more than a few cases on this forum of professional alignment being cockeyed - some of the symptoms certainly sound a little suspicious..

You'd hope the Japanese would still value doing things correctly over western style, "she'll be right" get it out the door work, were the two alignments at the same shop?

 

Alright, updates since I think I've mostly solved the issue (tldr, threw the parts cannon at it since the car is old and the bushings appear original):
-AutoExe sway bars (I got this mainly to reduce body roll, but it helped alleviate the issue greatly, much to my surprise). Confirmed previous sway bars were OEM once I got them off.
-new, rebuilt steering rack ($200)
-new SuperPro steering rack bushings
-new tie rod ends (bought new tie rods as well, but they work with the OEM lock washers and the originals looked to be in good condition so just re-greased the OEM ones and left them in)
-fixed a power steering leak on the short piece of hose on the PS pump body
-realignment after

Car still has slightly different left/right steering feel but it's very minor now and quite livable. Also don't feel nearly as much slop in the front wheels. Rear still feels odd sometimes, so I think next I need to replace all the bushings on the car and then get rid of these Teins and put on something nice to rule out differences in spring / damper rate causing issues (probably should've gone with OEM to begin with as a cheap option...)

Alignment specs as of today:

Front-
Caster (L/R): 6 deg 25' / 6 deg 19'
Camber (L/R): -1 deg 04' / -1 deg 06'
Toe: 0deg 09' / 0deg 09'. Total toe: 0deg 18'

Rear-
Camber (L/R): -1deg 13' / -1deg 06'
Toe: 0deg 08' / 0deg 06' Total: 0deg 14'
Thrust angle: -0deg 01'

Others:
SAI (L/R): 14deg 11' / 13deg 58'
Included(?) angle: 13deg 07' / 12deg 52'
Toe: 0deg 08' / 0deg 06' Total: 0deg 14'
Setback (F/R): 4mm, 2mm
Wheelbase Left/Right difference: 1mm