Bump Steer, front suspension check

[howdo]

1988 944 Base, with option M474: Koni yellow sport struts.
I have what I guess is called bump steer, when i go over a bump the steering wheel shakes. I noticed that the passenger side front strut has oil all over it.
I jacked up the car and am trying to check ball joints, control arm bushings and tie rods.

I assume I'll have to fix the strut, but I don't know of that's the cause of the bump steer. Its confusing what my options for repair/replace. Can I repair them with the koni hack inserts I have read about? I was also considering getting a used one just to get me through the year since I might sell it next year.

How do check the rest of the suspension parts? I tried the 3 and 9 oclock wheel test, but the steering wheel doesnt perfectly lock in place, so i see the motion actually at the steering wheel. I tried the 12 and 6 oclock wheel test, and I feel a little play, but I cant tell where it is coming from.
thanks,
Howdo

[danmartinic]

A blown shock will cause that steering wheel shake, yes. I would replace them both with Koni 1414 inserts (or at least the one if you are selling). Relatively simple & easy; if you have spring compressors and a hack saw, you're good.

Wow the inserts are expensive these days.. but if you keep the car, Koni will replace those inserts when they start leaking. They just replaced mine after 14 years of daily driving. Make sure you generously oil or anti-seize them before inserting!! You or the next person will be very thankful.

To check the rest, you are basically doing a front end safety. Off-load the wheels & take a crowbar to gently pry around various connections like ball joints and the places where the A-Arm connects to the body. There's a difference between slight rubber movement (normal) and worn-out loose connection.

9 & 3 is difficult to discern as you say since the steering wheel moves and the steering rack connection might also be loose. But, once you know what a worn tie rod feels like, you'll get it. Try watching: if bad, the tie rod will move before the steering wheel or rack connection

The tapered wheel bearing will always have a very slight play at 12 & 6. There's difference between very slight and too loose. You might be able to adjust a bit of too-loose; look up adjusting the wheel bearings. If it's just a super slight thing, you're probably fine.

Start with the strut. Surprisingly easy to remove (using spring compressors which you can get cheap these days)

[NC944er]

If you push down hard on the front suspension individually, left side / right side, you should see the body pop back up and immediately settle in. If you get any amount of bounce on the return, the shock is toast and you're basically riding on the spring.

Cut-a-strut is the way to go, both sides - when one side fails, the other is usually not far behind. If you install a used sealed strut, you'll be back in the same position before long. Here are the DIY instructions for the Koni Strut Conversion - 8641-1414S for late 944, 968 - https://www.paragon-products.com/kb_results.asp?ID=50

Alternatively, places like Paragon Products and 944Online sell strut conversion kits where the work is already done for you, just remove the old and the install new, but there is a price premium as a result.

[danmartinic]

If you push down hard on the front suspension individually, left side / right side, you should see the body pop back up and immediately settle in. If you get any amount of bounce on the return, the shock is toast and you're basically riding on the spring.

I have known this diagnostic since time immortal yet never have I ever seen or experienced this in practice. On my own cars, the shocks presented signs of leaking long before any bouncing could induce "multiple bounces" upon release.

Either that, or I just never felt comfortable pushing that hard on a fender

[NC944er]

Either that, or I just never felt comfortable pushing that hard on a fender

Yeah, I get it. For the NA cars, I push on the aluminum front bumper, it's quite stout. For Turbo, S2, 968, the corners where the front bumper cover meets the fender and is more supported.

I have generally seen shock oil leaks coincide with the bounce, but a few cases where oil residue was minimal and one side was discernably more bouncy than the other.

[howdo]

Thanks NC944er and danmartinic for responses.
You guys have convinced me to do the cut a strut, both sides.
I am nursing a bad back, so progress is slow with checking everything. But 2 things I checked:
Yanking on tie rods, it is solid.
When I do the 12 and 6 test on the side with the oily strut I see something interesting... there is alot of movement where the shiny shaft meets the strut body. I don't see this play on the other side. So I am assuming that in addition to poor damping , the play in the strut shaft is contributing to the bump steer.

Before I jacked it it, I did try to bounce check, but it wasn't obvious to me; but my big head couldnt see the strut too well .

I'll try checking the control arm bushings next, but either way will plan on ordering the inserts.

Thanks!

[danmartinic]

Can't remeber what but some front end check is done under load (shops lower one side onto a tall stand to press the wheel)

Might be control arm bushings? Perhaps someone can clarify

Whatever it is, you could just jack up the tire a bit while the front end is raised on jack stands

Good decision to install the inserts. Besides spring compressors, you'll need either a wrench with a very large bend (hard to find) or a socket with a slot (easier to find) for final torque of main nut when installing

Don't just spin it on with an impact

[dr bob]

Since you'll be doing an alignment after your work, I suggest you make a deal with your alignment shop to let them take a look before you do the work. Car goes onto their alignment rack, and they get to push and shove on things to identify components that need attention. You decide what you want to replace, do so, then the car goes back to them for the final actual alignment.


TL;DR --
That said, I regularly share guidance that includes replacing suspension wear parts by 100k or so. Wear creeps up slowly, rubber bushings gradually harden with age and heat plus UV/ozone/petro exposure, while grease-lubricated ball joints and tie rod ends suffer as the grease turns to wax. These are things that may not show up in a typical push and pull on the wheel 'test', especially the hardening rubber bits. Suspension wear is kind of like that nagging mate, whom you seem to endure until you finally swap for a different one. Symptoms you don't recognize until they are gone. Better than the nagging mate though, new suspension doesn't bring a new collection of nags, at least not right away. Do the rear at the same time. The difference is transformative. It will be a new car again.