Front end vibration...welcome to my nightmare

On my 1984 Porsche 944 I have a front end shimmy. EASY you say, balance the wheels? Done that, 3 times. It's the tires then? Tried 3 sets, on 3 different wheels. Tie rods? Nope, no issue there. Ball joints? Nope, all good. Rotors? OEM in great shape. Wheel bearings? Maybe, not sue how to verify. Alignment? Had it set up twice by the best guy in the area.

Wheels were checked and are true. Tires are good. All new bushings and parts in the front end. WTF? Why does this thing shimmy??

The front struts have been replaced with inserts. I personally don't like how they fit but apparently that is how they are installed. Couold it be the fact that there is a tiny bit of play between the body of the strut and the insert?

What am I missing? I'd like to buy some coilovers, but I'm not doing it until I can get the shimmy sorted out, Anybody been through this hell?

Pop the dust caps off the hubs and try to move the washer with a screwdriver. It should barely move. If it is easy to move, then you could try to tighten it up.

I know you replaced a bunch of the front end parts, but how are your upper strut mounts?

How about the strut towers themselves? Do they move appreciably when a load is placed on the control arm?

Steering rack? Power Steering pump and system?

Did you align the caliper pistons properly?

Bent/out of balance front hubs?

The upper strut mounts are brand new.

Rack is a rebuilt unit, no leaks, works great.

I will check the washer. Strut towers SEEM fine, Is this a visual thing? Are you thinking it could be metal fatigue?

Caliper pistons? Misaligned? Wouldn't this hinder brake operation? Not sure how this would happen.

Could be bent hubs, I could set up a dial gauge and see the runout on the front wheels as a starting point? Good idea.

johnnytorque wrote: I will check the washer. Strut towers SEEM fine, Is this a visual thing? Are you thinking it could be metal fatigue? Caliper pistons? Misaligned? Wouldn't this hinder brake operation? Not sure how this would happen.

Yep, visual. On my 924 the passenger side was clobbered at somepoint and I noticed that the passenger strut tower moved quite a bit as I placed weight on it.

There are notches on the caliper piston faces and they are supposed to be oriented a certain way for best braking performance and wear. Doesn't stop the brakes from working, they just may not work to their full potential as der fatherland specified.

At what speeds do the shimmies come and go? Stock OEM wheels or aftermarket? If aftermarket, got the hubcentric rings in there?

rodrammage wrote: At what speeds do the shimmies come and go? Stock OEM wheels or aftermarket? If aftermarket, got the hubcentric rings in there?

Shimmies at around 60-70mph with either the OEM 16" phone dials or my OEM 15" cookie cutter track wheels.

First thing that comes to mind reading your list is rotors - "OEM in great shape" doesn't really tell me much. I'm a 944 n00b however, I'm not familiar with their suspension design or other quirks.

Run_Away wrote: First thing that comes to mind reading your list is rotors - "OEM in great shape" doesn't really tell me much. I'm a 944 n00b however, I'm not familiar with their suspension design or other quirks.

The OEM rotors are made by Zimmerman and are really nice parts. They come balanced. My machinist at work said they were the nicest rotors he's ever seen on the lathe as far as being straight and true.

Motor mounts? Rear axle Drive line? Get a bigass bar and see what moves when you pry on it. No personal experience with this model but back up and check other peoples work. Scuttle shake sucks.

Rotating things shake. If you have tried different front wheels, and the shake is exactly the same, thats not your problem. Try rears, if you have not already.

What sort of frequency- a shake, a tremble, a buzz... Driveshaft shake will be very high frequency. Of course, on a transaxle type P car, the driveshaft is engine speed, so it would phase in and out with engine speed, more than road speed.

How about CV joints? A dry joint will usually shake more on acceleration or decell, lighter load will lessen it.

Rear tires will show up in the seat, not in the steering wheel, although thats not always true.

At speed, during the shake, depress the clutch and drop the engine to idle. Shake gone? Look at motor mounts.

Rotors are true on the lathe, but is there a chunk of rust on the face of the hub making it run out on the car?

Good luck. Vibrations and noises are the bane of the mechanics existence.

Dynabeads

....ooops sorry

sadly, the early 944s were prone to exactly this kind of shake.

I've heard that all 944's are like this.

I like the idea of putting the clutch in, to check motor mounts. The thing is, they are new too.

I really think it may be wheel bearings, I may just do them as they are not that pricey. The rotors are good, this car has barely seen rain in the last 9 years so not much rust anywhere.

Oh and the shake is in the steering wheel. And you can see it in the hood. It seems to go away at approx. 140kph not completely, but it does smooth out a touch.

Could seized upper strut mount bearings (the ones that allow you to turn without "winding" the coil spring) be causing this?

mad_machine wrote: sadly, the early 944s were prone to exactly this kind of shake.

Pontiacs too. Does the shake disappear at 80 mph or under hard braking?

So did the 924s to some extent. The early cars had an extra damper for the motor that attached to the cross member.

I wonder how it eventually was resolved in the later 944s?

I wonder if it is an issue with the caster blocks?

The later cars had an improved design for the caster blocks is why I ask.

Also a company designed a brace for the caster blocks as well, seems like there is some potential for improvement there.

I've chased this sort of shake around on other vehicles. Almost always the result was the same.

Somewhere, a suspension bushing was torn/worn/missing/degraded, letting the whole wheel assembly move.

Many times I couldn't generate enough force by hand to make it deflect while inspecting it. Be it on the ground or up on jacks or on a rack.

By doing careful side by side inspections, I could sometimes find the damage. Either by comparing the two sides of the vehicle, or comparing against another of the same. Usually the clue would be subtle, like the top of the struck sticking up a mere 1/4" more, or a funny little gap at the edge of a suspension arm where it rides the mount. Things like that.

Don't discount the possibility to doing appreciable damage for the greater good. As in drive the car in the vibration mode, and leave it there. Let it do its thing for as long as you can stand it, and then inspect. See if the vibration has forced bits of a bushing out, created interesting shiny spots, left a pile of shavings, etc.

How did you determine that the tires are "good"? There are a variety of things that can be wrong with a tire that will make it shake. The kind of vibration that makes a hood shake is usually a tire problem. Also, while you may have a lot of new parts on it, that doesn't mean they are all good. Check them again.

I had a MR2 where a front end shake was pronounced with v-tread tires but the shake was non-existent with more traditional tire tread.
Not "V-rated" but rather a V-shaped tread.

bravenrace wrote: How did you determine that the tires are "good"? There are a variety of things that can be wrong with a tire that will make it shake. The kind of vibration that makes a hood shake is usually a tire problem. Also, while you may have a lot of new parts on it, that doesn't mean they are all good. Check them again.

I've had 3 sets of tires on the car and it shakes the same. Actually 4 sets but the first set the rims were bent. I had the tires checked, and the rims by a local tire shop on a Hunter Road Force machine.

Falken Azenis(rims were bent) Toyo Proxes 4 Hankook Z214 R-comps Currently on Yokohama s-drives

What about steering rack bushings? Maybe I should go with some new ones?

turboswede wrote: I wonder if it is an issue with the caster blocks? The later cars had an improved design for the caster blocks is why I ask. Also a company designed a brace for the caster blocks as well, seems like there is some potential for improvement there.

I just replaced these bushings with OEM Porsche parts. The PO had used Energy Suspension bushings which were in bad shape, which is where I thought the problem was. No dice.

A little bit of play is unacceptable. How is the alignment ? Caster comes to mind, as some one already mentioned. Check runout. Lateral should not exceed 2.5mm. Radial runout should not exceed 2.0 mm Do 944's have a steering damper ?

Alignment has been checked twice by the best guy in my area.

No steering damper that I know of, how would I even go about installing one? I've only seen them on big off road trucks and motorcycles.