bd0nalds0n

I have an '88 S4 Auto. It has Louie Ott front droplinks with greasable urethane bushings. It has had the thrust bearing/TT fix performed. I swapped brake pads a month or so ago, the car has had a recent alignment where it was cranked down to the correct height. Front tires were also recently replaced. Near as I can tell, the shocks and springs are unmodified.

I noticed recently that, under heavy acceleration from a stop, especially after hard braking, that there is a "clunk" sound originating somewhere from the front of the car. The clunk is not immediate, but somewhere between a fraction and a whole second(s) from the time I accelerate/the car lunges forward. There is a similar clunk heard if I then brake hard after accelerating hard. Imagine you had a bowling ball in a metal box 2 feet long. You accelerate, the ball moves to the back wall, and clunk. You brake, and the ball moves to the front wall, and clunk. Not immediate, some delay.

Because I can make the car clunk under moderate to heavy braking, this leads me to believe it is either brake- or suspension-related, rather than driveline. Does this seem reasonable? It does not occur as readily if I shift to 2 for a first gear start, accelerate from a rolling start, and use engine braking to slow the car from high RPMs

If anyone has ever had a spring move in its seat after replacing shocks, it's similar to that sound, only it's every time I brake/accelerate hard, rather than if I turn the steering wheel, as one might expect when springs go clunk in their seats. It also is a solid clunk, rather than springs which seem to have an harmonic boinggg when they move.

Another analogy is the clunking sound 944 clutches make when the rubber center breaks, and when you accelerate, the clutch clunks on the metal stops, and when you let off the gas, there's a clunk as the metal stops are hit going in the other direction. But it's more delayed than that, and not quite so metallic sounding.

My question is, where should I start looking first to try to isolate the problem? Anyone BTDT with a similar situation? I can probably get under the car sometime this weekend and start looking for things out of place, but I'm more interested in disproving the idea that it could be driveline related ASAP rather than some suspension or brake quirk that I can sort out over time and ends up being a nuisance more than something where I risk some sort of catastrophic damage as I drive the car.

I also had the engine rebuilt 4-5 mos ago by a very competent shop/mechanic, so motor mounts and all kinds of miscellaneous parts were replaced while the engine was out of the car.

Thanks in advance for your thoughts...

Jim bailey - 928 International

Brian is your battery hold down bolt in place ? even though it sounds like the noise originates up front ??

bd0nalds0n

Yes, when the car was at Greg's recently for the 1k timing belt tension, there was a cold start problem and we replaced the battery and fuel/ignition relays. The battery retainer was missing, and Greg installed a new one. Cold start problem ended up being a short @ the temp II connecter.

I thought it was at the rear, too, at first, having just installed the Louie Ott droplinks in the rear, I thought maybe I got the preload wrong or the links were banging against a spring during a hard compression or extension associated with the weight transfer of hard acceleration or braking...

But I am 99% sure it originates up front.

Shane

Check your upper a-arms. Similar clunking I heard right before smelling burnt rubber when my wheel leaned over onto the coilover. The upper a-arm ball joint came loose from the steering knuckle. Could have been when I replaced all the components up front that I failed to torque the nut down properly or it could have been that the "Alignment Specailist" didn't get it right, who knows! Worth 30 minutes to check it out though.

Steve J.

Brian - That's an excellent description. I have been chasing the exact same clunk in my '87 for years and I am stumped. I've been over everything. No loose suspension joints or brake calipers. Very predictable - I know exactly how much acceleration or braking will make it clunk. I can start off very gently with no clunk. Seems to clunk more readily after the car has warmed up. The sound seems to come from somewhere between the passenger side front suspension and motor mount. I can hear it and feel it. I can't wait to find out what your problem turns out to be because mine is the same.

Mark

Along the lines of Shane's suggestion - check the upper A-arm bushings.

Dennis Wilson

During braking and acceleration, the engine shifts which can cause loose or improperly mounted exhaust components to contact the body or other components. Also, you might try checking the CV joints.

Dennis

bd0nalds0n

I adjusted the rear drop links (which I had installed within the last two weeks) over the weekend. One of them was twisted a little bit which might have caused the spherical bushing to bump against the limits of its travel under certain conditions, and I straightened it out.

I also pulled off both front tires and nosed around a little bit under the car. Everything seems tight and the control arm bushings are all there and intact. The calipers are firmly attached, and were not molested in any way during the brake pad change (I did make sure the retaining clips were still fastened). I greased the sway bar bushings again.

The CVs were rebuilt last September, and the boots are still perfect looking.

I remain convinced that it's coming from the front of the car. I think it's got to be somewhere in the suspension. In fact, I find that I can brake sufficiently to create a squeaky clunk, like how lug nuts can make when they break free, which I assume is the offending part taking a "set," which then translates into a clunk when I accelerate, which I assume to be the "set" giving way.

Is it okay to use any sort of lubricant on the control arm bushings? Does anything that you could spray on have any hope of penetrating? With what degree of frequency should the bushings be replaced? I assume this is a very labor intensive job...

I was gratified to hear that a reader has a similar situation that spans multiple years--misery loves company, and it's nice to know someone is on the treadmill further ahead. All in all, seems pretty benign. I'll be sure to post if something significant breaks or falls off. Car handles and drives great, otherwise.

Gretch

Ball joints come to mind. ANd they are going to be hard to check, better to do it with the wheel on and the car on the ground. grab the top of the tire and pull / push in and out. see if you have any movement.......

Check the bottom ones like this, but with the car in the air, grabbing the bottom of the tire. (Please put car on jackstands safely). If you get any clunking or perceptable movement......take the car to an expert on ball joints on the 928.

Good luck.

heinrich

I too had a clucking sound once, turns out I had been travelling through chicken country, and a little cornish hen had got herself stuck in my intake, *under the air filter* a la Ed

Shmurzik

I have a similar issue. What about the weight attached to the torque tube [?] ?

bd0nalds0n

I saw a thread referencing something called a "harmonic dampner." Is this the weight you refer to, Schmurzik? Can anyone shed some light on this? Can it come loose and slide fore and aft? We might have a candidate...

heinrich

Yep, I have one too. No way to hear when I play the harmonica in the 928. That damper works very well ... Brian the harmonic damper is the orange thing that sits on the front of the crank shaft, with the pulley. Hopefully it's very very tightly on there

bd0nalds0n

Yeah, I did a search on harmonic balancer and it doesn't seem to fit the bill. If I have something moving, it's moving more than a few mm in each direction.

I have done the push/pull-on-the-tire/wheel to check for play. Nothing. The car drives rock steady. No vibrations at any speed.

I have noticed that the unit comprised of the vanes that direct airflow is loose and rocks back and forth. Mine has been disconnected (the actuator arm is completely gone). I think it's a candidate for removal. However, since everything associated with it seems to be made from plastic, I don't think it has the heft necessary to create the clunk. And the more I think about it, it's more of a clank than a clunk.

I've seen threads that talk about the TT bearings creeping. Is there anything along the driveline that can come loose and move fore and aft? I did have the thrust bearing fix done when I had my engine rebuilt; I would not expect a problem in this area so soon.

I can feel both the compression and the release (at least that's how I'm characterizing this) in the shifter handle. For those others who have similar symptoms, can you feel it in the shifter, too? I can also feel it at my feet.

Gretch

Shifter handle is attached to the torque tube which is attached to the negine, isolated from the frame by motor mounts and the transaxel, isolated from the frame by springs and bushings. Fire wall is close to the front suspension and is isolated from it by springs and bushings. You may be able to isolate the location of the noise by driving by a concrete wall slowly with your window(s) down and see if you can induce the noise. I am betting if you "feel" it at your feet it is in the front suspension. Doesn't explain feeling it in the shifter though....