The Mysterious, Heat-Sensitive Susp Knock..., ...driving me nuts! Options

[horizontally-opposed]

Hey all,

So I've been noticing a knocking (light but loud enough to hear) sound whenever I crank up the 914 and drive away. Any undulations or bumps at all get it a-knockin. So of course I turn off the engine, pull the transmission out of gear and try to figure out where it's coming from while I coast down to a stop, rolling over bumps along the way. Hard to tell, but it seems like the rear, maybe the right rear.

Now here's the wierd part:

Once the car is warmed up, the knocking is gone. Completely.

There's no funny suspension movement or bump steer, I've checked the inner trailing arm nuts, the shock nuts top and bottom). I did, on Brad's recommendation, check all the above a couple of weeks ago and found the driver's side shock and inner trailing arm nuts were "hand loose" (scary) and then tightened them. It seemed to help for a day (or maybe my mind was playing tricks on me, making me assume I'd found the problem) but the same sound is still there and all those fasteners are tight.

It sounds like a chassis-related, suspension-movement related knocking -- but why does it go away with engine heat. Has anyone a clue?

Thanks!

pete

[davep]

Could it be that the RR shock is binding when cold, and works better when warmed up some? I often find that worn shocks will "snap" when they move. This may be related to the looseness in the parts previously. If the shock in question is old, that is a very likely problem. You can test this by using the bounce test; when cold, push down hard and quickly on the fender in question. You should be able to detect a hesitation in the movement that is related to the sound. The seal may be drying up and sticking to the shaft. A bit of action could suppy enough oil to lubricate it again.

[horizontally-opposed]

Tis a good idea! And they are who-knows-how-old Konis... will check in a while when the car cools down. I love 31-year-old daily drivers!

pete

[skline]

Check your engine and transmission mounts also. I drove my yellow one and it started making a noise like that, turned out the bolts on the motor mounts were not there and the mount bar bolts were loose. Not a good thing to be loose.

[bondo]

Check the heat exchangers/exhaust.. I've got an annoying knock when my idle goes too low, and it's the heat exchangers hitting stuff.. I don't think it would be too big of a stretch to think a bump could do that too if something is loose.

[horizontally-opposed]

Alright, so I finally got a chance and it looks like it is the right rear shock.

Did check the engine mount nuts (great tip!) and they were all wanting in terms of a little tightening -- so it might be a good idea for everybody to check theirs, because I would not thought to have checked them otherwise and they took quite a few turns to tighten -- and they weren't SUPER loose.

Anyway, I then pushed up and down on the car, thinking maybe I had solved the issue again -- though suspicious because the mounts weren't really that loose -- and the click is definitely audible from outside. And it was the right rear, somewhere near the wheel. I opened the trunk up, put a finger the top of the shock before pushing down on the bumper again and I could feel the "click", "tap", or "knock" through the top of the shock. I think it's just old and is binding. Good to know the car's not gonna come apart on the freeway, but me thinks it's time for a new pair of Konis in the rear.

And maybe the front, too...

Many thanks,

pete

[rick 918-S]

I think "B" just posted about a shipment of Koni's that arrived. Better hurry while they last. (IMG:style_emoticons/default/wavey.gif)