CLUnk noise when coasting...?

[otto in norway]

Hi!

Yes, got a clunk noise when I'm coasting, but not when I'm accelerating or braking. Any Ideas?


More info:
The noise seems to come from both left and right rear wheel. The sound can be heard in any gear and neutral, and sounds more like a sharp "metal-on-metal" scraping sound at very slow speeds. The frequency of the clunk's are equal to the rotation speed (Frequency) of the wheels. It can be felt as a slight vibration in the car, but, as mentioned it disappears during braking and accelerating.

I have recently done an engine rebuild, and also replaced the CV joints for brand new ones, with plenty of grease. The gearbox has new oil too.
Also, the brake pads were replaced apx. 1500 miles ago, and look great. (I know they are not to blame for this)

I jacked the car up on one side at a time, and spun the wheels to see if I could spot the source of the noise, but I got silence.

Anyone?

[Shawn 357]

Check to see if all the lug nuts and hubs are tight and double check those cv axles. The cv axles would be causing a vibration at speed if they were loose but it is worth a look.

[DW SD]

I have gotten a similar noise from brake pads. Are you sure you can rule this out? Metallic noises aren't necessarily made from metal on metal.

Doug

[otto in norway]

Thanks for input.

I do have a ever so slight dragging noise from the brake pads. But that noise is not nearly as loud and painful to listen to, as when my old pads were worn out. And that noise didn't go away when I accelerated, and got worse when I applied the brakes...
Anyway, The disks look fine, and I had no clunk before I started the rebuild. The pad noise is not audible in the car.

The vibration is more apparent when driving very slow. And so is the clunk noise. It feels like it's giving a small, short burst of resistance at the wheels for every clunk.
I have had it at 120 Mph, and it feels smooth. (It's always smooth during acceleration)
The clunk seems to have built up slowly from when I started the break-in. (apx. 400 miles ago)

I suspect the wheel bearings, but I can feel no slack at the hub/wheels, and no noise when i turn the wheels by hand.

Anyone had this experience?

[DRACO A5OG]

What Year is your Baby?

[otto in norway]

Hey..
It's a '79 SC, with turbo widened wheel arches and 43mm spacers on the rear hubs.
Why?

[mca]

Give this a try ... open trunk, grab inside trunk under the smile (grab something solid), and pull up really hard and really fast. You may hear the "clunk" and be able to isolate it if it is coming from the front of your car.

I had a similar issue and it turned out to be a failed strut insert - passenger side, front.

Since you think the sound is coming from the rear, a strong pull up on the bumper may also help you isolate the sound. Worth a shot!

[911st]

This is a long shot but you have a lot of leverage on the rear bearings if you have a turbo look conversion without 930 rear arms.

If one of the bearings if failing to a small degree the wheel could move relative to the brakes and drag some.

Dought that it what it is but try grabbing the rear wheels at the top of the tire and shaking them using your body weight.

[otto in norway]

Thanks for the input.

Hmmm.... The idea with the struts made me think about an observation I made when I rebuilt it.
I noticed that the left rear shock was worn one side.

Check out this picture:


You can see the wear there is quite significant. I didn't care, because I'll replace them this winter. Anyway, it looks like it must have been like this for a long time. And now, with new CV joints, wich can probably be a little tight, and "bind" slightly along the rotation, causing the vibrations to shift the position of the shock.

Just a theory, will check it out tomorrow...

[robert walsh]

Quite significant indeed, I believe you have isolated the problem area for sure, must in some way be related to the wide body setup, that is a helofa wear mark there, almost a grind. It should be fairly simple to identify whats happening, I hope it as simple to correct.

[Shawn 357]

check the spring plate bushing on that side for sure.

[911st]

Somethings up!

Unless that is an early car with alloy arms there should not be anywhere near that kine of ware on the side of the shocks. The spring plate retaining arm plate should restrict is from moving very much. Yes, look at it and see it the torsion bar tube is rubbing on the plate.

Also check the inner rear arm bushings. The limit the movement in that direction. If this is not it this car has been in an accident or something.

[otto in norway]

Thanks guys!
I didn't get time to check it out today, but will probably try it tomorrow.
I'll get back to you on this!

[otto in norway]

I found out what the problem was today.
First: I'm glad I'm still alive!

I started today, by jacking up the car, and feel for slack on the wheels. And there was some slack in both wheels, so I started to dismount one wheel. Then I was going for the spacer: You wouldn't believe my expression; I discovered that all of the nuts on the spacer were loose.
It turns out that BOTH right and left wheel spacer had all loose nuts!! They were only finger tight. (At best!!)

Despite this, everything looked OK. I just cleaned everything up, and made sure to tighten the nuts properly this time.
I have a theory to why this happened: The nuts in the spacer need to be tightened with a thin-wall pipe, attached to the scroller. This does not give to much leverage. I tried tightening it with this first, then with a longer bar attached to it. -And sure enough; I could tighten it about 0,5 turn more, until it felt as tight as my wheel nuts.

This picture shows the spacer after I reinstalled it. But when I discovered the loose nuts, you could actually see some of the threads inside some of the nuts!!

[911st]

Two suggestions.

Get a proper snap type torque wrench.

Use lock tite on those bolts. They are un-accesable and can not be checked easly.

At the track, you can see most Porsche drivers out with the torque wrench between run groups checking there lug nuts.

[otto in norway]

911st:
Thanks, will do!
I just never thought I would ever need to torque those nuts, because I've done quite a few wheel changes in the past, without problems.
But now, I know better.

[Shawn 357]

Good you found the problem before it found you!

You should still take a look at that rear suspension and figure out why that shock is rubbing.

[SteveinTO]

Did you check for a bent shock? Just a thought. Weird wear patten.

[otto in norway]

Yeah, I checked the suspension, and the shock is bent. That's why the "cup" of the shock grinds on the leg. No biggie...!
I'll replace all shocks, and maybe some more suspension details this winter....

[Ned, NYNA11]

Otto,
Replace those spacers with the kind that Porsche uses. I don't like the hidden bolting arrangement that yours have.

While you are at it, replace the alloy lug nuts with steel fasteners. I replaced them on my car. I just don't like blind fasteners.