thumping guru advice requested

terryb · 03-12-2006, 03:50 PM

No, not that kind of thumping...

I've started hearing a thump or clunk sound from behind me when turning left. It doesn't happen every time though. I put the car up on the lift but can't see anything obviously wrong. The sway bar mounts seem okay. The only things I notice are the left drop link seems out of round compared the right side, the left transmission mount washer is bent downward, and I can see slightly more hole where the frontmost bolt goes through the left spring plate than on the right plate.

The only recent change is I replaced the Dunlops with SO-3's (man, what a difference).

Can any of you much more experienced folks see anything wrong? Sorry the shots are so blurry, gotta learn how to use macro mode on the camera... Thanks for any advice.

Left sway bar mount. The flap on the top is the undercoating stuff:

Left rear drop link looks out of round:

Left transmission mount with bent down washer:

Left spring plate showing gap amount above front bolt:

Right spring plate for comparison:

Rot 911 · 03-12-2006, 04:14 PM

Looks like your sway bar mount might have torn loose, but really hard to tell from that photo. The transmission mount may also be loose. I would see if it tightens up any. If it is not either of those two check to see if a rear shock is loose at the top. Worse case scenario is a bad cv joint.

terryb · 03-12-2006, 07:11 PM

Thank you Kurt. The sway bar mount photo is deceiving because of that flap of undercoating that's sticking out at the top. I'll see if the transmission mount tightens up any. Thanks for the tip to check the top of the shocks--I don't know why I didn't think of that. Actually, I do--because I don't know what the hell I'm doing most of the time!! Thanks to everybody who's answered my newbie questions and helped me get a little more comfortable wrenching. I hope someday to be able to return the favor and answer a 911 question.

terryb · 03-17-2006, 01:04 PM

I tried to tighten the transmission mount but couldn't get the bolt to budge, even with a 2 foot persuader on the end of the wrench so I don't think that's making the sound.

When I checked to see if the top of the shock mount was loose, the threaded part and the nut both rotated when I put a wrench on it for a 1/16 turn. It didn't feel loose and it looked about the same as the right side. I was afraid to turn it any further. Is that normal for both to rotate? The shocks were replaced with Bilsteins about a year ago.

I double-checked the sway bar mounts while up on the lift and also just using a floor jack on the left side to simulate the unloading in a left hand turn but they both look fine.

How would I go about testing to determine if it's a bad CV joint?

Is it possible that a torsion bar has broken? If so, what are the sounds and symptoms of that?

Thanks for any pointers.

74threeliter · 74threeliter's Garage

Checking to see if the shock mount is loose:
a) raise car b) remove wheel c)drop the ft. sway bar b) loosen the tie-rod from hub c) loosen the upper strut mount. this is not easy if the right tool is not present. d) with the tie rod, sway bar and top strut nut removed one should be able to push top of shock down and out under wheel well.

Checking the CV Joint:
Rear CV's used on 911 only so I personally know of a nice paved road with a brick wall. this is my drive test area where i can troubleshoot for clicking sounds .
a) raise car b) remove suspect rear wheel c) inspect boots for tears and with e-brake off turn hub for click sound (this may only be detected if the joint has gone bad)

Broken Torsion Bar:
I changed all 4 of mine but i have seen a broken one on a car. the car will drop in height ridiculously and it usually preceeded with a large bang.

Hope this helped

burgermeister · burgermeister's Garage

Your drop link looks odd to me too. Unless the sway bar is loaded because you only jacked up one side, that bolt ought to be centered. I'd take the bolt out and give the drop link bushing a gander.

It's unlikely to be your issue, but you can take the trans mount washer off and bend it back into shape pretty easily. That sure is odd to see bent like that ...
My trans mounts were all full of air on top like yours. You can cut a ring of rubber from hardware store 1/16" gasket material and sandwich it between the bottom washer and the rubber mount (make sure it doesn't interfere with the washer / internal spacer contact). Might raise the hair on some folks' back, but it works and beats shelling out whatever ludicrous price for a new crossmember w/ new mounts.

911st · 02-17-2009, 03:20 PM

Lug-nutts?

Happened to me once after a tire change.

blk911 · 02-17-2009, 04:02 PM

Terry,

Pull the axle on that side and examine the CV joints. Look for pitting on the ball bearings, race and housing. Shiny spots are probably ok. Look for threads on this forum for rebuilding CV joints. New ones from our host are not so bad, probably a good time to replace boots too. I just did all this on my 79 SC. Didn't have a problem, but slid on the slippery slope of "while you're in there".

Good luck.

terryb · 02-17-2009, 04:03 PM

Thanks for the replies 74threeliter and burgermeister.

The issue was resolved and I apologize for not posting the fix back in 2006. What it turned out being was the bolts in the sway bar mounts were pulling through the welded in nuts--their threads had been stripped. So I followed a recommendation from DWSD and drilled them out then used new stainless bolts and nylock nuts. It's been nearly three years now and still holding.

burgermeister, you're right and I have since replaced both drop-links.

burgermeister · burgermeister's Garage

D'ouh! I ddn't even look at the original post date ... hehe. Good for a laugh at any rate, and I needed just that at this precise moment for reasons I shan't discuss here. Thanks!

moneymanager · 02-17-2009, 05:03 PM

You will get a clunking noise when turning if the sway bar at the back is way off center, ie more of it sticks out one side than the other. I'm not sure this happens to all Porsches but it happened to my 74 about a year ago. Easy to check. A few mallet blows will move it back to where it should be if necessary. The sway bar can also contact something under the car as well, though I can't recall what it is...maybe the tranny? Look for signs of rubbing or physical contact near the center of the bar. The solution to that problem, which I also had, was a couple of washers under the sway bar mounts to lower the bar just a tad. FWIW.