[MCL968]

Sounds like either a bearing or the exhaust system. Both change with temp. My Volvo S60 had a bent hanger and when I would hit water, the pipe would contort and rub on the driveshaft. True story, straightened

the hanger, noise went away.

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[ds968]

' ya know, the exhaust set up might still be a possibility ; I don't recall this noise happening before I had the catback segment replaced ( full story on another " what's that noise " thread ) , and even though all the clearances looked as nothing could possibly even come close to touching, I wonder if on sharp right hand turns when accelerating and the exhaust is hot , with the car dipping low enough on one side , something, somehow comes close enough to either touch or to create a resonance which sounds like a rumble . As I mentioned before, it sounds like a much louder exhaust note at that point , smooth , no rattle or vibrations . Hmm, it would be great if it's that ; I can adjust the end pipe's position on the last bracket by maybe 1/4 " or 1/2 " ( it's at the highest point on that " travel" slot now ) and test if that makes any difference .

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[MCL968]

Sounds like a reasonable and cheap course of action. The situation could also be exacerbated by failing or failed engine mounts. Is the new exhaust larger in diameter than the old one? That would certainly affect the clearances as well.

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[ds968]

The engine mounts are fairly new and same as before the exhaust exchange so no chance those might factor in,  and the replacement catback is the exact same ( OE ) as the old one, but when it was installed chances are better than not that the position of its being set  on the two different mounting / holding brackets could have just enough of a variance to get things closer than they were before.. 22 years might have loosened the old set up quite a bit .     

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[ds968]

My mechanic inspected the wheels and suspension yesterday and said he does not detect any problems whatsoever with either of the wheel bearings or the cv joints . Also checked the exhaust set up to see if anything could make contact on hard sharp turns , but that was also eliminated from possibilities. Last, he inspected the differential fluid which looked clean and bright colored ( not burned ) .

One more test to be conducted Monday ( have to wait until then because he's finishing some other work on the car ) : he'll switch the wheels to see if by chance the right rear tire has developed some defect which causes that noise on the turn. So I'll test it then and see what happens . If it is the tire that would be really good news because he can't think of anything else except the differential clutches or gears or whatever else is in there that could be going bad, and that's going to be pricey .

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[ds968]

Just tested it with the switched wheels and it's not the tire,. Ugh . Guess I'll have to live with this until ( and if ) something breaks.  It's the old story  " - Doc., my arm hurts when I lift it over my head, can you help me ?  Doctor: " - sure.. don't lift it over your head anymore ! "      Like I said, the noise is there ONLY on very sharp,  near-90 degree right hand turns, and only if accelerating INTO the turn, so i'll just stop doing that ..            

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[Rap]

Go faster into the corner, trailbrake in and then squeeze the throttle. You might even induce a little slide! Did you check the control arm? Sway bar or bob's brace underneath?

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[flash]

except maybe from the wife, none of those would create a moan/groan, which is what he has going on.  my bet is rear axle bearing

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[ds968]

except maybe from the wife, none of those would create a moan/groan,

LMAO ..

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[ds968]

Ok, so I have to understand how things work : the axle is a straight, rigid, hunk of metal without joints or any flexible components, running from the differential to the wheel, right ? So noting really changes in the dynamics when you take corners no matter how sharp, and the bearings shoulldn't have any greater load on them than they would under straight line driving, or sweeping curves, etc.

Thus the noise of a bad bearing would manifest itself in most situations not just hard cornering ...or am I completely missing how the dynamics work here ?

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[flash]

nope - there is a bearing, with a "joint" of sorts, on each end

 

   

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[ds968]

Ok, so I just thought of how to best describe the noise ( best that I can come up with, anyway ) ;  it's very similar to the sound you hear when you drift onto the shoulder of a highway and run over those embedded ridges they place there.. to wake you up I suppose.    So that rumble sound, but WITHOUT any of the vibrations !   From everything I hear, IF it was a differential starting to go bad, and considering all tiptronics have the LSD, it would be nearly impossible for the symptoms to occur only on sharp right hand turns, and it would very likely make the exact same noise on left hand turns as well, or even sweeping turns, in both directions or maybe even straight off the line take offs . True ?

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[Waylander]

Bad cv joint

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[ds968]

Bad cv joint

 

 

Doesn't that 1) make more of a clicking / rattle noise  and  2) can also be heard at all times, including driving in a straight line ?     I had two CV  joints go bad in the 944s , and those were the symptoms I experienced before replacing them .. but maybe if its' JUST starting to deteriorate, it could manifest itself in this way also ?   Oh man, just too many possibilities here..        

It also gives the seat of the pants sensation that the tire is spinning / slipping in place in that hard turn, although I'm not on the gas hard enough to do that so it probably only feels like it spins .

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[968Syncro]

.... all tiptronics have the LSD, .....

I had no idea about this.   So my Tiptronic has the LSD inside, and how would I ever have known since I don't get on it that much.  For example, I've never tried to "lay a patch" like I once did with my '66 GTO in high school while trying to attract girls.    So a couple of questions:

• for Dan, do you notice a difference in your Tip car vs the 6 speed?
  
• anybody have an idea why Porsche included the LSD in all the Tip cars?
  
• I wonder how this changes the daily driving experience -- if at all.
  

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[flash]

they likely put it in there to manage the load on the box.   my suspicion is that it is not designed for as much torque as the engine puts out.  not sure what kind it is though.  not likely a high lockup rate in any case

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[ds968]

I was VERY surprised when I read ( on this forum ) about all Tiptronics being fitted with LSDs, whereas for the six speeds it was only an option.  To me, logically, it should have been the other way around, but anyway..to answer the question whether or not I notice a difference in the tip LSD  vs. my six speed which does not have an LSD , the answer is  No.  However, that might be because the greater difference all around in driving the two cars dwarfs anything I could possibly detect as incrementally attributable to the LSD .   Heck, even with 300+ HP and 300 ft/lbs of torque, I can't spin the tires on the Tip.  With the six speed I can leave rubber on the asphalt on takeoff, and get a damn loud squeal into second as well ...  I also don't take the tip anyway near its capabilities in corners, so guessing the fact that I have an LSD in that car is basically useless ( to me ).    

 

Hey, if it's not the differential that's causing the noise, I wonder if I can switch it with the six speed so that one has the LSD ?  Just kidding, if only it wasn't connected to two different types of transmissions ..       

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[flash]

well, there are likely a couple of things at play there.  i am not at all surprised that you have not "felt" the lsd in operation.

 

first, you don't have nearly that much power in the tip.  i had to detune that kit quite a bit in order to keep things together.  i couldn't dyno that kit, but if i had to guess, i would say you are putting out about 275 hp and torque.  as it is, you still managed to rip up a new flex damper.  this goes to show how weak that system is.

 

second, because you only have 4 gears to work with, a lot more rotating mass in the box itself, and a torque converter designed to smooth out the application of power, it limits how fast you can spin things up, and therefore the likelihood of spinning the tires.

 

third, the final gearing in the tip box is different than in the 6 speed.  the tip has a 3.25 final drive ratio, vs the 3.778 in the 6 speed.  that means that it is a lot easier to launch the 6 speed, and in doing so, easier to spin tires when you lose traction.

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[ds968]

makes even more sense now. 

 

ok, so while we're on tutorials .. the axle bearing :  why would a bad bearing make no sound on those turns when the car is cold but when all is warmed up it does : is it because it expands when warm and also the grease

packed in there becoming much thinner facilitates the problem manifesting itself , or it's something completely different  ?         

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[Bulti]

Early cars had a plate LSD, later ones ('93-onward?) had Torsen. You can check the code on the gearbox. Porsche968CS has more info on that should it come in handy.

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