Downshift Shudder - I have HAD IT - LONG POST
06-11-2003, 11:27 PM
#31
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I found this on the web, from a quote from Bruce Anderson...
"21. Worn constant velocity joints can cause a driveline vibration similar to the shudder caused by a weak center support bearing on car with a two-piece driveshaft. Lead-footed-owners of turbo models may "accelerate" this wear and need replacement joints as soon as 50,000 miles. Play and pay."
Hmmm???
"21. Worn constant velocity joints can cause a driveline vibration similar to the shudder caused by a weak center support bearing on car with a two-piece driveshaft. Lead-footed-owners of turbo models may "accelerate" this wear and need replacement joints as soon as 50,000 miles. Play and pay."
Hmmm???
06-12-2003, 12:52 AM
#32
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Call this guy and ask him what he thinks.
Tom Charlesworth (head of PCA technical comittee) 918-664-8714 I memorized his number because I call him with so many questions, and he doesnt seem to mind them. By far the nicest, most knowledgeable person I have ever met concerning 944's.
Tom Charlesworth (head of PCA technical comittee) 918-664-8714 I memorized his number because I call him with so many questions, and he doesnt seem to mind them. By far the nicest, most knowledgeable person I have ever met concerning 944's.
06-17-2003, 08:34 AM
#33
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SAME PROBLEM HERE!!! <a href="http://forums.rennlist.com/forums/ultimatebb.php?ubb=get_topic;f=15;t=021653#000000" target="_blank">http://forums.rennlist.com/forums/ultimatebb.php?ubb=get_topic;f=15;t=021653#000000</a>
06-17-2003, 04:37 PM
#34
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A loose torque tube, in my experience (P.O. forgot to put all the bolts back), is usally a firm, solid, thunk. Low rev, torquey vibration could be the engine stuttering, and causing the springs/rubber clutch to whack agaist the stops, but you seem to have that ruled out. Some people mentioned the synchros, but if the car is all the way in gear, the synchro has no torque on it, and isn't doing anything. I have heard of problems like this just prior to rebuilding a autocrossing tranny. Teeth were broken off of the ring gear. You may have teeth broken off that, or the 2nd gear (from someone powershifting, or just gunning it too much). When you are at low speed, you jump teeth, causing the shudder. At higher speed, there is less torque, and it just engages.
It could also be your CV's. If the cages are badly worn, or broken, the ***** may bind, and cause a shudder. It usually only takes a hundred miles for something like that to go "BANG" and fail catestrophically.
Check your wheel play (like perry 951 said) to see if the CV's are shot. Then drain your trans fluid and look for chunks of metal that don't belong. Both of these are cheap and really easy to do.
It could also be your CV's. If the cages are badly worn, or broken, the ***** may bind, and cause a shudder. It usually only takes a hundred miles for something like that to go "BANG" and fail catestrophically.
Check your wheel play (like perry 951 said) to see if the CV's are shot. Then drain your trans fluid and look for chunks of metal that don't belong. Both of these are cheap and really easy to do.
06-17-2003, 06:11 PM
#35
The stuff you are describing sounds a lot like sone kind of balance issue with the drive shaft/torque tube. Is it possible that the shaft is slightly out of true, and is most noticable in 2nd with all the engine load and car weight on it as the RPM's fall? If the tranny and tube are really slapping around under there it seems logical that the balance is off somewhere.
06-17-2003, 06:43 PM
#36
Burning Brakes
Give IMA Motorsport a call. They're in Merrifield/Fairfax (Route 50 and I66). They are fantastic on clutch and drivetrain issues. (703) 849-9590
They did an outstanding job on my 968 engine swap working out all the drivetrain issues, etc.
Usual disclaimers apply.
Matt
They did an outstanding job on my 968 engine swap working out all the drivetrain issues, etc.
Usual disclaimers apply.
Matt
06-18-2003, 12:10 PM
#37
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Got a customers '91 S2 with the SAME problem. Replaced the clutch again with NEW flywheel- SAME PROBLEM.
Just talked to Ian from 944online and there seems to be a disc problem so he's sending me a "factory" rubber centered disc. Round 3! I'm about to give up on the car and send it down the road...
Just talked to Ian from 944online and there seems to be a disc problem so he's sending me a "factory" rubber centered disc. Round 3! I'm about to give up on the car and send it down the road...
06-20-2003, 09:26 AM
#39
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Paul,
I suggest to do a check in a controlled situation. First of all, lift the car with your mechanic lifter, leaving the rear (traction) wheel free to move while the car is 6-7 feets from ground. You have to stay inside the car, while your mechanics is below it, ready to hear noises and to detect vibrations and part movements.
Try to reproduce the sequence of downshift and the level of RPM you know generates the shudder. Repeat the sequence many time, with your mechanics listening/touching/guessing where is the problem.
This setup is not equivalent to the road conditions, because the wheels have no load. But you can easily feel even minor problems.
With this setup I was able to clearly and immediately identify a bad dual mass flywheel in my 968, generating elusive vibration problems. Substituted the DMF, the problem was solved without multiple "try and error". Detecting problem with the car on the road is a mess.
Let us know what you find.
Bye
Ugo
I suggest to do a check in a controlled situation. First of all, lift the car with your mechanic lifter, leaving the rear (traction) wheel free to move while the car is 6-7 feets from ground. You have to stay inside the car, while your mechanics is below it, ready to hear noises and to detect vibrations and part movements.
Try to reproduce the sequence of downshift and the level of RPM you know generates the shudder. Repeat the sequence many time, with your mechanics listening/touching/guessing where is the problem.
This setup is not equivalent to the road conditions, because the wheels have no load. But you can easily feel even minor problems.
With this setup I was able to clearly and immediately identify a bad dual mass flywheel in my 968, generating elusive vibration problems. Substituted the DMF, the problem was solved without multiple "try and error". Detecting problem with the car on the road is a mess.
Let us know what you find.
Bye
Ugo
06-20-2003, 10:32 AM
#40
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What exactly is shuddering? Is it just the stick shift, or do you feel it in the steering wheel? I had a similar problem, sometimes accelerating, but almost always decelerating and always at the same speed range. The problem persisted for a while with no "solution" fixing the problem. If this is what is happening with you check the following: Tie-rods, ball joints and rims... the rims for cracks. The rim was the original culprit, sent vibrations at a certain speed, but after time, it eroded the joints and ends. Good Luck!
06-21-2003, 12:02 AM
#41
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The shudder is a vibration that seems to grow in intensity, not correlated to speed, that shakes the drivetrain to the point where the transmission hits the underside of the car. It only occurs in 2nd gear, when the revs are about 2K off from the engine speed (lower revs). It cannot be mounts, clutch, flywheel, shocks, transmission as these have all been replaced or tested, and the problem remains.
06-25-2003, 08:58 AM
#42
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Paul,
Any updates? I'm taking the '91 apart slowly and checking everything closely as I go. I hope the rubber disc is the fix because so far everything looks good.
???
Any updates? I'm taking the '91 apart slowly and checking everything closely as I go. I hope the rubber disc is the fix because so far everything looks good.
???
06-30-2003, 09:49 AM
#43
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FIXED! I replaced the spring centered unit with a rubber centered. Also I noticed on the torque tube that the front bearing had a plastic insert that tightened up the clearence between the tube and the shaft has slide down the shaft about 6". I went through the slit of the tube and put it back in it's place. The clutch is so much smoother, less vibration and no more of the horrible downshift shudder.
06-30-2003, 10:27 AM
#44
Burning Brakes
good to hear this...most give the rubber centered clutch bad marks because it breaks after a lot of miles, years or abuse...what moving part wouldn't break?
unless it was a racer...I'd prefer the OEM Sachs rubber centered for smoothness and long R & P life
unless it was a racer...I'd prefer the OEM Sachs rubber centered for smoothness and long R & P life
06-30-2003, 12:55 PM
#45
</font><blockquote><font size="1" face="Verdana,Tahoma,Helvetica">quote:</font><hr /><font size="2" face="Verdana,Tahoma,Helvetica">Originally posted by PaulK:
<strong>The shudder is a vibration that seems to grow in intensity, not correlated to speed, that shakes the drivetrain to the point where the transmission hits the underside of the car. It only occurs in 2nd gear, when the revs are about 2K off from the engine speed (lower revs).</strong></font><hr /></blockquote><font size="2" face="Verdana,Tahoma,Helvetica">I have EXACTLY the same problem on mine. It still is on the original clutch (81,000 miles).
<strong>The shudder is a vibration that seems to grow in intensity, not correlated to speed, that shakes the drivetrain to the point where the transmission hits the underside of the car. It only occurs in 2nd gear, when the revs are about 2K off from the engine speed (lower revs).</strong></font><hr /></blockquote><font size="2" face="Verdana,Tahoma,Helvetica">I have EXACTLY the same problem on mine. It still is on the original clutch (81,000 miles).