LaughaC

You're on target Chaadster, but that was a weak moment. When I look outside at my 928 I'm still excited about the prospect of making it reliable enough to replace my Infiniti as my daily driver.

I don't mind doing the work if I know there is a light at the end of the tunnel. Let me know if I've forgotten a common S4 ailment to check, or if the priorities are out of order:

1. Timing Belt
2. Steering rack
3. Motor Mounts
4. Torque Tube
5. Intake gasket
6. Pan gasket

LaughaC

I'm 1 hour West of DC in Winchester, VA. It would be great to find a trustworthy, reliable shop to do the TB for me since space is at a premium in my garage.

Of course I would be happy to buy the beer and pizza if anybody wants to come and help with some Shark projects this weekend.

Oldtee

Whoa, slow down for a minute. I had the exact same thing. Every guru known to 928 dom swore it was motor mounts. I put in a new set, thanks to the help of Dr. Mohr but the ones we removed were OK. It seemed to help just a little. Maybe 10% of the vibration abated. Then I was fortuant enough to have my wheels aligned by Capt Dr. Earl 928 Gillstrom and he asked if I had addressed the flex plate issue. I have him a blank look, where upon he raised the car and we loosened the pinch bolt, check the end play, in spec. That removed another 10% or so of the vibration. Then I removed the intake, replaced all the hoses, new plugs, new wires, new coils, new distributro caps and a bunch of other stuff, including some fuel lines, something needed doing after 60K+ miles of missed service. That removed another 50% or so of the vibration. Then, it just went away. Maybe just running the thing helped. My thought is I have a valve sticking a little along with all the other stuff.

If it is the same vibration, it is not the torque tube. It happens between 1200 and 1500 rpm under a light load, like going up a slight hill in D. It was driving me nuts, since I thought a 928 was suppose to be silky smootlh. It is now. Go figure.

heinrich

Oldtee ... I was thinking that also.

Bill Ball

It's real important to give a full description.

From the above I would assume that there is no vibration if you rev the engine in Park or Neutral sitting in the driveway. That rules out the torque tube. Also, it largely rules out the motor mounts (see below).

I gather you have a bad vibration in the same low engine RPM range only when moving regardless of forward gear, but under no other circumstances.

That also rules out wheel balance and half shafts.

It still may be motor mounts - say one is sagging and only allows the engine to make contact with the crossmember under forward load, while in reverse the motor lifts on that side. So, I'm suspecting the passenger side motor mount.

I'm going to have to leave it at that right now and puzzle over it a while.

Bill Ball

Tming belt is maintenance. Steering racks can be an issue, but mine is still good at 160K miles. I think it's use it or lose it. Motor mounts are generally good for 15-20 years. Torque tube is still good in my car at 160k. Intake gasket?? No issues there. Sometimes the oil filler neck gasket gives out and creates an oil leak. Mine is still good. Pan gasket - same as motor mounts and replaced at the same time.

You bought an old car. Expect issues, but if you buy carefully and get a bit lucky, these cars are reliable. Mine has been a reliable daily driver for 6 years, and I don't exactly baby it.

chaadster

In the number two spot, I'd put thrust bearing check, and bump the rest down. OldTee mentioned it in passing, but since you've had the trans out, I'd say that you are in greater risk than those who've not had it out. It's very easy to release and measure endplay, but can be a real killer if left unattended. Run a search on thrust bearing failure and you'll get plenty of horror stories.

Also, I'd add number 6, pan gasket, to #3, motor mounts, if it's leaking, that is. There's no reason not to attend to a leaky pan gasket while you're in there...er, unless you're supporting the engine from below instead of above.

The items steering rack, intake gasket, and torque tube I would remove from the maintenance list and address on an as-neccessary basis. I would add vacuum system check & refresh to the maintenance list, and also fluid replacement (incl. brake & cooling). You've probably already got those items covered, but they're good to reiterate.

SharkSkin

Find a very dark place -- like a garage with the door 3/4 closed and the lights off at night. Run the car with the hood open. Do you see lots of sparks around the ignition wires? From your description I'll bet it looks like 4th of July under there.

khalloudy

Guys,

I have to respectfully disagree. I have had the sammmme issue since i bought the car. I have new ignition wires, spark plugs, caps and rotors, did the vacuum service under the intake and have new vacuum connections everywhere, new Motor Mounts, new Torque Tube, etc etc. Still my vibration persists between 1400-1800 rpm. I can feel it when the car is in P or N, but it is at its worse when i drive off. I can bypass the jittering either under full acceleration (zing past it) or under very light loadso i cruise through it gently. Any other mid punch and the car shakes like a wet dog. I am planning on removing my intake one more time to replace the Throttle Switch and Idel Stabilizer Valve and install a GTS breather kit and an external oil seperator and install new injectors. I am putting out another post with the pics from my spark plugs which have about 6k on them. There is a lot of ash and residue on them. I smoke at start and it smells like Fuel I think it could be bad injectors... i still have not figured out my issue! My car is an 87S4 Auto as well

P.S. I asked Rich Andrade who is a local expert here on the causes, he mentionned to me that his 87 S4 makes similar vibrations while his GTS does not. Both are automatic. He pointed that the stall speed of the auto is in the same range where we are feeling the vibration, and it could be attributed to our Torque Converter fins wearing out? just an extra opinion to add to the list.

Sincerely,

Oldtee

Your vibration is different if you can feel it in P and N. I only felt my vibration when in D or 3 at thoes RPMs. It is gone now.

LaughaC

I have only felt the vibration in D and 3, so Oldtree's description fits closest to my problem (so far). I've ordered the spark plug tool and will do a complete maintenance job as my next step.

The MMs really seem fine, as I can sway the motor back and forth a good .5 inch and feel the rubber supports doing their job.

The smoke from underneath is new, and seemed to start when the vibration got worse the other day. Could the connection the flex plate problem be so bad that it has shaken my rear main bearing into a leak? Thrust bearing failure is sounding more likely.

Searching the threads on the Thrust Bearing horror story-- and am afraid that might be it. "...to do with pressure from the drive shaft ( connecting the engine flywheel to the transmission input shaft. ) When there is a constant and abnormal force on the crankshaft, it will chew up the bearing and then the block." (OMG)

I'm starting to feel like a 1st year Medical student who thinks he has symptoms of every new disease he learns about.

heinrich

I get good vibes in every gear. They feel like ... BWAAAHH!!

LaughaC

Replaced spark plugs, cleaned some connections, and re-arranged plug wire insulators... and viola!! No more shakey!!

Thanks all.

G Man

Nice going! Check that thrust bearing load any way. Just to make sure all is good.

SharkSkin

Your plug wires may be marginal, especially if they were discolored(usually a lighter grey) where they were touching each other. Did you try running it in the dark & looking for arcs?