LaughaC

I'm getting a BAADDD Vibration beteen 1200-1400 RPMs only. Today a mechanic told me that torque tube vibrations increase with speed, and he suspected this was a case of bad motor mounts.

He told me to try shaking my engine and if it won't move compared with the body then my motor mounts have collapsed. Well, my motor moves about 3/4 of an inch each direction, so the motor mounts still feel rubbery enough.

Am I back to suspecting the infamous torque tube, or should I move on to mysteries like the harmonic balancer?

I will mention that this car has been sitting for 2 years and sorely needs a tune up. I bought new spark plugs yesterday, and the parts store told me they are the 13/16ths variety, but my 13/16ths socket won't fit down the tube to the spark plug. Okay, 2nd question: Did I get the wrong plugs, or do I need a special "thin" walled socket?

I will stop rambling now. Yes, I'm a newbie to the 928, but I'm beginning to develop a new appreciation for my 911. Just got my '87 928 and thought I was prepared to go through it all, but I'm obviously on foreign ground. Thank God for Rennlist!!!

Normy

I suspect the both: mounts and torque tube! But you need to tell us the year and perhaps, if if applies, the model of your car.

N!

FlyingDog

Auto or 5-speed? In gear or out of gear? Motormounts make the car vibrate some, but it's not all that bad. The standard motormount test is to rev the engine while looking at the engine compartment. If the whole car rocks, the mounts are dead. If the engine rocks seperate from the car, the MMs aren't completely collapsed. Unless they've been replaced at some point yours are probably collpased.

I don't remember the socket size for the correct plugs, but a regular socket wrench should fit in the holes without any trouble for the correct size.

chaadster

If the car has been sitting for two years, might the tires be "flat spotted" and out-of-round? The description does suggest motor mounts to me, too; try FlyingDog's test method, or get underneath, pull the belly pans, and visually inspect for crossmember contact with the oil pan.

Also, the tool kit in the rear panel of the hatch houses a spark plug wrench. Try that.

Bill Ball

The bad TT vibrations I have felt have been throughout the RPM range. As Flyingdog mentioned, if you have a 5-speed, the shaft does not rotate when you are stopped and the tranny is in gear with they clutch depressed. So, if you feel it then, it's not the TT. 1 minute test in the driveway. If you have an AT car, that test does not apply.

Motor mounts most likely - you should directly observe them and the space between the oil pan and crossmember, as Chadster already mentioned. On the passenger side mount you will see top and bottom plates on the mount that have interlocking (well, overlapping) hooks behind the crossmember. On the driver side, they are in front of the crossmember. As the mount collapses, the space between the hooks grows. If you can get more than one finger between the hook ends, the mount is collapsed.

The spark plug holes are small. Even the plug wrench that came with the car is barely fits. Otherwise you will need a thinwall socket.

LaughaC

Thanks for your replies. My car is an '87 S4 Automatic (engine #81H06629) and the viBBRRAtion only occurs when moving forward and any gear reaches the 1200-1400 RPM range. It smooths right out after that, so with a little throttle finess I can bypass the vibration quickly most of the time.

However, when idling through my neighborhood at 25 MPH I have to downshift to 2nd to keep the RPMs above the tooth-jarring range when I touch the gas. The vibration only occurs when I apply a very little bit of throttle.

The rack is leaking pretty badly, so I will replace it and do the motor mounts at the same time. If that doesn't fix the vibration, I suppose the next thing to look at is the TT? Is there anything in the rear main bearing vicinity that could cause this problem? I saw some smoke coming from that area when I stopped the car last night, and it smelled like motor oil. Hmm, this Shark might get the best of me, AND my wallet.

My car does not have a Porsche toolkit, and neither does my 911. I guess I will start searching online for the right spark plug tool. Are you confirming that the plugs are 13/16ths?

heinrich

your torque tube turns even with the car stationary.

chaadster

Well, if we assume the motor mounts are sagging, the driveline could be misaligned, which causes roughness and vibration. Doing the rack and MMs will probably fix things up, don't worry! You sound stressed!

The spark plugs are 13/16ths. Check out this tool from www.stamstagSales.com, it's pretty trick, if a bit pricey at $50. Those guys are Porsche tool specialists, but you could also check with 928 Int'l to see if they have the factory supplied wrench.

SteveG

Might I suggest a socket with the rubber sleeve inside that holds the plug snug and helps pull the plug out and again helps when trying to thread it in. That is if you don't already have that in mind.

LaughaC

Thanks! I'm on www.SamStagSales.com ordering now. I'll also read up and order parts for this weekend's projects. Rennlist makes all things Porsche possible.

You read me right. I'm getting a little stressed over the number of hours I need to spend on the Shark. I've restored (or restified) antique Mercedes and built several hot rods. Right now I'm considering setting the Shark aside while I install a recently acquired turbo kit on my 911. My wife actually likes this old Shark better than my 911, though, and I think I will too if I can afford to make it reliable. (and maybe even Supercharge it)

Depending on how the research goes, my first Shark project might need to be the timing belt. If I decide to bail out of this car I won't want to sell to anyone without a fresh TB.

My original plan was to bring this Shark up to daily driver status, and then invest in a repaint and A/C repairs. At this weak moment I think I would consider trading it for a reliable turbo-charged diesel with a moonroof.

IcemanG17

LaughaC
Doing the rack and motormounts at one time is a good idea.....after you get that done it will give you a better idea what to do next....A/C can get costly to repair too....or it could be really simple?

chaadster

It sounds, LaughaC, that you bought a fixer-upper (no tools, bad paint, no a/c, vibrations, parked for years...what else?), probably the wrong kind of 928 for what you want. You might look at one that has been better cared for. They are out there.

Hey, let's face it, if you're weighing the 928 against a VW TDi (or did you have an old MBZ in mind?), you've probably gotten more with this shark than you want to deal with. Obviously you can do the work, but do want to??

Like Smokey says, "Only YOU know when to cut and run."

LaughaC

Yep, I'm adding it up to see whether the math makes more sense than my desire for this S4.

Do you usually have to replace the belt tensioner when with a new TB, or is there a way to test the tensioner?

I have a lot more reading to do before I pull this Shark apart. At least right now it runs and has fairly new transmission.

FlyingDog

928s rarely, if ever, make monetary sense. Remember, they're Porsches. Just be glad you don't have a 911... oops, you do.

For the tensioner, just pull the guts, clean them up, put them back in and reseal it (boot and a rear gasket if you pull the tensioner from the block). 928 Specialists has a 'kit' on their site that lets you select the common parts to be replaced.

Where in the DC area are you? There are several of us around. We normally have get togethers the first saturday of each month.

heinrich

What Dawg said.