Oli928

I read about 25-30 threads regarding flex plate and TT bearing noise, but didn't find one that matched my experience exactly...so I wanted to share, so that someone can learn from my experience.
Car Background:
'89 928-S4 / Auto / 108,000 miles / bought with 104K miles / only owned 1 year / few receipts of prior owner work / I owned '85 944 9 years prior to 928

Here is what I heard that prompted me to take in for service:
1) Low volume sound which changed with engine speed. This sound (the main reason for this post) wasn't a hum, whine, clinking or whirring sound like other posts (...but since "sound" is sometimes difficult to describe, my sound "may" be the same humming or whirring sound others described). Soooo....here goes my description of what I heard:
a) Almost like a power steering pump noise when they are low on fluid.
b) I might also describe it as the sound like an aquarium pump
c) Another description is that it sounded like a small electric motor whose bearing or bushing was old
When I hear the word "hum", I'm thinking of a constant noise with no texture.
My noise had a textured or ridged sound. It raised pitch and eventually you couldn't hear it past about 30MPH because the RMB kit drowned it out (or maybe the pitch was too high).
Comparison "A" is my best description of the sound.
Where did sound come from?
1) When inside the car, it came from the front hump area, behind the ashtray area. At first, I thought my new radio was having EMI noise.
2) When outside the car, you thought it was from the driver's wheel well area, then when you kneeled down, the sound was coming from the front of the TT area, then it sounded like the other side...eventually I figured out that since it seemed to come from everywhere under the back third of the car, it was probably the TT bearing emanating the sound down the center.
What Porsche Tech found:
(I'm double lucky on this)
1) The TT did creep up and push a little on the flex plate. Once they released the pressure, the noise went away. Yes they checked the specifications and I was in really good shape...no damage or excessive play.
2) The TT bearings were fine. The front one had very, very little noise when spun and wasn't worthwhile to change yet.

I went ahead and had them replace the O2 sensor, since it was literally 5 minutes of labor.

Another item learned during all this:
Since I bought the car, I always had a very quiet hum coming from the torque tube area and after reading a few posts, I realized this was normal since it is always spinning and the car had 104K miles+...THIS IS NOT NORMAL
The sound almost completely went away. It is so quiet now, I can actually hear the fuel pump in the back (no it is not going out...). If you hear any abnormal noise from the TT area, get it checked out. I'm very lucky to have not damaged anything (I drive the car gently...okay a few times my leg had a spasm and floored it)

I know I only postponed the TT bearing replacement, but this is still good news.

I admit I was somewhat skeptical on the whole flex plate horror stories (meaning that it probably only happens to a few people or to those who drive their cars like they stole them) but not anymore. EVERYONE (WHO IS SUSCEPTIBLE TO THIS ISSUE) SHOULD CHECK THEIR TORQUE TUBE/FLEX PLATE AS A REGULAR SERVICE ITEM EVERY 30K MILES! Maybe just plan for it when you change the timing belt.

Like some threads have mentioned, Porsche didn't really admit fault on the TT clamps, but it is a real issue.

Sorry for the long post, I just wanted to be as detailed as I could so someone else can benefit from my experience.

PorKen

30K is wayyyy too long to wait.

Check @ every oil change!


Get a 'PKlamp' to stop the creep - http://928sRUs.com

Oli928

(PKlamp) I thought about the clamp, but since I didn't know whether this was going to be a $300 or $2,000 repair (or worst case, I already damaged the engine) I didn't plan on adding anything extra to the bill...I also didn't have time to research the clamp. Thanks for the input about it.

I should probably clarify the 30K mile check statement; this was from an old Porsche service bulletin dug up from a while back...real life experience/suggestions from Rennlist people should always take precedence.

If someone wants to answer this (if not, I'll do my research)...do you need to balance the TT after installing the clamp (like a drive shaft needs to be balanced) or is it a non-issue?

PorKen

Does not need balancing. The clamp has bolts which mirror each other.

It is so close to the center of the shaft that a small imbalance would not have a great effect, anyway.

borland

Replacing the torque tube and torque converter bearings at intervals of every 75K miles, goes a long way at reducing bearing noise and shaft migration.

PKlamp, per the installation manual, requires re-inspection every 12 months. Why the re-check if it really stops the creep?

Oli928, If it actually exists, please post a reference to that specific Porsche TSB.

Oli928

The shop owner didn't show me the actual service bulletin, but he remembers reading it and making sure to put in 928 customer's files to check this issue every 30K miles maximum. It was 15 years ago...barely an internet then. There is a chance it was a PCNA bulletin based in conjunction from an earlier Porsche TSB: "Porsche bulletin 928 group 3 3903 -9203 may 5 1992" which talks about correct tube replacement procedures.
Sorry I couldn't be more help.

Black Sea RD

Porsche techs really don't understand how critical all this is for 928 automatics and the health of their engines. They also will not be the ones paying for an engine rebuild.

Thankfully you have a few different opitons to take care of this situation.

Best,

NC928S4

As a relative new 928 owner, with 104K miles and some odd noises(I've previously posted and had excellent recommendations) coming from rear mid-section, I with the help of a major 928 dude will be rebuilding the TT and also installing PKlamp next week. To keep my blood pressure in high normal I'll also be installing a PorKensioner. I recently had the "Toothed Belt Service" light come on even though the belt an WP were done about 1K ago. A very unpleasant feeling. It will be remedied, can't wait to dig in!

FredR

It is normal practice to check/re-tighten belt tension [about 1 flat usually does it] after an initial running period of about 500 miles or so. Get yourself the Jay Kemp tool from Roger- dead easy to use.

That the belt tension light worked is something to celebrate- not fear.

Regards

Fred R:

FredR

Those who ignore flex plate creep or the potential for it do so at their own peril! Those of us in the know keep saying this. Index mark the position of the collar on the drive shaft with white paint and check for no movement during oil changes etc.

Whatever your pre-disposition, at least you had the good sense to eventually do something about it and whereas there is no certainty destruction would have followed, it is a fair bet you have saved your engine from the self destruction that goes with flex plate creep. To my knowledge, no one who has taken appropriate action in time has suffered TBF.

Regards

Fred R

Jbws86928

Does the super clamp take care of always having to check the flex plate at 30000 miles? Does anybody have audio of a flex plate or TBF ? or audio of a bad TT?

NC928S4

Thanks Fred I will sleep better. Roger has been awesome in diagnosing and guiding the restoration. I'm apprenticing with Ray Munsch in NC which has been enlightening. I'm also getting good at sweeping.

Black Sea RD

About the Super Clamp, it has been designed to completely replace the front flex plate clamp as well as to clamp around the total circumference of the drive shaft uniformly and with much more clamping force.

Even with the Super Clamp you should keep checking the flex plate and drive shaft union to make sure all is okay. We advise at least yearly if not whenever you are under the car since a quick visual check of this area only takes about 15 extra minutes to do.

Cheers,

Captain_Slow

This week I noticed my 86.5 auto started to make this same "textured" sound from the REAR (to me it sounded like a worn speedo cable gear, or one that needs grease -- not in the dash -- other end, where cable connects to driveline somewhere).

After reading many posts like the own that started this thread I'm more concerned. I'm hearing a noise from the rear that matches this exactly: "My noise had a textured or ridged (low frequency texture) sound. It raised pitch and eventually you couldn't hear it past about 30MPH".

Now I'm concerned it's the sound of a bearing in the torque tube, or the bearings on either side of the torque converter. Flex plate has been released at every oil change by previous owner and once under my watch at oil change about 2500 miles ago. I do drive the car hard occasionally (but amounts to less than 10% of driving). I no longer have a place to work on the car. Should I drive to the shop immediately to release the flex plate? I also tend to agree this may just be postponing the inevitable. Can I drive it (continuing to release the flex plate when needed) while putting aside some money for what may be replacement of torque tube and torque converter bearings? Of course this is all worst case scenario talk. But if continuing to drive the car is playing with fire I'll drive it straight to the shop.

Thanks,
Jon

Oli928

In my opinion, I would drive to the shop and have the noise listened/looked at as soon as possible. I only work 7 miles from home, but I still took my car in within 3 days (only because they didn't have an opening in their schedule until then). TBF is too scary...better to err on the side of caution.

FYI Even though my bearings only had a little noise, they did go out 4 months after this original post. The great people at Jones Autowerks (San Antonio) were kind enough to give me a small labor break on the invoice, since they felt that they didn't twist my arm enough to replace the bearings during the flex plate service. They also replaced some rivets with actual bolts at the transmission/torque tube area (I don't have the invoice handy at work, but if someone needs details on this, let me know)...in theory, there was a service bulletin about replacing these rivets.