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Need Some Advice (Read 1787 times)
KGB
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Need Some Advice
Jun 27th, 2012 at 1:15pm
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I have a 87 944 S........have a great opportunity to own a 1993 968 with a 6 speed manual.

Drove it yesterday, all is well except a distinct whine coming from the rear end at speed.  Shifts and drives perfectly.  Is this the pinion bearing issue I have read about?

The car has quite a few miles on it (223,000), has a very good service history over the past 5 years that includes pretty much everything BUT the rear end. 

Current owner great guy that I know.  Very honest, knows and pointed out the whine and has the car priced accordingly in my opinion.

Talk to me about this pinion bearing issue and educate me as to the in's and out's of having it corrected.

Thanks in advance.

Dr. B :>)
  

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Grandpa#3
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Re: Need Some Advice
Reply #1 - Jun 27th, 2012 at 7:41pm
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Hello, You would do much better to ask your question over on 968Forum.com as there is not that much traffic here. I have a Tiptronic Trans so I'm not much help.

Cheers,
Larry   Smiley
  

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KGB
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Re: Need Some Advice
Reply #2 - Jun 27th, 2012 at 9:33pm
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Larry, thanks for the info. 

Dr. B :>)
  

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Dawgz83948
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Re: Need Some Advice
Reply #3 - Jun 27th, 2012 at 9:49pm
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968's have pretty stout transmissions. Unless he rean it out of tranny oil..... or never changed it.
  

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Re: Need Some Advice
Reply #4 - Jul 4th, 2012 at 3:39am
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The 968 six speed transmissions were a great transmission and were basically the same type of transmission as the G-50 911 transmission.

Your description Sounds like the dreaded pinion bearing\differential carrier bearing failure. the pinion bearing noise in a 968 is very specific - it sounds like a jet engine, is constantly there regardless of gear or rpm (though it changes in level with speed) and is very hard to miss

Pinion bearing failure seldom fail unless they are run dry, The defect is caused by excessive axial preload between the bearings that support the pinion gear. The factory that built them set the preload wrong. Since it happens to a small, but noticable number, my suspicion is that the tight end of the assembly tolerance was just a little too far over the structural limit of the bearings, and it's those cars, assembled at that end of the tolerance, that have problems.

Also look up pinion bearing revised assembly procedure and backlash of the R&P too.
  

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Re: Need Some Advice
Reply #5 - Jul 10th, 2012 at 1:33pm
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as a minor correction, the manual transmission is the 968 is an amalgamation of other boxes.  it has the differential similar to the G50, but has most of the transmission parts of a couple of different versions of the Audi 01E.  it was a joint venture between Audi and Porsche.

re: 968forums.com, yes, there is a whole lot more info there for the 968 enthusiast.

as for the noise, the jet engine sound is almost certainly the pinion bearing.  don't lose your mind on that though.  if nothing else in the trans needs work, that job can typically be done for under $2k.

the failure has nothing to do with mileage, age, or year of the car either.  it has entirely to do with tolerances.  the bearing was mechanically installed into a cast casing.  this opens the door for tolerance accumulation, and if the preload was wrong, the resultant bearing failure.

so, no matter which 968 you get, unless the bearing was replaced by a shop that knew how to set the preload, you could be looking at this at any time in any car.  i would not let the pinion bearing issue sway you one way or the other.  get it fixed and you're good to go.  buy one that hasn't had it done, and you could still have to deal with it later.

good luck.
  
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Re: Need Some Advice
Reply #6 - Aug 16th, 2012 at 8:00pm
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there is a known problem with the pinion bearing on the  968

Pinion Bearing Failures
Everything you wanted to know and were afraid to ask:
What is a pinion bearing: the 968 has a transaxsle i.e. the gearbox, final drive and differential all in one unit. The gearbox output shaft has at its end a pinion gear driving the crown wheel. This shaft has a big 'pinion' bearing on one end and a smaller one at the other end. A pre-load is applied by way of shims and a nut at the smaller end of the shaft.
Symptoms: Road speed related whine audible from 35-40 mph. Test on straight road with smooth surface for minimum tyre noise. Close roof and windows, accelerate to 80-85 mph, lift off, if you hear noise resembling a jet plane slowing down on a runway - you have a problem ! Alternatively you can secure the rear of the car on stands, run the car in top gear and listen to the noise from the gearbox. If you haven't got LSD you can stop one or the other wheel to eliminate possible wheel bearing and CV joint noise.
Cause: Too much pre-load on the pinion bearing at assembly. Getrag ( who made these transmissions for Porsche ) uses a computer controlled robot, which has not always been accurate.
Repair: This requires complete dismantling of the transmission. Porsche allows 15 hours, but everyone says it is not enough. One London, UK, dealer quoted 40 hours at 70 plus tax = 3290 = over $5000 just for labour. Parts are not too expensive, but it may be wise to replace all the bearings. Setting the correct free play - 'backlash' while at the same time achieving the correct pre-load requires an accurate measuring instrument, choice of shims, patience and experience.

Make sure your mechanic / shop have the necessary skills.
Prevention: Check for leaks, correct oil level. It may be a good idea to change the oil at 20,000 miles or maybe even more often.
  

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Re: Need Some Advice
Reply #7 - Aug 28th, 2012 at 2:55am
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while it is a lot more common than a lot of other problems that cars have, it is not that common of a problem, and has only affected about 5% of the cars out there.  that's a lot, but it's not like you are doomed to have this problem.

it has nothing to do with mileage, year of the car, age, or any other factor, and is entirely due to tolerance accumulation in the fabrication and assembly process.  sometimes the tolerances just added up in the wrong direction, and the casting tolerance, combined with the preload, resulted in too much stress on the bearing.  you might have it very early, or not at all.  there is no telling.  it should not keep you from owning this fantastic car.

the job generally costs between $1700 and $2000 to have done, if nothing else is bad.  the R&R of the trans is about 12 hours for the average porsche mechanic. i've seen it done in 8.  it took me 14, but i had to do it on my back.  the repair itself is about 3 hours.  parts are about $200.

the real problem is that most shops do not know how to properly set the preload, and instead just replace the worn parts.  this leads to another failure, as they repeat the incorrect preload issue that caused the problem in the first place.
  
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