Help with diagnosis please

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Help with diagnosis please

Postby Cajundaddy on Fri Oct 07, 2011 8:18 pm

Ok, my car recently developed a thumping sound that varies with speed (tire rotation) and not rpm. It started as a faint sound like tire pickup on the left rear. As I drove home it became more like a nail in the tire, then a lag bolt in the tire, now getting louder more mechanical sounding. I changed the wheels, inspected the brakes and rotors, inspected the CV joint boots and all looks a-ok. The wheel bearings are 6 months old. Preliminary diagnosis from my trusted local Porsche mechanic is that the trans is going south.

What say you??

This is a 98 2.5L Boxster 5spd with 97K miles and 50+ track days. Trans fluid is changed annually with no obvious signs of serious problems. I have noticed that she has been stiffer shifting lately but attributed that to cables and bushings. I generally shift gently and have never had a synchro failure. I adjust my driving style so I rarely generate wheel spin on the track. What are we missing?
Dave Hockett
09 Cayman 2.9L PDK #129
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Re: Help with diagnosis please

Postby rshon on Sat Oct 08, 2011 2:54 am

Did you jack up the rear of the car (please use jack stands), release the parking brake, and check the bearings for grinding by rotating the wheels (I know you just changed them) as well as pushing and pulling on the tire to see if you have play? Also, you might want to double-check that the axle nuts are tightened all the way, as loose axle nuts can hose up your bearings really fast.

You also might want to check the CV joints for play by rotating the wheels back and forth, and make sure that the inner CV joints are securely bolted to the tranny.

Hopefully you will hear where the bad sound is coming from by rotating the wheels while the car is up. If it's coming from the inside of the tranny, start shopping for another one...
Russell
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Re: Help with diagnosis please

Postby Cajundaddy on Sat Oct 08, 2011 8:02 am

Thanks for the input Russell. Pedro also suggested loose axle bolts which sounds plausible to me. When I checked underneath last week the noise was faint so I may have missed something and I did not put a wrench on the bolts. Now it is much more obvious and consistent with loosening bolts. I did test the bearings thoroughly and I think they are ok. I will check it again today.
Dave Hockett
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Re: Help with diagnosis please

Postby Cajundaddy on Thu Oct 13, 2011 7:51 am

Update... my trusted mechanic is right. All the bolts are tight and the noise is coming from the rear of the trans. It sounds like internal bearing noise. Anyone got a nice spare Boxster trans laying around? :cry:
Dave Hockett
09 Cayman 2.9L PDK #129
CC07
PCA Zone 8 DE/TT Chair (SoCal, NV, AZ)
PCA National DE Instructor
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Re: Help with diagnosis please

Postby rshon on Thu Oct 13, 2011 9:32 am

Dave -
If you can't source one locally (LAPD, Autobahn), you can look on eBay. They run from $600 to $2600 (!):

http://www.ebay.com/sch/i.html?_nkw=boxster+transmission+-%28mount%2C+wiper%2C+auto%2C+automatic%2C+top%2C+plug%2C+control%2C+axle%2C+filter%2C+cable%2C+tool%2C+brain%2C+valve%2C+shifter%2C+spacer%2Ccrossmember%2Cconvertible%29&_sacat=0&_sop=15&_odkw=boxster+transmission+-%28mount%2C+wiper%2C+auto%2C+automatic%2C+top%2C+plug%2C+control%2C+axle%2C+filter%2C+cable%2C+tool%2C+brain%2C+valve%2C+shifter%2C+spacer%2Ccrossmember%29&_osacat=0&_trksid=p3286.c0.m270.l1313

One of the ways to vet a potential source on eBay is to look at their feedback and see if they have (many) other satisfied customers for the same or similar large items like engines (I bought my engine from a yard that sells on eBay). Also need to look at shipping, as that's half the challenge.

If you're not worried about your "spec-ness", you could put in a newer 2.7 5-speed, or go whole-hog and get a 6-speed. But then you wouldn't be able to keep Dan quiet... :wink:
Russell
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Re: Help with diagnosis please

Postby Cajundaddy on Fri Oct 14, 2011 7:32 am

Stock trans in route.
Loren had a nice, low mileage, 2009 3.4L w/PDK sitting in his shop :idea: I suggested he might just slide it in my car instead but he figured Danny might notice the difference. :roflmao:
Dave Hockett
09 Cayman 2.9L PDK #129
CC07
PCA Zone 8 DE/TT Chair (SoCal, NV, AZ)
PCA National DE Instructor
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