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Discussion Starter · #1 ·
So my new Boxster S (2009, manual) has been pretty well taken care of, most everything is in very good shape and only 30k miles. However, the when shifting, I noticed some gear lash, especially going into third. My first thought was the obvious: synchros going bad. Likely, this is the inevitable problem.

But then I started thinking about the other possibilities. The car has a Numeric adjustable shifter, and as I really paid attention, I noticed that it wasn't lined up very well with the neutral position perfectly between 3rd and 4th. I had a mechanic tweak that, and it helped a little.

Then I went through all of the previous owner's records (provided with the car, nice!) and noticed that from 2009-2017, the manual transmission fluid hadn't been changed - ever. So I put up the Boxster on ye ol' jack stands and drained the trans fluid.

It was dark to the point of opaque, and when I gave it good look under the light, it was rather sparkly from what looked like metal dust. I assume all that's to be expected to when the fluid has been running for that many years.

I refilled with Redline 75w90, and after a twenty minute drive, Boxster's transmission felt considerably better - not good as new, not as smooth as my 2008 (rest in peace) but still a huge improvement.

Here're the questions I've come up with:

1- Was 75w90 (GL5) the right choice to get maximum protection of the synchros?

2- The Boxster has a Wavetrac TBD (supposed to be maintenance free), but I found a lot of mixed data on limited slip differentials using slightly different oils in the transaxle. Does that only apply to actual LSD's or would TBD's need that, as well?

3- I'm planning on driving the Boxster gently for 6 months or a 1000 miles and then changing the trans fluid again to remove any remaining "sparkly metallic bits." Is that a waste of time? Have I done enough already? Or should I put in something like Royal Purple with special additives for synchros?

Thanks for reading all that. All advice appreciated. Cheers!
 

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30K miles is not much for any transmission fluid. Also I think noticing "metal dust" as you define it is not unusual on MT. I don't know about Porsche but on other cars, like Miata, the LSD uses different, specially formulated differential oil. Obviously on the Miata the differential is separate from the transmission but maybe it is worth to research about the Porsche where they are one unit.
 

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I just went through this.

I used Swepco 201 dino 75w90 in my 2006 CS, last year. Mistake.

I just swapped it out after 12 months in the car. Perfectly blue, zero discoloration, zero metallic sheen.

Now on a fresh fill of Mobil 1 Delvac 75w90. Feels better, and I know it will flow better in the cold.
 

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Discussion Starter · #4 ·
Morde5-
That's why I asked about the difference between a TBD and an LSD. The TBD isn't as friction dependent as a true limited slip diff. Plus with the trans-axle, as I understand it, the differential and gear box share the same oil. There are just so many nuances to lubrication and gears... And once you have non-factory parts involved... Even the "knowledgeable" guys at the parts shop weren't too sure of their answers once you use phrases like "mid-engine" and "trans-axle" and "torque-biasing differential"...
 

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Discussion Starter · #5 ·
Boulder_Geek-
I would have picked up the Delvac, but I couldn't find any local so I made due with Redline for now. I read some really good reviews on the Delvac. Next time, I will order ahead so I have it on hand when I have the time to swap gear oil.

Also, tomorrow, I can snap a pic of the old gear oil. I haven't recycled it yet. It's pretty easy to see the metal dust in it.
 

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Did a 3 day DE at Indy in Aug. Mid day on day 3, my 3-2 downshift gets a bit crunchy. Facing a 9 hr drive home the next day, I gave up some time and avoided downshifting to 2nd in the last 2 sessions. Got home and decided to change the trans oil, hoping it was old fluid vs a synchro. Read good things about Motorcraft's fluid, so I used that. The viscosity of what came out was very thin. Thankfully, no more crunchy downshifts during street driving (haven't tried it in earnest on the track yet).
 

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Morde5-
That's why I asked about the difference between a TBD and an LSD. The TBD isn't as friction dependent as a true limited slip diff. Plus with the trans-axle, as I understand it, the differential and gear box share the same oil. There are just so many nuances to lubrication and gears... And once you have non-factory parts involved... Even the "knowledgeable" guys at the parts shop weren't too sure of their answers once you use phrases like "mid-engine" and "trans-axle" and "torque-biasing differential"...
TBD are not friction dependent at all. Well other than gear and bearing wear and tear. So any good oil should suffice. Where as any differential that employs clutches would be very dependent on what oil and what viscosity. Bottom line if you do indeed have a TBE any good oil should do.
As for transmission oil, I've noticed the same thing as you did. I bought an 07 S2K and not being sure of the previous maintenance schedule I changed the transmission oil. It really made a difference with smoother, less notch shifting. So when gears are being mated and de-mated and Synchromesh (a type of clutch) is being used then both the oil and viscosity is important.
 
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