Why not synthetic in a 915?
 

There seems to be a general consensus on the board to not use synthetic lube in the 915 tranny. Why is this?
My lubricants guy is recommending Kendall 75W-90 GL-5 synthetic gear oil.
What does it matter, as long as it is a GL-5?

Thanks.

Well the consensus is non synthetic due to age and design of the syncros. So if the board is saying NO synthetic - believe the board. Your - lubricants guy - doesn't know old 911's as much as he thinks. Sorry but its true. Read the umpteen dozens of threads on the subject and become your own - lubricants guy -

I have to add that at times I to don't like to follow the crowd - just because that is the way its been done for years. Sometimes I believe there is something new out there - but not in this case

B

Too slippery
Swepco actually designed 201 in consultation with Porsche years before the G50

Steel syncros need friction to work as designed..I don't think anyone but Porsche used the design as in the 901 and 915 gearbox. Racing transmissions like our 915 are different.

I'm running Kendall dino in my 915, but here's something peculiar - the guy who rebuilt my 915, and who is a genuine Porsche tech and Porsche racer, recommended Amsoil Severe Gear synthetic. When he returned the rebuilt 915 to me it was filled with the Amsoil and it shifted just fine.

Nevertheless, due to all the advice here I changed to Kendall. I don't notice much difference in shifting between the Kendall and the Amsoil.

What might the story here be?

Use Kendall NS-MP 80w-90. It's the cats meow for 901's and 915's. Look else ware for posts by 915 guru Peter Zimmermann on this subject. Synthetics are too slippery for this design of syncro and do not allow the snycro to synchronize the different speeds of the gear sets efficiently. The gearbox will feel notchy and you will get premature dog tooth wear using synthetic.:cool:

Where did you hear that? Swepco 201 and 210 were designed for the truck and service vehicle industry. I seem to recall that Jerry Woods tried Swepco out of desperation to get ring and pinions to last in the 935 race cars he worked on. The rest is history....

Scott

search on baulk ring for more detail; maybe someone spelled it balk ring too

Of course there is no point in getting into a thing about this - the subject has been talked to death already. I've had some exchanges with Peter Zimmermann and I have read all the posts about baulk rings, Porsche-specific syncros, etc., etc, and that's why this is peculiar to me.

My experience has been that the 915 did not feel notchy with Amsoil. I can't speak to the idea that dog tooth wear is increased, but otherwise I simply didn't notice any difference in shifting in spite of all the admonitions to use dino oil only.

As I said, I am using Kendall, but not because of how it feels as compared to Amsoil, but just because of all the advice here.

When I worked for Porsche the Swepco was recommended and even had a part number. The story was Porsche wanted something that was durable and would help the customers with shifting. I heard the same story. Porsche may have used some field experience from racing and went to Swepco. I was told Porsche developed the gear oil with Swepco too..back in the day.

Sorry to give you all my 50years of experience. In the future I'll keep my tuning secrets to myself and my customers.
Have fun.

Do not assume that no one else's experience has any value in comparison to your own. This is a discussion forum, therefore, people discuss.

Enough with the self-pity. No one here is going to stop you if you want to take your ball home and play by yourself. Jeez....

Scott

There are a few racers in the PRC that run Red Line synthetic oil in there 915 transmissions. Of course at the very least they match revs on down shifts. I know one double clutches on downshifts.

Their synchros live just fine....

Scott

For about ten years, due to my ignorance, I used Valvoline synthetic gear oil in my 901/911 trans. Never had a problem shifting. No noticeable wear on the synchros during that time either. On the bottle it stated that it was compatible with limited slip differentials, perhaps that allowed the synchros to function correctly.

When I rebuilt my 915, I wanted to go against the tide. As an AMSOIL dealer, I knew I had access to a superior product. I tried the Severe Gear, and felt that the shifting was notchy, stiff, and generally unacceptable. I added the Amsoil friction modifiers to the mix, and the shifting became serviceable but still not 'smooth'.

On the advice of some here, I switched to the Kendall fluid. Again, it was serviceable but not as smooth as I felt the 915 should be.

Eventually, I switched back to the Swepco. Of the 4 fluids, this has given me the best shifting feel and the least problems with the stop bands in the synchros.

Your type of usage will make a difference, too. Autox requires a lot more gear rowing. You need your stop bands to reliably and quickly stop the rotation so the gears can mesh immediately, or else you end up chipping teeth. On the track, you have a little more time to ease into a downshift. In daily road driving, you may not have an issue at all. So, ymmv.

Now that's interesting. I always double clutch when downshifting, a habit from driving transmissions without any synchronizers at all, so maybe my trans is 'good enough' in shifting, but could be better. OK, I'll give Swepco a chance. If that isn't a panacea, then I'll give other possibilities another look.

Thanks.

Thanks everyone.