Best Synthetic Transmission oil for 915

If "spirited" driving is the order of the day for the car, look at Redline.

I use standard 90 wt oil in my 915 transmission which is quite good for street use and won't make the synchros work too hard as many synthetic oils do, including Swepco.

I use Swepco 201 in my 915 transaxle in my 1973 911S.   Some Pelican Parts board members swear by Kendall.   I've used both and Swepce is my choice. 

If you go to www.pelicanparts.com and type in Swepco it will show you the product

Also, type in Kendall and again,it will show you the product.

And either one is good.  You can't go wrong with either one and the TRG/Rolex Porsche guys use Swepco.

Could you explain, please?

Synthetic oil itself isn't the bigger problem, it's usually incorrectly using oils containing friction modifiers for use with limited slip diffs and such. With those friction modifiers, the synchros can't match speed fast enough. Not to say you can't sometimes notice the difference between synthetic and dino even without friction modifiers.

And you also need an oil with extreme pressure additives due to the diff's hypoid gears. It should specify it's for use with transaxles/differentials or hypoid gears.

Swepco 201 is a bit better in copper corrosion than Redline 75W90 NS GL-5, but the Swepco also has LSD friction modifiers in it that the Redline doesn't.

Why not just run a subaru trans with your subi engine?

Quite rapidly, Justin, I'm learning that you really know what you are talking about.

I recently had new 3rd and 4th gears, the syncros, and the R/P replaced in my transaxle. I'm running a Type 1 IRS with an AL rhino case, all the strengthening tricks, and most importantly a ZF LSD diff.

Two LSD additive packs got added to the case when it was built, and I filled it with Castrol 80/90 dino oil with LSD additive. I also replaced the bushing, coupling, and shifter. Stationary, the linkage moved very freely.

Running, however- the trans could not be made to go into ANY gear. I played with the linkage for about 3 hours, then remembered this post. I dumped the trans fluid and put in some housebrand semi-synthetic 75/90 without an additive. The trans was, well, transformed.

Thanks, Justin.

I'm sure there is plenty of LSD additive left in the trans to allow the diff to do it's thing, and I'll likely just run this until the trans breaks in. After that, I'd like to run a full synthetic 75/90 (to keep the shifting easier in cool weather), but want my LSD to work. I can get Mobile 1, Valvoline, and Royal Purple, all are GL-5 and have LSD additives.

Thoughts?

Kevin-

Your stuff is cool, but Marty (and the rest of us) don't want to switch out the transaxles we've already got. We'd just like to talk about gear lube for old-skool transaxles.

There's a time and place for showcasing your stuff. This isn't it. Please give it a rest.

If you are ok with the shifting feel using the straight Mobile 1 LS, Swepco 201, etc w/ LSD modifiers included, then I'd say stick with that because it's easy.

You can also try to blend your own. Start with a non-LSD hypoid gear oil. Go drive in some slow corners/circles under acceleration. If you notice any chatter, shuddering, or vibration from the sticky clutch pack, then you know you need to add some additional friction modifiers. Go get a bottle of friction modifier (GM #1052358, CRC SL2411, or http://www.redlineoil.com/prod...px?pid=41&pcid=4  ) and add an ounce at a time, go drive half an hour to make sure its mixed well and warmed up and then try the circle test again. You're trying to get just enough in that the LSD chatter stops. You can also try blending oils, but it's more work and expense to get right: take a non-LSD oil like Redline 75W90 NS and cut it down with some percentage of regular Redline 75W90.

Unfortunately it's a compromise between the synchros and LSD clutches and running only non-LSD oil will shorten the clutch life. I don't know how easy or expensive it is to get new clutches for the ZF.

It's neither easy nor inexpensive, so if a compromise must be made, I'd prefer it was towards harder shifting/ longer clutch-pack life.

There's quite a bit of "folklore and common knowledge" floating around regarding the compatibly of synthetics and older design syncros. I'd love to hear your thoughts. I'd like to run a 75W80 synthetic over a 80/90W, as the "90W" part makes shifting a lot like rowing through molasses in cold weather.

Here is an interesting article worth reading:

http://www.widman.biz/uploads/Transaxle_oil.pdf

That yellow metal compatibility is why I mentioned the copper strip corrosion tests earlier. If you can find how the oil did on that test you'll know how compatible it is with the synchros. The ratings on that test range from (lowest tarnish) 1a-1b, continue through 2a-2e, 3a-3b, to 4a-4c (highest corrosion). For example, Swepco 201 is rated 1A. Redline and Mobil 1 are rate 1B. As examples of stuff you don't want to use, Royal Purple Max-Gear 75w90 is rated 4A and Lucas 75/90 Synthetic is 4B.

Your synchros will have a pretty normal lifespan even with GL-5 oil if it is in the 1A-1B range. For comparison, GL-4 oil falls into the 1A-2A range.

Of course, the gear oil must be changed at the recommended intervals too.

As long as you stop any chatter, your clutch pack should have a normal life. Excess friction modifier beyond that will simply reduce the amount of torque you can transfer between the wheels (besides making shifting harder).

Justin-

This information seems to be hard to come up with (for me), but it reenforces my preconceptions regarding Lucas (well promoted snake-oil), and Royal Purple (overpriced "nuthin-special") products in general.

I've found some Pennzoil 75W90 synthetic in GL-4 available for sale on the web. The GL-5 is available at FLAPS everywhere. Any idea on the copper corrosion rating of these oils?

I've got a gallon of Swepco 201 coming (Cory Drake is bringing it out from Annapolis for Corn Daze), but I'd like to try a synthetic for cooler weather if I can find one that isn't going to eat my syncros.

Stan,

I suspect your answer is somewhere within that ten page technical overload Transmission/gear oil manifesto that Jowdy posted! 

I read all 10. It was a good article, in which the recommendation for the Pennzoil was made. There were, however, no copper corrosion ratings. Hence, the question.

Also, it should be noted that Swepco 201 is GL-5 rated (rather than GL-4 as everybody is recommending).

The quest continues....

Stan, don't OVERTHINK the oil recommendations.   The syncros aren't going to mystically dissapear overnight with GL5.   Hundreds of thousands of people are using GL5 products regardless of brand in their early Porsche and VW transaxles and with normal maintenance, they work great and the transaxles are still working as they should.

I suspect your original problem wasn't the additive but the weight of the oil.   If you have a LSD then simply run the lesser weight oil 75-90 and the additive and everything should work as scheduled.   In fact, you can even run GL5 Swepco and nothing adverse will happen to your syncro's.

Larry-

I agree 100% about obsessing over (what in the end is really just) oil. The GL-4/GL-5 debate has been raging on the Samba for years (I think we're up to page 50 on it). It is ridiculous. As I said originally, there's a lot of "folklore and common knowledge" passing for fact. Everybody is entitled to their own opinion, but not their own facts.

There's a lot of bunk going around about synthetics and old engines and transaxles as well. I'm not hung up on either the dino/synthetic or GL-4/GL-5 debate, as long as the copper corrosion rating is good. That rating is hard to come by.

Ideally, I'd like to run a GL-4 synthetic 75W/90 with an LSD additive. My original problem was a combination of viscosity and the additive (remember, there were two full packs of additive, as well as additive in the oil itself). When I drained it, you could see the additive suspended in the oil. I'm 100% sure there's enough residual additive left in the transaxle right now to be just fine. The oil in there currently is a semi-synthetic Mystic GL-5 I've had "not bad" luck with previously.

I'm going to change the oil at 1000 mi though, and would like to go with something that strikes a nice compromise between the needs of the syncros and the needs of the LSD. I'm hoping the Swepco can do it, but I suspect it will be pretty thick. Redline or Mobil 1 look good, but I'd like the coper corrosion rating of the Pennzoil 75w/90 GL-4 synthetic before I make a final decision.

I think that's what Marty was asking in the very first post.

I went through this a couple of years ago.  I finally decided to default to Rancho's recommendation since it was their transmission.  Also, I learned that they have a business relationship with Swepco.  Guess what they recommended ;-)  

I got it, but subsequently found out that my issues were clutch issues.  I did notice a slight improvement in shifting, though.

I figured it was good to change it anyway and there were some filings on the magnetic drain plug.  I learned later, that Rancho recommends changing the oil after the first 500 miles (which I was a little tardy on).

Also, I learned that it was a major PITA to drain my trans because the camber compensator goes right over the drain plug and has to be disassembled first.

Any GL-4 synthetic isn't going to hurt the synchros. The GL-5 Penzoil 75W90 synthetic is rated 1B. It does have LSD additives already in it.

More discussion on same topic

http://forums.pelicanparts.com...st-915-gear-oil.html

Hey, Stan thanks

I too have a 915 trans and enjoy it. I even offer a conversion install kit for them into a VW. I just thought you guy would like to see another option.

No blood, no foul, Kevin. Thanks for doing what you do.

Tom--the camber compensator does indeed cover thev tranny drain but it isn't hard at all to take off and put back on.

Marty, I'd use this:

http://www.redlineoil.com/prod...px?pid=46&pcid=7

My bad. I misread it, and put up the wrong link. Sorry to steer you astray.

This one, perhaps:

http://www.redlineoil.com/prod...px?pid=47&pcid=7