Mobil 1 synthetic gear oil in 915 gearbox

[agabriel]

I'm trying to figure out why people don't like Mobil 1 synthetic in a 915 gearbox. My mech put it in my gearbox about a week ago, and the transmission feels great. The car is shifting better than it ever has for me and really feels great! With the dyno oil I needed to touch the second gear synchro to prevent grinding going into first and reverse, I would still get a stiff shift into gear. With mobil 1 everything is much smoother and not nearly as stiff.

Before the gearbox was switched to synthetic oil, I ran it for 3k miles with fresh dyno oil to clean it. I don't think the oil had been changed to that point.

Also no spots of oil on the garage floor.

Looking for info from people!

Thanks,
Anthony

[s_wilwerding]

What sort of dyno oil were you running in it before? When I changed my tranny oil from whatever generic stuff was in there to Swepco, it was a night and day difference. Also, what weight of Mobil One did you use? If I remember correctly, Swepco is something like 90 weight, which not only helps with shifting, but protects the transmission during extended periods of "spirited" driving.

[Bill Verburg]

Anthony, Do a little experiment, try to shift a little faster than usual.

Let us know what you observe.

[Don Plumley]

There is an engineering explanation behind this - not that I can give it - but it has something to do a property of the oil (viscosity?) that is more suitable for the design of the synchro; common wisdom is that Swepco is for 915 boxes and M1 for G-50's.

Don

[agabriel]

Don,

I have heard that; thats why 3k miles ago I ran dino oil that was the same weight as the swepco. I do not remeber the particular brand, but I believe it was the number 2 recomened here.

Last week when I took it the garage I wanted to change the gearbox oil again, to be sure everything was clean. Previously to that oil change the gearbox was bad, and I thought it would need to be rebuilt. Jerry, the shop owner, wanted me to try the M1. He said he had good luck with it, even in 915 gearboxes. I decided he looks at more of these in a day than I look at, so I let him. I don't know what weight M1 oil he used. He put it in took the car for a spin and said the gearbox felt outstanding. So I took it for a spin and it really felt leaps and bounds better than before. Keep in mind it felt dramaticly better when I changed the dino oil before.

Bill - I did play with the shifting a bit. I noticed a few things that I like. The gearbox shifts better when cold. Before the gearbox would get better as the car warmed up a bit, now its much smoother at initial start. Shifting faster works a bit better than before, it feels the way it did with the dino oil; a bit stiffer. However with the slight delay it feels almost silkie smooth. I was suprised to say the least. At normal shift speeds, for the 915 gearbox, shifts outstanding.

The main reason I posted this story is when I asked the last time I was told to try dino oil, and I did. This time I took the mech's reccomendation and that was excellent. I was suprised and maybe the parts in my 915 gearbox have woren to the point the M1 worked.

Anthony

[pwd72s]

Anthony? Count me among those who uses synthetic in his 915 gearbox and is quite happy with the results. I've used TORCO 75/140 GL6 with limited slip additive for several years now. Call around...many motorcycle shops carry TORCO products. If they don't stock it they can get it for you. I buy it by the case of 12 quarts. If memory serves, it's around $10 per quart. Schwepco? My thinking is that many of the guys here are sold on it because the gurhu Sweet Old Bruce Anderson plugs it. I've heard the worries that 915 synchronizers don't work well with synthetics, but I haven't experienced the problem. The 915 isn't a gearbox to try speed shifting with anyway...

[Neilk]

I have used both Swepco and Mobil 1. I didn't really notice a difference between the two. What really helped the car was a set of new bushings for the gear shift lever. Before anybody considers a transmission rebuild, check the bushings, they might be shot.

[agabriel]

pwd,
Agreed, the standard I heard was say Porsche while shifting. Althought thats a little slower than my gearbox needs to go, it was a good way to learn. I'm curious how many of the people that are die hard against synthetic gearbox oil have actually tried it.

Neil - I thought I may need a rebuild at the time just due to how stiff the shifts were...

Anthony

[Jack Olsen]

I will quote the very well-respected Steve Weiner from Rennsport Systems:

"Do NOT use a synthetic on your 915. [Synthetics like] Redline oils are very fine products and entirely appropriate for the later-model G-50's, but the baulk-ring syncromesh used in the 901-915-930 transmissions require a non synthetic oil to prevent excessive wear.

The very best product for these transmissions is Swepco.

[pwd72s]

Jack? With all due respect...I disagree. Try synthetic...you might like it. The high temp protection of synthetics has been proven. If this works in an engine, why not with gears??? If I were wearing synchros, wouldn't I notice metallic particles in the drained oil or on the magnetic plug? So far, none...

[Sonic dB]

PO had Mobile Synthetic in my 915.

It caused leakage. I know...because the tranny had grease all over it from apparently the main shaft seal leaking.

After I switched to Swepco...the leakage stopped. I cleaned the old grease off of the tranny and no new grease has appeared.

[TimT]

Thats funny, Ive run Mobil 1 in my 901 for years. My cars are track use only and only see a few thousand miles a year. They dont see day to day use like a street car might, but they shift fine for me.

Do the sintered bronze syncros work better with dyno rather than synth?... maybe in small increments..

Ive used swepco,amsoil, Mobil 1, and other gear oils. Im having a hard time believing one is a magic elixir.

but thats me always doubting

[pwd72s]

Sweet Old Bruce says... Schwepco So we must believe, right? Keep in mind, Bruce wrote his Schwepco plugging piece some time ago. I've used Schwepco...I like the TORCO synthetic better. I will admit that I don't speed shift these days...a lesson learned from a bitter and somewhat co$tly experience. Schwepco works. I just happen to believe, for my purpose at least, that synthetic works better.

[agabriel]

I'm going to wait a few months to determine which I prefer. The preliminary data looks good for synthetic thou. I was under the car today and didn't see any fresh oil on the transmission or under the car. The car is also shifting much smoother.

Jack I'm suprised, do you Synthetic? Since you race I would expect the synthetic to hold up better under the temperatures that are produced on the track. Am I off with this assumption?

Anthony

[red-beard]

There is way too much "This guy told me it was so, etc" stuff on this board.

Swepco IS dino oil. There is nothing magic about it. I bet that when most people switch, they are more in need of a change of oil than anything else.

Now, as far as synthetics being too slippery. Whiskey Tango Foxtrot ?!?

Someone. ANYONE! Show me some data. Not anecdotal 2nd, 3rd hand statements.

James

[TimT]

Someone. ANYONE! Show me some data. Not anecdotal 2nd, 3rd hand statements.

LOL yea.. I agree......Ill give you first hand data and experience... come to NY and drive my car....

My anecdotal statement comes from using various synths since the early 80's....The 915 and 901 will never be slap happy boxes like you see on speedvision.... new bushings, and a performance coupler can do wonders... the next step might be sport mounts.... or even solid mounts...

[speeder]

The answer to that would be that transmissions never reach temps where a high-quality dino oil would break down or lose viscosity, in fact our motors don't either. At least not w/o siezing, synthetic or not.

The bottom line is that it is your car, use whatever you want. It is just a matter of whose advice you value, "Sweet Old Bruce Anderson", who wrote the book on high performance 911s, (still an unchallenged book after ~20 years), and Steve Weiner, (both obviously on the take from Swepco), , or a very small minority of owners who believe that synthetic works better w/ Porsche style synchros.

And with all due respect, Paul, with the amount and type of use that your car gets? It could probably have olive oil in the trans and you'd be fine.

[Early_S_Man]

James , a.k.a beard ...

Your misunderstanding about gear oil is rather profound!

Bruce Anderson's data about gear oil came from several years managing the 'Warhorse Gang' 935 team for Bob Garretson. Ring & pinion lifespan in a 935 went from 40 hours [slightly LESS than two 24-hour races] to an entire season of racing after switching to SWEPCO from traditional petroleun gear oils! So, indeed, there IS something different about SWEPCO's additive package!

[Schrup]

I put Swepco in about 500 miles ago, didn't notice any difference & was wandering what all the hype was about. After about 200 miles I have noticed a big difference, especially between 1st & 2nd. I bought the bushings & hope to install them tomorrow, but I can't imagine the impact will be as stark as the Swepco was. 75% of the balkiness is gone. Once again this board has come through for me. Thanks to all.

[Sonic dB]

Swepco didnt make any difference in the shifting of my 915 as opposed to the Mobile One synthetic.

They shifted the same. Swepco may be better for the longevity, but didnt make it shift smooth. No matter what is in there, every time I shift I am one shift closer to a rebuild on the 915.

What DID make a significant difference in shifting was new clutch cable and adjustment and new shifter bushings. Im gonna do the coupler next along with fresh mounts.