Transmission Fluid

[agabriel]

I will be taking my baby to a new mechanic early next week and one of the things they are going to do is change the tran fluid if it needs it. I had a conversation with someone over there about it and they like to use Mobil 1 synthetic Transmission fluid. I know everyone here digs the swepco. However here are my questions:

1) Is the Mobil 1 good stuff? I'm assuming yes since I haven't heard of any garbage coming out of Mobil....

2) I was concered that tranmission seals on my '86 wouldn't be able to handle sythentic oil as they were not formulated to handle it way back when. Is this a valid concern? They told me that if I was in the engine I would have a valid concern but the tranny seals are fine.

3) I'm not sure when the last time the valves were looked at, so I wanted them adjusted. I also mentioned that I should prob get a tune up as long as its all apart. As a side not the car runs rough after rain/car wash and I wanted this fixed as well. What parts should I expect to be replaced?

This shop came recommended by an indvidual on the board of my local PCA chapter.

So what do you guys think?

Thanks for all responses,
Anthony

[cstreit]

I'm sure it's fine. Mobil makes quality stuff, if not a bit more expensive than some.

[Don Plumley]

The general concensus is that the 915 box "likes" Swepco better, the G50 seems to work better with M1. Has something to do with the mechanical nature of the synchros (search the archives on this). If it were my 915, I'd hope the wrench would put Swepco in it. But as Chris said, M1 is good lube.

Sounds like you are looking at a major service. There is not much to "tune" on your engine. But I'd expect plugs, belts, filter, dizzy cover, valves. If you have original spark plug wires, check the wires and boots for cracking. This could be a run bad when wet problem.

Also should be checking to see if you have the upgraded Cylinder Head Temp sensor.

Don

[ChrisBennet]

Mobil 1 is good fluid but is too slippery for pre-87 (901 and 915) synchros. Mobil-1 is not without its problems however. Last year this was posted to Rennlist by Paul Guard (Guard Transmission, supplier to lots of Porsche teams). Draw your own conclusions.
-Chris

Date: Fri, 12 Jul 2002 14:39:25 -0400

Author: "Paul Guard"

Subject: RE: Castrol SAE 75W-90 GL 5 instead of Mobil?

Body: I’m no oil expert, and I’ve merely formed my own past opinion based on
discussions with my many customers. I’ve repeatedly recommended Mobil 1
for late model 911s, because it has been the factory recommended oil, used
by most GT3R teams.

But in a recent conversation with one of our gear manufacturers, I learned
that all oil-related premature wear problems that they’ve seen have been
with synthetic oils, with the worst failures being in transmissions using
Mobil 1. Reportedly, there have been changes in Mobil 1’s composition
over the past year or so.

Until I learn otherwise, I’m now back to recommending only Swepco oils for
ALL transmissions, both early and late, just as at least one top mechanic
has told me all along. Your results may very well vary --

Paul Guard
Guard Transmission

[BGCarrera32]

I'd be leery of changing to a synthetic lube on an 17 year old transmission. I've heard too many good things about Swepco 201. I'd order a jug from Pelican as I doubt its as common as M1 for your shop to get ahold of. Actually, you might be advised to run a jug of good ol' Valvoline fluid through for a few hundred miles first just to flush out the tranny if it hasn't been done for some time. That way when the $40 jug of Swepco goes in, its going into a cleaner tranny.

IMO, replacing shift coupler bushings and checking/adjusting the clutch will give you better bang for the buck than synthetic tranny lube.

As for the run rough condition after the wash/rain, I'd be looking at the distributor cap and wire connections, seeing as how they are located under the AC grill on the trunk lid where they could get spritzed with water. *Could* be a tiny crak in the distributor cap, or an exposed electrical connection grounding out somewhere.

[joehahn]

WTF??? where was that Paul Guard guy LAST year before mine crapped out? Incidenatlly I have used nothing BUT mobil since I got car 3-4 years ago. I will now (finally) try swepco.

joe 68 L

[agabriel]

interesting about the M1....

[Bill Verburg]

In the past 20 yrs I have never heard anyone recommend anything for a 915 but Swepco. The reason is the design of the Porsche synchros which need a bit of friction and a sensitive hand to work correctly. The have their own pace and will not be hurried by anyone.

[gr8fl4porsche]

I am planning on changing my tranny lube tomorrow in the '87.
How does the Swepco do in the G50?
Anyone use it?

[red-beard]

Can anyone _show_ me anything that is not anecdotal about Swepco. From everything I've found, 201 is nothing more than 90W gear oil.

James

[Mike Feinstein]

86 or earlier = Swepco
87 or later = Mobil 1

Joe...it seems you ran Mobil 1 synthetic in a 68 Sportomatic...probably wasn't a good idea.

[pwd72s]

I've been shouted down on this subject enough that I should know better. But FWIW, I have a 915 gearbox, with factory limited slip. I have tried Schwepco, and I like a synthetic better. Torco 75-140, with limited slip additive, GL6. Non synthetic Schewpco won't hurt you...but if you'd like to experiment with TORCO? Check your local bike shops, they can probably order it for you, at about $10 per quart.

[jmohn]

Originally posted by red-beard
Can anyone _show_ me anything that is not anecdotal about Swepco. From everything I've found, 201 is nothing more than 90W gear oil.

James

James,

To a point you are correct, 201 is (actually 75w-90) gear lube. But, there's a bit more to it, I'll try to sumarize my (limited) research. Like all transmissions the 915 requires a lubricant with sufficient lubricity to protect the gears and bearings, but (important difference) not so slippery it prevents the 915's sychros from working. The synchros in the 915 depend on a certain amount of friction to function correctly, if the lube is "too good" the synchros do not develope enough friction to "spin-up" the next gear and allow a smooth shift. There are probably other gear lubes besides Swepco that have the precise amount of lubricity that will alow the 915 to function at it's best, but I don't know what they are. Anecdotal or not, to me, Swepco is a known quantity. I don't consider it "cost effective" to experiment with other lubes in my transmission.

Jerry M
'78 SC

[pwd72s]

Really, I mean it this time...I give up. Use Schwepco...if for no other reason, Bruce Anderson says so...he said so back in the 1970's...and the faithful remain.

[yelcab1]

That blue stuff.