915 Performance Trans Oil Reccomendation

[asphaltgambler]

In my resto-modded '85 Targa which only has @150 miles on new build, I'm not happy with the way the trans shifts.....at all. Some time back, I had a reputable ( recommended here ) guy rebuild it, add the double bearing plate from the 930 box, and go through it, open check book. The N/A engine is making @ 310HP at the flywheel with a lot of torque. I put Swepco in it originally, but cannot remember what number.

I have a WEVO shifter, coupler- set everything up correctly and there are times where it won't go into lower gears when moderate RPM downshifting and if I'm in it hard from 1st, frequently reluctant to go smoothly into second. I'm well aware of the trans reputation, I'm definitely easy when going through the gears as not to shock-load them. I spent @$4500 on the trans 15 years ago, have done everything that could be done to make it better to hold the power, but am disappointed how it shifts.

So at this point, I'm getting ready to change out all the fluids, check / adjust the valves, etc, etc. I'm ready to try a different trans fluid, possibly something like Motul or Redline. I think a lot of people use Sewpco just because of the name. I've used a lot of Redline products in cars and motorcycles and am always pleased with the results. Case in point: my E39 M- sport 6 speed trans had worn 1st, 2nd, and 3rd syncros and shifted horribly most of the time. The only solution was to try a different trans fluid. I called Redline's tech dept, explained the situation and they made a very specific recommendation which after installing their oil, made a world of difference.

So this is not a stock application, does anyone here have direct experience with similar issue and then trying a different trans oil?

[grb008]

Is the bushing in the tunnel and the ball bushing on the shifter ok?

I had a similar problem and new synchros fixed it but sounds like that was done

[asphaltgambler]

Yes, all new. I stiffened the shifter gate springs - which are adjustable, and that made a noticeable difference.

[winders]

The 915 needs a non-synthetic oil. My 915 has been in front of a 3.6L engine (325 HP then 430 HP) for a years using a RennShift shifter. I have used Swepco 210 the whole time. In that time I had to replace 3rd gear once. The 8:31 ring and pinion still looks almost new.

I have never had problems getting into any gear, including 1st, on the race track unless it was late in the season and the 2nd gear synchro was almost worn out.

[grb008]

Swepco also. Once warms up shifts real nice.

[Matt Monson]

Did he replace dog teeth? What brand did he use? If he used the German OEM ones (in a white box) they lack backcut and will instantly have a shifting issue if not modified prior to installation. Oil won’t fix that.

[asphaltgambler]

Good question- I'll have to look over the receipt. Did not know that....

[Matt Monson]

Here’s a current thread for more details.

https://forums.pelicanparts.com/porsche-911-technical-forum/1133476-synchro-diameter.html

The reason a more slippery oil, like Redline, will make it worse is because it’s already not getting enough friction against the shift sleeve, because it’s pinched too small. So the gear isn’t slowing down and is just getting jammed into gear forcibly.

[asphaltgambler]

Interesting Matt, so you're recommending stick with Swepco, so which number? There appears to be several choices.....

[Matt Monson]

201.

[winders]

210 is better……better when it is cold and certainly better when it gets hot.

[PeteKz]

I'll toss in my limited experience. I went thru my 915 box 20+ years ago and replaced first and second synchro rings. It had about 105Kmi on it at that time. I used Swepco per a Porsche rebuilder's recommendation. It shifted okay (for a 915), except I would sometimes get a grind when going into first from neutral at a stop. I had to wait about 1 second between stepping on the clutch and pushing the lever forward. I put a couple thousand miles on it then the car sat for 20+ years while my project stalled due to family etc. When I got it back on the road, I figured I should change the oil, so I tried the Mobil 1 synthetic stuff. It made the shifting harder to get into gear for downshifts. Upshifts seemed about the same. I also got grinding going into 1st when stopped and then going from neutral into 1st, unless I waited about 2-3 seconds before pushing the lever into 1st. Several aficionados suggested to use an ordinary mineral gear oil instead of synthetic. I put in Valvoline 90/140, and now it shifts about like it was shifting with Swepco, but I still have to count about 1.5 seconds before shoving the lever into first from neutral at a stop. I have about 10,000 miles on the Valvoline. Next time I change the tranny oil, I think I'll try the Swepco again, to see if that changes the N to 1 shifting.

BTW, I did change the shift coupler bushings 3 years ago as I was getting it back on the road, so that's tight. I used the ones Pelican sells that you have to press into the old yoke (Glen Sager, excellent phone sales guy at Pelican, recommended them; he has a 1971 S, so he knows what he recommends). I also replaced the shifter rod bushings in the tunnel, and the cups at the bottom of the lever, and installed the OEM short shifter. I don't have any play in the linkage.

So, my experience is that the oil does make a significant difference in shifting behavior. I don't yet know if Swepco is noticeably better than Valvoline in my 915 tranny, but both are better than the M1 synthetic. Knowing that everyone's gearbox has a little different amount of wear on it, YMMV.

[Matt Monson]

That Valvoline is a perfectly good gear oil. I’ve used it myself and recommended it to customers who didn’t have easy access to Swepco.

[asphaltgambler]

OK, so what is the difference between Swepco 201 VS 210?

[Matt Monson]

There’s no reason to run 210 in a street car. 201 is fine.

[Mahler9th]

For street driving, folks like Jerry Woods and Bruce Anderson recommended Swepco 201 for decades.

I started using it in my Porsche street cars in 1992 or so. Those cars were also used in AX and track (time trial) events. Great stuff.

For my current race car, I used Redline (NS-- non-slip) for about 15 years without issue. It was not too slippery in my use case.

More recently I switched to Swepco 210 in my race car. I did this when I was doing some refreshing and had a Guard Transmission (GT) LSD installed. The LSD joined some Guard gears in my transmission... been using those GT gears for 20 years.

[Cory M]

I've always used Swepco 201 because that's what was recommended to me by the experts. A few years ago I sold a Carrera with 238k miles. I had receipts going back to 1985 and it appeared that the transmission had never been rebuilt. The shifter was sloppy from the usual wear but otherwise no issues. The fluid was changed regularly with Redline 75W90 synthetic. I was impressed.

[Geneman]

Cory. was that 85 a racer or street only? interesting data point.

[Cory M]

Street car only.

[Kemo]

something to check...I had my shift rod simply break on me right under the cup bearing. it was shifting really bad and i thought it was the transmission going out. broke clean off one day at a DE.

i have a Rennshift with Stomski coupler, 964 cup bushing and stock rod slider bushing. worked great until it just started going downhill. started with difficulty coming out of a tight corner in 2nd and just trying to get into 3rd.