I want to change the fluid in my 915 transmission. I currently have red-line in there and want to change to swepco. Is it ok to switch from sysnthetic to non-synthetic??? Should I just keep using the re-line?

 

Yes, it is OK to switch. The trans should never have had synthetic in the first place.
Pete

 

It's fine. If a 915 has old/unknown gear oil in it, you can switch to a conventional dino oil, run it for 100 miles, then flush it out and replace with the (expensive) Swepco. Synthetic is a bad choice for a 915.

 

Thanks for the input.

 

That is REALLY good advice,....

 

While we are on the 915 topic, I learned some interesting stuff this weekend. I rebuilt my motor and had my trans rebuilt (by REZOOM in Blountville, TN. Thanks Mark Finley!) over the winter. I had trouble at the track due to the short shift kit and improper shift coupler adjustment. After hours of work, we yanked the shifter with the short shift kit and installed an older shifter with full throw, and then did a proper adjustment to the coupler. It now shifts better than it ever has, although I need to make a tiny rotational adjustment to the coupler to get it to go into 1 and 2 a little easier (without upsetting 5-R).

So here is what I learned from a 31-year experienced 911 mechanic and a very experienced club racer: Dump the short shift kit. It fights with, and will eventually destroy a 915. The long throw takes some getting used to, but it is what the 915 prefers. The 915 likes the slower input caused by the long throw. Of course this recommendation is without considering the WEVO shifter. Many club racers swear by them, but that is $600 I am not ready to spend.

Don

 

Don: Amen! I put the "super-short" factory shifter ('86 type) in my PCA race car and hated it! I then tried the stock '85 shifter, which is 10% shorter than the stock SC unit, and loved it. A great compromise, good throw without the heaviness of the super-short shifter.
Pete

 

Is that the only year that works and is slightly shorter, or is there a range of years a person could use. Any mods at all to make it work. The 85 was still 915 right? Showing my still newbishness here...

 

All the 915 shifters, except '72models, were basically the same. I think that the neutral gate adjustment was added in '77. The throw was the same until '85, when the factory shortened it by 10%. In '86 the super-short option became availabe, it was 10% shorter than the stock '85 (of course, 20% shorter than '84 and earlier models). However, the strength required to change gears, with the super-short version, approached, for me anyway, an uncomfortable level, and that heaviness was too big a trade-off to get the shorter throw. And yes, the last year the 915 was used was '86.
Pete

 

Interesting info (to me anyway). Thanks Pete.

 

Exactly what Don said. I ruined my shifting with a short shifter. I kept all the urethane bushings and fancy coupler but put the factory shifter in it and the shift quality improved dramatically. Since then I have installed the Wevo internal shift gate and shift quality improved only marginally but I no longer lock two gears together.

 

Great info on the factory shifters Pete, thanks! I think a good-condition 915 w/ the stock shifter, where the synchros as well as all the bushings/coupler/linkage in good shape, shifts just fine. You have to take it a bit easy, but in some ways that's good since it will force you to think about it and ultimately make your internals last longer.

We have installed a few Wevo kits on customer cars (the one where it replaces the entire shift gate and shifter) and they are pretty good. I love the fact that neutral is spring centered, but the shifting is perhaps a bit too notchy. I am also worried that with some owners, the new-found shorter, tighter throws will perhaps encourage them to rush things too much and thus wear out the synchros prematurely; remember you are only changing the shifting mechanism, not the internals of the trans! However, the Wevo unit is good for the fact that it is less likely that you will misshift.

A great update that I did once was to install one of those upgraded shift couplers on a customer car, I believe it was from Stomski Racing. It took a lot of the slop out of the linkage and made the shifting a bit more precise without being too notchy.

---Chris A.

 

Chris: My greatest fear regarding "improved" linkage pieces is exactly what you just said - they allow, even encourage, faster shifts. Which, as you stated correctly, will cause premature wear to internal synchro parts, because it's those very synchros that are not designed to be shifted fast! I have never subscribed to the "shift faster" theory relative to the 915, I didn't shift my PCA car any faster on the track than on the street. Sure, almost all track shifts are done over 4500 rpm, while the opposite is true for street driving, and that makes the shifts smoother, but not faster. I've heard people talk about missed shifts on the track, my wife did just that, but if the car is balanced when gear changes are made there shouldn't be missed shifts. If a car is mid-corner and heavily loaded, and for some reason a shift is attempted, the chance of catching a wrong gear go up dramatically, and maybe a Wevo pays big dividends in those situations. I've always done my downshifts under braking, and when a mid-corner shift might seem necessary I always chose the next higher gear before the corner. About the time that I was starting to turn some pretty decent lap times I had an instructor, who drove SCCA Nationals, Can-Am, and other venues, tell me, "More driving, less revs." That is really one of the keys to being quick and keeping your equipment together. It also taught me that you don't have to keep a 7200 rpm engine at 7200 rpm in a corner, with the car balanced on its tiptoes. If you do you're doing two bad things: (1) You're wearing out the car at the maximum rate, and, worst of all, (2) You're limiting your own ability to do that corner even quicker (less revs, more driving), because you can't shift up under those circumstances. If you do shift you stand a very good chance of flying off the road, or missing a gear and hurting something. 915s are really good, but you have to "go quick, slowly," to keep them happy, and nothing more, in my opinion, than a good, correctly adjusted, o.e. shifter is needed for that.
Pete

 

I too switched out a Weltmeister short shift for the stock unit. The Weltmeister never felt quite "right" for that transmission and my shifting improved with the stock one and it does feel "right".

 

I just put a Renn-Shift in this year which is very similar to the Wevo but a bit less expensive. Centered in the 3rd/4th position with spring loaded gates for all other gears and reverse lockout. 20% shorter throw then stock. Not a notchy feel. Driven with it on the track and the street and it feels more precise then the stock shifter. I dont shift fast as being a track driver every input is smooth. Bottom line is I like it!