f4 plt

I currently have a Wevo shifter on my SC with the 915 gearbox and have some binding on downshifts from 5th to 4th at higher RPM under load. It has been continually adjusted. Is the renin sport shifter any more precise, or is there a third alternative . The vehicle is tracked so mechanical over revs caused by a miss shift is a real concerned. Thanks

Steve Weiner-Rennsport Systems

This is quite rare and I'd speak with Wevo (or the folks you bought it from) about that.

Make sure your motor mounts aren't the problem, first........

f4 plt

Thanks. Motor mounts are good as they were replaced a year ago with the engine re-build. The Wevo shifts great except for downshifts from fifth to fourth at higher RPMs. I will first adjust that shift gate.

That said anyone tried the Wevo and the Rennsport and has a comparision?

Steve Weiner-Rennsport Systems

Do you have the OEM mounts, the sport (954) ones, or Wevo ones? Makes a BIG difference here,......

Make sure the shift coupler is in PERFECT condition and the spline adjustment is spot-on.

f4 plt

Steve:

You caught my attention, I think that when we rebuilt the engine last year we used OEM engine mounts and with the capability of the engine we may in fact be torquing the assembly ( Engine and tranny). I will look in to the WEVO engine mounts and talk with "my guy" who by the way learned his initial skills as a journeyman at the Porsche factory long long ago.

I noticed on the WEVO webpage that they make transmission "beam braces for the 901 and the G50 transmissions but not for the 915 ... am I missing something?

Jack

Steve Weiner-Rennsport Systems

Jack,

ANY excessive movement of the engine & transmission under high torque loading (high RPM, full-power shifts) puts the whole assembly (engine/transmission, shift coupler & shifter) into a bind, hence the need for a stiffer mount. This is critically important at the engine.

The 915 transmission mount is plenty stout and doesn't need anything besides mounts that are in excellent condition. Unless your car is a dedicated track or race car, I'd stick with rubber on the tranny mount and use the black Wevo ones at the engine.

Naturally, this all just my opinion.

f4 plt

[QUOTE=Steve Weiner-Rennsport Systems;11008896]Jack,

ANY excessive movement of the engine & transmission under high torque loading (high RPM, full-power shifts) puts the whole assembly (engine/transmission, shift coupler & shifter) into a bind, hence the need for a stiffer mount. This is critically important at the engine.

The 915 transmission mount is plenty stout and doesn't need anything besides mounts that are in excellent condition. Unless your car is a dedicated track or race car, I'd stick with rubber on the tranny mount and use the black Wevo ones at the engine.

Naturally, this all just my opinion.[/QUOT

Thanks Steve

I went to the WEVO site and looked at the mounts, the black ones would be better for my use. Some track, some street and some autocross. Would like more track but my neck and back say different. Too many years and too many "g's"

JCP911S

Old crusty dude weighing in here... this is a pet peeve.

I've driven and raced 911s with 901/915 boxes for more than 25 years, and no linkage works better than the factory.

Sure the factory linkage requires long throws, but it was done that way on purpose. It makes the shifts no-brainer simple, and doesn't overwhelm the synchros.

"Short shift" kits simply reduce the ratio between the shifter movement and the gear change... they don't make the shift more accurate, they just add leverage, and reduce the margin of error... the tranny is going to shift the way it shifts regardless of the linkage.

I know lots of guys with expensive shift linkage upgrades who also had expensive engine rebuilds.

With my clumsy factory linkage, I have never had any trouble with a 5-4 downshift.

Maybe the Porsche engineers who won multiple races with these cars are not the class dunce? Maybe you are over-thinking the room?

Texas RS

I have a Wevo shifter and Wevo engine mounts on my '82 911SC race car with 915 tranny. No issues and the car has had a lot of track time. Get the engine and transmission mounted securely.

f4 plt

Nice avatar crossing the finish line at TWS

As to JCP 911S I don't refute your comments as I have owned and driven Porsches with the 901 and 915 transmissions back to the 60's. The question in my original post was to have comments from people that have driven both the WEVO and the Rennsport shifters. I am not unhappy with the WEVO in fact I find it better than the OEM Porsche shifter for the 915 it is just that I have the downshift issue from 5th to 4th and I have concluded from the posts that upgrading the engine mounts is a logical solution. Thanks

Jack

Texas RS

Correct on the picture location, thanks on the comment.

Even the GT3 RS has an issue under hard lateral loading downshifting from 5 to 4. Entering T1 running CCW is a problem spot for at least two RS's. One of my my running mates is putting in RSS motor mounts and we will see if that fixes his issue, then I may follow. For now I am just very deliberate with the downshift.

JCP911S

Yes, the OEM shifter is inferior to the WEVO in every way except that it never misses a shift from any gear in any situation.

If your car has enough power to overwhelm the engine mounts under full braking in 5th gear, then I want one of them too.

The solution is simple... keep the WEVO and don't shift into 5th....

Just kidding... have a happy new year:cheers

porsche0nut

Steve, I am curious: why the stiffer mounts at the engine and the rubber at tranny? My initial instinct (up for review) is to think that this allows the transmission mount to flex more than the engine ones.... and does this not result in the engine & tranny shifting/flexing relative to one another?

Not doubting anything, just looking to understand the logic behind it.

JCP911S

On a more serious note, years ago I remember a similar problem on my 911SC. I upgraded the coupler, put in hard engine mounts.... no help.

Turns out the shift rod was coming apart. When under tension... e.g shifting into 2nd or 4th, the cup under the shift lever would flex... result was no-shift. (it eventually jammed in 3rd, which made for an interesting trip home to Philly from Lime Rock... a story for another day)

Anyway, before you spend a lot of money, I'd make sure that rod is OK.

Good luck.

Steve Weiner-Rennsport Systems

Hi Jonathan,

You've asked a great question!!

The main purpose for stiffer engine (and transmission) mounts is to limit the amount of movement in the whole assembly under high torque loading. Since the engine weighs far more than the transmission and has a longer lever arm, restricting its movement using harder rubber (or solid) mounts makes a bigger difference than doing the same for the tranny one.

Further, installing harder rubber transmission mounts transmits a lot more vibration and noise into the car than harder engine mounts do. For this reason, I don't recommend them for anything but dedicated track & race cars.

I hope this helps,