I am now thoroughly confused. Will post later. Still at work.

 

Still at work at 8p? Go home!!!

Nothing confusing though. SHC is what WAS used, then replaced by Delvac which is NOW used. At least in my car. Not sure what exactly your gearbox wants but I am sure you would be just fine as there are many on here that use Delvac in 964/993 gearbox as Delvac is rec'd for the G50.

***my only caveat would be that I have NO experience with the 993 gearbox so hopefully 993 guys can chime in on experiences with gear oil choices***

 

No, Mobil 1 75w/90 is the store bought oil that is too slippery.
Mobil Delvac SCH (new name) and Mobilube SHC (old name) is the proper gear oil.

Dell, your GT3 gearbox is essentially the same as the 993 gearbox.

 

Geoffrey....glad you chimed in. I was about to PM Mark your contact info since you have (based on previous thread inputs) a good command on this subject.

 

Another source of the 2-3 crunch that probably no one wants to hear about in the G50 trans is the slider for the 2-3 gear syncro assy. It is a sleeved ring with a groove the shifter fork sets into. If it has the teeth rolled over slightly, the actual syncro ring can't mesh properly, giving you an unnerving "cruch", especially trying to hammer the shift coming out strong from a corner, like 3B in Seattle. Easily overlooked when replacing syncros, you have to look really closely to detect the slight wear on the teeth on the outer edges.


It's the left-most part in the assembly labeled #8 in this diagram.
http://dcauto.gotdns.com/catalog/ima...OG/pg_0127.jpg


Hold onto your wallet, however. Seems the slider ring cannot be purchased seperately - you have to buy the entire assy shown.
For a cool 900 bananas.
Ouch.

 

Okay, thanks, guys. I thought you were going to tell me that Mobil 1 was the smae thing as Brad Penn oil.

 

Mark,
Any consensus? I get a clunking as well under loading in that corner. As another poster mentioned, may be attributed to flex? Not sure if we put Mobil, or Swepco the last time it was at the shop.

Thanks,
Sam

 

The 964 chassis lacks the forward trans mounting supports that the 993 chassis has. I'm not sure the exact reason why Porsche made the chassis modification, but it certainly makes the engine/trans more rigid and keeps it from moving fore/aft in the chassis. I believe this helps in improved shifting in the 993 over the 964.

 

I have the earliest version of the G50, but I also have a crunch if a 2-3 gear change is rushed exiting a turn. I tried solid motor mounts for the last event of the season last year at VIR , coming out of 1 and oak tree, it was still there. Most likely the slider as mentioned above.
If I just give a tiny pause between 2-3 shift and don't rush it, it slides right in.
I'll also get the crunch on the 3-2 downshift once the trans gets hot. I know a rebuild is in the future, and damn are G50 parts expensive!

 

Mark, did you have this issue w/ your last clutch as well? Also, do you get this crunch out of certain turns when the car is early into a race or practice (less then 6 laps or so)? -Derek

 

Sam,

Genady used Redline shockproof oil that last times. The lube to get is the stuff that L&N Engineering sells.

Derek,

It occurred whether with the stock clutch or the RS clutch. It doesn't matter if the car is warm or hot. As you may have guessed, I don't crank on it until it's good and warm. It doesn't happen with every shift out of the "problem" corners. Sometimes I can go ofor ten laps with no crunching and then the it crunches and then nothing for another four laps. This started after I had new brass 3rd and 4th synchros put in.

 

Mark

My old 993 had the same issue for about two years of heavy track duty before it finally gave up and we had to have the box rebuilt. I had the RS motor and solid tranny mounts the whole time. Unfortunately, at least for that car, it just kept getting worse and worse until I could not get third at all.

To add insult to injury, the box was rebuilt but the shop did not re-gear it for us as we asked. (Car probably will not be returning to stock class as I think Joe is going NASA GTS3 full bore, ie. fiberglass, flares for bigger tires, stripped interior, etc).

 

We were able to prolong the service of our G50s and made the problem much better for around 2 years by using the Redline heavy shock proof gear oil. Made a big differance. I know several racers that use the shock proof gear oils with great success. This is a common problem...

 

Joe's out of G class?? Damn, I won't get to run with or see either of you.

Someday, I'll graduate to a real race car like you two.



I run the Redline shockproof oil now and will try the Mobil 75W-9p Delvac SHC stuff. Just ordered it.

 

I contacted Redline about 2 years ago about what to use in the 928 to help reduce 2nd gear crunching. They recommended against shockproof in a high powered car. They said something about torque and pressures degrading it too fast vs the high rev/low torque bike/kart applications for which is was designed. A mixture of 75W90 and 75W90NS helped over whatever was in the transaxle before, but it's not cured (downshifting 3-2 still sucks).

Where did you buy the Delvac? I was thinking of trying Royal Purple or Liqui/Lubro Moly next, but the Delvac sounds interesting from the comments above.