jstyer

Thought I'd share my rebuild details, gearing choices, upgrades I decided to do, and my experience with California Motorsports.

My transmission has shifted poorly since I got the car, and when I changed the fluid at 84k miles there was all sorts of bearing debris.on the drain plug. Based on the fluid condition and prior receipts, I had no reason to believe the fluid had ever been replaced. In any case, I figured the diff was losing needles, and chose to continue to drive and track the car (not recommended btw). During a track event last August the transmission stopped shifting into 2/4/6 and I figured that debris had finally worked its way behind the shift shaft. This later proved correct.

I contacted Matt Monson at Guard for pricing/details for parts as I planned on rebuilding the box myself. Matt directed me towards Roger at California Motorsports for parts, and a few upgrade bits that they manufacture. As many of you can relate to, life got in the way and I ended up shipping the gearbox and various parts I'd accumulated to California Motorsports to let them handle the rebuild.

Here's pics of what was in the diff housing when I pulled the side cover off:

jstyer

Roger and his crew were incredibly accommodating by giving me detailed pics of everything I requested during the tear-down and build process. Things to note in these tear-down pics:

• Slight pitting on a few gears, and on the ring and pinion. Did not replace R&P.
• Completely hagged main bearings.
• Pretty rowdy shift shaft and shaft bushing. These were both replaced.

And now, mega picture dump.

jstyer

jstyer

jstyer

ilko

You're lucky the R&P isn't in too bad of a shape. But all the needle bearing components at the bottom of the case are making me mildly nauseous.

What ratios did you choose for the re-gear?

francisluu

Good luck with the rebuild! My transmission was sent to Roger as well, did an awesome job. Taller first gear, 8:33 final drive, Guard LSD. It's quite the workout but oh so invigorating.

jstyer

Because I'm not a very bright guy, I decided to go ahead and make this the stout, shorter geared box that the rest of the car deserved. Here's what I decided to do:

• Guard 60/40 LSD
• Change 3,4,5,6 gear ratios
• Billet 1/2 and 3/4 shift forks
• Steel synchros in 1-4
• Get rid of all the plastic caged factory bearings.
• New 4-point, main, and pinion bearings
• Port for oil cooler
  • Used California Motorsports combo sump adapter/sensor port.
  • Drilled the top of the case myself to return next to (but not on) the ring and pinion. This is very similar to what Geoffrey Ring did with his 964 race car.
• Then general rebuild hardware, seals, gubbins, etc

Here's where I ended up on gear ratios. This is pretty similar to a G50/32 gearbox, just a tad shorter. My selection ended up being somewhat of a compromise from what I'd originally planned based on what was available at the time of order. All gear sets were ordered from Guard. I went back and forth on the ol' 5th to 6th and then filling out 3-5, but I feel like this will ultimately be a more versatile box. I would've preferred a few more "walking" gear sets, but they just weren't available. I'm not going to lose sleep over it.

jstyer

And finally, the rebuild. The boys from CMS did an amazing job. If it runs half as good as it all looks, it should be a riot. I'll update with driving impressions as soon as I get everything buttoned up.

jstyer

jstyer

Churchill

Looks great. That's going to be fun. What's the history with the box -- why was is so gnarly?

MD355

Is the Guards LSD 60/40 better than the factory OEM ZF or GKN 25/65 ??

Why is there such a difference in lock up numbers ?? 60 vs 25 (acceleration) and 40 vs 65 (deceleration) ?

I believe the Porsche 993 RS is GKN 40/65

NYC993

Thanks for sharing! With track use I started flushing tranny once per year.
Any reasons for not changing R&P ratio? Wasn't necessary with new gears?
So where are those needle bearings from? The stock diff?
What's the rough cost brake-down for parts and labor for a job like this...gears, LSD, syncros, labor?

ilko

Those are good ratios. Mine are similar, just a little shorter, still.

You don't want to change the R&P ratio if you keep the stock G50/20 1st & 2nd gears since they are pretty short to begin with.

The cost varies a lot depending on the parts that need replacement and the labor rate. Looks like this gearbox needed a few extra items...