John McM

In the 14 years that I have owned 964s I have seen few threads on gearboxes. I suspect that's because the G50 is renowned as a strong box and also because gearboxes are a mystery to most of us, including me.

I'm writing this thread because my gearbox is being refreshed and I thought I'd share my experience.

John McM

My car is a 1990 C4 and has 150,000km (94,000 miles) on the odometer. Over the last 2 years it has been extensively tracked and recently developed a graunch in the shift from 2nd to 3rd. I tried new oil, which made no difference, and then shifting around the problem, but on the track all reason goes out the window. The only viable option was to get the gearbox refreshed. The initial diagnosis was some new synchros which retail at circa USD 100 ex tax each if you look hard enough. If only it was that cheap! The C4 engine and gearbox must be dropped from the car, then separated. You can count on ~ 10 hours of labour to drop and refit. This was on my bucket list so I did it myself. Believe me it's a lot of work so apart from the satisfaction of doing it myself, paying someone else 10 hours is worth it. However one advantage of dropping the engine and box is that you can send the box away and work on the engine while you wait - just make sure you can keep the box upright on transit! I haven't finished rebuilding the box, however I've had an estimate of 12 hours labour to disassemble and reassemble the box. So you are up for 22 hours labour plus parts.

Goughary

I wish I knew a good place in the New York area to bring a G64 to be rebuilt...mine is ok, but I was thinking about going through the entire box including the planetary gear (welding to reinforce), checking out the clutch packs maybe refreshing with new discs, new syncros etc. perhaps a different set of gears...

Would be good to use someone that knows the G64 specifically and make it better along the way. There's always something.

If you could share your experience since you are in the process, that would be fantastic...

John McM

My understanding is that the synchros are made of a brass material and are sacrificial i.e. they wear not the steel parts like the gears and gear sleeves UNLESS you persist in shifting when you know the syncro is worn.

So what's the diagnosis? I need three new synchros 2nd, 3rd and 4th gear. I also need a new 3/4th gear guide sleeve and 3rd gear. Respectively they are USD 298 (for 3), USD 687 and USD 707. The lesson here is to replace the synchros before you damage the steel parts!

John McM

Of equal or perhaps more interest to C4 owners is the condition of the parts specific to the G64 box.

Before I started track driving, I suffered a planetary gear failure. This part retails for USD 2,100. Mine had a crack and was repairable. The weld has held up over the last 16,000km of spirited driving on road and track

If you are really unlucky you can crack the sleeve that the planetary gear runs inside. That will be another USD 1,100! There doesn't seem to be a conclusive diagnosis why these failures occur. I suspect the peening on the planetary gear pins fails to hold them in place. If I had my gearbox out of the car I would check these parts. That advice saved me $$$ 2 years ago.

John McM

Another part of the G64 transmission is the 4wd clutch system. Inspection of the clutches showed that my lateral clutch (controls wheel spin in the rear axle) had one plate needing replacement.

Unfortunately Porsche changed the supplier for these discs during the 964 model run and the ones in the 1990 model (Gylon) are no longer available. So if one plate is gone then you must change the plates completely to the Valeo system. That's USD 1,100 if you have a later model, then you may have the Valeo type and you just replace the worn parts. Mind you the cost to get into the box to replace them is still large.

John McM

By now I imagine the paranoia is starting to build in some C4 owners reading this. I was asked if I had any symptoms with the clutch pack and the answer is none.

I probably could have used the gearbox on the road for many years, as is, but I want to drive the car hard for many years to come and living with a compromised box isn't for me.

If you do have an interest in keeping your car for a while and using it as intended then this like the engine top end rebuild is likely in your future.

If you are buying a used C2 or C4, then you have an idea of what it costs to refresh a gear box. I'll add to the thread when I have more info.

Duck

I was starting to stress. Already going to drop a lot of money on a rebuild. No way have the money now to address the G64. The only good thing is that dropping the engine in the future to have the G64 looked at is not very difficult.

koenig_roland

very interessting!
I track my c4 too and i thought about a gearbox refresh, but:

these G64 boxes are so cheap to buy here in germany, it makes more sense to replace a defective G64 with an other used part... G64 boxes are between 1k and 2k € here.

An other option is the downgrade :-) to C2 with a used G50 box...

John McM

I'm surprised the spare boxes are so cheap. Certainly if I had that option I would look at it, even to keep as a spare. Unfortunately in New Zealand it's not easy to come by used spares.

John McM

A few frustrating weeks sourcing items. The best price I could find was at Rose Passion. Very efficient even though I don't think they normally ship to New Zealand. 3rd gear set was USD 700 and appears to come with a synchro. It's interesting to fit the synchro to the cone and feel how it grabs as it's pushed on, which is how they work.

The Valeo discs came to USD 1,100 for the full set. As the final one is a shim to meet a certain overall height I had to buy the full set to make sure my rebuild isn't held up finding the right shim.

In hindsight those parts were easy to get. The guide sleeve as a lot harder. Not available at Rose Passion, Cogs Cogs or Porsche New Zealand. All had the same story, on back order with Germany and no certain supply date. In the end my mechanic sourced one off a Rennsport contact. I also bought a used example off cogs cogs. Who would have thought that a key gearbox part would be in short supply?

During all of this I toyed with a second hand box. The thing that put me off is that I couldn't find a Valeo fitted example. I don't want to replace a whole set again.

Next time I update this it will hopefully be talking about the box performance after all of this work. Fingers crossed.

John McM

Photos

Duck

You are braver than me. Good luck.

John McM

Another issue to work through. At some stage the dog gear on the fourth gear (thin ring in the image) has skewed itself and no longer has an interference fit. The solutions are to fit a whole new gear set or a new dog gear. Apparently the latter is a recent option so that's what I'm going with.

hockenheimr

Your G50 looks cute in a blankie!

When I read there were clutches in the C4 system I was completely turned off. I'm also a Jeep guy and 'Jeep Guys' completely frown upon clutch systems...albeit Jeeps are not as well made.

How hard is it to switch to a C2 setup? i.e. lose the 4-wheel drive.