So i am in the middle of the LSD installation phase of my massive project and just thought I would share a few pictures and observations.

So first off, the stock bearings on the side over was really shot. Like scary shot. As in possible catastrophic failure in the future. Talking with several porsche gearbox guys, this is pretty common. Supposedly this us caused by moisture. But either way, scary.

So what we are doing is measuring the existing height from inner bearing race to ring gear. We also measure the bearing heights on both sides to get a good starting point. We are using a precision granite flat surface and height gauge. The idea is to measure and compare the dimensions to the new diff and start there. We have two sets of the same bearings where one is honed out to slip fit. So we will start by shimming to the same depth as the factory as a starting point. However I do not trust the factory setup so we will be checking gear lash to make sure it matches the specs scribed on the ring gear. Their is a special tool for checking hear lash. This tool is very helpful, but you can check lash without. The idea is to measure lash at a point directly over the ring gear bolts. What the Porsche tool does is mount into where the stub axle goes and provides an arm that the dial indicator will index off of(over ring gear bolts). An alternative is to make a bracket that bolts to the stub axle and locates over the diff bolts. I will post pictures of this part of the process when we get there.

A note about diff shims. The porsche shims are ~$7 each. The inner dimension of the shims should be 1.975"-2". Outer dimensions should be no more than 2.5". I have no doubt that another source besides porsche should be available snd acceptable. These are similar to pinion depth shims. And porsche lists these in .05mm increments. From 1.5mm-2.8mm. The factory open diff is shimmed with 2mm on each side. But for now I measure that I will need 3.83mm worth of inner shims. So I will get $70 assortment based on this.

The differential going in is a factory GKN with cup steel plates in side. Below is a picture showing the GT3 versus Cup diff clutch. The 997cup setup uses 8 clutch plates and has a static preload of 140lbs on the acceleration side. Way to much for street. The cup belleville washer is significantly thicker than the GT3 washer. The cup clutches and steel plates are 1.1mm to fit the same depth diff housing. So I am running this diff in 6 plate configuration which brings preload down to 100lbs. Still aggressive, but streetable.

Anyways, I will share more as I get more done..

 

Don't forget to install the cup shift selector lever while your gearbox is apart. It's a $90 part..

 

part #?

 

Sent you a PM Steve. You need the bracket and lever....

 

Ditto with the PN.

Are we talking the shifter assembly in the cockpit or the level on the side of the transmission? I am doing the cup shift cables.

 

Most transmission builders overlook these parts or are just not familiar with them and that's a shame is it totally changes the feel of the gearbox for the better. It's the selector lever mounted on the transmission case (mounts from the inside). The lever is about 30% shorter than the TT lever and does not have the heavy counter weights. You also need to mount the Cup cable bracket to that the cables are mounted on the transmission at the correct angle to the lever. The lever shortens your shift throw 30% as it's designed to be used with the Cup shifter.

996Cup shifter 996.424.010.9A
996Cup shift cables 996.424.040.75
996Cup cable bracket 996.424.165.9A
996Cup selector lever: 996.303.031.9A

 

This would require opening the transmission too, though. VAG is only replacing the diff, not rebuilding the transmission (or did I miss something?).

Thanks for the PNs John. I've got a ton of threads bookmarked with valuable info - and about half of that info comes from you.

 

Once the gearbox is out it only takes a few minutes to pop the case off. It's not a big job for someone that is knowledgeable in building these boxes.

 

Will add to the Google spreadsheet :-)

https://docs.google.com/spreadsheets...it?usp=sharing

 

What if any specialty tools are needed for a trans rebuild?

 

Besides a large collection of feeler gauges and pullers for bearings, gears and seals, i am not sure. Not sure if it requires special tools. I do know that Porsche builds special tools for literally everything. And with that comes the assumption that you can't do it without them. And sometimes that is true, but often times it is not true.

I personally would be afraid to tackle a rebuild on my tranny. I have never rebuilt any transmission and the G50 derivatives are definitely amazing mechanical pieces that require much knowledge, precision and respect. And if you have experience in gearboxes you could probably tackle the rebuild. Otherwise it would be best to send to guard or CMS. Just my .02

 

Mainly the. Tools in the picture below and a bit plate to heat the bearing race for installation. The huge socket that's about two feet long is interesting.

 

Thanks for the comments. Good to know that no Porsche specialty tools are needed.

 

There's a great thread on RL with a DIY gearbox rebuild - albeit GT3. Search for "My descent into madness" by rbahr (?).

 

Thanks Steve. I'm looking for any tips I can find!