rbahr

It goes without saying that if folks have any questions or thought let me know. There are many more pictures, and I will likely miss detail...

The Symptoms:

I bought the 2004 GT3 which was used as a track car. I guess I assumed that rich folks who track their cars tend to be a bit careful with their car – or at least maintain them well. This turned out to not be the case for my car – even with owners who could have easily afforded to maintain it. Even though I had been assured that it was a great car by a number of different people, a couple of small details were ‘overlooked’ – this is a nice way of saying that I was dealing with that rare breed – the LSOS – (Lying Sack O’ $hit) or affectionately known as Thieving Ba$tard.

The transmission could NOT be shifted into 1st without a lot of fanfare (of the noisy grinding type). Shifting into 5th was a little less dramatic, but still a problem. When discussing this with my good friend the LSOS (AKA TB), I was told that ‘we racers don’t need no stink’in 1st gear’, which is a reasonable point, but 1st gear and 5th gear still falls into that ‘nice to have category’, and I was expecting one…

Being of the type made famous by Click & Clack – ‘Unencumbered by the thought process’, I decided that if I put some sweat equity into this project I could save a lot of money and learn a lot, with a nice side bonus of being able to justify even more tool purchases…

1st thing is to remove the transmission and might as well remove the motor while I’m there (I love pulling on those little bits of yarn, that magically become loooong bits…), so I call a few friends with the ‘Watcha doing, Wanna have some fun’ tag line, and being like minded AND even more adventurous when it’s someone else’s car, they were glad to help. The motor and transmission were out and separated in fairly short order and there are many description on doing that, so I won’t go into that.

Disassemble
To set expectations, this diatribe is all about the 996 GT3 transmission model G96/96.

There are a number of tools that are essential in disassembling/reassembling the GT3 tranny (and many others):

• The MOST important is a camera. Yep, you will want to take pictures of every angle and every stage. The transmission is nothing more than a bunch 'O gears, but the level of detail is striking – emphasis here!!!

• The Porsche Parts manual - Pet V6 is good, Pet V7 is much better

• The Porsche Workshop manual

• A motor stand with the special Porsche flanged holder thingie – there are time when it is easier working on a bench, but not at first or towards the end

• A magic marker with lots and lots of freezer bags

• All the other tools are detailed in the Workshop Manual. With that in mind, with just a little work, most of these can be made or improvised on – EG a used clutch plate can be used when you need to either turn or prevent the mainshaft from turning…

I will provide the most detail in the reassembly portion; the dis-assembly will be a bit sketchy – after all that is the easy part!

A bit more on specialty tools:
There are time when, without the right tool, your chances of messing up things is even great than when you have the correct tools
The following picture shows some I made, and (1) I borrowed from a Porsche tool junkie friend of mine.

• The long tube is the Porsche special wrench needed to install/remove the nut on the long end of the input shaft.

• The gear with the opposing ends ground down fits over the other end of that shaft to prevent it from turning when you are going the ~200 lb-ft of torque needed to tighten the nut…

• The Long pin with the head is for aligning the shift fork rods – during assembly – more in the write up.

• The tool that looks like a bearing splitter with tabs in the middle is proof that sometimes cheap Harbor Freight tools do have value. I used a simple metal cutting blade in a jig saw to cut out the lip – this is used to hold the LSD in a vice when installing/removing/ torquing the various parts.

• The cut up toothed ring is used to help when putting the little detent ***** back into their proper position in the slider assemble after they all jump out when you make the mistake of accidentally moving ANYTHING… and they will get out..

• I also have more gear pullers/pushers/distorters than anyone should have – some are shown in action…

When you start with:



and end with



You can use:


To get it all back together will probably take a couple of hours the 1st time. This is getting ahead of myself, but (sadly) it may come in handy, so When, not if, when those pesky little check ***** all launch themselves from the guide sleeve, do the following:[/size]

• Get a nail set with the largest depression you can find and make a tool (if you have the bits laying around, by cutting up a ring as shown in the picture.

• Start with the rings and synchros installed on back side so holes are covered behind
  • Hard to see in the picture with everything loose, but the underside of this little setup has everything installed which will prevent the spring/check ***** from pushing out the other side. Install the blocks and springs as shown.
  • Move the check ball off to the side, and set a check ball onto the end of the spring. You will need 2 hands for the following - Using the nail set, push the check ball into the hole on the block - LOTs of tension here, and with your other hand push down on the block. This will serve 2 functions: it will keep the check ball from launching to far AND when the check ball is mostly contained in the block, the block will push into the depression. You have now got the 1st check ball installed.
  • Use the small part of the ring you cut up to cover the now installed check ball and move to the next one.
  • When the 2nd is installed, remove the small section and install the larger cut section over the 2 check *****. Now install the 3rd check ball...
  • Now it gets tricky - MAKE sure that the selector is centered and that there is no inclination one way or the other or the check ***** WILL launch themselves again. Now install the other synchro rings, cone rings, etc and USE tie wraps until the last possible moment.

rbahr

A brief description of how the transmission really works.

Every gear (except for reverse which has 3 gears) has 2 gears. One of the two is fixed by way of splines or in the case of 1st and 2nd actually part of the main shaft. The other free wheels but has what is called a slider alongside of it. The slider will be between 2 freewheeling gears for 2 different gears. The slider will have splines and be fixed to one shaft or another.



This shows one of the freewheeling gears. They all sit on a rollarbearing assemble and a sleeve



The fixed gears will have a spline that fits over a corresponding spline on one of the 2 shafts. Note the pinion shaft and its bearings in the background



The following picture shows a gear along side of a slider and the synchro assembly next to it.



This is a picture of the inside of a guide sleeve. The slider will be moved by a shift fork, but they have these ball & spring & plate arrangements that tend to push the slider in one direction or another once it is off center. The indentations are the neutral position for the ball.



The follow shows the synchro assemble for the 1st & second gear synchro. This one is a brass one. There are 2 sets of these small dog teeth. One on this ring where the synchro sits in the middl of and a second on the actual gear. The slider 1st engages with the synchro portion which speeds up the gear allowing the slider to cover that as well. The synchro is a friction material. It will either speed up or slow down the gear assembly so that when the slider and the dog teeth engage they are traveling at roughly the same speed. This is why double clutching is good for your transmission



The following shows a gear and just the (worn) synchro ring. The synchro ring has (4) tabs that physically engage with the gear The smaller teeth on the gear are called dog teeth. The slider will engage with these and in turn spin the gear. This particular one is damaged from my good friends the previous owners (AKA LSOS). When you hear a grinding sound, it is these teeth that you hear grinding. They should be triangular and have very sharp teeth. The following picture shows how the (in this case worn) synchro transfers rotational energy to the actual gear



Tying it all together:

Here are adjacent gears with the slider in between. In slow motion, as you are going through neutral and starting to shift into gear, the slider engages the 1st set of dog teeth. This transfers rotational motion to the synchro, and through friction starts to speed up or slow down the actual gear, this allows the slider to (hopefully) easily engage with the dog teeth on the gear where now the is a direct connection with the gear.

blake

rbahr - sorry to hear about the transmission mess with your 6GT3, but nice work with the DIY!

Thanks for the detailed posts & pictures! Now get that car on the track and out it through the paces!

-B

lordpantsington

Informative and Entertaining!

rbahr

I will continue posting the teardown and reassembly process, just tend to do some of the writing offline. The car is getting glued backtogether and the details are being cleaned up as I am writing this. In addition to the transmission, I installed a RSR suspension in the car so I expect to find myself spinning MUCH faster than my cohorts . I will need to get that monster aligned. This summer should be interesting...

Ray

cfjan

You didn't catch the transmission issue when inspecting the car?! Too bad that is sort of affecting your friendship. (Not sure if you were joking or not..)

Lucky that you are doing all the work yourself!! Good luck!!

rbahr

The failure to detect this problem is a long and embarrassing story - https://rennlist.com/forums/996-gt2-...and-story.html

Any implication of friendship is entirely sarcastic...

Ray

cfjan

Man, really sorry about that. Yeah, I bought my car from a fellow Rennlister (many years ago). I trust this community. Still did a PPI, though, and some small issues were found and all repaired under CPO. So it was an easy transaction.

We all live and learn, right?! No worry. Once you are done with it, it will be better than new! Might as well use this opportunity to re-gear the box!!

AudiOn19s

Another great thread here. So are you at least treating yourself to some performance advantage while you're in there with everything apart? Re-Gear, different ring and pinion....both?

JohnPG

Awesome work Ray and props for taking this on, though it goes without saying that you'd rather not have had this "opportunity". The bright side is you will know more about these cars than 99.9% of the guys that own them.

Take your time with setting the ring and pinion, the tolerance is critical and tighter than the proverbial .....

rbahr

Here is my 30k boat anchor...





Just your run-of-the-mill ‘don’t need no stinkin 1st gear’ GT3 transmission

• After you get the lift chains off and tranny bolted to the engine stand, drain all the oil.
• Remove the Oil cooler/oil pump assemble – take pictures and label and bag everything. Couple of screws and it just pulls out
• Remove both axle stubs, remove LSD cover plate, Reinstall the stub axle on the cover side to give you something to grab and remove LSD (carefully) and set aside for examination.

Now remove the rear cover - bunch 'O bolts, nothing tricky, couple of taps with a rubber mallet might help.



Sorry for nagging BUT I cannot emphasize how important it is to take pictures from all angles - unless you do this for a living. The successful rebuilding of this thing is completely dependent on one’s attention to detail. In this picture, you see reverse, 5th and 6th gear, along with the reverse slider, and the 5th-6th gear slider.



From this angle, we see the oil sprayer – an update that can be made to the run-of-the mill 996 trannys, the reverse shift fork and the 5th-6th gear shift fork.

Remove the rear cover and you have a couple of big honkin nuts to remove



If you shift the transmission into gear and use the old clutch on the splines of the input shaft to prevent it from turning, it will be easy to remove these.



OK important points I skipped over:

• When using pullers – be careful, esp with the bearings
• When you get to the 2 shift forks, undo the nuts that are holding them on, and loosen them. You will want to remove them as you are removing the sliders carefully as a single assembly. You will leave the rods in place… Go back several pictures - the one with the oil spray bar and you will see the shift forks and nuts
• If you are successful in removing everything without losing springs and detent *****, use tie wraps to keep every thing together
• When you get to this stage, the slider mechanism is a problem waiting to happen

The before shot:


the after shot:


The above is a typical slider: each has a center section, an outer section, and 3 tabs with check *****. These are designed so that when you move the outer slider past an equilibrium point, the spring PUSH the outer ring towards the direct it started in. This is what gives you the ‘snicking’ feeling as the tranny essentially pulls the gear. If you get past this equilibrium point, the springs and ***** will try to escape – this MUST be avoided at all costs, since getting this back together is really really annoying…
Remove all the gears and bearings that are currently exposed, take LOTS of pictures, and be careful! I used wood dowels as holders to keep track of my parts, pinion shaft and input shaft, pinion shaft, gears and bearings…



Now time to remove the intermediate cover. You can see a number of things here – there are 2 groups of 2 nuts – these have springs and check ***** (see below) – they provide feed back when you are moving the forks.

The top hex nut holds yet another detent for the gear selector directly below it.

Remove all of these, bag and label them.



Whit I did not highlite in this picture was there is a spring assembly in between the top two shown in this picture that needs to be removed - looks like this:



and yes - you need to drive an awl or equiv in the cover to pull it out.



this is the part that was replaced when the trannys were jumping out of gear...

And the other 4 look like:

rbahr

At this point we have probably just dropped this on our foot:



After removing the intermediate housing cover we see yet more gears, more shift forks, more sliders, and more oilers. There are several small tricks to removing the housing. The biggest being to rotate the gear selector shaft as you are pulling up.

Now that you have this cover off you will see the following: 1st, 2nd, 3rd, and 4th gears, with the 1-2 selector, and the 3-4 selector



The opposite view - with labels:





From this side you see 5 rods – (2) have shift forks on them, (2) were the shift forks that you removed earlier, (1) is a ‘selector’ rod – the middle one. This selector rod is what does ALL the work.

The (2) shift forks and rods will be removed as a unit with their respective slider, and will bring small parts with them.

At this point, remove the (2) bearings, label and bag them. You will ONLY be removing the gear on the pinion shaft, and all but the top shift fork.

Removing these forks can also be a bit tricky because there is a mechanical interlock arrangement also.

Note in the picture below, that the small pins go through the holes drilled in the rods, and the medium size dowel goes between the shift rods.

This plate and pins and dowels are NOT sold individually by your friendly Porsche dealer – you would need to buy the complete transmission. They, however CAN be bought through Motorsports.





http://www.bethnrayndogs.com/Testing...l_IMG_0203.JPG

From this picture, the thin pins go into the small holes in the 2nd and 3rd rods, the (2) short/wider pins go BETWEEN the 1st – 2nd, and 3rd – 4th rods.

When you have removed all the gears on the pinion shaft, you will want to remove the (7) nuts holding the ‘tensioning plate on the transmission.



Notice that 4th gear is left on the pinion shaft until the pinion shaft is removed.



The pinion shaft has been removed along with 4th gear.

Words of caution: When you get close to this point, you will eventually find some shims – these should not be mixed up. Mixing these up can end up costing you a new transmission. There are a total of 5 shims – referred to as S1, S2, …, S5. They are used to set pinion depth, lash, and also position of differential…

cfjan

Will you be welding the coolant fittings at the same time?! Might be a good time to do so if you also dropped the engine as well!

rbahr

Yep already did that - except that I pinned them...

Ray

rbahr

Hi Andy,

My next installment will go over what I replaced and with what - I chose to not spend the money to go for the good / trick parts. As it was, I spent close to $9K on the transmission for parts, I also replaced the suspension, bought rims, a wing, exhaust, and other stuff. I spent time going over choices with Matt @ Guard and my choices included: $1200 for a new OEM main shaft with 1st and second gears. The MS part would have been close to $4K for the same stuff. All in all would probably have added $5k-$6k in costs for the parts. The R&P was a real option, my concern is that the cup parts seem to wear faster than the OEM parts - this is from talking with a few knowledge transmission people. That had me worried, and there was the pesky budget thing...

John:

Setting the shims was the only thing I farmed out. I have a lot of good measuring tools eg 0.0005" is within reason, just could not get the reference points established. The VW tools (what the repair manual calls for) would have cost $4k (not kidding), and I had thought about using a CMM system up in the NH area that is accurate to a millionth of an inch. With that machine, I could establish a precise (virtual) centerline where the LSD rides, and the accurate measure from that line to the pinion gear. I have a friend that had built in the past, a setup with an old open diff and an embedded dial indicator which would have worked, I would have needed to source a diff, bearing and some other stuff... That was only one of several critical measurements - the shims come in 0.05mm increments - 0.0019" easy to be off by enough to have more bits for your wall of shame, so I just spent the money...

Ray