911, 911 Porsche, 993TT, 997TT, Forced induction, porsche performance, Porsche transmission, Porsche transmission rebuild, turbo Porsche, Uncategorized

A time for change….A 930 transmission gear swap


When one opens up a book and sees this many parts the normal person would run like hell. Many years ago when I opened that book I must have a laspe in sanity because I went, “COOL”! I think I can put that back together. I must be insane, but that probably has been well documented by now.



I will do my best to explain how and what we are doing here. I say in all seriousness do not try rebuilding a tranny unless you have prior experience. There are measurements and work that is not going to be discussed here for times sake.

For those wondering when I have time to do this and where is their 3.8S X51 swap in the Cayman and my 930 EFI conversion I assure you they are being done in the background.

  This steed of a tranny is out of a 79 930 that is one hell of a good looking track car. Tartan interior still in and complete. The goal with this gear change is a to have a radically long first gear with short ratios in-between the later gears. This keeps the car in the rev range and the turbo spooled. As you inter the next gear based on the math done you will be in the meat of the RPM band and therefore in the TQ band as well. This is always an issue with a turbo car since the turbo must spool up and that is always based on load and where it occurs in the RPM band. I am not certain that the pit crew isn’t going to have to push him out of the pits with this tall of a first gear but once going it should be a treat to have 450HP on tap as soon as you come out of a turn. No, I didn’t forget to mention the ratios. Do your own math =)

I realized that I didn’t shoot a picture of reverse gear on the tranny so this is the where it sits over the nose. You will need to remove the nose cover and access this gear and remove it.


Ok, now back to the nose. Throw the reverse gear back on and the nut. Same deal, TQ and punch the head into the shaft. If you are going what the heck is this guys problem, violent with all the punching you have not read the whole article. Lost turn, go back to start!

Once the bearings are off it is time to pull our gears off. Karl offered some excitement. I believe this is the same pose he did for the centerfold of, mmm what magazine was that again? Oh never mind. Once the nose cover is removed you will want to get an impact and take the stationary reverse gear out. In the picture above that is the lower gear(big one) in the pcture. Once this is complete you will need to remover all the 13mm nuts and spring washers from the int cover. This is where our gear sets are.


Next you will need to remove both sets of nose bearings. On the output shaft you will need to impact the nut off of here as well. Same as you did for the pinion shaft. The next thing is to use a pair of gear pullers and pull the nose bearings off as they are keeping the gears and cluster in place. Once this is done you can pull the gears off and the party gets going. Make sure you set the phone to vibrate, you do not want to forget where these things go.


Once the bearings are off it is time to pull our gears off. Karl offered some excitement. I believe this is the sam pose he did for the centerfold of, mmm what magizine was that again. Oh never mind.


Next remove the detents. These are under three 17mm bolts in the diff cover. The purpose of these is to center out the shift rods which in turn center the shift sleeve and keep two things from occurring, one is riding in the syncro and wearing it out to soon and two is to keep some hot rod from grabbing two gears at the same time. Like 2nd and 4th. It has been done. Don’t ask me how I  know.  Under the bolts is a long spring then the detent that pushes on the rod.



Now pull the gears off. Keep in mind that when you pull a gear set apart there is a larger gear and a smaller gear. How the tranny works is these two gears make up your ratio. For example 28:25 means one gear has 28 teeth and the second gear has 25 teeth. gear has the syncro and syncro teeth on it and is locked into the stationary gear when you move the shifter. The shifter pushes the shift sleeve over the gear and locks the center that is in between the two gears (it is stationary to the rod) and the gear together. The syncro simply slows the speed of the gear spinning freely to match the rest of the cluster without grinding. You really need to pay attention during this process. There are lots of little needle bearings, spacers, shims and so on you will loose or forget where thet go. In addtion there are a few gears that have to go a certain way or you are in big trouble down the road.



Once the gears are off you can start putting the new gear set together. You will need to installthe syncro teeth (process not shown) you will need to fit a new syncro and install the syncro stops and clip on the hear gear set. Here is the first gear compared to the OEM setup. The new set is on the left and the old set on the right. Look at the difference!!dsc02119.jpg

So before we start putting things lets talk about why my transmission grinds, pops out of gear or is hard to get in gear. The first line of fire to the gear is the syncro. We have established that its purpose is to slow the gear up to the cluster or better yet match the speed. As the syncro wears it looks like this. This one is in pretty good shape and as they wear chunks will actually come out of it. This causes the shift sleeve to be forced over the syncro as the speeds are not right.


Here is a brand new one.


Here is the second question. I changed my syncros but the car still grinds. Why? Well once past the syncro the shift sleeve has teeth in it as well as the actual gear. The little teeth on the gear are often referred to as “dog teeth” these mate with the sleeve teeth. When the snycro can not slow down these teeth have to take the blunt and mate. The pressure you are putting on the shifter forces them together. The sharp edge of the teeth will wear or even get knocked off as this continues. This is a worn set of dog teeth. Notice how they are blunt and shiny. Yea, these are toast.


And…the new one.


Last question I get is why does my shifter flutter downshifting or pop out of gear. The shift sleeve which combines the two sets together will get worn. It will wear a pattern larger than the syncro. As the shifter sleeve engages the masses it is held into place with the pressure from the syncro and the teeth. If this becomes two worn then the pressure is not great enough to hold the sleeve in place and when you let off the gas the mass shifts from backlash and the sleeve falls off. If you are getting the shaking ion down shift or upshift then this is a sign that the sleeve is badly worn and the popping out of gear is next.


The good one. One thing to notice on this one is this is the 1/2nd sleeve. If you look at one side the teeth are symmetrical and asymmetrical on the other. The asymetrical side mates with 1st gear. The dog teeth also are matched to sleeve. don’t mix these up!


The matching dog teeth.


Now you can start putting your gears on! Keep going you have two more gears.


Don’t foget to put your shift forks in with the shift sleeves or you will be undoing what you just did.


Remeber we talked about the detents keeping these rods in place. This is what they should be centering. But I noticed during the swap that the last person in here didn’t follow the rules. Notice how the sleeve is resting off to one side, well this is bad. Shame on the past wrench. Now we simply need to correct this. A simple measument and adjustment to the fork and we are back to factory spec.


Correctly adjusted.


Now slip second and first gear on there. Make sure that the sleeve is going the right way, remember the teeth. Also look at the first gear. The one that is stationary. Recall I said some things have to go a certain way. This is one of them. Forget this and you will have a pop out issue with first for a whole new reason. Notice the edge on the gear going to the inside? This is to allow the operation sleeve to fit over the mass with full connection and not run into the hear behind it.


Now heat up the bearing to spec and slip it over the shafts. there are two bearings, one for each shaft and cluster.


On a swap like this a mod here and there is not uncommon. In this case we needed to grind away a little of the opening for first gear. Remember the difference in size! Just a little off the edges please!dsc02138.jpg

Nuts please! Go ahead and get them on the shaft and TQ them to spec. Once completed take a punch and punch the edge of the nut into the shaft. This prevents the nut from coming off.


Make sure at some point you get your detents back in and the bolts TQed in. Now slide the gasket and the int cover back on. Also slide your shift fork back into the cover. Make sure you get the arm in the grooves for the shift forks. (yes it is upside down here) If you are one of the chosen ones that jams two gears into place, you can clear the shafts by interting a large tool and moving the shafts back into place. Next time you are speed shifting think gentle! Do it to hard and to much you get to pay someone like me to fix it =)dsc02139.jpg


What the hell is this a tuning fork? Nope, this is the bottom plate you are putting in next. This keeps the shift rod on a pivot point so it is not a floppy fish in the case. dsc02064.jpg

Ok, now back to the nose. Throw the reverse gear back on and the nut. Same deal, TQ and punch the head into the shaft. If you are going what the heck is this guys problem, viloent with all the punching you ahve not read the whole article. Lost turn, go back to start!


Throw the other reverse gear on the shaft in the end cover, a gasket on the end of it and throw it on.


Throw the mount on the bottom, the ground cable and you can all it a day! 


Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out /  Change )

Google+ photo

You are commenting using your Google+ account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )


Connecting to %s