G31 Transmission Synchronizer Replacement

NOTE: Although there are many in-line pictures here, you can look at all the photos I have of this project, by going to my "photo essay" of the work. I've shown thumbnails in this article to reduce download time. Click on a photo for a larger view, or open the photo essay in a separate window and follow along.

In doing my research before getting started, I discovered some confusing information in the manuals. I have the factory manuals for both the "base model" and the turbo, as well as the Haynes and Chilton's manuals. Comparing procedures, line drawings and photographs I was able to "piece together" an almost-complete picture of what needed to be done and how. But, as with most work that you do for the first time, I discovered some "gotchas". None of the manuals were very detailed in exactly what had to be done, a lot of steps were assumed. Also, the drawings and photos were a mix of transmission models, I had to be careful in interpreting the images and "relating" what was presented to what was actually seen on the car.

Special thanks goes out to the membership of www.924.org, their assistance with this project was helpful and greatly appreciated.

In doing the repairs I replaced the following parts:

Part Name	Porsche Part#	Source of supply	Price
First gear synchronizer band	931.302.301.02	e-Bay, Partwerks of Chicago	$99.00
Second/Third gear synchronizer band	931.302.301.01	EuroWebParts.com	$45.00/ea
Transmission fill plug	111.301.127E	Dealership	$4.00
Gasket, transmission to differential housing	477.301.191.A	Dealership	$3.00
Input drive shaft seal	999.113.247.40	NAPA #NOS9706	$8.00
Output seals [both]	999.113.183.40	EuroWebParts.com # J7041-24000	$7.00/ea
Shift-shaft seal	001.301.227	EuroWebParts.com # J1162-52304	$2.00
Shift-rod coupling bushings	911.424.223.90	PelicanParts.com # C-424-223-90	$16.00/pr
Shift guide rod rear anchor	477.711.176A	EuroWebParts.com # J1079-40253	$39.00

Click here for a list of other supply sources.

Preparations:

This is going to be some messy, slippery work. Have lots of rags and some "quick dry" or clean kitty litter handy to absorb any spills. I also recommend that you have a supply of plastic containers and/or Zip-lock bags to put pieces in so you don't lose or get anything mixed up. They will also help to keep dirt off of things. There are several needle bearing assemblies involved, and you need to ensure you don't loose any parts or get them mixed up. All the bearings need to go back with the same gears, oriented in the same way they came out. I recommend you have a clipboard, paper and pencil handy and make notes of how things looked when you took them apart. I marked the gears and bearings with a magic marker as I took things apart so I could reassemble everything exactly the same way it came apart. The gears and bearings will have markings on them to help you remember their orientation. This is a perfect project to use a digital camera on, it is a shame I didn't have a quality camera to document the work.

To perform these repairs you'll need:

• 8mm, 17mm hex head (Allen type) sockets
• 13mm,16mm, 18mm, standard sockets
• 22mm, 36mm deep-well sockets
• some extensions
• ratchet handle
• 13mm combination wrench
• some decent flat-headed punches
• wood block
• hammer
• gear puller
• retaining ring pliers
• tweezers
• anaerobic gasket sealant like Loctite 573.

• Put the transmission on a suitable engine or transmission stand of some sort. I don't have either, so I improvised by using a Black & Decker WorkMate. By spreading the tabletop the transmission was cradled in the gap pretty nicely. At other times I stood it up on its tail end and that worked a little better. I had to move it around and shift it to access various parts, so the table wasn't the ideal surface, but it is what I have. The transmission is heavy (approx 100lbs) and un-wieldy so be careful not to drop it.
  
  
• Drain the unit by unscrewing the 17mm hex drain plug on the bottom of the differential housing. As you separate the cases additional oil will drain out, so it is a good idea to leave a catch basin of some sort under it even after you drain it through the main drain hole.
  
  
• Remove the coupling that mated the transmission to the car's drive shaft by rotating the input shaft until the remaining 8mm hex (Allen type) bolt is accessible through the cut-out in the front housing and taking the bolt all the way out. There is a groove in the input shaft that the bolt goes in, and unless the bolt is completely removed, the coupling cannot slide off the shaft. Make a note of how far back on the shaft this coupling is, so on reassembly you can duplicate its position.
  
  
• Remove the 13mm bolts holding the front casing to the central section of the assembly. After all the bolts are off, make sure you are ready to catch some oil that is going to come out when you separate the sections.
  
  
• Using a small block of wood and hammer, gently tap on the edges of the backside of the front section to break the seal between the front and center sections of the assembly.
  
  
• There is a thrust washer on the end of the shaft holding the double gear, and it may fall off its shaft as you separate the sections. If you hear something fall inside the case, that is what it is, and as you pull the sections apart, don't lose the washer.
  
  
• Pull the front casing off of the shafts. If the thrust washer did not fall off the double gear shaft, take it off now so it doesn't fall off unexpectedly. Put the washer in a bag or container.
  
  
• Put a rag in the four oil passageways so parts or junk can't fall down inside the transmission (This is Gotcha #1).There are three shift shafts that are controlled by the main shift shaft that protrudes out of the transmission case (and attaches to the shift rod running to the gear selector): Reverse and 1st go to the fork in this outer section. The notch where the selector "tang" goes has a spring-loaded "lockout". First is engaged by pushing the selector tang into the lockout then pushing the shift shaft into the case. There is a center "neutral" position, and reverse is engaged by pulling the shift shaft out.
  • (Gotcha #2) The shift shaft, shift fork and shift sleeve can come off (beyond reverse) if pulled too hard ... don't pull it off yet.
  The center shift shaft engages 2^nd and 3^rd gears and the outermost engages 4^th and 5^th. The lower number gear is engaged by pulling the shaft out, the higher gear by pushing it in. All the shafts will "stop" in-gear or in the neutral position because of a spring-loaded detent.
  
  
• Engage 1^st and 5^th gears: Push the outer shift shaft all the way in (5^th). Grasp the shift fork for the 1^st/reverse gear and push it in to engage the sleeve on the large first gear. This should lock up the transmission so neither the input shaft or pinion will rotate.
  
  
• With one of your punches or a very small chisel, gently "un-punch" the lock tab of the collar nut on the pinion shaft.
  
  
• Remove the pinion shaft collar nut with a 36mm deep-well socket.
  
  
• Remove the 17mm bolt on the side of the transmission housing that retains a detent and spring that engages with the 1st gear shift fork shaft. (It is below the backup light switch as shown in the second photo up above). Remove the spring and detent, and put them in a container or bag. There will be another of these, so remember which spring & detent goes where.
  • (Gotcha #3) If you don't remove the detent and spring, you risk having them fall back into the depths of the transmission on re-assembly.
  Put the cap bolt back in the hole to keep dirt out and so it isn't misplaced.
  
  
• Unscrew the backup light switch (22mm) and with tweezers extract the pin at the bottom of the hole.
  • (Gotcha #4) This pin will block the shift shaft hole on reassembly if it isn't removed.
  
  
• Gently but firmly pull forward on the 1st gear selector fork/shaft and shift sleeve until it comes completely out. What you will be doing is moving the selector sleeve out, off of 1st gear at the same time as you pull out the fork and shaft. There is no need to drive out the roll pins connecting the fork to the shaft.
  
  
• Pull off the sleeve if the fork disengaged before it slid completely off the guide.
  
  
• Pull off the sleeve guide.
  
  
• Remove the shift selector (that shaft with a foot on it that engages either of the three shift shafts).
  
  
• Gently pull the entire first gear assembly off the pinion. The synchronizer parts are kept in place by a retaining ring/clip, so don't worry about losing them
  
  
• Be careful to keep everything together. There is a thrust washer, and the gear itself along with the internal synchronizer parts. Between the gear and the shaft there is a sleeve and a set of caged needle bearings. Make a note of how these parts fit in relation to one another and put them in a container or bag.
  
  
• Remove the double gear idler gear. Be careful to keep the parts in order as they slide off the shaft. You removed the outer thrust washer earlier, now take off the gear, a washer-type needle bearing and another washer. Between the gear and the shaft are a caged needle bearing, a spacer and another caged needle bearing set. Don't lose any of the needle bearings and keep everything straight so they can be replaced in the same order with the same orientation.
  
  
• Pull out the 2^nd-3^rd shift shaft until 2^nd gear is engaged
  
  
• Drive out the roll pins that hold the 2^nd-3^rd selector yolk to the shaft and remove the yolk.

• Unbolt the 13mm nuts and one bolt holding the center section to the differential housing.
  
  
• Position a drip pan to catch the oil that will drip out when you separate the two sections.
  
  
• Using a small block of wood and hammer, gently tap on the edges of the backside of the center section to break the seal between the center section and the differential housing. There is a paper gasket between the sections, and depending on what kind of sealant was used on the gasket, it may be difficult to separate.
  
  
• Pull off the center section case.
  
  
• (Gotcha #5) Put a rag in the oil passageways so stuff can't fall down inside the differential.
  
  
• I was never able to remove the fill plug in this center section, so at this point I drilled out the plug and replaced it.
  
  
• Drive out the roll pins holding the 2^nd & 3^rd gear selector fork on its shaft. Pull out the shaft then remove the fork. To replace the 2^nd & 3^rd gear synchronizers, you have to remove the pressed-on outermost bearing. The bearing is the only part pressed on that has to be removed in order to replace the 2^nd/3^rd gear synchronizers. The factory manual says to remove the entire pinion assembly at this point and press everything off. I don't have a hydraulic press, and I didn't want to remove the entire pinion and/or main shaft from the housing because of alignment issues during reassembly. So, I used a gear puller.
  
  
• Push the 2^nd & 3^rd gear selector sleeve rearward onto 3^rd gear.
  
  
• Measure the space between the second gear and the thrust washer between it and the outer bearing. Get a "go/no-go" measurement: mine was 0.012" / 0.013"
  
  
• Measure the distance between the outside of the outer bearing, and some identifiable part of the pinion shaft. On reassembly you need to try and match these values.
  
  
• Assemble an appropriately size gear puller, and have it grab under 2^nd gear, between the gear and the shift sleeve. Grip the gear itself, not the row of "dog teeth". I placed some thin brass shims on the gear-puller jaws to ensure that the puller didn't damage the gear. The 2^nd gear is free spinning, but what you want to do is to pull on it to remove the outer bearing. The washer between the two will evenly distribute the force and remove it.
  • Gotcha #6 Only pull the gear up far enough so you can grab under the washer. Pulling the gear too far will cause the gear to damage the Mainshaft End-bearing.
  
  
• Reposition the gear puller under the washer and finish pulling off the bearing.
  
   
  
  
• Push the selector sleeve onto 3^rd gear.
  
   
  
  
  
   
• Remove the 2^nd gear, taking care to not lose any of the synchronizer parts. They are not held in place by anything.There is a synchronizer band, a thrust block, a stop and a locking band. I found it easiest to first extract the needle bearing and sleeve, then remove the gear because the gear will hit the mainshaft bearing if you try and remove it with the bearing and sleeve in place. On re-assembly, positioning the gear first and then inserting the bearing & sleeve is the way to go.
  
  
• Make a note of how the caged needle bearing and second gear fit, and put all the parts you are removing into a container or bag so you don't lose those needle bearings, and you keep the right bearings with the right gears, oriented in the right direction.
  
   
  
   
  
  
• Move the selector sleeve off of 3^rd gear and remove it.
  
   
  
  
  
  
• Remove 3^rd gear and the parts that come with it. Again, the synchronizer parts can fall off, and watch out for those needle bearings, don't lose them and keep them along with the gear in a separate container or bag so you don't mix them up with the others.

If the 4^th or 5^th gears, or the last bearing on the pinion need replacing, they may need to be pressed off instead of using a gear puller because of the long reach. Also, removing the clamp plate to separate the pinion from the differential housing will cause the current alignment of the pinion and ring gear to change when you reassemble things. To properly align everything, several measurements using a backlash and run-out dial will be needed. If you don't have them or the expertise to use them, I would not recommend doing this work yourself.

Synchronizer band replacement:

• Assembling 2^nd and 3^rd gears' synchronizer assemblies is a piece of cake, and are the same. The "stop" goes into the notch cut into the locking band. The thrust block goes into the open space in the locking band. The synchronizer band fits inside the row of "dog teeth", with its open section surrounding the thrust block. The synchronizer and locking bands are like concentric "C's" with the thrust block in the opening. Coat everything with oil and put it together in the proper order
  
   
  
  
• The 1st gear assembly is held in place by a wide retaining ring. This ring is very strong and is difficult to remove, and harder to replace. I recommend covering your sturdy worktable with heavy cloth or several layers of newspaper, and (Gotcha #7) wearing gloves to help prevent hurting your hands if something slips. Remove the retaining ring with a pair of retaining ring pliers by opening the ring far enough to get it out of the groove it locks in.
  
  
• Once the ring is off, assembling it is similar to the 2^nd/3^rd gear assemblies. The only difference is (this is important!!) that, if the stop block is at 6:00, the opening on the lock ring is at, like, 1:00 or 2:00 in relation to the stop, whereas on the 2^nd/3^rd gear assemblies, the opening is directly opposite the stop.
  
  
• To get the retaining ring back on is difficult. To spread the ring far enough and to get it to "catch" under the locking lip on the gear takes some hand strength and persistence. I ended up clamping the assembled gear to the table with a wooden Jorgenson clamp to keep the ring from "buckling" when it was opened far enough to go over the lip. Once I got it started (while still clamped down) I drove it the rest of the way around with a small brass drift. The synchronizing ring will want to come un-seated as you man-handle the thing, and if unseated, the retaining ring can't engage the lip. Once you see it, this description will make more sense.
  
  
• Once the retaining band/clip is back on, make double sure it has engaged the inset ring above the synchro ring, and then rotate the retaining ring so it's split is not over the stop or thrust block. Mine was assembled so the retaining ring opening was like at 4:00 or 5:00.

• I strongly recommend replacing the shift shaft coupling bushings, the shift guide rod anchor and output seals on the differential casing while the transmission is out, and to also replace the drive shaft input seal and main shift shaft seal. All together the seals only cost about $25 and it's good insurance. The bushings and rod anchor run about $45-$50. You sure don't want to pull the transmission again just to replace any one of these items.
  
  
• I reversed the 2^nd/3^rd gear selector sleeve when putting things back together. The 2^nd gear side (top two photos at right) had more rounded splines than the 3^rd gear side (bottom two photos at right). Since I was having noticeable grinding in 2^nd, I think that maybe reversing the sleeve will help out. This was a gamble, I don't know if it will pay off or not.
  
   
  
  
• When putting the2^nd gear back on the pinion shaft, put the gear in place first, engage it's teeth on the mainshaft, then drop in the needle bearing and sleeve, otherwise the gear will hit the roller bearing on the end of the mainshaft.
  
  
• You will have to tap the pinion shaft end bearing back onto the pinion if you removed it using a gear puller like I did. Do this gently and equally all the way around the bearing to prevent it from galling, and be sure and drive the collar of the bearing, not the cage holding the roller bearings. I took a wooden Jorgenson clamp and stood it on end and used it like a double- footed punch to re-seat the bearing. Duplicate the spacing between the bearing and the thrust washer like it was when you pulled off the bearing.
  
  
• Don't put the detents or their springs back in place until everything is assembled. I say this because the detents make it difficult to manipulate the shifting motions you will have to do when putting things back together. If the detents are in place and you accidentally pull one of the shafts out, you can lose the detent inside the transmission or differential (Gotcha #3) and you will have to open it back up to retrieve it (or at best, turn the thing up-side-down and hope the detent comes out one of the oil passages). This happened to me, and it wasn't fun.
  
  
• When reassembling the 2^nd/3^rd gear shift fork and shaft, remember to engage the fork in the shift sleeve, and then push the shaft through the fork. You'll have trouble reassembling things if you put the fork on the shaft first, and then try and put the shaft in place. Brace the fork and shaft as you drive the roll pins back into place so you don't strain the shaft or its mounting holes as you hammer the pins back in place. An alternative method to re-seat the roll pins is to use a "C clamp" and press them back in place.
  
  
• Clean the flanges and replace the gasket between the differential housing and the center section. Dress the gasket properly and seal it with an anaerobic flange sealant like Loctite 573.
  
  
• Also brace the yolk on the 2^nd/3^rd shift selector yolk as you drive the roll pins back into place so you don't strain the shaft or its mounting holes as you hammer the pins back in place. An alternative method to re-seat the roll pins is to use a "C clamp" and press them back in place.
  
  
• There is another detent that goes sideways between the shaft holes for the 1st/reverse and 2^nd/3^rd selector shafts. This detent can block either of the holes, and you have to make sure it is in between the holes on reassembly (Gotcha #8) or you can't get the shafts in all the way.
  
  
• Make sure to remove the backup switch activation pin before reinstalling the 1st gear selector fork shaft (Gotcha #4).
  
  
• Just like the 2^nd/3^rd gear detent, make sure you don't put the 1st/reverse detent in place until everything is reassembled. The fork & shaft are not anchored, and if pulled out too far, the detent can fall back inside the central housing (Gotcha #3).
  
  
• Clean the flanges and seal the front transmission housing with an anaerobic flange sealant like Loctite 573.
  
  

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