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How to build an Audi-style shift linkage for a G31 gearbox

 
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ideola  



Joined: 01 Oct 2004
Posts: 15462
Location: Woodstock IL

PostPosted: Thu Jul 23, 2009 6:23 am    Post subject: How to build an Audi-style shift linkage for a G31 gearbox Reply with quote

Tools required:
  • Drill
  • Sawzall, hacksaw, or bandsaw
  • Punch
  • Metric taps & drill bits (6mm and 8mm taps with requisite drills)
  • Wrenches & Sockets: 17mm, 13mm, 19mm, 10mm allen head, 3mm allen head
  • Bench vise
  • Lathe (if possible)
  • Bench grinder
Parts needed:
  • Audi torque tube (for comparison purposes only)
  • G31 torque tube
  • Audi shift rod
  • Audi shift lever
  • Audi shift saddle
  • Audi ball socket
  • (1) M10x55 hex head bolt
  • (2) A10 flat washers
  • (1) A10 spring washer
  • (1) M10 nut
  • (1) M10 lock nut
  • (2) M8x20 hex head bolts
  • (2) A8 spring washers
  • (1) conical screw (PET #901.424.229.00)
  • ~5" section of .625" diameter steel rod
  • (1) low-speed pin-and-block u-joint, 5/8" bore diameter, 7/8" bore depth, (McMaster Part #6445K5) : $14.56
  • (5) metric alloy steel cone point socket set screws, M6x12x1.0, McMaster Part #91210A320 : $9.85 per 25 pack


Modifying the shift lever
  • The first step is to modify the Audi-based shift lever.
  • Grind off the weld that holds the pin on the stock lever, and punch the pin out.
  • Using a punch, mark the location for the new pin at about 3/4" or 20mm below the original pin location.
  • Drill a pilot hole first, then enlarge the hole using a 3/8" drill bit.
  • Use a round file to open up this hole just large enough to fit the shoulder of the M10x55 bolt.


Transfer Audi shift lever to G31 Torque Tube
  • The next step is to drill the G31 torque tube to attach the Audi-style shift lever, saddle, and ball socket assembly.
  • I don't have the exact measurements at the moment, but what I did was to lay an Audi torque tube and a G31 torque tube side by side, making sure that the FRONT flanges were flush with each other. I then used a ruler to transcribe where the punch mark for the two bolt holes needed to be drilled on the G31 torque tube.
  • Apparently, there is either a bearing carrier or the infamous snailshell vibration damper in about the exact position of the front most hole, because my drill bit definitely hit something there. No interference on the rearward hole.
  • Once these holes are drilled, tap them with an M8 x 1.0 thread pitch tap.
  • Transfer the two M8x20 bolts and accompanying spring washers, the saddle, ball socket, and your modified shift lever over to the G31 torque tube.
  • Finger tighten the bolts on the saddle for now.
  • Finish by attaching the torque tube to the G31 gearbox on the bench (floor).


Modifying the Shift Rod
  • Now we can turn our attention to the shift rod. Put your Audi shift rod in a vice, and using a Sawzall or hack saw, cut it off just before where the tube is flattened out, as depicted by the blue text in this photo (showing a side view of an unmodified audi rod on top, and a modified version on bottom):

  • Once you've shortened the Audi rod, there are a couple of minor bends that will need to be made.
  • About 5-6" before the cut you just made, bend the end of the rod DOWN by about 5.
  • On the other end of the rod, where it attaches to the shift lever, you want to make that bend a tad shallower, by maybe 3 or so.
  • See above side view picture for approximate locations of these "vertical" bends.
  • A tube bender would be ideal for this, but I just put it in the vise and used my jack handle as an extension for extra leverage. The bends aren't huge and don't need to be terribly precise.
  • There is also a slight "horizontal" bend that needs to be made at the end of your newly shortened rod. At about the same point that you made the downward 5 bend, you also need to bend the rod toward the LHS of the car, again about 5, as depicted in this photo (showing a top view of an unmodified audi rod on top, and a modified version on bottom):


Making the Solid Connecting Rod
  • The hardest part for the home hobbyist will be tweaking the 5" piece of steel rod that will attach the modified Audi shift rod to the pin-and-block universal joint. We will call this piece the solid connecting rod.
  • The metal stock I purchased was supposed to be 5/8" (.625") but was actually about .670" when I measured it with my calipers. The inner diameter of the Audi shift rod at the point where you cut it should be about 14mm, or ~.551".
  • This means that you need to turn down at least .07" of material, plus or minus, depending on the exact diameter of the stock you are working with. Since I don't have a lathe, and this was just a proof of concept, I used a grinding wheel. Crude but effective (eventually).
  • You will want to turn down the diameter for about 3" or so of the length of your 5" piece.
  • When that is done, if you started with truly .625" stock, the other end should slide directly into the u-joint. In my case, I had to turn that end down too.


Drilling the Solid Connecting Rod & U-Joint
  • When you finish adjusting the diameter of the ends of your new solid connecting rod, you will now want drill it for the set screws.
  • The wall thickness of the hollow shifter rod is not very thick.
  • Drill and tap two holes in the hollow shift rod for M6x1.0 thread pitch.
  • Insert the solid connecting rod.
  • Screw in two of the set screws. This will perfectly scribe where to drill the continuation holes in the solid rod.
  • Remove the solid conneting rod.
  • Drill the two holes.
  • Reinsert the connecting rod into the hollow shift rod, line up the holes, and then tap the solid connecting rod for the same M6x1.0 thread pitch. This will make sure your set screws can be screwed directly into the connecting rod.
  • Next, drill and tap two M6x1.0 thread pitch holes at 90 angles in the u-joint.
  • They should be positioned about 1/2" back from the edge of the u-joint because we will later need to trim some material off of this end.
  • One hole should be "on top" and the other hole should be 90 down on the LHS side, i.e. the same side that the stock shift linkage screw attaches on a stock setup.
  • As before, insert the other end of the solid connecting rod into the u-joint.
  • Torque down two of the set screws to scribe the rod, and then drill and tap for M6x1.0 as described above.
  • In this case, I drilled the horizontal hole all the way through, and the vertical hole until it intersected the horizontal.
  • When you're done, your solid connecting rod should look something like this:


Attachment of U-Joint to Gearbox Input Selector Shaft
  • Now let's setup the other end of the u-joint for attaching to the gearbox input selector shaft.
  • On my snailshell, the input selector shaft was pre-drilled with a detent designed to accept the "conical screw" (PET #901.424.229.00).
  • This bolt has a 13mm head, with M8 threads, and is about 15mm long.
  • The one on my car was already pre-drilled for safety wire. This is a Good Thing.
  • The detent on the input selector shaft is about 90 of vertical, i.e., the screw is designed to go in horizontally, with the head facing toward the LHS of the car.
  • Drill and tap an M8 hole in the other end of the u-joint...this hole will be on the same side as the horizontal hole described above for the solid connecting rod.
  • Now, because the input selector shaft is only about 14mm in diameter, but our u-joint has an I.D. of about 15.8mm, there will be a tiny bit of slop here, even with the conical screw torqued all the way down.
  • To combat this, I also drilled and tapped an M6 hole on top of the u-joint, and inserted one of my allen head set screws there as well.
  • Once both are torqued down, everything is solid. When you're done drilling and tapping, your u-joint should look something like this:


Clearancing the U-Joint
  • However, we're not quite done yet. This particular u-joint is a little long, and when the G31 input selector shaft is in the foward-most positions (Rev-2nd-4th), the barrel of the u-joint can intefere with the flange (where the torque tube mounts to the gearbox) as well as a cast-in taper on the gear box itself.
  • You will need to shorten the barrel of the u-joint that attaches to the solid connecting rod by about 3-4mm.
  • You will also need to grind a taper onto the bottom portion of the barrel to provide clearance for the u-joint above the aforementioned taper on the gearbox housing.
  • When you're done, your modified u-joint should look something like this:

  • Here is a shot showing the clearance issue described above when in 4th gear (note the front-to-back clearance at the flange, and the top-to-bottom clearance beneath the u-joint barrel at the taper on the gearbox housing):


Final Assembly
  • Now you can assemble everything.
  • Insert the solid connecting rod into the hollow shift rod.
  • Torque down the two allen head set screws in the shift rod.
  • Insert the other end of the solid connecting rod into the shortened and beveled end of the u-joint.
  • Torque down the two allen head set screws there.
  • Attach the u-joint to the gearbox input selector shaft, and torque down the stock conical screw and the upper set screw.
  • Your shift lever should already be attached to the torque tube from before.
  • Insert the M10x55 bolt through the lower hole you drilled in the shift lever.
  • Add a flat washer.
  • Slide the shift rod over the bolt.
  • Add another flat washer.
  • Add the spring washer.
  • Hand tighten the M10 nut against the spring washer.
  • Screw on the locking nut and tighten lock it firmly against the other nut.
  • Slide the saddle on the torque tube forward or backward so that the shift lever sits at approximately the 85 angle depicted in the FSM, and torque it down:

  • Done! (Well, except for putting it in the car...but that's a different tutorial).



Should look something like this when finished:





Neutral:


Reverse:


1st Gear:


2nd:


3rd:


4th:


5th:

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15 981 GTS | 88 924S SE | 82 931 Holbert | 82 931 Rallye | 81 937 | 81 Euro 931 | 81 Weissach | 80 US 928 | 80 US 931 '941' | 80 US 931 | 80 931 GTR | 79 Sebring | 78 D-Prod Replica | 78 w/D-Prod kit | 78 Poli-Form | 78 Limited Edition | 77 Martini


Last edited by ideola on Wed Feb 08, 2012 9:37 am; edited 1 time in total
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Slam  



Joined: 07 Jan 2005
Posts: 1690
Location: Wainwright, Alberta, Canada

PostPosted: Thu Jul 23, 2009 7:25 am    Post subject: Reply with quote

Very nice work and good write-up. I do have a question, though. With all those set screws, how do you plan to prevent them backing out and/or freezing in due to age and contamination? I'd think blue Loctite would do the trick. Anything stronger and you'd risk stripping out the heads. The Audi conical bolt is wired in (as you know).
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ideola  



Joined: 01 Oct 2004
Posts: 15462
Location: Woodstock IL

PostPosted: Thu Jul 23, 2009 8:05 am    Post subject: Reply with quote

I thought about using pins, but was worried about them backing out too. Ultimately, if this works the way I think it will, and if I like the feel of it, I'll just have the solid connecting rod welded to the shift rod. In some respects, this is still at a proof-of-concept stage of development.

As for the u-joint, I've gone back and forth between just welding it on to the solid rod as well, or keeping it easily serviceable with the set screw method of attachment. The other obvious improvement I've considered is replacing the allen head set screws with conical screws like the stock one and safety wiring them together. The allen heads were cheap, which is what I wanted for the POC. Ultimately, I'm not sure I like this particular u-joint. There are other,better options, but they are orders of magnitude more expensive, and I didn't want to spend that much on the POC, in case it didn't work.
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15 981 GTS | 88 924S SE | 82 931 Holbert | 82 931 Rallye | 81 937 | 81 Euro 931 | 81 Weissach | 80 US 928 | 80 US 931 '941' | 80 US 931 | 80 931 GTR | 79 Sebring | 78 D-Prod Replica | 78 w/D-Prod kit | 78 Poli-Form | 78 Limited Edition | 77 Martini
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Rocco R16V  



Joined: 03 May 2009
Posts: 498
Location: PNW

PostPosted: Thu Jul 23, 2009 8:08 am    Post subject: Reply with quote

Thank You!!!!!!
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morghen  



Joined: 21 Jan 2005
Posts: 7674
Location: Romania

PostPosted: Fri Aug 21, 2009 4:33 pm    Post subject: Reply with quote

will it not knock against the gearbox housing? IMO it seems very close...and because of vibration it will probably knock against the gearbox..
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ideola  



Joined: 01 Oct 2004
Posts: 15462
Location: Woodstock IL

PostPosted: Fri Aug 21, 2009 6:19 pm    Post subject: Reply with quote

It might, but the closest place would be at the flange where I illustrated the clearance issues. Won't know until the car is running...
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15 981 GTS | 88 924S SE | 82 931 Holbert | 82 931 Rallye | 81 937 | 81 Euro 931 | 81 Weissach | 80 US 928 | 80 US 931 '941' | 80 US 931 | 80 931 GTR | 79 Sebring | 78 D-Prod Replica | 78 w/D-Prod kit | 78 Poli-Form | 78 Limited Edition | 77 Martini
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morghen  



Joined: 21 Jan 2005
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Location: Romania

PostPosted: Fri Aug 21, 2009 6:45 pm    Post subject: Reply with quote

i would stick some thick FELT PAD on the possible contact area...just to be sure...i'm sure you'll need to keep your ears open for other sounds in that car at the begining...one knock less would be helpfull.
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931Owner  



Joined: 15 Feb 2009
Posts: 352
Location: Chicago NW Suburbs

PostPosted: Thu Dec 02, 2010 1:38 pm    Post subject: Reply with quote

How's the modification holding out?
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leadfoot  



Joined: 11 Dec 2002
Posts: 2222
Location: gOLD cOAST Australia

PostPosted: Wed Mar 21, 2012 6:52 am    Post subject: Reply with quote

Hey Dan,
excellent writeup,
If leaving the pin on the shift lever in the same spot does this interfere with the back of the tunnel opening near the shifter?

Someway through this conversion now,
the audi shift rod is hollow and measures a smidge under 15mm ID and 20mm OD

found a hardened steel u joint for $16 that utilises a partial ball joint and pin arrangement, come from "Genius" brand impact drive range
it measures approx 68mm but cutting off the squared 1/2" dive end will allow a round flush fitting at 20mm and reduce the overall length to 53mm.
the larger end has a 1/2" female drive end but enough meat to drill out to 15mm and fit over the trans input. It also has a 5.5mm hole in the side so this should be able to be tapped, haven't measured the locating pin diameter as of yet. the depth of the drive is 20mm.

cheers
Stu
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leadfoot  



Joined: 11 Dec 2002
Posts: 2222
Location: gOLD cOAST Australia

PostPosted: Mon Jun 11, 2012 10:26 pm    Post subject: Reply with quote

below is the setup I made, I left the shift rod intact without lowering the pin height, this seems to work well with the shift gate about 150-200mm front to back...
as for the details, the u joint was cut at the front 1/2" drive, as a note this could have been flush with the end of the round section, you can see the small 5mm gap between the bolt head and the u joint.
I wasn't really happy with the sleeve I inserted into the trans end of the u joint, it has a 1/2" female end so you need to drill it out to around 20mm, my machining skills weren't the best on this job so I ended up cutting off the end and welding on the original shift rod end for a good fit.
Also the only bend I made was the angle a few inches in front of the ball coupler.
The shift rod is hollow so I welded a M10 nut onto the end of the cut and used a M10 100mm bolt with a shank of 50mm, this fits right inside the hollow rod with around 50mm of adjustment, the bolt also had a normal thread so if preferred you could pick something with a fine thread. I then used a jam nut to secure the adjustment.
Stu

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