Mk. I to Mk. II trans drilling

[Dakotakid]

Many years ago, in a galaxy far, far away....I parted out a little unsuspecting '83 gas Jetta. One of the "treasures" from it's carcass was a low-mileage "FN" code trans. Yes, this was one of the "FN's" with 0.71 fifth. About that same time, I got out of the Mk. I "business" and never looked back. At that time, I drained this trans and saw that the oil came out very clean, so I felt it was a good trans. I refilled it with a gear oil-diesel combo and it sat in my dry storage for the next almost 7 years. Once a year, I got it out (along with all the other storage trans) and make sure the fluid got distributed throughout. My plans were to use the 5th gear in another trans.

Recently, I refurbished an engine and I had this overpowering urge to employ this trans. However, the housing was NOT drilled to accommodate Mk. II mounting. I had always been told that a person really needed to drill one of these in controlled conditions on a mill  (to ensure proper spacing of the holes). I discussed this with my 82 y.o. friend who promptly exclaimed something concerning male bovine fecal material!


This is a pic of the "before" and clearly shows the (is it?) bosses which need to be drilled.


Over the years, I had always felt there might be a way to use one of the Mk. II mounts as a "jig" for drilling purposes. I showed a spare mount to my older pal and he quietly said, "....that's it." I grabbed a second spare mount and we made our way to his shop. We concluded that a hack saw could be used to produce the appliance we needed for the task.


Here is a photo of the resultant product. The intact mount (at top) shows the sharpie-ized cut line to be made with ye ol' hack saw. It also displays a SAE bolt and nut (you will need two of these to make this drilling happen) which with will be used to stabilize the placement of the "jig." The two bolts will be just the right size to fit through the Mk. II bolt hole mounts. Your appliance is the original mount hemisphere on the right.

Look back at the top pic.: you will need an extended drill bit to produce these holes and I do not remember the size (can get it later).

Your first order of business is to remove the existing bolt which secures the original Mk. I pivot point in the shift linkage. This will ultimately be your middle bolt hole for the Mk. II mount. You then use a bit of lube oil  to keep the drill shank rotating freely and carefully (keep drill as well-oriented as possible) extend the original pivot point hole.

At this same time, you use the long drill bit (or a shorter one the same diameter) to very slightly open up the three threaded holes in the jig. At this time, you will discover that the threads are actually inserts (helicoils is a good term) and you will pull these out with pliers or vise-grips (those crafty and thoughtful Krauts!).

[Dakotakid]

Ok, so far you have: 1) the jig hemisphere you will use 2) you have drilled out the first of the three holes for the Mk. II mount (extended the original Mk. I pivot point) 3) and you have drilled out and removed the threads from the three guide holes (for further drilling and securing of the jig to the trans).

Next step (no photos from this point) is to use one of the extra bolts to secure the jig to the transmission to be drilled. Your "holder bolt" will go through the original pivot hole and the center hole of the jig. You will do your very best job to place the jig in the optimal spot for further drilling. Make sure the holder bolt is good and tight as you don't want that jig to move while drilling. Make sure and use plenty of lube oil to keep the drill shank from seizing and, perhaps, moving the jig out of optimal position.

This is where things get a little dicey. You might want to put down a few "weisers" to keep the tips of your fingers steady!  But, resist the temptation to consume the entire 12-pack though as you need to maintain yer equilibrium!

You will select one of the remaining holes to drill. Make sure you keep the drill true to your intended hole. It takes more effort than you might think to get through the aluminum....so keep your wits about you and keep to the task. Once you feel the drill pass through, breathe a sigh of relief as you are now one step closer to your goal.

Now, insert the other "holder" bolt and nut and tighten down. If all has gone well (and, really, it should) you are now in a position to drill the final hole.

Once, you get all three holes produced you are now in a position to use the intact trans mount (from the pic above) and see how well everything lines up. On the one we did, it was CAKE! However, I suspect there is room for error. One error is the natural tendency for the long drill bit to wonder. To counteract this, start with a good bit, use plenty of oil (cutting) lube, and take your time and NOT grunt too hard on the drill.

This job is NOT for everyone to knock off. In my case, a local machinist would probably "hit me" for at least $100 as the trans will take quite a bit of work to stabilize on a mill prior to drilling. Plus, my machinists seem to always work 8 months "out" on projects (I drop it off and my project is not ready to go for at least 8 months!). Then.....there is paying the bill.

And, in my case, I have plenty of other trans sitting around and my failure would not have been totally disturbing to me. For you, that might be different.

If the holes do not end up being perfectly centered in the bosses, fear not. I have two later-model gas 020's which look like the factory machinist DID INDEED finish his noon 12-pack! The important part is how the holes now allow the original metric bolts to intersect with the mount.

I am sorry I had no more pics of the process. It is fairly straightforward. My holes lined up without a flaw. Take your time and be thoughtful.

Edit: Some of you will not be totally happy with me as I "swiped" the 0.71 and inserted an 0.75 fifth in this. Actually, the swap was taking place as the drilling proceeded (NOT a good idea) and my safety wire on the shift shaft to fifth came off and I later spent almost 2 hours getting the shifters and shaft "replaced." Clearly saw the benefits of my beta blocker THAT day!

The 0.71 is going into one of the gassers. What can I say................

[theman53]

I will need to use this if I ever get to putting the 7A trans in the mkii. It apparently was only offered in 83 and that is MKI

Great writeup