I`ve been running a variant of the 02A gearbox for the last 15 years. The box was released by VW back in 1991. The 02J was basically the same but with bolt in drive flanges and some minor casing changes. The 02S is the 6 speed variation from a Touran that I fitted in early 2018. 1st to 4th is the same but the end casing is larger and contains a 6th gear in addition to 5th.
The gearbox and ratios themselves were fine but after swapping to 17″ wheels I started breaking outer CV joints. The end of the joint would shear off at the weakpoint under high load conditions.
It`s possible to upgrade the driveshafts and CV`s to much stronger ones but that would move the weakpoint to 3rd gear. If a CV joint fails, I can replace it and be back on track in half an hour.
If 3rd gear breaks it’s day over so I ran it with the CV as the ‘fuse’ in the drivetrain.
I was looking into several option, the most common is the 02M gearbox which is a stronger setup was looked at, if combined with the Monster Gearset, that`s pretty much bulletproof but it’s heavy. Quite a lot heavier than the 02S and would need a gearbox, new plate diff, monster gearset and build which made it prohibitively expensive. I had a conversation with Mart at Gas ‘n’ Gears about uprated gearsets and asked if he could bear me in mind if he ever came across a suitable setup.
“Funny you should mention that Nige……”
Under a minute later I had bought a Quaife Gearset 
I stripped my 02S, removed, inspected and rebuilt the Gripper diff with some new clutches to reset the preload. # I`ll be writing a post about that shortly # then sent the Diff to Martin to fit into the new housing along with the gearset.
The ratios are far better spaced for track use too with the rpm drops keeping the engine in the right range each gearchange.
He supplied 3.938 pinion shaft and crownwheel, vapour blasted case, VR style upper pinion bearing support rather than the pressed plate type. All new bearings/rings etc. Powder coated lower support and fork pins. Finishing the whole box in stainless hardware.
Brand new Synchros still with the the moly coating from VW.
This gearset had been sat for many years and there is some light rust staining visible. The gears have never been run and this is purely cosmetic.
Rather than going full dog-box I preferred to stick with the synchro setup instead. Life is just easier that way 
5th and 6th top retaining shafts
Mart has found several issues with the Gripper diffs which is a shame. They built them using the same housing for the 02a press-in drive flanges AND the 02j/s Bolt it. Unfortunately this causes issues. They are wide, the journal for the drive gear too shallow and the body touches the case. It requires some machining to the plastic speedo drive to stop the bearing resting on that instead of the machined shoulder.
A bigger issue is the addition of the hardware for the bolt in drive flanges pushes them outboard and causes leaks from the lip seal as the flange isn’t seating on the seal properly. I’d noticed that on the 02S when I was running the Gripper but didn’t understand why.
The only solution is to take a couple of mm off the splined end of the drive flange so it sits into the casing properly.
Once done it sits perfectly in the case and doesn`t weep.
1st to 4th and Gripper
Once the preloads are all set and the casing boxed up 5th and 6th can be fitted
One 02J casing with full 1 – 6 Quaife gearset and Gripper Diff, stainless hardware and powdercoated externals 
So what’s the point of all this ? Well apart from much nicer on track ratios it’s stronger. A LOT stronger. These side-by side photos clearly show the difference.
Now the gearbox is stronger I can upgrade the CV’s and the failures of the last couple of years should be a thing of the past.
The final thing is the noise. As the gears are far straighter than standard, they whine, but in a good way. ! When testing on the road on part throttle I struggled to hear the engine over the gearbox whine and was concerned it was going to be too loud. On track at Cadwell and when on full throttle it just has a whine that gets higher and higher pitched the faster you go. It’s audible but not so bad that you can’t hear anything else.
I think it sounds ace.
Now the Gearbox is strong enough, it`s time to finally upgrade the driveshafts and CV joints.
Somewhat surprisingly I`ve had a few messages from people asking if they can support me in some way. I`ve set up a buy-me-a-coffee page for those of you who would like to do so, it allows the opportunity of making a small donation towards future Golf development 
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