519 Gearbox Rebuild

[58A - 71E]

Then first speed gear



Then a thrust washer and the synchro spider with notch toward first gear. Now in the 356 registry book Vic Skirmants says to fit this the other way round, as per the photo, but I went back and re did it as per the workshop manual and Elfrink book, time will tell which way is best! i.e. NOT as shown here – I had to go back and reassemble this the other way round; then another thrust washer, the roller bearing inner race and cage with rollers



Then first to second gear shift sleeve



Then second gear with the synchro facing the shift sleeve



Then another thrust washer, inner race and needle cage

[58A - 71E]

Then third gear



Then another thrust washer and synchro spider with the mark towards fourth gear. Then another washer



Then the inner race for fourth gear (this is the only stubborn one)



Then the needle roller cage



Then fourth gear and the one thin washer



The synchro sleeve is not fitted yet. This is done after the adjustment of pinion / crown so that a gear puller can easily fit behind fourth gear, otherwise it means dismantling the whole lot!

[58A - 71E]

Then a special spacer sleeve is put onto the assembly and the nut tourqued up to 115lb ft to push everything together. Now I don’t have this special sleeve – so a bit of old scaffold came in nicely



This can then be removed and the double row ball bearing fitted, again another (shorter this time) spacer sleeve is then fitted and the nut tightened to 58lb ft. So another bit of old scaffold came to the rescue



Reverse gear is not assembled yet as this goes in front of the intermediate plate.

Then it was time to check the axial play on the pinion gears. This is done with a feeler gauge, 1st gear 0.20 – 0.30mm, 2nd – 4th gears 0.15-0.25mm. In my case they were all ok although second was very tight.

[58A - 71E]

Here you can see the pinion up to this point laid in the case half with the intermediate plate over to show the relative positions of everything. Reverse is only installed once all the adjustments have been made.





So here’s all the old synchros and bearings



I did not take the crown / half shaft assembly apart. There is a lot written about cracked diff carriers and sure enough there appears to be the tell tale signs of a microcrack in mine. TBH it looks like its been there forever, and has been quite happy up to press, therefore I wasn’t about to start taking it apart. Philosophy of if it aint broken don’t fix it!!

Now comes the fun parts!

[58A - 71E]

The manual requires not just an accurate determination of the R value to be obtained, it also requires the diff bearings to have a preload on them.

Now here is the first problem

How the hell do you accurately do this?

Well first thing is to determine some of the measurements shown on the diagram



This was not easy, especially when you’re faffing like this



I also placed a flat bar across the case half and measured down from the centre point to determine the depth of both case halves and the total depth of housing

I must have done this 20 times! But in the end I am fairly sure I measured length of diff carrier 138mm, total depth of housing 145mm.

The difference is made up by using spacer rings and shims. Here are the spacer rings, they are bevelled and only fit in one way, with the bevel towards the diff carrier.

[58A - 71E]

Now the manual says that there should be a 0.2mm difference between the left and right side spacers, for some reason on mine I measured them to be 3.2mm and 3.8mm i.e. 0.6mm difference. I really don’t know why this was the case, I can only assume it was done to help get the correct backlash or something like that. The right diff was 3.8mm with a 0.25mm shim, the left was 3.2mm with a 0.25mm shim. Therefore the total length would be 138 + 3.2 + 0.25 + 3.8 + 0.25 = 145.5mm.

Here’s what the diff looks like in place with the spacers and shims



And then with the right case half put on



Its worth noting that the half shafts have different colour bands placed on them, mine were green, which relate to different sizing groups, there are also pink and blue versions as well

[58A - 71E]

Now the problem is the bearings are supposed to have a preload on them of between 0.13 and 0.17mm but I wasn’t sure how I would be able to measure this. Furthermore, how the hell was I going to be able to measure the R value with the case half on without the special tool shown here?





The answer is speak to a man with far more knowledge than I have – DDK member John Fletcher.
John is currently restoring his 3rd 356 and has rebuilt GBs before and had this very clever “gauge” made. I really must take this opportunity to thank John for his time to help me out with numerous phone calls, emails and allowing me to borrow his gauge.





The measurements for this are critical – the outermost diameter of the gauge is equal to the internal diameter of the diff bearings – i.e. 50mm, the centre section is 138mm (same as mine thankfully) the total length is 255mm but this doesn’t really matter, its just to make it manageable putting in and out of the cases



And the centre “crown” ring is twice the R value. In my case that would be 118.08 – John’s gauge is 118.98 i.e. 0.90mm bigger (half of this is 0.45mm R value bigger)



I would just have to compensate for this in my measurements

[58A - 71E]

Here is the gauge in the case instead of the diff



With a few through bolts just holding the case halves level without any torque on them you can then measure along the joining surfaces to ensure that the desired amount of preload is present i.e. 0.13 to 0.17mm





Thankfully on mine this worked out to be spot on – so I guess the rings and shims were correct, even though not 0.2mm different.

Then the R value can be measured. First off I measured the depth of the pinion end bearing from the end of the case with the gauge in place and pinion tapped up touching it



This was 8.2mm

[58A - 71E]

Then with the gauge removed



The value was about 7.45 on average

I knew that there was 0.45mm difference to take into account with the oversized gauge but this left a difference still of 0.3mm. This just happened to be the difference in amount of the shims on the end of the pinion that I’d left out. Therefore I knew that I needed to add 0.3mm in shims behind the end bearing next to 4th gear.

I later checked this by measuring (with the shims in) the pinion bearing to the case with the gauge in and it was exactly 0.45mm longer than without the gauge in.

So I put the gear puller on 4th gear to insert some shims



Luckily these original ones were not damaged and I added a new 0.3mm shim in



Then the shift sleeve could be added before reassembling 4th and the bearing, (here shown with reverse gear just to hold it all together before putting the nut on)

[58A - 71E]

I checked all the teeth on the gears to ensure there were no burrs or marks and removed any ones with the Dremel, thankfully there was only 1 small burr on one of the pinion teeth



I could then tighten up the bolts on the selector forks to make sure they were in the middle of the selector sleeves, through the access holes shown earlier.

I then removed the gauge and placed in the diff, and covered the teeth with engineers blue to test the mating pattern



This is the pattern required



Now mine wasn’t perfectly like that, but not far off!

[58A - 71E]

I then removed the nut and spacer (scaffold) off the pinion and I then applied the case sealer to the two case halves ready to put them together



I used this VW sealing compound



I then inserted the clutch throwout bearing shaft into the case half



And mated the two halves,



Now looking back I shouldn’t have sealed this yet, as I had not measured the backlash of crown and pinion, and if it needed adjusting then I’d have had to take all this off and start again.

[58A - 71E]

I had previously had all the nuts/bolts/fasteners shot blasted and read that on these GBs they were originally black oxidised as a finish. I managed to source a kit from here http://www.caswelleurope.co.uk/coldox.htm I was really pleased with the result



The bolts can then be inserted and torqued up in the order provided in the manual.

Then it was time to fit the intermediate plate, again, the bearings are preloaded as per this diagram





So first I measured the bearing seat in the intermediate plate



Which was a depth of 7.21mm, the depth of the bearing to the case half is 7.76mm, and the compression required is 0.05mm therefore I needed to shim 0.5-0.51mm with paper gaskets

[58A - 71E]

Then the intermediate plate can be fitted



I then assembled reverse gear assembly, including the small shaft holding the double idler reverse gear, reverse gear on the pinion has bevelled teeth that face outward



Before tightening the nut onto the end of the pinion shaft



The nut could then finally be put on the end of the pinion (tightened on by inserting a chisel between the gears to stop them turning)



and cotter pin inserted

[58A - 71E]

Now it was time to check the backlash on the crown and pinion, the manual once again shows a special tool that clamps around the half shaft



Well not surprisingly I didn’t have that either, so improvised a bracket to hold my dial gauge on the end of the intermediate plate and measured the backlash on reverse gear





The backlash required is between 0.1mm-0.3mm and mine was about 0.2mm so thankfully didn’t need stripping and readjusting! (it is marked on the pinion as being 0.15mm but I reckon its within tolerance so it should be alright)

[58A - 71E]

Then the nose cone (with selector rod inserted into 1st gear first) could be put on with a gasket in between the intermediate plate



Then it was time to put on the axle tubes, surprise surprise these are also shimmed with paper gaskets to give the specified clearance, as per this diagram



With gaskets



Inserting the feeler gauge between the case and the end of the tube to check clearance of between 0.15 and 0.3mm