rear diff ring and pinions part numbers and supersessions

[ottawa coupe]

So, i decided to treat myself with something a little silly and i purchased a 2.5 tdi trans from Issam for my s6. it's got enough power to turn such long gears now and it then frees up the 5 speed for use with the 4.2 in the coupe. that said, it's a 3.89 final drive vs the 4.11 in the s6. i did some digging in online catalogues and found that the ring and pinions for the rear diffs are shared across at least b3,4 and c4. i happened upon a 3.89 rear diff nearby and a friend just happened to be going by there at the time anyways so i picked it up. based on poop photo, thought it was a b4. turns out it is a b5 rear end.

so here's the question: the b3/4 and c4 part number for the ring and pinions is 017525143A, the b5 r&p of the same ratio is 01H525143A. before i tear them open, anyone know if this is simply a part supersession or are the gears actually different? the pinion bearings are the same so i tend to think i am ok but i am not sure at all. i have a spare c4 rear end so i can take my time and sort it, but would prefer not to get greasy if it's not gonna work!

[ottawa coupe]

so, seeing is this is like the ONLY forum left in the world and facebook sucks for actual info, i am gonna put my findings here.

i have had a chance to open up both my spare c4 4.11 rear and my b5 3.89 and i am cautiously optimistc in VAG's laziness in terms of designing new parts and that the b5 ring and pinion will fit in the C4 housing (and thus b3/4). Here's the info so far..

diffs.jpg

for reference, here are the exploded views of the C4 and B5 diffs, respectively:

diff assy.png
b5 diff assy.png



as you can see, the construction of them is very similar

at this point all i have manage to do is get the input flange and the diff out on both of them. other than stripping rusty torx heads. first thing i noticed is that the diffs looked awfully similar, would i be so lucky as to be able to simply swap the diffs? the answer is no, different bearings and slightly different axial dimensions. however, most importantly, the ring gear ID and PCD is the same. so the gears will swap.

and this gets us to where i am stuck for the moment, the pinions. pinion nut removal will require special tools (of course!) i have not found any of them for sale and old links show absolutely insane prices (just wait till you look up the tool prices for setting the pinion!). the nut is not a hex nut (because of course) and because german complications, the nut is to be fixed and the pinion is turned.

this is the nut, 017525215A

017525215A.jpg


this is the tool to fix the nut, VW3132

3132.jpg

and this is the tool to turn the pinion VW2052/2

2052-2.jpg

here's the illustration of the tool setup

tool assembly.jpg

at this point i have confirmed that the pinions are approx the same length. They will be slightly different for different ratios as the ring gears will be different diameters of course. looking at the parts listings from the above diagrams, the bearings, crush sleeve and pinion nuts are all the same. so at the moment, i am confident that the pinions themselves are interchangeable.

where am i going from here? well, firstly i will be visiting a local transmission shop to talk about the actual assembly later down the road. the reason is as i mentioned above, the tool cost (if you can find for sale) to set the pinion and diff in accordance with the manual is crazy. $6000 USD. i am certain a proper specialist transmission shop can set it up for far less! secondly, i believe i am gonna start makin some tools as tapping the pinion nut with a punch is not producing positive results. the only question i still have on the matter will be the issue of shims. there is a source for them but spendy ($30 per after shipping) who knows how long that will remain. i hope the shop can tell me if there's a generic supplier for them.

vw3132 is gonna be "fun" to make but i believe i will simply weld a socket to the coupling sleeve from the b5 diff (same as the c4 so is now extra) to make VW2052/2.

1000004737.jpg

i will add to this as i get deeper but i believe this will be viable. the reason for this effort is $ and availability. it would seem that C4 automatic rear diffs have disappeared from the face of the earth now. tradition DOES have some listed but they are quite expensive. as of this writing they are ~1400 Euro, down from something insane like 3600. dunno if that's temporary or if that's for final blowout. at the moment, i consider that a last resort if i happen stumble across the money tree but if it comes to that, i think i would sooner just sell the tdi box and buy another 4.11 01e for a lot less $

[ottawa coupe]

so, here's the quick n dirty drawing of the part that needs to engage with the pinion nut to emulate VW3132. i have sent it out for waterjetting. i have checked this with a paper template so i know it will fit in case someone else wants to have a go at this. it's a bit beefier on the inner dimensions in case, you can always take material off, harder to put it back... i will weld it to some scrap exhaust pipe and a mess of scrap to bolt it to the diff case. it won't be a pretty thing but it should work.

image_92570.jpg

[maxiice]

Tryed something simmilar, making a b3 diff 3.89, they only came in the 2.8L so quite rare, i tryed with the b6 internals but the ring gear was to large

[ottawa coupe]

I got the b5 ring gear off today, looks quite possible. Not gotta do anything with the c4 part until i get the tool made for the pinion. I checked torques on the bolts as i removed them. Looks like roughly 60ft-lbs or 75nm is the torque from the factory. Please correct me if i am wrong, i have not found a spec in the manual yet. EDIT : torque spec it 66ftlb/90nm

1000004752.jpg

[ottawa coupe]

B5 pinion out. Tool works well except the piece i drew up needs to be probably 3/4" thick as opposed to the 3/16" i got it cut from. The reason being that the pinion shaft is pressed into the bearings so when the nut is undone, it rides up the threads while the shaft stays put axially. I need to get some pipe tomorrow and i'll get the c4 pinion out and i will be able to determine if b5 gears will work. I am fairly positive at the moment though.

20250930_143143.jpg

[ottawa coupe]

Conclusion: b5 rear diff gears are the same size as b3/4 and c4. This means the b5 rear end is a viable source for both 100mm flanges for an 01e and 3.89 gears for the rear diff.

I need to look at the whole shim situation still but as of now, this $100 rear end and $100 in material for making tools has been money well spent

20251003_180010.jpg

[ottawa coupe]

I stand corrected.....

FB_IMG_1759595817707.jpg

What would you do? Give up or have the gear machined ~6mm on the diameter?

edit Compared cases, geometry is different. Pinions may be the same fitment but it ain't gonna work. Back to the drawing board. I think i am gonna sell the tdi box

[ottawa coupe]

Well, i searched a bit harder on tradition and found a 3.89 diff for a 100 for a much friendlier 260€..... shipping still sucked but i diluted the pain with other stuff i needed.