I’ve recently noticed a rather acrid burning oil smell coming from the car, and having swapped the nearside rocker cover gasket I thought I check if that was the problem. Unfortunately not.
The leak was gearbox or differential oil, flicking up onto the exhaust downpipe and burning off. I traced the problem to the nearside and it was fairly obvious that the leak was coming from the nearside flange that goes into the gearbox. It wasn’t a bad leak, but the occasional drip on the driveway, the smell of burning differential oil (I HATE THE SMELL OF GEARBOX/DIFFERENTIAL OIL!) and the worry that there could be damage to the differential meant that I had to do something about it.
From my research there didn’t seem to be anyone else who had come up the issue before. Mavada had problems with the O/S differential (too much play?) so my research had to go further. I have a Bentley workshop manual for the A6/RS6 and the differentials aren’t mentioned much, just the procedure for changing fluids. I found a post from the a VW Phaeton forum whereby it mentions that the N/S flange unbolts fairly easily on the W12 model (which I think uses the same ZH5HP24A gearbox as ours), but that you need to drop the subframe to get it out. I also found some YouTube videos of the overhaul of our gearbox when it is removed from a car.
You can see my original post here: viewtopic.php?f=2&t=132603
The actual front differential is mounted to the O/S of the gearbox, and the nearside has a support bearing/flange and connects to the diff via a long shaft. The shaft goes through a long tube that I believe is sealed from the gearbox.
Looking on ETKA there are quite a few parts fitted to the flange/shaft, so it makes sense to change them all whilst its removed from the car. I also filled with new oil (75W90 Audi spec), bought 4 new subframe bolts (as they are stretch bolts and have been known to come loose if retorqued) and a new CV boot clamp.
Here is a photo of all the new parts. I will try to supply the part numbers and cost (from TPS though I might add). Here is also a screen shot from ETKA to show how they all fit onto the hub/flange and shaft.
Parts needed: (Part number, desc & RRP exc VAT)
01V409380: Shaft spacer (£4.78)
01V409379: Shaft mini spring (£2.79)
01V409297: Circlip (£2.68)
01V409144: Bearing (£44.60)
01V409133: O ring (£8.66)
01L409399: Shaft seal - this is the one that was leaking (£19.59)
01V409187: Wheel speed signal ring (£14.46)
G052145S2: 2 litres of Audi spec 75w90 differential oil (1.3 required for fresh refill, but depends how much you can get out via the fill plug) (about £20 for 1 litre from Audi)
4B0407643A: Wheel hub bolt - supposed to only used once (£13.21)
New parts:
Optional extras:
O rings for wheel speed sensor x 2.
6 new bolts for driveshaft to flange
Fill plug for differential (as its not a drain plug the fluid level doesn’t go above this. There isn’t much of a gasket so I reused mine)
I originally planned to change it all back in early August but things got in the way. As I was driving to Norwich and back, then Devon and back in the space of 3 weeks I checked the fluid to make sure it wasn’t low. I added around 300ml before it was the correct fill level. The book states it takes 1.3 litres so must have lost 300ml in about a month previous.
I knew it was gonna take some time, and the bank holiday weekend was coming up and I could set aside a couple of days without needing the car for anything.
Tools required:
2x Axle stands
Large trolley jack
Socket set (3/8” probably enough): 13mm/16mm/17mm required
Long reach extension bars
Allen bit set (5mm/6mm/8mm & large on for hub bolt)
Triple square set (only M10 needed)
Torx set (only T40 needed)
Circlip pliers (external)
Oil drip tray/Cement dust if you spill anything
Cleaning cloths
Brake cleaner/Degreaser
Breaker bar (for wheel hub bolt)
WD40/Penetrant spray
Soft head mallet (rubber/plastic/copper)
Hammer and drift punch (for upper control arm bolt – that’s sometimes gets stuck)
Oil syringe/vacuum system.
Hydraulic bench press & some bearing presses (you can use large sockets if they are big enough)
Assembly lubricant/grease
Difficulty:
I’d probably say 3 out of 5 spanners. If you’re used to doing cambelts then this shouldn’t be a problem, just a pain as there’s not much space. If you haven’t got a hydraulic press you might be able to find ways to get the old bearings out, but its much easier with a press! It took me about 7 hour in total. It was mega hot though, and technically did 4 hours the first day to get everything removed and cleaned. Then bearing and shaft in freezer overnight, then 3 hours the next day.
So, one of the hottest weekends of the year……
Step 1 - Wheels off etc:
Jack the car up. Remove the front wheels. We’ve all done this a million times. No photos needed.
Step 2 – Drain the differential fluid:
Round to the O/S. Use an 8mm allen socket to undo and remove the fill plug from the differential housing. There is no drain plug. Oil needs to be drained prior to removing the differential flange(s) otherwise there is a risk of contamination/mixing of the gearbox oil/diff oil. I couldn’t find any reference to this but I believe it is mentioned in the electronic workshop manual. I drained around 900mls out. The level could have gone down a bit in the last few weeks, but its likely there was still some oil in bits of the diff that I couldn’t reach. Drain as much oil out as you can. Mine wasn’t really black but a lot dirtier than the new stuff.
Here is the O/S with the fill plug removed:
Step 3 – Wheel hub bolt, heatshield and driveshaft flange bolts:
You’ll need a friend to help with this bit. Put some of the wheel bolts back in so the discs are locked to the hub. Get a friend to hold the brakes and loosen off the Hub bolt. Now remove the 3 allen bolts that hold on the driveshaft heatshield (circled in red). If you have long thin extension bars and slim allen keys its ideal as there’s not much room to get the through. Get a friend to stamp on the brake again, and loosen off the driveshaft inner CV flange bolts. There’s 6 in total. You should be able to get atleast 4 of them loose, before the CV needs rotating and you can get to the others.
Photo of everything still fitted:
Step 4 – Upper arm bolt and steering arm:
Remove the upper arm bolt. I think these are 16mm and 17mm. I’ve removed mine a few times before and when I refit I always add a little anti seize compound. If it’s the first time its been removed it would be in very very tight, so a replacement bolt might be needed and you’ll likely need a lot of effort to get it out. A hammer and punch drift was enough for me, but if yours is stuck you could use an air powered chisel to loosen it. This is fairly common on the audi platforms I believe. I’ve wrestled with a few friends cars to get these removed (A6, A4 etc..)
When this is removed, remove the 13mm bolt holding the track rod end in, then undo the 16mm bolt that aligns the ball joint cross section. The TRE should come straight out now. With the steering arm out you can pivot the suspension and pull outwards so the driveshaft will come out. If the outer CV is stuck in the hub, put the bolt back in a few rotations and tap it with a hammer to push it backwards. Be carefull with the everything removed as you can stretch the sensor cables. I put the top arms back in for the time being.
Here's a photo with lots of things removed:
Step 5 – Wheel speed sensor connector:
Unclip the wheel speed sensor electrical plug (circled in green). There could be a heat protector around it so just lift this out of the way to get to the plug. Press in the metal spring and push the upwards (towards sort of 10 o’clock position) and it’ll come right off. There isn’t much slack in the cable, so push it back away from the flange to give a bit more space for later jobs.
Step 6 – Wiring loom bracket removal:
Remove 6mm allen bolt that holds on the bracket for the wiring loom which goes to the gearbox (circled in orange). There may be a cable tie for the loom further down at the bottom of the differential flange. Remove that too. It should drop down low out of way now.
Step 7 – Gearbox mount bolt removal:
Remove the 8mm allen bolt which is for the gearbox mount (not circled but just to right of the rightmost driveshaft flange). You aren’t removing the whole mount, just the bolt to give enough space to remove the diff flange.
Step 8 – Flange bolts removal:
Use a T40 Torx to remove the 3 bolts that hold the flange onto the gearbox (circled in yellow). You may need to rotate the flange slightly to get to all of the bolts. A little oil may leak out so be prepared with some Shop towels etc.
Step 9 – Turbo oil drain pipe & wiggling:
Now this looks like you’re done!. Except the flange won’t come out. It moves out about an inch but then hits on 2 things. A – the turbo oil drain pipe, and B – the gearbox mount. Ideally I’d remove the gearbox mount, but there is one more bolt holding on it I think you need to get the downpipes off to get them. So, there are 2x 5mm bolts that hold the turbo oil drain pipe on. I was worried about taking these off as I didn’t have a replacement gasket, and as these probably get hot they could be seized. There also isn’t much space to get to them so I need some very slim allen sockets (the kind you normally get with screwdrivers sets). To my surprise they came out quite easily! And the gasket was intact. The bolts are circled in blue.
Its easiest to get under the car and look straight up to remove the flange. Push the turbo oil drain towards the outside of the car and it gives you a little more wiggle room for the flange. It just clears if you rotate the flange. Although the pipe is hard is has a flexible connection further down the pipe. When the flange is past the pipe it seems free to pull out completely, but the subframe gets in the way.
Step 10 – Wheel speed sensor:
Remove the wheel speed sensor now (so you don’t break it later). There is a long plastic arm that comes out from the top of the sensor. You simply push this arm down and twist the sensor. It can only be twisted in one direction (clockwise). A quarter turn and the sensor comes straight out.
You can now pull the flange and shaft towards the outside of the car. Rotate the flange (about 180degrees) and you now have enough clearance to pull it out completely! Wahey its out.
This is what the gearbox looks like with everything out. Can’t see any further seals so not sure how it’d contaminate the gearbox oil. Perhaps it might be concerning the differential O/S?
Step 11 – Taking it apart:
This is the complete flange and shaft when removed. Pretty big and oily. The shaft is heavy so could be steel, whereas the flange looks like aluminium.
First off, pull the shaft spacer and spring out from the tip of the shaft. Its only really held in place with press fit bit its not mega tight. You might need some pliers to get it out. The O ring comes off really easily.
Next up it’s the circlip next to the bearing. Pretty easy to get out with circlip pliers.
Right. How do you get the shaft out? Well I have a great hydraulic press, but its not big enough to fit the shaft under. Instead I found 2 bolts that have the same thread pitch as the driveshaft flange bolts, screwed them through the driveshaft flange until they touched the differential flange. Tightening them up pushed the differential flange back off the shaft. It wasn’t on that tight either. Yay!
When the shaft is removed you can see the wheel speed sensor ring. Its just plastic (and has magnets in for the hall effect sensor?). It just pulls off the shaft easily. It fits in a slot on the shaft too so it can’t spin when fitted.
Next up you can see the seal that was leaking. No obvious signs of damage to mine, but excess play in the bearing would compound and problems with the seal so will make it leak. That’s why I’m replacing the bearing anyway. I removed the seal with some mole grips. Just be careful you don’t damage the outer case where the seal fits in.
And we are onto the bearing!. Again easy to press out in the right direction. It can only be pressed out in one direction. I made a note of which way round it was fitted but both new and old bearings look the same on both sides. Both have chamfered edges too – the only difference is the writing on the inside.
And its all apart!
Step 12 – Give it all a good clean!
Yep that’s right. Give it a nice clean so that when its back together you don’t get any dirt in the oil, or damage the seals. I’ve got various things to use, degreaser, Shop wipes, wire wheel (don’t use on the bearing contact faces), scotch brite pads, Raceglaze alubright is good but strong and corrosive. Once clean give it a rinse with brake cleaner and let it dry.
Step 13 – New parts to be fitted: Bearing
Depending on what type of tools you have you may want to do a few things differently to fit the new parts. Although I have a hydraulic press, I often use heat to assist the process of installation and removal. For removal of stubborn parts heating the outer casing up can work wonders to press a bearing out. For installation though I like to stick the bearing in the freezer for 24 hours and then press in. Makes it so much easier. Use the old bearing as a press against the new one and push in carefully with the hydraulic press. It can only be pressed in so far as they is a large lip on the inside.
Step 14 – New seal fitting:
With the contact face cleaned up and new seal can be pressed on so far by hand. I then used a flat piece of wood and a few taps with a hammer helped it in square.
Step 15 – Fitting the shaft:
I also put the entire shaft and driveshaft flange into the freezer overnight. I applied a small amount of differential oil onto the oil seal to lubricate. Take the shaft out of the freezer quickly and push on the on the speed sensor ring. Don’t forget to locate it against the machine bevel. Stand the shaft up on a worktop and try not to touch it. Lift the Differential flange and slot over the tip of the shaft. Mine fell straight to the bottom and over the bearing. A few light taps got it to the bottom. The shaft is quite bit so will take a while to heat up. If your hydraulic press if large enough you should just be able to press the shaft through the flange. Yay again! Make sure its down far enough to see the circlip groove in the shaft, then fit the circlip. Fit the O ring onto the assembly. I added a little grease to almost stick it in place – will be helpful during refitting so it doesn’t fall off.
Step 16 – Give the car a clean:
No not the whole car. Put an old rag into the hole left by the differential shaft and clean the area around it. Now is the last change before its going back together.
Step 17 – Refitting stuff:
Its not quite the reverse of the earlier steps. Put the shaft in through the gap, and as before rotate the diff flange so that it goes through the space between the bodywork and the subframe.
Now slide the wheel speed sensor in (with new o rings) and turn it anticlockwise whilst pressing down the locking section into the bit on the flange.
When its pretty close the turbo pipe gets in the way again, so a combination of moving the pipe and rotating the flange again will get it near to bolting on.
Now bolt the turbo oil drain pipe back on – if you don’t do this now you might not have enough space later on. I don’t know lots of the torque specs but none of the bolts were mega tight. Put on a new gasket if you have one.
Next up it’s the connector for the wheel speed sensor. It took me about 20 minutes to get it on, only to realise that the metal clip needs to be depressed for the clip to be refitted. Pull the heat resistant cover back over the clip. Mine was also secured with a small cable tie.
Your now in a position where the flange can be bolted back on. Its worth double checking that the large O ring is still in place before trying to seat it against the gearbox. Press the flange up against the gearbox, and the spring fitted to the tip of the shaft will be pushing against you so the flange won’t be flush if you let it go. Put all 3 bolts in an tighten (again not too tight). You may need to rotate the driveshaft flange to get all the bolts in. The shaft may need a tiny rotation to locate the splines at the differential side, but you’ll be able to tell pretty easily if it hasn’t located as it won’t push in.
Put the bolt back into the gearbox mount and tighten up.
Put the driveshaft back in place and fit a new hub bolt. Put in the 6 driveshaft bolts and tighten up. You’ll need a friend to stamp on the brakes again to tighten them up fully (I’ll try to find the torque specs).
Put the top arm ball joints back in and slide the bolt of death in and tighten up. Reattach steering arm (TRE) and also refit ball joint bolt, as well as top small 13mm bolt.
Refit driveshaft heatshield and tighten the 3 bolts up.
Remount the small bracket for the gearbox loom to the bottom of the flange and tighten up bolt. I cable tied the loom further along also.
Put the N/S wheel back on and tighten up wheel bolts.
Now back across to the O/S. Refill the differential oil. The filling procedures states that it take 1.3 litres from dry, but you cannot simply refill until it starts dripping out. The workshop manual states the differentials are quite sensitive to overfilling so make sure you don’t put too much in. The manual states that if you have overfilled it (and its overflowing) then you can syphon out 300mls and you should be ok. You can also make a little tool to check the level. With the car flat find a small straight metal rod (a welding rod works well). Bend over the end at a right angle (by about 10mm) and make a mark 6mm from the bend. With the rod inserted into the fill plug and sitting flush with the bottom edge the oil level should be 6mm below the bottom lip. Now put the fill plug back in. Not mega tight.
O/S wheel on, tighten bolts.
Might be worth starting up the engine to make sure you haven’t got an oil leak from the turbo oil hose. Diff leaks will only really be evident after a drive around.
Drop it off the axle stands and your done!
