Author Topic: How to replace differential bearings in an 085 gearbox  (Read 22970 times)

Offline hayesey

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How to replace differential bearings in an 085 gearbox
« on: May 23, 2008, 04:29:30 pm »
How to replace differential bearings

Time required:

To do this properly you need to order a specific size fitting washer to set the bearing preload, this means you have to assemble everything, then order the washer and then fit the washer before you can use the gearbox.  So the car will be off the road a few days unless you put a spare box on.  You might get away with not doing this and just using the same fitting washer that was in the box from the factory if you are simply replacing worn bearings and using the same differential.  However if you are doing this because you are replacing the differential or fitting an LSD (which is what I was doing in these pics) then you must order the correct washer!

Tools required:

- normal selection of sockets and ratchets.  
- bearing seperator or puller
- allen key bits for ratchet (or selection of normal allen keys)
- kettle and a freezer! (Not essential but make life easier)
- dial gauge capable of reading up to 2mm and stand
- a vice always helps too

Parts/consumables required:

- set of diff bearings and bearing oil seals as per this picture:

These came to about £50.

- fitted washer to set preload.  You can only order this once you're half way through the job.  It only costs 50p.
- gasket sealant
- ~3 litres of gearbox oil


Firstly, remove the gearbox from the car (see Haynes manual!) and drain the oil (store it in an airtight container if it was replaced recently anyway and you plan on reusing it, ideally always replace it).  Support the gearbox on a bench with the clutch housing facing upwards.  You need to remove both the driveshaft flanges first, these are held in place with a single allen head bolt through the middle of them.  You'll need to stop the flange from rotating as you undo the bolts, I screw two bolts into two of the driveshaft bolt holes and hold the flange still with a breaker bar against these bolts.  Once you've removed the centre allen bolt the flange will lift out.

There are about ten 13mm bolts holding the two halves of the casing together, remove these.  Now tap underneath the clutch housing with a mallet to crack the gearbox open.  Remove the clutch housing half of the casing and you are left with this:

The diff is the big part at the right with a large ring-gear around the bottom, cone shape and then a roller bearing at the top.  It simply lifts out of the gearbox now.  I took all the pictures here whilst fitting a limited slip diff to my gearbox but the procedure is exactly the same if you are just replacing bearings on your existing diff (except you have the option of not bothering to get a new preload washer).  I moved the diff into a vice now so grip hold of it to remove the old bearing inner rollers.  Use your bearing seperator to remove both inner bearings as per this picture:

It's possible your seperator or puller works differently but you get the idea.  You can now fit the new inner bearings to the diff.

Important note: when you open the new bearing packages, there is the inner roller and the outer race, you MUST keep these with the part they came with as they are machined to match from the factory.  I just marked them with a felt pen and was careful not to rub it off.

Since metal expands the hotter it gets, dropping the rollers into some just boiled water makes fitting easier.  So this where the kettle comes in.  

Let it sit there for a couple of minutes.  Then lift it out of the water using some pliers or whatever and tap it onto the diff, you will need to use a piece of tubing or the old bearing inner race to tap it into place.  Apply a thin film of grease to the hub on the diff first to help too.  When tapping it into place, ensure it is going on straight or it can get stuck or bent.  If it starts to go at an angle, pull it back off and start again.  Here's my LSD with the top bearing inner race fitted:

And here's the new bottom bearing roller fitted:

That's about it for the diff itself, you need to put it to one side and go back to the gearbox casing halves.

Use a drift or a large flat screwdriver to tap the back of the oil seal till it pops out, they aren't tight so a few taps will do it.  Then from the other side, remove the seal:

Do this on both the clutch housing side and the gearbox side of the casing.  Now you need to drift the bearing outer races out of the casings.  These are quite tight.  Look where you have just removed the oil seals from and you will see a gap at either side of the casing above the back of the race allowing you to get a drift or large flat screwdriver against the back of the race.  You can see these gaps in this picture from the other side of the clutch casing, the race is removed in this picture.

Keep hitting the back of the bearing race using the dridt/screwdriver and a decent sized hammer, dont be scared to give it a good whack.  You will however notice that there is a washer behind each race, try not to damage these as you will need to re-use at least the gearbox-casing side one!  In this next picture you can see the gap to hit the back of the race along with the fitting washer behind the race, this was with the new race fitted:

once the race comes out the washer will fall out too, make sure you keep the washers, they look like this:

The one fitted to the gearbox half of the casing will be 1mm thick and you will re-use this one no matter what.  The one from the clutch housing side will vary in thickness between gearboxes.  If you are going to properly measure and reset the preload (best to make sure the bearings wont wear out prematurely) then you can bin this one.  Here's a picture of the gearbox half of the casing with the outer race and washer removed:

Clean out the insides of the casings where the outer bearing races fit and apply a thin film of grease where the race will fit to assist in fitting.  Again, temperature can help you out here by shinking the races slightly by cooling them down.  I left them in the freezer overnight :)

Fit the new race to the gearbox half of the casing first.  Put the original 1mm fitting washer in first.  Then start tapping the race in.  It shouldn't be mega tight but wont just fall in.  Again, make sure it goes in strsight, this can be quite fiddly.  I used a 3/8" extension bar as a drift with the wider end against the race:

Keep tapping round the circumference of the race so it goes in straight and keep tapping till it's fully in.  You can tell it's in by the noise heard when hitting it, it turns from more of a "ding" to a "thud" once the back of it locates against the casing.

Now do the same with the clutch housing side of the casing except fit NO fitting washer behind the race (unless you aren't bothering to reset the preload, in which case fit the old washer)!  Now you need to put everything back together in order to measure for preload (or to put back on the car if you are reusing the old washer).  Put the diff back in the box, put the halves of the cases back together (apply sealant and oil seals as shown later on if you aren't replacing the fitting washer) and tighten up the bolts that hold the cases together.  I think there is a torque figure in haynes for this but I just do them "good&tight".

Now sit the gearbox up on the bench, doesn't really matter which way but if you put it clutch housing down, then any oil still inside will leak out.  Now setup you dial gauge and stand on the gearbox (I clamed a piece of steel to the casing so the magnetic stand would stick to it).  Place the stylus of the gauge so that it touches the top of the diff through the driveshaft flange hole and set the gauge to read zero:

Poke your fingers through the other driveshaft flange hole and push the diff up inside the casing as far as it will go.  Write down the reading on the dial gauge.  You have just measured the free play between the bearing roller and outer race.  in my case, this free play was 1.34mm.  The pre-load setting for these bearings (from the Haynes gearbox rebuilding manual for 084 gearboxes) is 0.3mm.

Free play + preload figure = Fitting washer thickness

So in my case:

1.34 + 0.3 = 1.64mm

The washers are available from VW in steps of 0.05mm, they all cost about 50p each and part numbers are:

click here for etka screenshot listing bearing shims

Choose the nearest size to your measurement, in my case it was 1.65mm.

Clean yourself up, have a brew and order this from VW.  It'll probably be a day or two before it arrives.  It might be worth measuring the thickness of the old washer you took out to make sure it's not already the correct size!  Use a 0-25mm micrometer to do this.  Or a decent quality caliper.

When the new fitting washer arrives, check it is the right size with a micrometer:

Now open up the gearbox again and remove the diff.  Now carefully tap out the outer bearing race from the clutch housing side of the casing, don't damage it!  Now drop the washer in and re-tap in the bearing race (can put it back in the freezer for a while to help).  Re-fit the diff, clean up both mating faces of the gearbox halves using a blade and then some de-greaser.  Apply some gasket sealant to one of the mating faces, doesn't really matter which I guess:

Personally, I prefer to leave this for about 3/4 of an hour so the sealant gets a skin over it, otherwise most of it splodges out when you bolt the halves back together.  After that, fit the diff and bolt the two halves together once and for all!  Next fit the oil seals:

using a mallet, they sit flush with the casing.  Here's one fitted:

That's basically it.  Re-fill with gearbox oil (I prefer to do this before fitting to the car but you don't have to) and bolt the box back onto the car!

Feel free to post any ideas of how this is better done.  I've basically used the guide from the Haynes Gearbox Rebuilding manual (which has a section on the 4-speed 084 gearbox).

Paul Hayes.
« Last Edit: March 20, 2009, 10:28:54 am by hayesey »

Offline Jezza-7

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Re: How to replace differential bearings in an 085 gearbox
« Reply #1 on: October 16, 2014, 10:40:59 pm »
Just reading through this for the washer sizes but my free play was only around .90mm + the .30mm and there isn't a washer that small. I did measure the washer from the gear side of the casing with verniers and it was 1.70mm. Now i read that you said its 1mm, could there be a possibility that they have got mixed up?

Offline Jezza-7

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Re: How to replace differential bearings in an 085 gearbox
« Reply #2 on: October 17, 2014, 10:17:12 pm »
Sorted this out today. Took the shim out and measured the other one that got mixed up. 1.00mm exact and then read the volkswagen workshop manual where it does state 1.00mm is the gearbox side! Doh! Oh well, sorted now and 1.30mm was read on dti so new 1.60mm shim will be fitted tomorrow!