Differential rear. Water in it.

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It has happened:
It has happened from the early days of the club. Following the 1996 Holland Track trip one of our members checked and discovered that the oil was creamy from ingesting water during water crossings on our exit route. It was VERY wet! It also happened to at least two vehicles on the Rudall River trip in 2017. Please scroll or click photos for full view; and yes they are in reverse order!.

On top of the rear aluminium cover is a small breather cap. It is through here that water can be drawn into the housing when ‘fording’ or ‘wading’, particularly if it is deep or over a distance. This is caused by the hot air inside the housing contracting when suddenly cooled in water. Water and oil don't mix!

To check the oil in the diff remove the top ‘fill’ plug with a square 1/2” drive bar. NOTE: if the filler is brass and had an integral cable, (a temperature sensor - see photo) unplug it - it is tricky do to so take your time to determine how the 'catch' works! If the oil does not run out stick a small finger in the hole and dip into the oil. If it is cloudy, milky or frothy, change it immediately. If you are not sure, change it anyway, or ask your mechanic. The oil is at the correct level when it is lapping just below the bottom of the filler hole on level ground. Replace the plug but do not over tighten it as it has a tapered thread.

A preventative modification is to run a breather extension with a length of tube in place of the cap. The tube size must match, or be adapted to fit the breather sleeve. Run the tube high up inside the car through a convenient floor grommet.

The cap is difficult to get at so have a good look at the possibilities before starting. A hoist and elevating (or means of height adjustment) stand is needed so you might have to ask you mechanic to do the work for you. You will need mechanical skills, a helper and please be safe - OHS. This modification is awkward because there is very little space around and above the breather cap. You will have to remove or ‘shift’ some heavy mounting or support brackets. There are several major differences in the diff casing bracket mountings - see below. The breather cap and hole may also vary. Most will be a metal cap on a metal sleeve. Very early models may be a plastic cap on a plastic sleeve. Either way the tube must match or be adapted to fit.

Basically you need to lower the rear of the whole diff housing 50 - 100mm. Different models have different mounting brackets and bolts, but the aim and procedure is the same for all. The exhaust pipe might be in the way. The diff will need to be supported on an adjustable stand at all times so be very careful - OHS!

For early models support the diff and remove the beam running the width of the car immediately behind the diff. To do this remove the nuts from the two studs in the rear diff cover plate. Lock two nuts onto the studs and remove both, noting the threads are different pitches at each end. Be very careful when replacing the studs as it is easy to cross-thread the soft aluminium cover plate. You will now need two people to wrangle the next steps. Remove the huge nuts from each end of the beam and remove the beam and again be careful! Lower the diff hosing only sufficiently to get at the breather cap. Prise the cap off the sleeve which might be tricky as it has four ‘teeth’ to locate it. Do not be alarmed if the sleeve come out of the cover as this makes it easier to prise the cap off. Fit the tube, which for 5mm tube should be a friction fit into the sleeve. It may need a suitable adhesive. Replace the sleeve if it came out. Run the tube inside the car interior through a convenient floor grommet. There may also be a harness sharing this grommet for the Diff temperature and headlight level sensor; be careful. Secure inside and out with cable-ties. You can put a miniature fuel filter on the end of the tub (see photo).

For later models the aim is the same but access different. The exhaust may be in the way. You will now need two people to wrangle the next steps. Support the diff and remove the two studs as above. Remove the under-slung support bracket half way along the main diff housing. There is a long bolt through each rubber bush in the bracket which remains attached to the diff housing. Be careful. The diff will tip to one side (preferably to the RHS) allowing access to the cap as above. 5mm tube can be used - this one from Auto 1.

Work Safe!

Submitted by Ian Johnson 10/2014 from original 1980s handout #17 Subaru 4WD Club of WA Inc. Updated 09/2017.