A few years back I got tired of the labourious procedure required to top
up the oil levels in the bevel boxes on my vehicle. I intended to pull
down the bevel box seals and replace them at a later date. As it turned
out years later I did this on one wheel station (left rear) precisely to
the specs and it made no difference to the leak rate.
Pulling down a wheel station
is no fun. In the case of Aussie Ferrets, ours have had a mod done to them
which is a sort of skirt like piece of armour about 4" wide that goes
longitudinally along the hull above the rear springs and sits just over
the mudguard/wing/fender. It makes releasing the spring tension very
difficult and reinstalling the spring a huge struggle and downright
dangerous. I now look upon work on that part of a Ferret as a last resort.
So, in case this mod saves someone the grief of doing a pull down and
then discovering it has made no difference to the leak, at least they can
keep their bevel boxes topped with oil easily.
In the pic below you can see the amount of oil that has found its
way out of the bevel box and hub into my drip try. This is what accumulates
after several months of inactivity. That tray is about 1 1/4" deep and the
quantity of oil is somewhere between 300ml - 500ml. I have the vehicle
sitting on a timber block so that I can move the steering back and forth to
access the front view glasses.
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This mod does not damage any part and is fully reversible to original condition.
The picture below shows my modification of the bevel box pressure relief. All I have done is remove the pressure relief valve from the large plug it resides in. It simply unscrews from the large plug. Then I took the large plug to the local plumbing supplier and bought a barbed fitting with the same thread on one end as in the large plug. Some flexible hose the correct size for the barb fitting and a hose clamp too.
I then reinstalled the large plug in the inner bevel box and then the barb, hose and clamp. Working down in there beside the engine is no fun but it can be done.
The photo below is of a front bevel box, for ease of access to take the photo. The installation is identical on all 4 boxes. The arrow points to the replaced large plug and added bits.
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The hose was then cut to a convenient length and then another barbed fitting, this time with a larger diameter on the threaded end was fitted to the top end of the hose. An appropriate threaded cap was drilled and threaded to take the pressure relief valve that I had removed from the large plug in the bevel box. I did this for 2 reasons:
1. To again provide the bevel box with pressure relief, despite the fact that the flexibility of the hose would probably suffice.
2. Primarily, so that the pressure relief would stay with the vehicle and not become lost over the years in some parts box and would be with the vehicle should someone in the future want to reverse my mod.
See the picture below (you need to view it full size to see the annotations listed below):
Arrow 1. Barb fitting
Arrow 2. Locking ring made from section of sawn off fitting used later in this installation.
Arrow 3. Cap which was drilled and threaded.
Arrow 4. Pressure relief fitting.
The whole setup is on a homemade bracket and in the case of the one pictured sits just out of the way of the left driver's visor handle. This makes it very easy to access the fitting from OUTSIDE of the vehicle through the opening for the driver's side hatches. To add oil I remove the cap, insert the nozzle of my manual oil pump and whilst holding the nozzle in tight, pump in the oil.
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In this next picture you can see one of the fittings in the engine bay, again sited for easy access and attached to a homemade bracket which uses the bolt which holds the engine bay crossmember.
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The quickest and easiest part of this mod was the view glass for the gearhubs. I removed the level plug and fitted it in there.
My main concern was that the threaded "neck" of the view glass not interfere with the inner mechanism of the hub. Their is very little clearance in there. I measured the depth of the thread into the hub and cut the thread on the view glass about 2mm shorter than the final tightened length of the view glass.
The other concern is that the view glass does not interfere with the steering arm or knuckle, so I made sure the view glass was of a low profile. With my vehicle I only ever have to let oil out of the hub to get it down to the correct level; topping up is never needed.
You can see in the view glass that the hub has again filled.......
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Now for the trickiest part of the mod; here I needed to take great care that no part of the mod fouled any part of the steering.
The easy quick way
For simplicity it is easier to just remove the level plug from the outer bevel box and replace it with a shortened view glass. When filling the bevel box from the inside fitting, you will need to undo the view glass to let the air out and allow the oil to flow in quicker. I doubt you can leave the threaded tube in place that the plug used to fit in. This is due to the "squat" of the vehicle at the rear due to the engine weight, it sits lower and will give a false reading if the view glass were not in as close as possible to the bevel box.
Or - the fiddly, make sure you get it right way.
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Undertake this part of the modification at your own risk. If you are not confident of the safety of what is suggested here then don't do it!
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I bought 4 x female "T pieces" and 4 x "Thimbles" (threaded pipe with a spanner hex in the middle) in addition to the parts already mentioned.
Now for the hard part.
In order not to foul the steering drop arm I had to cut down the thimble and T piece (this is where the locking rings came from for the upper hose fitting) and continually install and remove them until I was satisfied that the built up fitting would not foul the steering under any circumstances.
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Note well: that the steering arm geometry alters with the up and down movement of the suspension. Make sure you allow for any for and aft movement of the tie rods and knuckles.
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Doing so doesn't leave a lot of thread, but the breather hose stops anything from undoing. The same goes for the thread which goes into the bevel box. Because of the short amount of thread used the fitting is not tight and does weep a bit, which is nothing compared to what the surrounding bits leak. There is also the probability that if it should foul the steering it will break off and fall away rather than jamming the steering. Despite what you may think, I have been using this mod for roughly 8 years now and have never had any problems with it being snagged when off-roading.
As to the external breather hose which comes off the "T"-piece, I have found it necessary to undo the cap at the top of the hose in order that the oil that has been added via the fittings on the inside of the vehicle will flow down quicker - this acts as a vent as the 90 weight oil is so thick and sluggish that it appears to block off the flexible hose going to the inside bevel box as it runs down.
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The hose and top fittings are attached to a simple hook which catches on a cable tie looped around a conduit up high under the mudguard. It is an easy matter to unhook it, remove the cap and then add the oil to the inner bevel box fitting.
If you add too much oil the sight glass fills up and if you have laid the hose down low the excess will run out it as the new fittings will allow the box to level off at the correct height.
In the picture below is a close up of the rear RHS outer bevel box mod. You can see the view glass which is threaded into the "T" piece and then with a nipple into the bevel box. The original extension tube and plug are screwed into the centre point of the "T", so that they are with the vehicle. When I am going to fill the bevel box (from the engine bay fill point) I first off swing the "T" thru about 90° to the right so that the extension tube is horizontal and then remove the plug. This allows the box to self-level as originally intended by the designer.
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In the case of the pic above. The bevel box is overfull, see the close up pic below (go to full size for annotations), the oil is the greenish colour above the sludge line:
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Following some questions I have received, here are some observations:
- Filling must be done conservatively, you do it slowly, if not you are going to have overfill problems.
90 EP is quite sluggish both when running through the flexible hoses to the boxes and whilst finding its way to level in the boxes. You have to give it time. Using a powered fill device will probably result in you ending up with far too much oil in things as will getting too enthusiastic and pumping away at a manual pump as if you were inflating a tyre. It takes 10 to 15 minutes for the oil to get from top of the fexible hose fill point to the outer portion of the bevel box where the sight glass is. Usually I just walk around each station and give each a couple of squirts and then do some other servicing (eg check gearbox and transfer box levels) then go back to the first fill point and see if any oil is visible, and so on.
- You soon learn that "X" station normally takes "so many" pumps to get back to full. Once you have learnt the quirks of each one, the process speeds up. I have written in permanent texta the number of pumps each station needs in an inconspicuous place close to each.
Ultimately, using my system, overfill is minimised and if it happens will just result in wasted oil running out the "T" pieces at the front or where I remove the plug in the extension tube for the sight glass(es) at the back.
Please note that gross overfill will result in overheating and failure of the box/hub. The classic example of this in an AFV was when the Yanks first put the M3 Grant/Lee into production: they were blowing gearbox/diffs during the factory durability tests. It caused them huge amounts of time and expense until someone had the bright idea of lowering the oil level. They actually ended up reducing the oil level by 2 gallons! More is not necessarily better!!!
Their are specified fill levels for all the Ferret's mechanicals - stick to them.
- As I noted below, the oiling process can be speeded up by installing larger diameter flexible hose to the inner bevel boxes and larger barb fittings to larger adaptors/plugs. HOWEVER, the larger flexible hose will be unsightly, get in the way, and means that the care I took to have all the original parts incorporated into my modification will mean that they will now in all probablility get lost. I am a firm believer in trying to keep original parts with a vehicle if anything is modified.
These mods allow for much faster oil level checking and topping up: in the case of the hubs - oil level lowering!
Conclusions and WARNINGS:
The mods are not 100% successfull as the thick oil used in the boxes flows quite slowly down the filling hoses, this takes time. The only way to speed up this process would be to buy plugs to replace the large bevel box plugs, drill and tap them and fit much larger fittings and hose - I have stated above my reasons for not doing so.
The view glasses seem to act as a sludge trap and need to be periodically removed and cleaned internally, otherwise you will think the dark colour in them is oil and may be running your boxes/hubs with no lubricant. I have found that the "dark" appearance is sludge (see pic below) and that a full sight glass has a colour lighter than honey. You will note in the pic below that there is no oil visible as the view glass is empty. What you can see is the line of sludge. The tell tale is the clearly visible brass machining where the base (centre) portion of the "T" was machined. This is not visible when oil is present.
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Only practice will teach you to tell the difference between a full one and an empty one quickly. Believe me, looking in the sight glass of an air compressor crankcase is so much easier due to better lighting and the difference in colour of the thin oil used in that application.
There is the risk of the installation in the outer bevel boxes fouling the steering mechanism.
You need a source of light to be able to see in the view glasses, otherwise they always look full.
To see the level in both the front hubs and bevel boxes, you must first check the hub view glasses, then turn the steering all the way to the right, have a look at that side bevel box and then all the way to the left to view that side, as both drop arms normally sit in the way of the bevel box sight glasses.
WARNING - This mod must be done skillfully and in such a way that there is no risk of fouling the steering of the vehicle. The responsibility is yours.
Should you figure out a better mod or improvements to this one, please let me know.
If you found this article usefull and especially if you apply it to your vehicle, I would appreciate an email so that I know I am not wasting my time writing articles such as this..
