Making Gearbox Refilling Easier

Topping up the gearbox was made far easier and far less messy by retro-fitting the SII top-fill cover a while ago, but there was still the complication of needing to remove the filler plug from the side of the box to check the level.

Since the transfer box oil level on SII and SIII Land Rovers only ever seems to rise as the main gear box throws oil aft (even with new seals), it seemed sensible to relocate the Rocky Mountain transfer box dipstick assembly to the main box, and fit the plain filler plug on the transfer box (in time I may get another dipstick assembly and refit it to the transfer box).

I can now check the gear box oil level through the circular hole in the left of the transmission tunnel cover (normally covered with a bicg rubber grommet) and refill it from the top without using any tools and without having to go underneath the vehicle at all, which given how quickly Series LRs lose gear box oil, must be a good thing.


  1. Hi, this is a good idea but i wonder if you drilled this top hole out? i would have thought this would interfere with the push down lock for the high range 4×4

  2. Hi Roger,

    I used the tunnel cover from the same vehicle the filler cap and retaining spring and 1st/2nd gear detent plug came from. You could cut the hole in a standard transmission tunnel cover – it is the same diameter as the hole in the side, and would normally use the same type rubber grommet. It doesn’t interfere with the gear levers in any way.

  3. Phil Hancock says

    Nick, if you get a series 2 or X-MOD gearbox tunnel section they have a sideways hinged access panel for accessing the top filler.

  4. Thanks, Phil.

    The tunnel cover I’m using came from the same late MoD SIII 109 as the filler cap and clip (or part of it is – I use the top of that one with the bottom flanges cut off, and the bottoms of the original tunnel cover with the top cut away – this means that the floor panels are properly supported, but I can access the top of the gear box by removing the tunnel cover without removing the floors, a bit like on a Defender). Since I have the Wright OFF Road matting, the grommets are omitted from the cover, making it very easy to access the cap. I cut the matting where the tunnel meets the floors to make it easier to remove the tunnel area of the mat or to just peel back the corner for topping up. The mat is normally one piece from door to door, but careful cutting with a sharp knife results in an easier fit with no gaps.


  5. Tiago Carvalho says

    Hi, Nick.

    That’s a great solution. Do you have more detailed pics of the filler? What models have it?

    The dipstick assembly is from Rocky Mountain? How does it attach to the gearbox? Do you know if it’s sold separately?


  6. The “filler” is just the cap and retaining spring as seen through the tunnel cover hole in the top photo – the circular steel disk is removed from the top of the gear box and replaced by that cap to allow you to pour oil directly into the gear box. The dipsticks are sold separately by RM, and simply screw into the filler/level plug holes in place of the square headed plugs.

  7. Tim Jarvis says

    Hi Nick,

    I am sure we have probably spoken through a forum but it seems best to post here on this occasion.

    I have found a few places that sell the military oil filler cap and o-ring to sit on the top of the gear box … how did you ‘retro fit’ yours? Can I simply pry the round metal disc out of the square-ish top cover? Mine seems to have four slots equally spaced around the round disc so I assume it is possible. Your military cap seems to sit outside the raised circle though – can I retro fit one onto my Series 3 gearbox? Is it a loose attachment, just held in place with the spring arrangement?

    Thank you, Tim

  8. Hi Tim,

    We probably have stumbled across eachother before on-line; I use the name “Snagger” on LR4x4, The Lightweight Owners’ Club and Expedition Portal forums.

    Retrofitting the filler cap is much as you guessed – the top breather vent disc is initially a clearance fit in the top cover and is held in place by the four peenings (applied by a hammer and chisel) at roughly 90 degree intervals. I removed the disc (it is actually slightly more than a disc – it has a splash guard incorporated underneath to prevent oil being slung directly at the breather vent by the rotating gears) by tapping it out with a hammer with the cover removed, but if you’re willing to damage the disc beyond the posibility of re-using it, then you will be able to pry it out without removing the top cover; you’ll just need to punch a hole in it with a hammer and sturdy small screw driver or punch and then lever it out. Be careful not to damage the seat around its edge though, as the big O-ring of the new filler cap has to seal against that.

    The edge of the cap does sit outside of the top cover aperture, but the O-ring sits inside the lip of the aperture – its outer diameter is just a little smaller than that of the disc you are removing. The cap has an inverted top-hat shape, much like the existing disc, which constitutes the vent splash guard and also locates the O-ring.

    The cap is indeed a “loose attachment”. Normally, the cap is held solely by the spring clip attached to the 1st/2nd detent plug. I drilled out the breather hole to fit a banjo union and remote breather to prevent water and dirt incress through the standard breather hole, but this is entirely optional. It doesn’t hinder the use of the cap as long as you orientate the breather assembly to one side of the spring clip. I found that routing the breather pipe directly aft, tucked down between the aft side of the transfer box and transmission brake gave the least interference with removing and refitting the cap and the gear lever linkages while being long enough and having a deep enough drop to ensure that water cannot be sucked in to the box with the sudden cooling from wading.

    The MoD used these caps for filling, but still used the side filler hole as a level plug, so they would remove that plug and look for the beginning of oil draining through the side to know when to stop filling up. This obviously still entails the use of tools, of getting underneath the vehicle and of getting filthy, so I would recomment fitting a Rocky Mountain transfer box dipstick or a similar DIY solution – it’s a direct fit and can be used through the large round hole on the left side of the transmission tunnel covered with the big rubber grommet. The dipstick does try to protrude a little in the hole, which could make fitting the grommet tricky. You could cut a hole in the grommet to allow the dipstick head to be accessible without removing the grommet, but the transmission (and thus stick) does move around a lot on the mountings (unless you fit the longitudinal tie rod between the cross member and bell housing, as documented in another post), so altering the dipstick to sit easily beneath the grommet is best – you can bend it a little and you could also reduce the length of the tube and stick by an inch or so so that the head of the stick is roughly level with the bottom of the tunnel cover’s hole.

    I hope that all helps!


  9. Tim Jarvis says

    Hello Nick,

    Thank you very much for your response .. and the huge detail within it.

    I have bought an MoD top filler cap and understand more clearly how they work now – I just have to build up the courage to pry the existing one out. At the moment it seems that everything I try to undo has rusted and seized and invariably 2 out of 5 bolts shear when being undone!

    I have also bought the Rocky Mountain dispstick (well, I have a dipstick and top fill cover for the transfer box fitted already) ready to fit to the main gearbox – I am just debating with myself whether I could fit the dipstick immediately and then use it (with an oil gun) to top up the gearbox until I do the top fill cover?

    I have spent the week fitting a disc handbrake and fairey overdrive (in between bursts of rain) ready to drive 600 miles around the coast of Wales to raise money for Mountain Rescue ( I am now … nervously … off to test that she will drive again!

    Thank you again, Tim

  10. Hi nick …. I have huge oil leaks from my gbox…. it seems to be coming from the top breather plate. .. do you remember when you got this military filler from ? And the other bit’s. .. I have the dipstick on order..

  11. Hi Ben,

    I got the cap and o-ring from Dunsfold LR. The gear box top cover is the original – it just needed the existing steel plate disc knocking out. The brass plug with retaining spring that replaced the plain 1st/2nd detent spring plug came from a friend’s scrap gear box. I’m sure DLR, Craddock and PA Blanchard will be able to help, but you can otherwise look on forums’ military sections to ask if anyone is getting rid of an MoD box, because they were standard on militry units.

  12. Hi all
    I have been trawling the web for one of these filler caps to no avail – anyone got any current idea what the part number is or where to get one?


  13. I cant help with part numbers as my manuals are in the UK, but I’d be surprised if none of Dunsfold LR, PA BLanchards and Craddocks Spares can’t provide them. Failing that, sourcing from an MoD vehicle being broken fr spares is an option. If anyone else has other suggestions, please chip in.

    If you are still stuck, then you could modify the existing parts. The cap is very basic – it’s like the existing steel disc but with rolled over edges and a wider overall diameter, but the steel disc will do amply as long as you can find a suitable o-ring or other sealing method (like a ring cut from neoprene or rubber sheet) and you fit a retaining system – it doesn’t specifically need to be a leaf spring from the brass detent plug, though I’m sure it wouldn’t be hard to fabricate a similar spring from flat steel and drill and tap the plain brass plug to fit a bolt for the spring. It’s a very simple set up that could easily be replicated, even if it lacked the finesse of the production parts.

  14. Found one from Dunsfold – after realising that talking to human was better than relying on internet to catalogue all available parts! Just waiting for decent day to avoid getting wet! I have got the parts and am surprised by the plastic breather that just sits in hole on cap – even with the spring over it it looks like it will just fall out on any rough stuff – will try and find a banjo union that will do the job the thickness of the cap is quite thin – what did you do to ensure a secure fit? also did you use solid copper breather pipe?

  15. My cap just has a small hole in the top for breathing, no plastic fitting. I used plastic fittings for windscreen washers and silicon tube from a motor factors to extend the breather.

  16. Geoff Holloway says

    Hi, did the roamerdrive dipstick screw straight into the gearbox? I know it needs the adaptor for the transfer box!

  17. Hi Geoff,

    The dipstick fits the gear box in exactly the same way as the standard filler plugs are identical.

    I don’t recall any adaptors, just the 90 degree elbow.

    I found it useful to cut the dipstick and tube down a little so that the stick was more easily withdrawn through the transmission tunnel side hole for inspection.

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