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Series 3 main box top cover breather


Gazzar

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Right, I'm putting together a series 3 box - all going well, but slowly.

I'm doing the top cover and gear levers now, and have hit a strange one.

I ordered a new top cover - the bit on top of the casting that contains the selector shafts. This has a breather, so I ordered this as well.

Actually, I ordered a genuine part and a britpart one - no difference that I can see - but anyway, The breather appears to be a loose fit onto the hole, and I was wondering was there some majic I should be doing to stop it falling out.

I've looked at another box and it has a rubber blank plug in the hole, which could explain the persistent leaking from the selector shafts.

Am I to melt this into place (first preference) or is there some other technique to fit it?

I'd appreciate a hint in the right direction, thanks!

G.

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The plate in the 109 has the right sized hole - but a blank grommet in place.

I think I'll hot air gun it into place.

G.

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The breather should be mostly internal, so only the top cap sits above the steel plate. A grommet will not allow venting or breathing, so would cause leaks in the transfer box. (this plate vents the transfer box, not the gear box, whose vent is in the circular plate over the selector shafts). In practice, though, the o-ring sealing the plunger operated by the yellow knob seals poorly and will allow breathing through that point.

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Are you sure Snagger? If you are, then my gearbox in the 109 can't breathe - explaining the constant leak from the selector shafts! The round cap on mine in the 109 is just a plate set in the alu, and this has a blank grommet, also the top plate has a blank grommet. I think may order some more bits, and fit the military cap.

Looking at the various sections of the box on the bench, I think you are right - there is no air path way between the main box and the cavity with the square plate on it. And there IS a groove on the mating surface of the transfer box that would allow air to escape into the cavity.

I've fitted the military cap and breather to the box I'm rebuilding, and I'll hot gun this breather in as well, so that should also help. The aim is a quiet leak free box, every little helps!

G.

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Yes, I'm sure - the breather you're working on, which sits atop the square "tower", is for the transfer box: a slot runs up the gasket face of the back of the gear box from the output shaft hole, forward of the oil slinger on the main shaft, into an empty chamber under the square plate you have in the photo. That slot is aft of the gear box's rear oil seal, so gear box pressure can't vent through that slot. The only way the box can vent through the breather on that tower is via the selector rod drillings in the casing, but the selector rods would seal fairly well with the oil, so I doubt it'd breathe well that way. The steel disc in the gear box top cover should have be double lined and have another plastic breather in it just like the tower's breather. Fitting an MoD spec top-fill cap is a good mod, especially when used in conjunction with the Rocky Mountain dipstick for the transfer box - if you bend the stick and tube a little, you can fit it to the the gear box without any other alterations, making level checking and refilling a really quick and easy job. I did it a while back - just remember to get the thick o-ring for the cap and the retaining spring/detent spring retainer (its a brass plug that replaces the existing plain brass plug the retains the 1st/2nd detent spring, but has a swing-away leaf spring that holds the filler cap down).

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Remember to cut a hole in the top of the tunnel to get at the filler. It should be the same size as the hole on the side (which you can use to get to the dip stick) and uses the same type rubber grommet.

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That I can't do - the whole underside of the tunnel is covered in 4mm of asphalt + foil backed camping mat as sound proofing. Which works.

I may keep the old school way of topping up = the squeeze bottle and cursing. Though if I cure the leak from the selectors I'll no need to topup - just need to check the level!

G.

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Don't be disappointed if the selectors still weep - I tried all sorts to fix them, with seals from various sources, substitution with suitable diameter rubber hose and now a set of o-rings double up (two per rod), which works far better but still isn't a cure. It's a bad bit of design having the rods exposed, rather than inside a section of casing which drains back into the box.

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  • 6 years later...

Evening, I have followed this historical thread with interest. Like you gents, I have the standard oil weep from the 1st/2nd selector rod. The gearbox was recon 2 years ago, but is a civilian model and not an MOD version - hence the round oil filler cap has been crimped in and has a single hole approx 1mm in diameter. It has been recommended that I simply remove the filler cap all together - but I would prefer to fit a breather to the main gearbox oil filler cap, to relieve oil pressure but also only fill the main gear box with 1litre of oil and not 1.5 litre.

 How have you got on with fitting the military oil filler cap and spring - or, have you fitted a Defender extended gearbox breather (looks to be a banjo style feeding a pipe) as per Nick's landrover website article - and does it still leak from the selector shafts? How did you un-crimp the oil filler cap - sharp chisel and patience?

I am trying to work out whether I continue to top it up every few weeks, or, crack on and modify so that it includes a breather. Oddly, no dripping whilst driving, nor after 30 minutes parked up, but I think as it cools, the 2 year old selector seals are just a weak spot for the oil to run. 

 

Thanks

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The box I rebuilt hasn't been used, yet. It's in a lightweight.  The plate just popped out with some assistance, and the military breather parts fitted in place.

Another thing that was suggested is to drill a return path for the oil in the selector bore, so oil at the seals just drops back into the box.

On my 109 the box leaks after about 50 miles of driving, but not much. 

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I wasn’t going to reuse the original breather plate, so I knocked it out with a hammer and drift with little care for damage.  But I only removed it because I wanted the SI/MoD type top filler.  It works fine as a breather, as long as it isn’t blocked up.  The banjo bolt and plastic line were added to the original breather plate and then the replacement top fill cap (which also has breather holes just like the original plate) to prevent dirt and water ingress.

Unless you are replacing the breather with the filler cap and already have the cap, thick o-ring and retaining spring (which is attached to a brass plug that replaces the plain plug covering the 1st/2nd detent spring), then leave the cap in place and just make sure it’s not clogged.  You may need to remove the top cover to do this, but you’d already be doing so to replace the selector seals anyway.  Wash the breather plate through with some solvent or diesel, using tooth picks or thin skewers to break up any compacted or congealed mud and dust that has collected.  You can also check the transfer box breather, which is at the top of the square tower at the back of the main gear box ( there is a slot in the base of that tower that runs down the mating face of the casing to the hole for the main shaft, just behind the rear seal of the gear box and in front of the transfer box input gear.  Yule some stiff wire to rod the slot clear of any muck to make sure the transfer box can breathe.

Unfortunately, doing this and replacing the selector seals will still result up in occasional drips from the box - it’ll still sweat through the selectors, whichever type of seal you use (the original rubber type seem better than the ring and white plastic “key ring” affair).  But it won’t be enough to affect oil levels within the box, just enough to be annoying and mark your parking spot.

If you are losing large amounts of oil from the gear box, it should be relatively easy to spot the leak.  You could have abs deals on any of the selector mechanism, which would show up if you clean the box with a steam wash and then drive a bit.  If it’s from the seal on the input pinion, you should be losing oil through the flywheel housing drain hole.  It may look black from clutch disc particle contamination, but you’d be able to smell the sulphur of the EP90.
 

The most common cause, though, is the rear bearing carrier not having been sealed in the casing by lazy BL staff on the assembly line - the main shaft rear bearing sits in an annular sleeve which in turn sits in the hole in the rear of the gear box case.  It is supposed to have had a seating compound, a little like thread lock, applied to the outside circumference before being inserted into the case, but almost none did, and that is how the oil gets from the gear box into the transfer box.  The test for that is to simply check the transfer box oil level by removing its filler plug (rear face, next to the speedo housing and hand brake).  If it’s over filled, then the gear box has thrown its oil into there.  The fix, unfortunately, is a full rebuild of the gear box, adding the seating compound.  That doesn’t have to be expensive, if everything else is in good order - you can reuse the old bearings, gears and shafts if they’re not damaged, and even the seals if they’re ok, but you’d need a gasket set, the bearing seating compound and I’d urge you to replace the three leaf springs on the 3rd/4th synchro while you’re in there.  A gasket and seal kit will include all the seals for the main shaft, the selectors and detents, so is a simple purchase.

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Gentlemen

Thank you both very much indeed for the advice. I will progress with fitting the MOD style oil cap and spring, removing the original. Temporarily, I might tap the original oil filler cap with an 8mm hole, just to see if this does help with relieving pressure, but reduce the oil from 1.5litre to just 1 litre.  The only gearbox leak I have is from the selector 1st/2nd. Oddly, it does not matter if I drive 5 miles or 50, it runs about 10 minutes after being switched off and parked. Hence the conclusion this is probably more to do with heat and pressure than the selector rod "ring". 

Thank you both very much. Hopefully, this will help my driveway to have the odd spit of oil, as opposed to the slick I have become a bit to relaxed with. 

 

Best wishes

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