Extending Pajero/Montero Front and Rear Diff Breathers
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By: Frank Zanetti - 11/17/02

Waterproofing your driveline is pretty straightforward.


After dropping my front diff oil after several trips that included numerous water crossings, I discovered some water in the oil evident as the nasty milky substance that runs out of the drain hole first. Obviously the factory front diff breather was not adequate for that kind of water fording!

Plumbing the rear diff

I inspected the front & rear factory diff breathers and discovered that the rear diff breather has a barb fitting welded into the diff housing with a rubber tube running from this into the rear crossmember. Not bad, but still not high enough. With the water and bog hole crossings that we have here, the diffs should really be vented to a high place under the hood. I removed the rubber tubing from the rear diff breather and replaced it with 8mm blue plastic high pressure tubing (for compressed air fittings) and routed it to high up against the firewall. The same could be done using normal fuel line. At the end of the tube I inserted a micro filter to stop any foreign particles from being drawn into the hose.



The front was not so easy!

The front diff has a plastic one way valve inserted into the housing. This is capped by a brass flap and capped in a rubber sleeve, definitely inadequate as water had indeed made it's way into the front diff. The oil was drained and the front diff cover removed (8 bolts) and it was found that the breather valve is only plugged into the housing and not threaded in. It was removed and a 1mm piece of metal was welded over the exposed hole. A hole was drilled and tapped and a high pressure female air fitting was inserted. From this, 8mm blue plastic high pressure tubing was inserted and routed to a spot high up against the firewall and a micro filter installed at the end of the hose.

Image courtesy of Frank Zanetti Image courtesy of Frank Zanetti
Front Diff High Pressure Air Fitting With Breather Line Attached Front Diff High Pressure Air Fitting With Breather Line Attached

I also had to grind a little metal out of the front diff mounting frame for the air line to clear, due to the position of the fitting. Another method would be to braze a barb fitting into the hole where the factory breather is pressed in and use normal fuel line for the breather hose (I used the high pressure plastic hose since we use it at work and I know how robust it is).

Research also revealed that all Gen 1 and Gen 2 (up to 1993) have the same front and rear diff breather assemblies. Gen 2 Monteros (from 1994 on) have a barb fitting welded into the front diff housing and a combination of rubber and metal tubing that is routed into the engine bay instead of the earlier one way type valves. This would be easier to mod as the barb fitting is already fitted, the old breather line could be removed and scrapped and a new rubber hose attached and routed to a higher position under the hood.

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