Putting a bolt into the gearbox before wading??? Thats a new one on me. Only possible reason I could think of for doing that would be if a gearbox breather had been disconnected/lost and you needed to temporarily plug the hole.
The gearbox has a couple of small holes in the bell housing where it mates to the engine to allow water to drain. Water will get past the clutch release lever boot and into the bell housing after any lengthy wading excursion there is almost always some clutch judder for a couple of hundred yards.
The gearbox itself is sealed apart from the vent hole at the top by the quadrant box with a plastic splash cap and that is an easy fix. Remove the cap and run a length of fuel hose high up into the engine bay while making sure to avoid the exhaust on route.
As for how capable they are. In standard form with a half decent set of All Terrain tires on they will climb straight up a 45 degree slope (possibly more but I dont have an inclinometer) with little problems provided its a stable surface. Hardpacked gravel, tarmac and even sand with a bit of a run up.
Problems can arise though when cresting hills as the underside of the vehicle can beach itself leaving all 4 wheels off the ground if you are particularly unlucky. Less likely with a SWB.
Approach and departure angles are not the best either so when coming to a steep incline the front bumper can hit the incline before the wheels start to go up, same goes for the rear once the front end is climbing, towbars and rear bumpers can drag on the ground before the rear wheels hit the incline. In extreme circumstances (very steep hill) the rear wheels can be left hanging while the car is supported by the front wheels and the towbar/bumper. Again slightly less likely with a SWB.
Ground clearance at its highest point is only about 11" on a standard frontera so picking your line carefully can avoid most of the inevitable knocks, bumps and bangs to the undercarriage.
Cross axleing (one wheel in the air spinning and no drive to the other wheels) is fairly common due to the front suspension setup (Independent Front Suspension, IFS) but as above picking your line can avoid most occurrences.
The lowest point under the whole car is the center of the rear diff. Its a fairly heavy duty item and I cant count the number of times Iv dragged it across something and its shape lends it to slide over objects rather then binding on them.
Standard tires are rather small, typically 29" or so and upgrading to a 31" or 32" tires will add another 1" to 1.5" under the diff. Doesnt sound like a lot but you will notice the difference.
Wading/fording is pretty good. When my truck was mostly standard (basic 2" lift, no snorkel) I drove through the better part of 500 meters of fast moving flood water which averaged about 2' in depth (much better then the handbooks 11" or 12" maximum). Carpets were slightly damp as the doors arent waterproof, more splash proof.
Hope that helps and Im sure other will add their thoughts.
I also drink Port and I'm not ashamed to say it!
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