When I bought my 1969 Series IIA 109, it had 6.50x16 military-spec tyres but I wasn’t satisfied with their performance and decided to change them for 245/80 R16s with a more aggressive mud pattern.
Shortly afterwards a driveshaft twisted, then the differential failed. Did the larger tyre cause all this damage? The failures always happened when I was driving on the road, suddenly and without any symptoms.
The 245/80 R16s are much bigger than any factory-fitted tyre. The largest used by the factory were 7.50x15, which are about 190mm wide – compared to the 245mm-wide tyres you have now. Also, that aggressive mud pattern is going to put a lot of extra strain on the drivetrain.
The overloading probably isn’t breaking the drivetrain straight away, but the effects build up over time until the components fail without warning.
However, the tyres alone should not really be enough to cause things to break, so there could be another fault. Maybe the previous owner drove very hard off-road and you’re seeing the problems, or you may have been unlucky with the new parts you’ve fitted. But it’s much more likely the Land Rover is actually stuck in four-wheel drive.
On the road, the Land Rover must use two-wheel drive. If four-wheel drive is engaged, the front wheels turn further than the back ones on a corner and this puts an enormous strain on the drivetrain, which is known as wind-up.
It’s very easy to check if your vehicle has this. Simply jack up one wheel. If it spins and skids as it comes off the ground, you have wind-up; if it doesn’t move, you don’t.
With the old 6.50x16s (about 165mm wide) the tyres were probably able to slip and release the stress, but with the wide tyres they probably can’t slip – and so the stress will just keep building up until something breaks.
It’s also very easy to check whether or not your vehicle is stuck in four-wheel drive: just lift one front wheel off the ground and try turning it. If you can only rock it about a quarter of a turn or less, it’s in four-wheel drive.
If this is the case, first check the yellow knob is fully up by selecting low range (pull the red lever back) then push it forward again while pulling up on the yellow knob.
If the knob comes up and the front wheel now spins freely, you need to replace the spring under the yellow knob. If this makes no difference, it confirms that the four-wheel drive selector shafts have seized.
To fix this, remove the right-hand front floor and remove the plate under the centre seat so you can reach the top of the gearbox. Next, remove the top cover on the transfer box next to the handbrake.
Remove the screw holding the four-wheel-drive lever in place and pull the pin
out of the top of the gearbox, taking careful note of how it was fitted. Now remove the two bolts holding the front cover over the selector shafts on the transfer box and slide the cover forward.
You’ll now be able to see the selector shafts. Clean up the front end of the shafts where they poke through the front of the transfer box and give them a good dose of penetrating oil.
Next, drift the four-wheel drive selector shaft backwards and forwards, working the red lever to help it move until all three shafts move freely.
Once they’re free, give the ends of the shafts a liberal dose of gear oil or grease and reassemble the gearbox. Check that you now have two-wheel drive again. Hopefully, that should be the end of your drivetrain failures.