Half of them i have looked at buying have rear prop removed. I know why .... VCU usually. But how can I then check IRD is working properly ?
 
Half of them i have looked at buying have rear prop removed. I know why .... VCU usually. But how can I then check IRD is working properly ?
You can only really test it under normal pressure when props/VCU are fitted. Turning it by hand for fault finding is ok but testing in anger is the only way to know it's ok. It's the only way to find vibrations and squeels.
 
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Half of them i have looked at buying have rear prop removed. I know why .... VCU usually. But how can I then check IRD is working properly ?
You would have to check the rear pinion for play. There will be an amount on rotary movement - but there shouldn't be any lateral play at all. You'd then have to drain the oil, if it comes out grey, then that's the bearings ground to a pulp and suspended in the oil. If it comes out looking like oil, then its either OK or they have replaced the oil since removing the propshaft! Then you'd have to remove the rear pinion and examine the teeth on the crown and pinion gears - if there's much (any?) signs of wear, then that's abuse from bad tyres/VCU that would result in an IRD not suitable for putting back to 4WD.

Those checks will give you an idea of if its OK. Also check give the RH driveshaft where it enters the IRD a wiggle to make sure there's no movement there - its support bearing is another failure point.

If the gears are OK - you can buy rebuild kits for under £200 which contain all the bearings, seals and a cooler. Its a big task to install one of those kits though. If the gears have damage, then you are looking at a recon IRD which will probably be £1K.

If they have the props still installed - I think checking the oil in the IRD is about the best way of find out if its OK.
 
If its had the rear pinion removed and a blanking plate installed, walk away if you want a 4WD truck - or budget for a recon IRD as well as VCU - and check that an IRD without a pinion is OK for exchange.
 
But how can I then check IRD is working properly ?
You can get a rough idea how much bearing wear has taken place by the amount of backlash in the rear prop output flange. It should be no more than 3mm or so.
Also draining the oil will give you a good clue as to the IRDs condition as GG said above.
Normal looking oil means the bearings are ok, but oil that's looking like it's full grey particles, means the IRD bearings have started to disintegrate.
 

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