D4 rear diff fill plug - should it go this far in?

[twr7cx]

Just finished draining and refilling the rear diff on our MY12 D4 TDV6. Tried to torque the fill plug up to 34Nm as per the D4 Workshop Manual but it seemed to keep winding. Took a look and found this:

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In my (limited) experience these types of drain/fill plugs don't usually go so deep into the thread. Usually they tighten up well prior (due to tapered threads perhaps?). Am I right that this isn't right?

Maybe a replacement (part number TYB500060) is in order...

[SeanC]

On my D3 the plug is pretty well flush with the top of the threaded hole.
That was torqued the specified 34Nm.
I tightened by hand to what I thought was fairly tight. Didn’t want to strip the thread. Put the torque wrench on and got at least an extra 2 full revolutions maybe more. (was awhile ago) Was really surprised.

[twr7cx]

It looks to me like the exposed threads in the diff housing case are clean, shiny and silver indicating that they weren't exposed to the outside environment (dust, dirt, mud, etc) over the previous 150k kms and so it's gone in much further than previously.

[SeanC]

It looks to me like the exposed threads in the diff housing case are clean, shiny and silver indicating that they weren't exposed to the outside environment (dust, dirt, mud, etc) over the previous 150k kms and so it's gone in much further than previously.
Maybe it wasn’t torqued originally. The difference between what I thought was tight enough and what was actually tight enough was 2+ revolutions which seems about the the amount of clean thread showing. I would be surprised if many mechanics torque things like diff drain plugs, sump plugs, etc.

[DiscoJeffster]

Does it leak? No? It’s fine.

[Eric SDV6SE]

If it isnt leaking then all good. I'm a big fan of using the correct torque settings, even on ancillary items. The workshop manual wasn't written overnight or at the pub over a few beers. If you've done it up to the specified torque then trust that it's done right.

The extra depth could be due to variances in the casting wall thickness of the housing

Note that most torque values are specified for lightly oiled or sometimes dry conditions. The drain plug for the diff would fall under lightly oiled status. If you put a lubricant such as NeverSeize or CopperCote on the thread, the friction factor is changed, and using the same torque value will result in the bolt being overtorqued and potentially damage the threads.

The only other reason for having the plug flush with the housing is that this will ensure you can get it out again. You don't want to fill the threads up with gunk or have them corrode so badly that you can't get the plug out.

I would therefore suggest that you wind the plug out until flush with the casing and ensure its not leaking.

Just my 2c

[twr7cx]

If you've done it up to the specified torque then trust that it's done right.

I haven’t done it up to the specified torque. As pictures it’s at around 25Nm only. I’ve stopped winding it in any further as with the torque wrench set to 34Nm, it seems to just continue to turn in without a sign of stopping. Obviously the hole isn’t blind which allows the refilling of the diff, but that worries me as if it keeps getting wound in it count potentially go the whole way nd fall inside...

I think my best course of action is to wind it back out and leave it flush. Given the cheap price of a replacement I’lol order one in my next parts order and try it.

[DiscoJeffster]

I have magic hands, just ask my wife. My hands have adept feeling and know what tension is required to do up a fastener. Is it a discovery thing where even farts need to be torqued?