Member Since: 06 May 2012
Location: Arizona
Posts: 48
Stripped drain plug for transfer box. Ideas?
Yikes, I stripped the drain plug for the transfer box when changing fluid. Has anybody else experienced this? Upon examination, the internal threading only goes 360 deg for the a few mm before there's an opening with only 2 narrow collars that are (were) threaded. See photo. So I can see where it could be prone to stripping.
What to do??
* My current thought is to simply buy a longer plug, which would extend to the non-stripped threading (see photo; there's a good 8 or more mm of non-stripped threading).
* Other thoughts are retapping (helio-coil or somesuch).
* Another possibility is to permanently install a plug that includes a valve for draining. I have full skid plates, so I wouldn't have to worry about scraping the valve.
Thoughts/advice appreciated.
2nd Mar 2015 12:23 am
Russell
Member Since: 24 Aug 2007
Location: Kent
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Before you install a longer bolt, what are the gaps inside for, do they allow oil flow and if uoi instal a longer bolt will it restrict oil flow?MY17 D5 1st Edition Namib Orange
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2nd Mar 2015 1:32 am
DVD
Member Since: 06 May 2012
Location: Arizona
Posts: 48
That's a great question. I assumed that the original bolt, when seated, covered those openings. Those threads on the collars are , so at least half or more of the opening is obscured by the drain plug. I just checked more closely but with imprecise tools (a pencil), and the plug either entirely obscures the openings or leaves just a pinch of opening. The drain plug has a slight conical seal, so hard to tell within a mm, and that's about the margin. So not much could be flowing through there.
Those openings also factor into the helio-coil idea. If the openings serve a purpose, it wouldn't be good to do the helio-coil threads, at least not over the openings.
But again, based on the size of the original plug and the depth of the openings, I doubt that they are intended for oil flow.
2nd Mar 2015 2:09 am
SHARKYSHARKS
Member Since: 20 Dec 2008
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What about Loctite stripped thread repair ??
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2nd Mar 2015 8:57 am
Madrilleno
Member Since: 13 Oct 2014
Location: Nottingham
Posts: 1742
I can't be certain from the photograph, but are you sure it's not the plug itself that has stripped, rather than the thread in the hole? It looks to me like there are bits of plug thread left in there. They can be (very carefully) picked out with a scriber or needle file; making sure you don't push the swarf into the transfer box.
Usually, plugs are made of a weaker material than the box so that the plug threads *should* strip rather than damaging the casing.
If it is the hole that's stripped, you could try a helicoil insert, but that would, again, risk pushing swarf into the gearbox.
Oops - just saw your helicoil comment in your second post.There are two rules for success,
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Member Since: 06 May 2012
Location: Arizona
Posts: 48
I use the vehicle on some fairly remote and rough trails, so I'd rather not try something like loctite and hope for the best.
The xfer box is aluminium. The plug is steel, and the plug is definitely somewhat stripped. I bought a replacement plug (same specs M16x1.5) but just a hair longer (11 threads vs 9 threads or 12 mm of threading on the stripped bolt).
There's enough internal threading left that the new drain plug went in well even from the start, but I didn't totally snug because I envisioned just a single good internal thread holding it, and I'd strip that if I snugged it.
IF it can be determined that those openings serve no useful purpose, then I think the slightly longer plug bolt (say 18 or 20 mm) would go into the virgin threading above the openings to provide a proper seal. The big question is what Russell stated: What are those gaps for?
3rd Mar 2015 1:28 am
DN D3 Decade
Member Since: 24 Jun 2006
Location: W.London.
Posts: 2293
Probably easier said than done, but what about getting a plug long enough to engage properly with the good thread furthest in, put it in a lathe and machine some of the thread + a bit more away in the middle, to coincide with those gaps, so that if oil needs to flow around it, it can? ........You may need to put some sealant around the part where the thread is stripped to stop leakage, or it may have a crush washer, either way I agree that you should not try to crank it up too tightly.
3rd Mar 2015 1:41 am
snailcove
Member Since: 21 Nov 2010
Location: Aberdeenshire
Posts: 460
I would go for a longer plug and drill a few holes to coincide with the openings and one down the centre of the plug to allow flow from one side to the other and flow in to the box as well to cover all flow routes
3rd Mar 2015 6:29 am
DVD
Member Since: 06 May 2012
Location: Arizona
Posts: 48
Good ideas. Thanks!
I started thinking in another direction this evening - something like this:
I know that I have a little grip left on the internal threads. And I have skid plates covering the xfer box, so I wouldn't be concerned about inadvertent ground strike opening the lever.
Slather the new valve plug with some permanent loctite and use the handy valve 2 yrs from now when I want to change xfer box fluid.
3rd Mar 2015 6:53 am
snailcove
Member Since: 21 Nov 2010
Location: Aberdeenshire
Posts: 460
That would work as well , save you from disturbing that bad threads again
3rd Mar 2015 7:10 am
snailcove
Member Since: 21 Nov 2010
Location: Aberdeenshire
Posts: 460
https://www.nospillsystems.com/index.cfm
We used to use something like this on auxiliary engine's , less chance of getting opened accedentaly but you could also use a blank on the end of your idea
3rd Mar 2015 7:26 am
DVD
Member Since: 06 May 2012
Location: Arizona
Posts: 48
Another idea, for future search reference in case somebody else has this problem.
I don't plan to go this route, but one of my local Land Rover buddies suggested that it might work to simply permanently plug the drain hole and use a suction device in the fill hole for future changes.
3rd Mar 2015 6:24 pm
snailcove
Member Since: 21 Nov 2010
Location: Aberdeenshire
Posts: 460
Only problem there is if the box starts to break up or start giving you grief you might not see small filings or metal debris flowing out with a suction pump as they will just sit on the bottom, just a thought
4th Mar 2015 5:44 am
garrycol
Member Since: 06 Dec 2010
Location: Canberra
Posts: 1115
Only guessing here but I suspect that the case of the tfr case is thin and there is an extension that goes up into the box to allow the plug to have enough threads to get proper purchase - however this creates a pool of oil when it comes time to change the oil so they have put the slots in it to allow the oil to drain out.
Why not get two helicoils put in - one in the top section and one in the bottom section.
Garry
4th Mar 2015 6:36 am
nighthawk
Member Since: 24 Jul 2010
Location: Malta
Posts: 1163
Was going to suggest helicoils too. Back in 2003 the rocker shaft in my Defender's Tdi300 came loose. The threads in the cylinder head where the stud threads into had stripped. Put a helicoil in and it lived 7 abusive years without a single issue, and sold it on Dennis
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, so at least half or more of the opening is obscured by the drain plug. I just checked more closely but with imprecise tools (a pencil), and the plug either entirely obscures the openings or leaves just a pinch of opening. The drain plug has a slight conical seal, so hard to tell within a mm, and that's about the margin. So not much could be flowing through there.
........You may need to put some sealant around the part where the thread is stripped to stop leakage, or it may have a crush washer, either way I agree that you should not try to crank it up too tightly. 
