Cross Threaded Rear Diff Fill Plug

This didn't happen to my truck (thank goodness) but a friend of mine cross threaded the fill plug on his rear diff and actually demolished the threads on the diff itself. I took a look and we could actually get the fill plug snug and it appears to have made the seal but wanted to ask if any here has done this before and solutions you all might have?

 

If it’s demolished as you mentioned, you won’t be able to tighten it down. You have 3 option IMO:

1) use a tap
2) time-sert or equivalent
3) weld on a nut

 

Demolished is probably the wrong word. It’ll get snug. If you continue to tighten it after it’s snug it will spin easily then snug up again. So there are threads and it appeared to seal the diff. Just doesn’t inspire a lot of confidence

 

Wondering about putting a really thin bead of rtv gasket around the outside of the fill plug to seal it - any thoughts here?

 

The threads are stripped. Anything you do from here on out is a bandaid. Tapping the hole out to a larger thread is problematic, cause you won't easily find a bolt to fit. A nut is an ok option, cause you control both variables. Helicoil is problematic cause the depth. Cutting off the diff cover and welding a dorman replacement is an option.

sealant, etc.. is just a wish and prayer.

 

You left an entirely new axle housing off the list...

 

or a fab housing…

 

Holy grail, cutting off the entire cover just to replace the damaged thread of the full plug is ridiculous. The amount of work involved to do that can be easily done with other options. I welded a few nuts in place of a damaged thread on a couple of damaged housings in the past, never had an issue. The downfall of a nut is the gap between the hex to the housing, since than, I been using rounds steel bung. Fit tighter and look better.

On one occurrence, I tap the hole to m20x1.5 and had no issue finding a “oil bolt” from O’Reilly for like $5 buck and they had half a shelf worth of oil drain bolt replacement on the sales floor.

 

yea, that will be easier vs cutting, flap disc to clean the surface, and welding.

heck, I see bare non-elock housing go for 50 buck and elock for 100 around here from offroad group who strips them for trail spares.

 

The thing is it's not totally stripped. It gets snug and almost seals. It appears to have a slight leak. Im really curious about blue threadlocker to keep it from rotating but still allowing it to be pulled off later and some RTV gasket around the outside of the fill plug to create a seal. I mean if they seal the transmission pan with this stuff I feel like it will seal the fill plug?

I should also say this thing stays on the road I'm not really worried about it coming loose offroading somewhere

 

I'd chase the threads with the same size tap,, let it "stand" the threads back up. Then try it out, make sure the plug threads are good and straight. I'd think this is worth a try since it's just a plug.

 

The issue is, you can’t torque it down. With that in mind, hand snug tight with blue thread lock and rtv will probably still end up rattling loose and leak regardless.

In contrast to your idea of rtv with the trans pan, you’re sandwiching 2 piece together with the proper torque and utilizing the rtv to seal whatever gap/deformation there is. That concept is different front your oil drain as you can’t torque.

 

FWIW, Murphy dictates the plug will de-ass the area at the worst possible time in the worst possible location...

 

imagine the plug rattled loose before getting on the interstate. 10 miles later, the diff overheat and blow due to lack of lube, potentially taking the transmission with it and sending the driveshaft as shrapnel to other vehicles.

 

I mean isn't this the same concept? The 2 pieces I'm sandwiching together are the fill plug and the diff. The RTV seals the slight gap/deformation between the fill plug gasket and the diff. The threadlocker keeps the bolt in place along with the threads that are still there. Again the bolt is very snug. You need to yank really hard on a 1/2" rachet to get it to move. It's not like it spins freely. I could use red threadlocker but future service would be an absolute bitch

 

I thought about this I'm really nervous about blindly drilling into the diff and actually hitting the gears and any metal shavings falling in there

 

I feel like if the diff plug fell off you'd hear a nasty noise before it got to this point. But I've never had a diff run dry I'm not sure what would happen

 

if you’re on surface streets, the noise will be more noticeable because your stopping and going but being on the interstate at 70+mph, highly doubt you’ll hear it

But you do you with your buddy’s truck. It’s not my truck. If you think thread lock and rtv is sufficient as a fix, send it.