How much torque to damage diff drain plug threads?

Made a silly goof today when I was changing the rear diff fluid on my 4Runner. The ratchet I had to remove the drain plug was too short so I grabbed my breaker bar to crack the drain plug loose. Got my lefty loosey righty tighty mixed up and accidentally tightened the drain plug instead of cracking it loose. Probably tightened it an 1/8th of a turn, no more than 1/4 turn for sure. It was torqued to 36 ft-lb before and I have no idea what the equivalent torque would be with an extra 1/4 turn at worst. Now I’m paranoid that the differential housing threads are deformed. The drain plug did have the OEM steel crush washer on it so I’m hoping that would have deformed first before the threads were damaged but I have no idea what the maximum torque the differential housing threads can take before deforming.

What do you all think?

 

If it didnt let loose, and if it doesn’t leak, it’s probably ok.

However, I would be gentle with the threads from here on out and use the torque wrench for final tightening.

 

Thanks for the input. I removed the drain plug and reinstalled it with a new crush washer and tightened with a torque wrench to 36 ft-lb. I’ll let it sit overnight and see if it leaks at all. I imagine they would have designed the drain plug to be weaker so it would strip rather than the threads on the differential housing so hopefully if anything was damaged it would be as simple as getting a new drain plug.

 

That would be my guess as well. The transfer case would be a different story, since the housing is aluminum. I just changed out fluids yesterday, and am ashamed to say I didnt bother to look up torque specs on TC bolts.

 

Maybe even order another OEM plug anyway, and install it at the next lube change, for the fresh threads if nothing else. Looks like they're <$20.

 

I wouldn't worry about it. The plug is steel, the housing is steel, the crush washer is aluminum IIRC. you would have to have REALLY cranked down on it to strip the steel threads - dealer oil techs hit them with impact wrenches all too often and shockingly tales of woe aren't on the forums daily. If the threads looked clean when you pulled it out, you used a new washer and where able to re-torque without a leak I would bet real money its 100% fine.

As mentioned above, be really careful with the transfer case, transmission and oil pan as those are all aluminum and its a lot easier to strip aluminum threads.

Trust me, you wont want them to make the plug out of something soft. An aluminum plug would be far too easy to accidentally strip the hex when removing it and then you would be getting out the drills and bolt extractors. Been there, done that, not fun (No aluminum on my truck but have used them in some other applications.



(Disclaimer, I'm speaking from experience working on my Taco - 4Runner is too new - but the Taco has the same transfer case and rear axle...)

 

Diff Torque specs:
Rear diff drain plug - 36 lb-ft (24mm or 15/16")
Rear diff fill plug - 36 lb-ft (24mm or 15/16" shallow)
Front diff drain plug - 48 lb-ft (10mm hex + 2-3" ext)
Front diff fill plug - 29 lb-ft (10mm hex)

Transfer case Torque specs:
Drain plug - 27 lb-ft (24mm or 15/16")
Fill plug - 27 lb-ft (24mm or 15/16")

References:

 

Thanks for this, although I just finished changing my diff/TC oils an hour ago lol. I just did gutentight.

That front diff sure is putzy with the different torque values.

 

I did the 20FT LBS of all those plugs ... 36FT LBS is a lot of damage ... the oil threads are higher damage of the threads I did it 20 FT LBS ALL 55 yrs .....

 

Yeah, and breaking free that front diff drain plug at 48 ft-lbs with a hex Allen bit takes quite an effort. I’m going to get the Lexus part which is a standard hex nut plug for the next oil change.

 

Fun isnt it?

The first time I had to do it on my Tacoma I put a long breaker bar and laid down on my back and leaned on the bar with my foot. That made short work of it.


Dealers will hit it with an impact I am sure....

 

That's the worst!

 

I double checked with a magnet and the crush washers I have are steel. I looked up the maximum torque for the threads although I’m not sure what grade they are. Even the lowest grade I could find for a M18 bolt had a torque of 95 ft-lb. As long as it doesn’t leak I’ll assume it’s ok and next time I change the fluid I’ll replace the drain plug and inspect the threads in the diff housing.

 

I wouldn't be surprised if that bolt, in that housing, is one of the strongest fasteners on the vehicle.

 

the torque gun is tightening the plugs then the damage ! auto shops !
I use 3 torque ratchets lower /med /higher ......... 20 ft lbs of the plugs ...oil threads are on the threads ...