Anyone who owns a 4WD Toyota and has dealt with the drain and fill plugs on the IFS front diff knows that they generally suck. They use either a 10mm or 12mm hex key, and that can be a problem for many reasons:
- The recess that the key fits into can easily get filled up with crud.
- If the recess isn't cleaned and the hex key doesn't fully seat, it's easy to round over.
- Hex key's aren't generally all that long, so it's hard to get the leverage needed to loosen the plugs.
- The plugs can get extremely tight, making it hard to loosen with a hex key.
There are ways around some of these shortcomings of course - you can fully clean out the recess, you can use a hammer to rap on the drain plug a few times before removing it, and you can try using a hex impact socket. But in all those cases, we're really just working around something that could be better anyway.
I don't know why Toyota did this to us all, but some number of years ago, they realized how terrible it was. And so they made new plugs that had traditional 14mm hex bolt heads. All was going to be right in the world, once again. Except that they decided they'd limit these new plugs to Lexus vehicles, continuing to install the hex key-style on Toyotas. 
Luckily for us Toyota owners, the Lexus plugs fit our differentials as well. And today, I'm making my life just a little less painful by switching out the drain plug for the front diff - since I'm changing the oil anyway. The process is easy.
- Loosen the fill plug at the top-front of the front diff. Always loosen the fill plug first, to make sure you'll be able to refill the diff after you drain it.
- Loosen and remove the drain plug at the left (driver)-side-bottom of the front diff. Drain the oil into a catch can.
- Throw the horrible drain plug in some bin somewhere.
- Replace the crush washers on both the fill and drain plugs with with new crush washers.
- Replace the drain plug with the Lexus OEM version (90341-24016). This plug uses a standard 14mm socket.
- Refill the diff with some new diff oil (I like Lucas 80W-90). Buy it by the gallon to save a few bucks.
- Reinstall the fill plug.
That's it. Your future self will thank you.
Update: April 2021
Well, I finally found the Lexus equivalent for the fill plug as well. It uses a 14mm head, and like the drain plug, eliminates the risk of rounding out the hole. Pick up your own here: Lexus Front Diff Fill Plug (90341-18060)
If both plugs are a bad design, ?why not replace both with the Lexus plug?
It's a great question Jim! I would absolutely replace both plugs, but I don't know the replacement part number for a front diff fill plug with a hex head instead of Allen key.
If you find out what it is, I'd love for you to post here and let me know!
Thank you turbodb.
I will investigate and if successful, I will let you know. Seems as if the drain plug gives everyone the problem. Not the fill. But would love to replace both. I really appreciate your reply here. Thank you.
The problem here is the torque required on the drain plug (48 ft-lbs). The fill plug requires less than 30 ft-lbs so is much easier to take off.
I'm not sure exactly what you mean by "the problem here," Cyrus - would you mind expanding on that? Thanks! ?
I think that what a lot of folks run into is the fact that the heat/cool cycles of the diff cause the plugs to tighten beyond the torque specs. That, and these plugs are often reinstalled to tightness's beyond the torque spec.
I've always found that a good tap on the plug prior to loosening can help with that, and of course, making sure to clean it out prior to inserting a hex key -- but not everyone is in a situation where the plug is still in good enough shape for that to work.
That makes sense. I would think a 100 hex would offer better bite than a 6-point bolt
I haven’t had issues before after changing my front diff fluid about 4 times now but tonight I was trying to loosen my fill plug and I managed to round out the female hex. Above, Jim has mentioned that the drain gives people a problem. It does because the 10 mm hex doesn’t provide enough torque to get the bolt out and then it gets rounded out. I’m going to try Lexus tomorrow morning to get the 14 mm socket drain plug. Next time I’ll tap the plug with something to loosen it up but the 14 mm should provide my force to loosen the drain in the future.
Ahh, gotcha! Yeah, I agree with ya ?. If you haven't gotten the fill plug out yet, you might try the tapping trick, and then make sure the hex key is as well seated as it can be.
Once you get it out, take it to Lexus and see if they have a hex head replacement for it as well - we all want to know! 🙂
Good luck!
I was able to get it out. I went to Lexus and they didn’t have it in stock. I purchased another hex from Toyota because they had it in stock. I have the 14 mm ordered though Lexus so the next time I take out the hex bolt I’ll put the new one in. Thanks!!!
I believe the lower profile plug is less likely to hang up on something while offroading. In fact, owners of older toyota pickups sometimes replace the oem bolts on the transfer case and diff with lower profile hex key bolts. See the vid for an example
https://youtu.be/GIbb7XfYiHE
Hey Jason, While this may be an issue for a rear diff or diff on a solid front axle (as shown in that video you linked), the front diff on a Tacoma (95.5-current) never has a drain (or fill) plug that hangs down below the diff. As such, you can't hang the plugs up on a Tacoma. Additionally, with a Tacoma, most folks who see a lot of dirt time have a front skid plate (to protect the diff, steering rack, oil pan, etc.) which is not something that solid axle trucks have.
Anyway, thanks for looking out, but it's not an issue for Taco's! ?
I've always switched my low hanging drain plugs to the smooth internal hex type for this very reason. Years ago I caught the flat of my rear diff plug on a rock and broke it loose. Eventually it vibrated and leaked.
I change all the others like fills and on the transmission and t-case just so I only had to grab one tool to work them. Debris or being suck has never really been a issue.
So I stuck with the big hex on a Tacoma for commonality but I like the Lexus one with a 14mm head, which would be different than the stock external hex plug anyway that use a 24mm spanner.
I totally get the "one tool to do them all" mentality, but unlike the rear drain, the rest of the plugs aren't really at any risk (ever) of getting caught up on anything. And, so many people don't clean out the recessed hex that they end up in really tough shape when they round that out. As such, I think that in all places except rear drain, a "standard" hex is a better bet. 👍
Does anyone know the thread size on the diff drain plugs
Do you know if those work for 4th gen 4Runners?
Pretty sure that they do, I know they fit all generations of Tacomas, so I would assume they fit the 4Runners (essentially the same drive train) as well.
Will this work on my 2003 4.7L V8 4wd Limited Tundra? I have called Lexus and Toyota and nobody has a clue. I tried looking up parts for Lexus vehicles that have the 4.7L V8 and have LSD, but I cannot seem to confirm anything there either. Hitting walls a little. If you happen to know, please let me know. Mechanical stuff is a bit out there for this southern girl, but I need to save some money and take care of a few things myself like changing out the diff fluids (besides, its healthy to learn new things and challenge oneself :). Thanks and God bless 🙂
Hi, I know exactly what you mean about learning new things and challenging oneself - I have exactly the same mindset. ?
I don't have first-hand experience with these plugs on the 1st gen Tundra, but given the number of similarities to the Tacoma of the same vintage, I'd expect that these plugs will work. My recommendation would be to pick up one of each and give them a shot. Worst case, you return them because they don't fit, and continue to use the plugs that you currently have installed in the Tundra!
Also, here's a tip for you when you go to remove the existing plugs (Note: these tips are in addition to the "ordering" instructions in the post):
Hope that helps and please do let me know if they fit, so I can update this post!
Does anyone k ow the thread pitch of the plug? (Front diff drain).
The big drain on clamshell diffs is M24-1.50.
All other Toyota drain and fill on diffs, transfer cases and manual transmissions are M18-1.50.
Engines are M12-1.25.
Don't know what automatics use since I've never owned one.