Official Crawlbox BS thread!

Huh, well I’m just repeating what they called it (oil sling), I know very little in this realm. A paper gasket will be what I do next time. After enlarging (poorly) the 1.5" diameter hole above the shifter base I was able to see, I believe, that I already had the oil sling/deflector in place and my leak was actually coming from the apparently custom (according to Marlin) shifter base:


So I put some Permatex Optimum Grey between the two halves (around the individual bolts, around the left hand shaft/shifter linkage (is that what it's called?) and all around the right hand side, as it is a link to nowhere). I also put an additional o-ring on the leftmost position of the left shaft, just outside the milled aluminum base. I'm crossing my fingers that this stops the leak...

 

You don’t need to do any of that. Just pop the 4 top bolts off around the shifter, check for a slinger. If it’s not there, throw it in and use good silicone or a gasket and you’re all set. 15 minutes.

 

So, as I type this, I have the truck up on a lift and decided to check the transmission level and pulled the fill plug only to be covered in a deluge of oil... I assume the transmission was way overfull. I also noticed the bleeder hose was off and it appears that it was leaking. The weird thing is that I haven't noticed this leak before - fairly certain the only leaking I've had was coming from the top of the Tacobox.

So my questions: Am I correct that the Tacobox does not share oil with the transmission? Is it possible that there could be a leak between the two? I've been adding oil to the Tacobox for the last 3000 miles, is it possible that it's somehow been going to the transmission? Also, has the transmission possibly been damaged by being overfull?

Thanks in advance!

 

You are correct that Tacobox does not share oil with the transmission. There's a seal that goes between them to prevent that from happening. If that seal failed, it would be possible for oil tcase oil to get into the trans. Not sure how bad that is for the trans...someone else can hopefully comment on that. There is an opening in the adapter plate of the crawlbox that allows oil into the transmission tail housing from the crawlbox. So that area will be full of oil if the crawlbox is full, whereas it is normally dry with a regular toyota tcase there.

When you said you're going through 12oz of oil out the top of the shifter, that sounds like a lot to just be spewing out the top. When I originally filled mine with 2 quarts, it spewed out about half a quart and settled down and now it's leaking but only barely leaking. It should settle to reasonable level and not continue to spew oil out the shifter when it gets low enough. The generally accepted quantity of oil for the crawlbox is 1.5 quarts.

 

The transmission pan has a drain plug and a "level check" plug. If you pulled the drain and transmission fluid came out that's normal. If you pulled the "level check" plug and a shit load of fluid came out, then that's a problem and you might have a leak at the transmission seal.

 

Depending on what adapter you used, it’s very possible for the seal between the transmission and tcase/crawl box to fail. Super common with the older ones to fail but it’s all gear oil since most are manuals and just share oil. Mine leaks transmission fluid into my duals but only in low range cause of the torque. No big deal though. I drain the duals once or twice a year and just watch the transmission level.

 

@ToyotaBurrito

I can't find the seal on Marlin's website, but the P/N on my oil seal is 90311-34011. Looks to be a standard toyota seal that you can get just about anywhere.

Edit: I believe this is it for the 23 spline, but they don't use the same P/N I cited.

https://www.marlincrawler.com/transmission/parts-upgrade/heavy-duty-transmission-output-seal

 

@Littles, thanks for your response. And based on it, I'm beginning to wonder if the oil level in the crawl box is actually going down via a leak into the transmission, past the seal you linked (though it lists the 2.7L and I have a 4.0L MT), and then it's leaking out the top of the transmission through the breather tube that I found popped off one of the T connections (not sure why it's a T, will have to crawl under there and look). The only thing that still bothers me - is after I drove the thing across the country it only seemed to collect oil directly below the Tacobox - but most recently the oil (after my first drive after I sealed the Tacobox custom shifter base) was all over the side of the transmission and that's when I noticed the disconnected breather tube...Also, I have no idea how many splines my Tbox has...

And thanks to you, @malburg114. I'm not sure what adapter is used on the Tacobox as I'm not the original owner. But you're saying the leak I probably have is no big deal? My one concern is that from my understanding, the GL-5 oil (I think Phosphorous and Sulfur compounds) in the Tbox is slightly deleterious to the brass synchros in the tranny (which I'm running GL-4 because it doesn't have the P and S compounds). Are the oil levels such that the Tacobox won't be starved for oil? I wonder why sealing the shifter base would present a different set of symptoms...it has a breather, so no pressure was building. How do you watch the transmission level? You mean you just open it up at the fill plug? Last time I did that I got an oily surprise.

Thanks again, much obliged for the help.

 

If your a manual transmission, it shouldn’t be a big deal as both the transmission and tcase are gear oil and can flow back and forth. Only concern would be atarving on steep incline or decline but they aren’t for long to cause any damage. I’m sure it’s not good for fluid to flow back and forth but the seals are such a bad design that it’s hard to eliminate all leaks between the two. (Atleast I’ve always had the two flow into each other). To check the transmission I just pull the dipstick.

 

Wait, there’s a transmission dipstick?!

(Edit: removed what appears to be an iPhone emoji translation error - man face-palming was turned into male symbol...)

 

On 1st gens (what I have) there are.

 

Dang, looks to be only first gens: https://www.tacomaworld.com/threads/manual-transmission-dipstick.433579/

 

That was my thought. If that seal is failing it could explain why so much oil is being lost. As far as I know, the seal is the same between the manual and auto as it sits on the input of the tacobox which is 23 spline regardless of trans. The one i installed was originally for an auto.

So it's really just an FYI, but your transmission is a 22 spline female output on the manual.

 

did you just assume your tranny’s identity?!?!

 

It’s a tranny so it gets to decide how it self identifies depending on the day!

 

So transmission identities aside... @Littles, I ordered the rear main seal, thanks again. I checked the transmission level through the fill plug and it’s overflowing again, my question : I don’t think the crawlbox is leaking externally, do I need to keep adding fluid to the crawlbox or will it settle to an ok level and I’ll just replace the rear main seal when I get it to the shop in a few weeks?

 

barring any other issues, the level in the rear of the transmission will equalize out eventually, takes a few drives. Just keep checking level and add as require.

 

Thanks for the reply @6 gearT444E. Like I mentioned previously, the transmission is already overflowing—when I opened the fill plug it started to come out, so I put it back without letting but a little bit come out. My biggest concern is starving the crawlbox… Does anybody see this as a possibility?

 

It’s been a while since I tore down one of the cases but I remember having to remove the oil pump screw on the stock output shaft so you’re now solely relying on splash lubrication with a crawl box. If the level gets too low there is def a risk of overheating things in there and wiping a bearing.