Hi folks. It seems to be leaking from the back-up switch or the gasket between MTM and transfer adapter. Just confirmed the switch isn't under-torqued (FSM says 32lbf and it took more than that to nudge it a hair tighter). I'm heading out for degreaser to isolate the source, and some GL4 to top it up. Waiting on MT-90 and crush washers (90430-A0003) to make things right, per info in other threads.

My many questions:
(1) Could low MT oil be the source of the low whizzing sound I get sometimes when coasting, which I've been trying to find/fix? Seems to make sense. Also sometimes have some trouble getting into first when just starting out for a drive, so maybe this explains everything.

(2) Is the back up switch a typical leak spot, or does the gasket make more sense?

(3) Assuming it's the gasket, are there any good alternatives to taking the trans apart? I'm not currently anywhere near needing a clutch.

(4) BONUS QUESTION: Is it bad to coast out of gear in these? I vaguely remember a web comment about a gear that circulates the oil not being engaged when coasting, so wear is occurring. Wasn't 3G4R specific though. I'm in a hilly area (Rockland County, NY) so tend to coast whenever possible. I'll stop if you tell me to, but I won't be happy about it. :-)

Thanks for any help! ~Mike

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A1: That's not enough fluid to cause low levels. It would be dripping to do that. The coast side of gears generally makes more noise than the drive side, so that may not be an issue. Old fluid can make the synchros work less well, so start with new fluid at the right level. If the first gear synchro isn't doing well, push in the clutch, go to 2nd, then up to 1st at a stop. That will stop the input shaft from spinning and allow it to go into first easier.

A2: The leak is probably from up higher - check for the shifter and its seal(s) up there. The shifter seats also go bad, so you should check those anyway. Marlin Crawler makes replacement shift seats.

A3: See above - I suspect that oil is coming out of the shifter(s), which can be fixed/sealed from above in the cab.

A4: Coasting out of gear (trans gear, not t-case neutral) is fine. The input shaft is spinning with the engine and the output shaft is spinning with the rest of the drivetrain. Everything stays fully lubed.

-Charlie

Low gear grease is always bad on any transmission manual or auto. Do you get the wizz with the clutch in our out when coasting?

Nope.. You have a transmission output seal or transfer input seal leaking
I would just pull the transfer case off and see where the leak is and replace the seals while its off. Also make sure you use the correct gear oil so you don't destroy the copper components in the manual Transmission there isn't any gasket in there on those cases just the shaft seals



I would not think so but why not engine brake? As your transmission output shaft is still moving unless your transfer is in N. The rear wheels are spinning thus the output shaft is moving. Only your engine is not engaged to the flywheel if ( clutch in engine disconnected input shaft) and if the transmission is in natural only the output shaft is not rotating input shaft is spinning. Its actually pretty interesting. Lots of videos out there showing you how the manual transmissions work out on the internet ..:-) I coasted manuals, Left the clutch in and engine braked for years in a pile of Toyota's and never had an issue with them.

You not thinking a shaft seal going? Quite possible the leak is above though that's another possibility. :-) I was thinking shaft seal..:-)

Thanks Charlie. I haven’t been under the shifter boot yet, so that will be new and exciting. 😂👍 i’m hoping you’re right. Shifter seals seem a much easier task than pulling the t-case.

Thanks Brillo.

Mama would scold me if I ever rode the clutch, so I get that whizz with clutch out. It doesn’t always happen, moreso in colder weather, but also in warmer months (heard it just last week for example). I will be getting that GL4 refeshed here shortly, one way or the other.

I’ll look at leaky shifter seal first with my fingers crossed. You make pulling the T-case sound easy tho, so thanks for that mental relief if it comes to that.

As for engine braking, I generally reserve it for urgent braking (or speed control on descents). Funny how the muscle memory just does it immediately when those times come. I grew up engine braking, but had a master Ford mech brother-in-law (RIP Bob) who years ago wisely said brake parts are easier and cheaper than engine parts. ~m.

Looks too high to be a shaft seal leak - but definitely still could be.

-Charlie

OK.. I really haven't seen the top seals ever leak. Yet most rigs around here are rotted rusted out by 200K to 300K at the most. I have even seen 150K gone by the environment harhness on the steel. :-(

Your probably right as mostly when the oil slings it would be covering it all in 360 degree spray pattern. :-)

My vote goes with shifter seal. Both of mine were leaking, or at least there was signs of leakage around both. I couldn't tell for sure if it was one or both. It wasn't leaking down the sides though.

NVM. Scratch that. I just looked again and the shifters are way farther back than that.