It didn't really happen until I got my truck up to highway speeds, but since I did that I've been smelling gear oil when I drive. Not burning gear oil, just gear oil. I checked the levels over the weekend and let any extra drain out, but I think I smelled it again this morning. Has anyone replaced the gasket that goes on the t-case shifter base? I thought about replacing that but figured it would be ok. I retightened those 4 bolts over the weekend too, but they're seriously hard to get at. I'm pretty sure I've got them as tight as they'll go, though. Any ideas? I really don't like that smell

 

Unless you see it leaking out that, it is likely due to the fumes coming up out of the shifter. That is where is is supposed to vent them as the case heats up and the air inside expands. You could make sure the shifter boots are all intact and sealing the shifter and floor hole well. Or better yet, drill and tap the shifter bases and install a hose barb fitting and attach breather hoses to run the fumes up into the engine bay:



http://www.4crawler.com/4x4/ForSale/...Shifter/3.html

I also find that running Redline synthetic gear oil works better in that it reduces the operating temperature of the tranny/t-case and also it has a less strong sulphur smell than the dino juice does:
- http://www.4crawler.com/4x4/index.sh...ntheticGearOil

 

Very interesting, thank you! I did forget to mention that I just installed a newly rebuilt transmission, but I guess that shouldn't necessarily matter. There are no leaks that I can find, nothing that's actually dripping on the ground anyway, so I guess it must just be venting. The rubber boot on the transmission is good and tight, same with the t-case as far as I know. I'll check them once more, or maybe even put some kind of RTV around the rubber base of the entire shifter (tranny and t-case) area in my cab? I have vinyl floors, so it should stick.

 

I recently replaced my master cylinder and slave cylinder because they were both leaking, the master would leak into the cab

 

Yeah, DOT 3 smells darn right refreshing compared to GL-5, though...
I did replace my release cylinder, pretty sure none of them are leaking, though.

 

i cant stand it jsut replaced the front output shaft seal on my 83 T-case, rebuild the front axle, and replaced all fluids in drivetrain. I watched my buddie dip his head in the bucket on accident tring to get a better look at something. I didn't have enough time to tell him. The look on his face was priceless.

 

Yuck!! That would suck. I was told I have a rear output shaft leak on my t-case...maybe that's the deal, but I don't really get why that smell would come in the cab so strong. I guess if it stinks enough under there, some smell will come in. I don't see any leak, but..

 

As the transmission and t-case heat up with use, the air inside the cases expands. Short of an actual breather fitting (which was put on some of the later model gear boxes) that hot air comes up around the shifter. Since that hot air comes from inside the box, it is loaded with oil fumes.

 

i like the idea of a breather like 4crawler posted. that's why most transmissions and diffs have them.

but i would say its a waste to run synthetic oil on a manual gearbox as they don't have high temperatures that normally break down dino over synthetic oils. your engine and auto trans would benefit from synthetic, but not a manual gear box.

Al

 

checked your rear brakse lately? your axle seals may have developed a leak into your rear drums causing an odd smell. thats what my gear oil smell is. something to check into for you anyways.

 

I run synthetic in my 5 spd, things felt smoother after replacing the old oil with synthetic =/

and ive dipped my head in gear oil on accident before, it really really really sucks.

 

Alright, thanks a lot everbody. I'll look into vents, and make sure there are no leaks anywhere else.

 

I prefer to run a good synthetic GL-4 gear oil in the transmission and t-case(s). It does lower the operating temps so less heat into the cab (with dual t-cases, that is a concern). Also, it smells less bad than conventional oil, so if some fumes do get into the cab, it is tolerable. Also, with something like Redline MT-90, that is built for manual transmissions, the transmission shifts much smoother and faster since the oil has the right friction characteristics for the synchros to spin up faster. And I find that the synthetic lasts longer than the conventional oil does. I don't routinely change the tranny, t-case or differential oils in my '85. I find I do get into those places every 5 years to work on something or so and the oil of course is changed then. But if I can save the hassle of a gear oil change or two, the few extra dollars of cost for the synthetic is well worth it to me:
- http://www.4crawler.com/4x4/index.sh...ntheticGearOil

 

Ok, maybe I'm just weird, but I like the smell of gear oil while cruising in the highway. That and mud cooking on the exhaust.

 

Actually on the highway I don't smell it. It's driving around town, and honestly it's starting to make me sick. I'm going to have to find out what the deal is. I just took it on a short trip and noticed that I don't smell it at highway speeds. I also just changed the fluid for the first time before I got in on the highway and added GL4 instead of 5. Don't know that that would make a difference. Anyway, I've noticed I have a t-case rear output leak, and a front diff output leak. Not sure why that would come into the cab so strong, but maybe it's my problem.

 

Hey, I hear a lot about making sure the differential breathers are not clogged. How do I make sure they aren't clogged? Can I just spray something on them? Does that little cap just pop off? I hate using force on stuff until I'm sure that it's supposed to come off....so I don't end up breaking anything.

 

I usually check by removing then (screwed into the axle) and see if you can blow out through the threaded end. The little cap is sort of crimped onto the top. Or better yet, ditch them and add an extended breather:
- http://www.4crawler.com/4x4/CheapTri...html#Breathers

 

Thank you.

 

Well.............I ordered the pinion seals and nuts for my front diff and t-case. Funny thing is, after changing the fluid and taking it on a short road trip, the smell is gone.

I don't know if this makes any sense, but I posted about this on the Marlin Crawler forum and one or two people mentioned that since the tranny is iron, it likely needed to "cure", just like a cast iron skillet. Well, the transmission is rebuilt, not brand new, but I don't know if Marlin does something when they rebuild them that would take off whatever "cure" it had. Not sure if that's complete bs or not, but it's kind of interesting. Either way, though, I haven't smelled gear oil since my trip.

I did pull the front diff breather yesterday, and it was clogged. I'm glad I got that taken care of before changing out that seal.