Smell of gear oil persists after transmission rebuild with no leaks

Hey y’all,

So my problem is I smell gear oil when I’m driving with the windows down. Especially on a steep uphill grade in second gear. I never had this issue until I had my transmission rebuilt and a new OEM clutch installed in November of 2022. The smell had never gone away since then. I don’t smell it when parked, at a stoplight, or driving with the windows up. I cannot find any leaks and any excess oil spillage should have burned off long ago. It’s my daily driver. This smell is driving me insane. It’s that gear oil skunky head ache smell. Bad. many ideas on how to fix this issue? I read that maybe it’s over-filled? Possibly more volatile oil than before. Clutch has already been disassembled to check for spillage on pressure plate. It’s fine. Going to try to replace the steering wheel bushing? Maybe the smell is reaching through there and the windows down “vacuum” the smell thru the cab? That was one Toyota mechanic’s theory. Sounds a bit far-fetched to me...
any ideas or insight is greatly appreciated! fire away!
Thank you

 

First thing - check to make sure that the transmission is not overfilled.

Second thing - check the breathers. Front diff, transmission, and rear diff. one or all could be not working properly. For the manual transmission- look for write ups replacing the shift lever bushings, they'll have info on what's going on around that area.

 

Fluid Level
Bushing/Boot
Breathers
Pinon?

 

I imagine the shifter bushings would have been replaced during a rebuild, have you crawled under there to see if you notice any gear oil leaks? A plugged breather would be my guess, I intentionally overfill my r150 by a small amount and it doesn’t smell

 

Is the transmission tunnel sealed off from the interior? That would do it.

 

No. It is not sealed off.

Both the tcase and the trans have vent tubes that "T" together near the top of the shifter and a single tube goes from there to the engine bay to the driver's side frame rail below the brake master cylinder. I can envision a scenario where those vent tubes are not hooked up correctly and are allowing vented off-gassing to enter the cab from the shifter boot area.

 

Well, yeah, the t-case and trans have vents but I was asking if the tunnel isn't sealed off anymore because of missing rubber. It doesn't take much for the stank from the vents to make it's way into the cab if the shifter isn't sealed off anymore especially if you crack the windows and it pulls the smell into the cab.

 

Mine smelled like that when the shifter seal to the transfer case was bad. I’d pulll the interior plastic and have a look.

 

Andy01 is correct

I had same issue
Found both tranny AND center diff overfilled

my smell was coming from both breather tubes, slowly seeping out making that smell
Btw
(This was on awd Subaru….2001 fozzie)

 

My wife reminded me of an old Land Rover we had decades ago that I filled the t-case with some gear oil that just stunk. Like 'gonna vomit' bad. She walked into the garage when I drained it and she isn't a fan of the memory. So it could just be stank oil.

 

I pretty much like this for the problem!

 

Thank you all so much for the replies!
I love Tacoma world
Ok, going to check to see if they are overfilled. Going to check the shifter seal and going to check breather tubes on transmission, t-case, front and rear diffs.
Maybe replace the tranny oil with fresh Lucas oil or Amsoil if I can get my hands on some. I hear that or Redline is the best.

Will get back to y’all as soon as I can which may not be for a few days as I don’t have my truck right now

thank you all again so much, I’m so grateful

 

Following

 

Skip the Lucas, run the Redline

 

UPDATE:
I apologize for the long overdue update but better late than never. I drained the gear oil from the transmission and refilled it with Redline MT 90 using a hand pump. Smell went away pretty quickly and it has not returned. I figure it was over-filled or maybe they used the wrong oil at the shop or maybe both. Either way it’s fixed and I couldn’t be happier. Thank you all for your help!!!

 

awesome!!!!!!!
me and Andy01 nailed it!

thanks for updating thread Kpsnyder