I have an 86 4x4 with 22r and a 5 speed manual. Every once in a while I get a whiff of gear oil, very distinctive. I don't smell it very often, usually its only when I turn a corner, with the windows down, slow speeds, etc... Anyway, I climb under the truck today and look at both diffs, and tranny. All of my fluids are fine. They all have the old gear oil smell and obviously need to be changed. I don't recall smelling this previously, (Ive had the truck for 10 years), but I cant seem to find the source. Is it possible that the differential breather needs to be cleaned plus the fact that the gear oil needs to be changed? Of course this leads me to my next question, which is what weight of gear oil do I need for my truck? I seemed to have lost my owners manual somewhere. I know that this question has been answered many times on this forum, however I cannot seem to come up with a result with a search.

Thank You in Advance

Likely you have no breathers on the tranny or t-case, the older ones vented through the shifters. Could be worn out rubber boots underneath letting the fumes into the cab. I get the same smell in my '85 with the right wind conditions, I run Redline synthetic gear oil in mine, since it tends to have a lot less odor. You can also add breathers to your shifters, I'll be doing that on mine like this:



Basically drill and tap the shifter base to accept a 1/8" NPT to hose barb fitting. Then add a hose and run that up to a filter on the firewall.