I have been hunting down a smell for the last few months and now i have it down to the tranny. I just flushed/ refilled the entire coolant system last weekend and replace the degass bottle and heater core. They were overdue ( i also thought the heater core was the cause due the the smell in the cab) I now know different but I can change the core out faster now if i need to. Anyway I cleaned the motor and there aren't any oil leaks or oil in the valley. Under the truck I get drips of tranny fluid hanging on around the edge of the pan and towards the back. There is some towards the front as well but more toward the rear. I can smell the pungent oder over the hump in the truck. That is how it gets into the cab. (i think) It only occurs when my tranny gauge gets to around 130 ish or more. On colder days it takes way longer. So I'm thinking its a seal or gasket but i don't know anything of where it would be and how big of a job it would be to do. And how would they find out where the leak is? I may take it to a local shop. any suggestions? The more I know before going in the better off I will be. I do have the stock 4R100 tranny too. thanks Jeff.

 

From what I've read here, the oem front trans seal can leak when hot, if at some point in the past it got very hot so that it puked fluid. From then on it will be a repeat offender, if you will. Replacements are now made of a viton material that resists that. 130 is not hot but it seems temp related. I think the trans must be pulled but not opened up to replace the front seal so a shop should let you keep one nut.

Someone who's had more trans problems than me will be along shortly.

 

David is right about the seals. If you did some hot heavy pulling, slow pulling with scarce air moving across the radiator and trans cooler, backing trailers-campers etc. that could be your problem. I went through it and decided to do a Heavy Duty rebuild on my trans while it was out. I also added a big trans cooler.