04 Tacoma MT really stiff when cold

I just went through this same debacle. It was getting down to around freezing temp and I couldn’t shift into gear even after warming the truck up for 10 mins or so. So I first swapped out the trans oil (and all my diff fluid) with Amsoil. This worked so-so. It was shifting (barely) into gear but I still wasn’t happy... so I ended up bleeding my clutch and completely swapping out all the old fluid. This did the trick. Nothing fancy, just straight DOT3, and it now falls into gear perfectly. It has way better clutch (pedal) play now and it’s a 180deg difference from what it was. Good luck

 

Any good info on how to bleed the clutch? I've been looking but can't really find much.

 

Just a heads up, Mobil 1 may not be safe for the brass syncros in our transmissions. The last time I researched the issue Redline MT90 and Amsoil were the only ones that I could find that were. MT90 made a huge difference for me and my buddy swapped from M1 to Amsoil and saw a big improvement in cold weather as well.

If fresh fluid isn't helping it's likely that the issue comes from the clutch not disengaging completely. You may need to adjust your clutch pedal, check the master and slave cylinder for leaks, and replace fluid or bleed the system at a minimum.

 

So I researched some videos on YouTube. Mainly for a technique to bleed the clutch w/o the need of another person.
https://youtu.be/v78CzIC3epk
I’d suggest first extracting as much fluid from the reservoir as u possibly can. A smaller syringe (plastic) w/ appropriate hose would work better than a Turkey baster. As far as the receiving jug setup goes.... a big Gatorade bottle works good. Just make sure it’s got enough DOT3 in it to keep it weighted down. I bought a big jug of Autozone DOT3 for cheap. Worked fine. I tie-wired the hose connection to the bleed nipple on the slave cylinder (so it wouldn’t jump off when I was actuating the clutch pedal. Final thing that’s noteworthy is make sure u don’t over-actuate the clutch pedal and run ur reservoir dry... or you’ll pull in air to the system. I was able to actuate the pedal about 15 times before I needed to top it off. Out of a 32oz bottle, I think I used about 2/3rd of it for the entire operation. Attached is a pic of the slave cylinder where I bled it from. Good luck.

 

The synthetic gear oil stays thin at low temps, regular gear oil is thick when cold so the synthetic will help if gear oil is the issue. I’ve heard of the issue with synthetic with the brass synchros, never checked that out. Good site for all things oil is Bob is the oil guy.

When highway trucks went to synthetic in their transmission and rear ends, they went to a 1,000,000 mile warranty. I know a fellow with a log hauling truck, did 2,000,000 on his rear ends, still like new when he opened them up.

I’d guess your shifting problem is somewhere in the hydraulic clutch, air in the system, or a bad component, just had that issue with mine about 6 months ago.