I had the man trans gear oil changed a few years ago. Whenever it get real cold like sustained 20 - 0 degree the transmission shifting become very sluggish…and impossible to shift into reverse. Feels like molassess. Since at worst I assume they put in a 85w-140w gear oil. If I switched to a 75w to 90w… Would that make much of a difference ? 92 Plymouth Laser. Thanks for any opinions…or experience . - Tom
Was it a synthetic gear lube that was used?
Tester
I have no idea what gear oil they used. I just ask for gear oil changed. Thanks for your response. Would a synthetic gear oil perform better in cold weather?
Is this the same transmission you had trouble getting into reverse May , 2020 ?
Did you not have it looked at ?
Yes, it would.
I wonder if this is the reasoning behind GM using ATF in their manual transmissions. It’s a very thin oil. They have been for decades.
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Yes, this. ATF lubricates OK. Im proves fuel efficiency a little but all shifting becomes easier especially when cold.
I would be very hesitant to put ATF into a transmission not made for it. Synthetic gear lube would be the best option for you.
You have an owners manual that lists the proper lubricant. If it lists 80w-90, you can substitute 75-90 synthetic and it will perform better.
Hard to shift manual transmission? hmmm … I don’t think this is related to the gear oil, provided there’s enough gear oil in there. Instead I’m guessing the problem is that the clutch isn’t fully releasing the engine from the transmission when you press on the clutch pedal. I presume this is a hydraulically activated clutch. If clutch MC is pretty aged, hasn’t been replaced in 10 years or more, might want to just replace that part, fresh clutch hydraulic fluid properly bled may well solve the issue. After that inspect the clutch linkage from pedal to slave output, may need to adjust something so that when the clutch pedal is pressed it moves the slave output linkage the spec’d amount.
The other possibility, hope it is not this as requires removing transmission, the bushing the transmission input shafts fits into the center of the flywheel, that bushing may worn out and binding.
Are you able to easily shift from gear to gear when engine is stopped, even with clutch pedal not pressed? Does pumping clutch pedal seem to help?
George, does that fact that this only happens at low temperatures affect your opinion? I’d change the obvious - go with the oils recommended above.
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Possibly. But I’ve had that exact problem on my Corolla, worse in cold weather. New clutch MC solved it. +20 degrees F isn’t unusually cold. Concur w/post above, use manufacture’s recommended gear oil spec.
At no time shall logic enter the thought process.
Tester
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You mean “Unencumbered by the thought process”?
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In medical school, students are taught that, when diagnosing a patient’s ills, think of the most likely explanation first. Typically, they use a metaphor:
If you hear hoofbeats approaching, think about horses before you think of zebras.
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Same here. I don’t think anyone suggested that you do that. Obviously GM trannys are designed to run on ATF. Not sure if others are.
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Yeah just because you hear hoof beats does not mean that it is not zebras. In her case she was Wrong with her diagnosis. Many a doc has been stumped until they turn the pages to the exotic chapter. Just sayin as all. My favorite doc spent time in Guam during the war an was always checking for zebras.
In thi case, yeah change the fluid as the simple thing to. You can always overhaul the transmission if that doesn’t work.
Let’s also remember that we are talking about a 30 year old car with a transmission of unknown condition. It’s also possible that there is normal wear and tear that is exacerbated by cold weather.
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I just have to ask… Where in your body did she locate the zebra?
I do not think they have Zebras in Guam. maybe he was taking the Meds. 
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It just means that you should not just accept the most likely cause without considering that it may be more exotic. If the kids have never isolated a more exotic disease and have no experience with them, they may make a quick diagnosis of the most likely.
Sorry I brought it up. Thought it was a common thing.