manual previa shifting issue

My 91 manual Previa has the following issues....
When warm or in Summer when cold temps aren't that cold everything works fine.
In Winter, before everything is warmed up I cannot get it into first unless the vehicle is at a complete standstill and it won't go into 2nd without a bit of gear clashing. No problems going into 3rd, 4th or 5th when cold. When warm it's all good.
I had put this down to 'worn components' but since my Pickup has the exact same symptoms I'm wondering if it could be the oil I'm using.
The spec is 75W-90 and I'm using 80W-90 Castrol limited slip. Could this be my issue? If I change the oil to check the theory I'd like to go to something lighter to really make sure I can tell a difference. Would using something with a 70W rating be harmful??
jw

Here's a quote from another thread:

Quote:

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Originally Posted by batook

Manual Transmission:
2.7 quarts All-Trac, 2.3 quarts RWD.
SAE 75W-90 multipurpose gear oil API GL-4 or GL-5
NOTE: Use GL-4 to protect brass synchros, GL-5 can cause additional wear to yellow metals. GL-4 gear oil can be very difficult to find. I am only aware of premium synthetic oil brands that still make it (RedLine MT-90 and Amsoil "MTG"). I am using the Amsoil synthetic MTG 75W-90 GL-4 in my AWD M/T Previa and the shifts are less notchy, no more synchro grinding going into 2, 3, or R (which used to happen occassionally with the old 75W-90 GL-5 conventional gear oil I had in there), and just smoother operation in general. Highly recommended, and even though it's $15/quart, it's good for at least 60,000 miles.

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Drained the gearbox oil a few days ago. Quite a mound of steel particles on the drain plug. Oil had a slightly glittery look. A few larger chunks of something in there too (the size of medium coffee grounds - brass from the synchro I assume since it isn't being attracted to the drain plug). The transmission has been kind of hard to get into gear from day one (owned it from new, '91).
I suspect a transmission rebuild is in my future. Anything I should be replacing or paying particular attention to as a routine matter, besides the synchros and gaskets, while I'm in there? 208k miles on it.
jonny

I assume a clutch kit would be included in your rebuild. I would also replace seals at the rear of the transmission and at the engine too. Those things wear with time. Give mt-90 a try if an immediate rebuild is not possible. I use the stuff, and mine shifts perfectly at 20 degrees. Notchy first gear is fairly standard in cold temps for most older cars, but a quick rev match should help it go in like butter. I always rev match when shifting to first when moving. Even my miata, one of the best manual trannies on the planet needs a good rev match when down shifting to first.

After doing more reading I decided to try 10w30 motor oil. This is the second winter now and although the problem is still there it is much reduced in severity.
jw

It has been 30,000 miles since I put the 10W30 engine oil in my transmission to address the 2nd gear grinding issue I had. I was very happy with the results - the problem basically went away except for very minor trouble only the first couple of minutes after start up in the depths of the SLC winter.
After this amount of time and miles I decided it might be good to put some real transmission oil in there.
The 10W30 still looked like oil when it came out. Only a small amount of greying. I probably could have run it longer just fine.
I chose Redline MT 75W90 GL4 - the weight and type specified in the manual for manual transmissions. Well, I am not impressed for my particular problem. 2nd gear grinding is now worse than with the 10W30 engine oil. I will probably change back sometime soon and run the Redline as very expensive chain saw bar oil.

I have never heard of motor oil being used in a manual transmission. Never thought I’d hear that it didn’t lead to a colossal failure. I wonder how long this would prolong your transmission.

I've always stuck to manufacturer's recommendations, but I've found motor oil and even ATF run in std transmissions. No adverse effects that I could see, but I wouldn't do it.

I have had two cars that separately called for motor oil and atf in the manual transmissions. I guess if the alternative is a new tranny anyways maybe it's worth a shot but otherwise I'm with Tim on this one.