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Discussion Starter #1
I use Valvoline 80w90 gear oil in my 3 speed transmission but, it grinds slightly going from 1st to 2nd when its cold. After it warms up, it shifts fine. Should I be using a thinner gear oil in the colder months? 75w-90 ?
 

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64 1/2 D Code Coupe,
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Keep the same weight and let it warm up a little more, A synthetic gear oil may solve your problem since it isn't as prone to thickening to the same degree as conventional gear oil.
 

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I know for a fact that a Borg Warner T10 4 speed hates GL5 gear oil. It only shifts properly when filled with GL4 gear oil. I'll bet any amount of money that your 3 speed will magically improve when you drain the GL5 and replace it with GL4 which is usually not available in an auto parts store. You will probably have to find it online.
 

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Discussion Starter #6
OK sounds good and worth a try. Should I go with the 85w-90 or a 75w-90 ? I dont know GL-4 from GL-5 but, I can find a NAPA store locally and search for the Sta-Lube oil.
 

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Look at patrick's photo right above the CRC emblem and you will see "API GL-4".
These old transmissions had brass synchronizers and the GL-5 actually attacks the brass. GL-4 is "brass safe".
 

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My 3.03 3-speed in my Econoline was the same way but I'd let it warm up, in neutral, with the clutch out to get the fluid circulating and warming along with the engine and by the time I was ready to go, so was the transmission.
 

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Discussion Starter #11
Well, you guys may have saved my transmission. Time will tell. I changed the GL5 oil to the 85w80 GL-4 this morning and look at the old oil that I drained out of it! Brass colored which I assume is from the synchronizers and there were a lot of shiny silver chips on the drain plug magnet. I only ran this oil for about 2 months so hopefully, the trans is damaged too much. It does shift nice now. No grinding at all. Seems a bit quieter too but could be my imagination. Should I be running this same oil in my differential ?
736502
 

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Discussion Starter #13
After seeing what came out of the transmission, Im going to drive it for a week and replace the oil again. I bought a gallon of GL-4 so, I have plenty. Hoping to save this transmission if I can.
 
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