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340 dart swinger

What oil should i run in a 1970 dodge dart 340 4 speed transmission ?

According to the 1970 Dodge Challenger/Dart service manual, it calls for 10w-30 or 10w-40 depending on climate, the 4-speed they call for SAE 140, although I expect that today, you’ll have to settle for a multi viscosity. Just be sure to purchase a bottle of Zinc (ZDDP) additive for the engine oil. I use Lucas “TB Zinc-Plus” in my car. At that point, you can essentially choose the brand you like most. There are some oil companies which offer both conventional and synthetic oils for older cars with the ZDDP additive, but they do cost quite a bit more than conventional. I will caution you DO NOT USE 15w-40 diesel oil on its own without additive. That used to be a method of getting the proper additives, but now days the ZDDP content has gone down on that as well.

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Thank you , i have a 1 gallon jug of sta lube sae 140 hypoid gear oil . I also have 3 quarts of mopar 80w/90w gear lube and a mopar 4 ounce bottle of limited slip additive for the rear diff .