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Transmissions and Rear Ends Three on the tree or four in the floor? Shift it all here.

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  #1  
Old June 7th, 2020, 05:22 PM
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jmfurgason jmfurgason is offline
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Default Tranny And Diff

How often should gear oil be changed on sm420 and 44 Dana . Just a Sunday driver ? Thanks be well be safe . JF
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  #2  
Old June 8th, 2020, 11:26 PM
James James is offline
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Default Re: Tranny And Diff

SM420 or the Dana 44 - Maintenance Manual says check every 1,000 miles, drain and refill every 10,000 miles.
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  #3  
Old June 9th, 2020, 02:39 AM
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Default Re: Tranny And Diff

Thanks James appreciate the response. JF
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  #4  
Old June 9th, 2020, 05:00 AM
GMC_Dude GMC_Dude is offline
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Default Re: Tranny And Diff

Remember that lubricants are vastly superior today as they were when those specs were written.

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  #5  
Old June 9th, 2020, 05:05 PM
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Default Re: Tranny And Diff

Hey Dude , soooo what would you recommend ?? Thanks to all JF
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  #6  
Old June 9th, 2020, 09:22 PM
tbucketnut tbucketnut is offline
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Default Re: Tranny And Diff

For casual drivers, I replace gear oil every other year.
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Gig Harbor, Wa

1953 Chevrolet 3100
261 cu inch, SM420
Finished Cab off restoration

1964 GMC 1000
305 V6, SM 420
Restoration is now started, still looking for an oldsmobile style power steering pump
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  #7  
Old June 10th, 2020, 02:21 AM
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Default Re: Tranny And Diff

I am using Valvoline 80w90 not conventional, every other year good?? JF thanks tbucketnut
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  #8  
Old June 10th, 2020, 02:22 AM
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Default Re: Tranny And Diff

meant not synthetic CORRECTION JF
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  #9  
Old June 16th, 2020, 04:24 AM
thenonoman thenonoman is offline
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Default Re: Tranny And Diff

I just replaced what seems to be the original oil in the diff on my 65. I suggest a little more often than that. It was sludge-tastic. I expect to find the same in the trans.
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  #10  
Old December 7th, 2021, 05:07 PM
Jim A Jim A is offline
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Default Re: Tranny And Diff

Since I found several places with very different capacities for the Muncie SM420 on my 1960 1500, I figured I would add one more.
Started with old oil just below fill hole and drained about 3/4 of a gallon jug .
I filled to the drain/fill hole through the shifter neck (since it was already off and much easier) with exactly 3 quarts.
At the current price of $10/ quart, it is nice not to buy extra.
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