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mechnical overdrive

1718 Views 18 Replies 3 Participants Last post by  docwatson
I heard about a mechanical overdrive (four speed) automatic tranny made in the mid 90's which might work in my 1990 Cummins 5.9 250. It currently has a 3-speed automatic. I have also been told there is a mechanical overdrive tailshaft I could use on my current tranny. Do you folks know which model numbers I should be looking for?
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gearvenders makes a od that goes on the back of your current trans they are 2500-3000 bucks if i remember right.there was one for sale on here not to long ago you might look back in the forsale section and see if its still there.
i tried putting 307 gears in my 91.5 with a 518 my fuel mileage went down.if your after mileage a lockup might work or a 5sp.i think there is to much loss in a 727-518 said above a 47rh is the way to go.
the 3sp 727 and 4sp518 transmissions are not lockup transmissions.the converters are always slipping a small amount a 47rh converter locks so it pulls like a might be ok with those 3.54 gears and a 518 thats what i have now.i am still not happy with mine,i am getting ready to put a 5sp in mine,i am a clutch guy i guess.
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