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Gear ratio


NLC
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I have a b61 with a endt675 engine Tri-plex trans and 6:34 ratio rears. Top speed now about 43 mph at 2100 rpm. What ratio could I go to and Still keep good pulling power and go 60 mph. Pulling a small lowboy and D5 dozer. 

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1 hour ago, NLC said:

Not really sure but I think it’s a single over. Haven’t been able to read the numbers on the transmission so much grease covering it. It has the aluminum box on the back. 

Right behind fill plug on left side is a flat area, scrape with a putty knife then a wire brush, there will be a TRT72 or 720, that will tell what front box is, back box is always a overdrive on a triplex or quad.    terry:MackLogo: Also a aluminum back box will be a TRTL series

Edited by terry
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Doing some quick math, if you're doing 43 mph with a 6.34 ratio, you'd need a 4.50 rear to do 60 mph (4.54 technically, but if I recall, Mack made a 4.50 rear that went into some of the Bs with the direct-drive duplex). I'm guessing you have a single-over triplex with final drive ratio of .85. On standard rubber that would give you about 47 mph at 2100, pretty close to the 43 mph you mention. I would think that you have enough power pull a dozer at 60 mph with the ENDT and a 4.50 rear, at least on flat ground. I once drove a single-axle R model with an END 673 (no turbo), single-over triplex, and 4.14 rear pulling single-axle trailers with maybe a 10-12,000 pound payload, and it would run about 70 until it hit a hill.

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