davehummell Posted October 15, 2019 Share Posted October 15, 2019 I have a chance to buy a freightliner air ride rear with 3.90 gears will this be geared to high for my b model? I am putting a 260 hp. 675 in and keeping the tr 70 duplex. Any thoughts? thank you Quote Link to comment https://www.bigmacktrucks.com/topic/59418-rear-axle/ Share on other sites More sharing options...
fuzzy buzzard Posted October 16, 2019 Share Posted October 16, 2019 If your trans is a TRD72 and you use 3.90 rears - top speed will be around 62-64 mph. Is that fast enough to suit you? I have a 675 engine in the old "draggin wagon" with 10 speed (direct in 10th) and a 3 speed Aux behind it (0.84 in OD) with 4.00 rear on tall rubber which gives 3.36 final drive ratio - top speed is 80 mph against the governor. I would love to have a double overdrive - 0.69. That would give 2.76 final drive ration but that would require an airplane radio!!!!!!!!!!!! Quote Link to comment https://www.bigmacktrucks.com/topic/59418-rear-axle/#findComment-433994 Share on other sites More sharing options...
Maddog13407 Posted October 16, 2019 Share Posted October 16, 2019 (edited) still wondering where your getting endt675, 260 hp ,237 hp motor.....more info needed the tr72 series came in single overdrive and double 9 speed, 10 speed,10 speed overgear, 13 speed double over, 15 speed single over, 18 speed double over, 20 speed single over, 20 speed direct... Edited October 16, 2019 by Maddog13407 1 Quote Link to comment https://www.bigmacktrucks.com/topic/59418-rear-axle/#findComment-434002 Share on other sites More sharing options...
davehummell Posted October 16, 2019 Author Share Posted October 16, 2019 I just bought the engine it was in a 1980 fire truck I was told it had low miles. I was looking at a 285 hp. 676 but it had water in the pan and it turned slow like it had rust in the cylinders and the owner of the junkyard wouldn't sell me the engine so we settled on this one.We settled on a deal for the engine and an air ride freightliner rear axle and 2 hub pilot high tread tires and 2 aluminum rims with good tires that should keep me busy in the shop most of the winter. My truck says b42 on the hood but it had the early 673 and the tr72 I figure it is just a straight 10 speed the way it shifts. I guess the truck has been altered. Dave the owner of the yard says all the mack stuff gets shipped to Africa. Summit core is the name of the yard in springville pa. I have been buying small stuff from him for 4 years and he has been fair on his prices. Quote Link to comment https://www.bigmacktrucks.com/topic/59418-rear-axle/#findComment-434012 Share on other sites More sharing options...
Hobert62 Posted November 16, 2019 Share Posted November 16, 2019 Just found your post. I have 4:30 rear, direct drive duplex, tired non turbo 673, and tall drive tires (12r 22.5). It runs 66 mph at 2300rpm. Ok bobtailing pretty sleepy with any kind of load. Quote Link to comment https://www.bigmacktrucks.com/topic/59418-rear-axle/#findComment-436026 Share on other sites More sharing options...
davehummell Posted November 16, 2019 Author Share Posted November 16, 2019 Hobert 62 I am just sliding a 3.90 rear under my truck air ride and with the 260 hp. engine it should do the speed limit on the highway I also have a direct duplex Quote Link to comment https://www.bigmacktrucks.com/topic/59418-rear-axle/#findComment-436028 Share on other sites More sharing options...
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