hicrop10 Posted October 2, 2016 Share Posted October 2, 2016 I have a 1979 r model with a endt676 300 series engine with 285hp.The transmission is the trxl107-low hold 5 speed.The rear ratio is 4.17.My question is to get more of a top speed.The truck tops out now at about 65,i would like to be able to cruise at 70.What ratio will I need? Thanks. Quote Link to comment https://www.bigmacktrucks.com/topic/47127-rear-ratio-change/ Share on other sites More sharing options...
terry Posted October 2, 2016 Share Posted October 2, 2016 Next faster would be a 3.86 might be hard to find, I would go with a 12 spd. overdrive T1070 trans, with 4.17 rears you will turn about 1750 rpm at 70 mph. terry 1 Quote Link to comment https://www.bigmacktrucks.com/topic/47127-rear-ratio-change/#findComment-347619 Share on other sites More sharing options...
hicrop10 Posted October 2, 2016 Author Share Posted October 2, 2016 I would like not to change the transmission,the truck has only 74,000 original miles.My dad brought 20 of these trucks. Quote Link to comment https://www.bigmacktrucks.com/topic/47127-rear-ratio-change/#findComment-347623 Share on other sites More sharing options...
terry Posted October 3, 2016 Share Posted October 3, 2016 25 minutes ago, hicrop10 said: I would like not to change the transmission,the truck has only 74,000 original miles.My dad brought 20 of these trucks. Then you will need a 3.86 or a 3.65 set of rears. terry Quote Link to comment https://www.bigmacktrucks.com/topic/47127-rear-ratio-change/#findComment-347626 Share on other sites More sharing options...
mackey58 Posted October 3, 2016 Share Posted October 3, 2016 You have 20 now nice Quote Link to comment https://www.bigmacktrucks.com/topic/47127-rear-ratio-change/#findComment-347629 Share on other sites More sharing options...
eddeere Posted October 3, 2016 Share Posted October 3, 2016 How about adding an auxiliary trans. 1 Quote Link to comment https://www.bigmacktrucks.com/topic/47127-rear-ratio-change/#findComment-347630 Share on other sites More sharing options...
hicrop10 Posted October 3, 2016 Author Share Posted October 3, 2016 I wish I still had 20,this is the last one. Quote Link to comment https://www.bigmacktrucks.com/topic/47127-rear-ratio-change/#findComment-347631 Share on other sites More sharing options...
mackey58 Posted October 3, 2016 Share Posted October 3, 2016 Oh lol got excited thinking about a fleet of 20 classics lol Quote Link to comment https://www.bigmacktrucks.com/topic/47127-rear-ratio-change/#findComment-347633 Share on other sites More sharing options...
theakerstwo Posted October 3, 2016 Share Posted October 3, 2016 4:17 is the proper ratio for that engine .Get any faster and it will kill it for a work truck but if its a fun truck go fast. Quote glenn akers Link to comment https://www.bigmacktrucks.com/topic/47127-rear-ratio-change/#findComment-347635 Share on other sites More sharing options...
hicrop10 Posted October 3, 2016 Author Share Posted October 3, 2016 The only work this truck will see is pulling a trailer with some antique caterpillar tractors and the B87 Mack tractor that I'm doing. Quote Link to comment https://www.bigmacktrucks.com/topic/47127-rear-ratio-change/#findComment-347641 Share on other sites More sharing options...
j hancock Posted October 3, 2016 Share Posted October 3, 2016 4.17 will be a good gear for pulling a detachable with a B87 riding along. Quote JimIt doesn't cost anything to pay attention. Link to comment https://www.bigmacktrucks.com/topic/47127-rear-ratio-change/#findComment-347644 Share on other sites More sharing options...
Vladislav Posted October 3, 2016 Share Posted October 3, 2016 Both swapping the gearbox or carriers you make modifications to your 74K miles truck. Putting 12 speed or similar style 10 speed you would have what you have now with additional overgear and some intersteps. Quote Никогда не бывает слишком много грузовиков! leversole 11.2012 Link to comment https://www.bigmacktrucks.com/topic/47127-rear-ratio-change/#findComment-347682 Share on other sites More sharing options...
hicrop10 Posted October 3, 2016 Author Share Posted October 3, 2016 Maybe I will use theB87 as the pull tractor.It has 9.10 ratio and top out at 72 mph.I know this to be true cause I was stop many years ago by Pa state trooper for doing just that early one Saturday morning with a D9 dozer on the lowboy. Quote Link to comment https://www.bigmacktrucks.com/topic/47127-rear-ratio-change/#findComment-347708 Share on other sites More sharing options...
terry Posted October 3, 2016 Share Posted October 3, 2016 2 hours ago, hicrop10 said: Maybe I will use theB87 as the pull tractor.It has 9.10 ratio and top out at 72 mph.I know this to be true cause I was stop many years ago by Pa state trooper for doing just that early one Saturday morning with a D9 dozer on the lowboy. To get 72 with a 9.10 ratio you must be doing some serious overwinding the engine ! terry 1 Quote Link to comment https://www.bigmacktrucks.com/topic/47127-rear-ratio-change/#findComment-347717 Share on other sites More sharing options...
theakerstwo Posted October 3, 2016 Share Posted October 3, 2016 (edited) Or three o/d trans.Just think ,how fast would the drive shaft speed be. Edited October 3, 2016 by theakerstwo Quote glenn akers Link to comment https://www.bigmacktrucks.com/topic/47127-rear-ratio-change/#findComment-347718 Share on other sites More sharing options...
Red Horse Posted October 4, 2016 Share Posted October 4, 2016 what is tire size? Quote Link to comment https://www.bigmacktrucks.com/topic/47127-rear-ratio-change/#findComment-347792 Share on other sites More sharing options...
Back In Black Pulling Posted October 4, 2016 Share Posted October 4, 2016 Here's a link that might help you see what Ratio you might want http://spicerparts.com/calculators/transmission-ratio-rpm-calculator 1 Quote Link to comment https://www.bigmacktrucks.com/topic/47127-rear-ratio-change/#findComment-347834 Share on other sites More sharing options...
Hobert62 Posted October 5, 2016 Share Posted October 5, 2016 That's a nice calculator to use. Quote Link to comment https://www.bigmacktrucks.com/topic/47127-rear-ratio-change/#findComment-347866 Share on other sites More sharing options...
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