MACK MAN Posted July 12, 2014 Share Posted July 12, 2014 Looking at a RD 688,1999 460MACK,fuller 8LL 11:24.5 tall rubber the guy tells me the rear end ratio is a 4.73? I'm thinking it's a 4.78 Mack rear.My Eaton road speed calculator tells me at 1600 rpm the truck will be running 58mph.The guy tells me it runs 70mph 1700rpm.I need a local truck but it need to run at least 68mph in the sweet spot. Quote Link to comment https://www.bigmacktrucks.com/topic/36334-gear-ratio-road-speed/ Share on other sites More sharing options...
MACKS Posted July 12, 2014 Share Posted July 12, 2014 What does it say on the rears if there original, you gotta drive it before you buy right? Quote Link to comment https://www.bigmacktrucks.com/topic/36334-gear-ratio-road-speed/#findComment-252672 Share on other sites More sharing options...
j hancock Posted July 12, 2014 Share Posted July 12, 2014 Is it a RTO? If it is, it will have a .74 over. A 4.73 with .74 over will be 63 mph at 1700 rpm. A little short of his 70 mph @ 1700.Time for a test drive. Quote JimIt doesn't cost anything to pay attention. Link to comment https://www.bigmacktrucks.com/topic/36334-gear-ratio-road-speed/#findComment-252680 Share on other sites More sharing options...
j_martell Posted July 12, 2014 Share Posted July 12, 2014 .....maybe the speedometer is out?.....*shrug* Quote Lack of planning on your part does not constitute an emergency on my part.... Link to comment https://www.bigmacktrucks.com/topic/36334-gear-ratio-road-speed/#findComment-252681 Share on other sites More sharing options...
MACK MAN Posted July 12, 2014 Author Share Posted July 12, 2014 I would like to test drive it ,problem is the truck is 900 miles from me,I hate to go that far super nice truck could really use it.Let me see what else I can find out there Quote Link to comment https://www.bigmacktrucks.com/topic/36334-gear-ratio-road-speed/#findComment-252682 Share on other sites More sharing options...
bts-4120 Posted July 13, 2014 Share Posted July 13, 2014 run the vin 4.64 on tall 24.5 was fairly common 4.78's not so much that I have seen or heard of them. if your wanting to run 68-70 1600-1700 4.42 or 4.17 with a fuller trans. Quote Link to comment https://www.bigmacktrucks.com/topic/36334-gear-ratio-road-speed/#findComment-252775 Share on other sites More sharing options...
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