r686st Posted February 20, 2015 Share Posted February 20, 2015 I currently have a 1991 RD690S with single frame and 38 rears camelback. I have 5.73 and would like to go to 4.17 but my gear specialists is recommending 4.64 for price and simplicity. Does anyone have a recommendation for a ratio? I pull dump trailers on the highway most of the time with some time spent pulling a lowboy with a dozer or excavator on it. The combo is no more than 88,000 pounds. Quote Link to comment https://www.bigmacktrucks.com/topic/39005-r-model-ratio-suggestions/ Share on other sites More sharing options...
j hancock Posted February 20, 2015 Share Posted February 20, 2015 Which trans do you have? Quote JimIt doesn't cost anything to pay attention. Link to comment https://www.bigmacktrucks.com/topic/39005-r-model-ratio-suggestions/#findComment-279800 Share on other sites More sharing options...
6368 Posted February 20, 2015 Share Posted February 20, 2015 What trans and what size tire? 4.17 is one of the cheapest to find used however i think they are a little fast unless you are running small rubber( 22.5). i would prefer 4.42 with 24.5 tires. Quote Link to comment https://www.bigmacktrucks.com/topic/39005-r-model-ratio-suggestions/#findComment-279801 Share on other sites More sharing options...
r686st Posted February 20, 2015 Author Share Posted February 20, 2015 I have a Mack t2090 with tall 11- 24.5 rubber. Quote Link to comment https://www.bigmacktrucks.com/topic/39005-r-model-ratio-suggestions/#findComment-279822 Share on other sites More sharing options...
David Posted February 20, 2015 Share Posted February 20, 2015 We have one rolloff with T2090, 4:64, and 11x24.5. It's a very good combination and runs about 75. 1 Quote Link to comment https://www.bigmacktrucks.com/topic/39005-r-model-ratio-suggestions/#findComment-279826 Share on other sites More sharing options...
Superdog Posted February 20, 2015 Share Posted February 20, 2015 I've got 4:42's behind a 2090 on 11R22.5's,pulls good but a little slow on road speed,my Liberty with 4:17's did a good job Quote Link to comment https://www.bigmacktrucks.com/topic/39005-r-model-ratio-suggestions/#findComment-279829 Share on other sites More sharing options...
r686st Posted February 20, 2015 Author Share Posted February 20, 2015 My truck has a 300 Mack with the fuel slightly turned up at the pump. Do you think the 4.17 will be a bit too high for pulling in the dirt or getting started? Quote Link to comment https://www.bigmacktrucks.com/topic/39005-r-model-ratio-suggestions/#findComment-279846 Share on other sites More sharing options...
Joe Ditchkus Posted February 20, 2015 Share Posted February 20, 2015 A Mack T2090 has a first gear ratio of 10.69 and an overdrive of .71.For the work you do I would want the 4.64 ratio.It gives a little better reduction when in soft material.10.69 is not very low reduction when loaded for startability or gradability in off road conditions. I personally would loose a few MPH top speed for better reduction. I run a Fuller 16908LL with 14.56 first gear and .74 overdrive with 4.56 rear axle ratio 24.5 tall rubber. It tops out at over 75 MPH which is more than enough for me. My combination has a total reduction of 66.39 which is ok for my work but if in soft clay is questionable. Reduction is the key. Good Luck Joe D. 1 Quote Link to comment https://www.bigmacktrucks.com/topic/39005-r-model-ratio-suggestions/#findComment-279852 Share on other sites More sharing options...
r686st Posted February 20, 2015 Author Share Posted February 20, 2015 Thanks for all the help and I will be going with the 4.64's. It should cost about 3k to rebuild the front rear end and regear both axles. Quote Link to comment https://www.bigmacktrucks.com/topic/39005-r-model-ratio-suggestions/#findComment-279933 Share on other sites More sharing options...
6368 Posted February 21, 2015 Share Posted February 21, 2015 Thanks for all the help and I will be going with the 4.64's. It should cost about 3k to rebuild the front rear end and regear both axles.Good choice on the ratio. Perhaps it is because I;am cheap but i would check a junk yard. 38s are not in high demand anymore. I know around here a good used set of center sections can be had for around a thousand bucks. Quote Link to comment https://www.bigmacktrucks.com/topic/39005-r-model-ratio-suggestions/#findComment-279936 Share on other sites More sharing options...
bts-4120 Posted February 23, 2015 Share Posted February 23, 2015 4.42 or 4.64 especially if your on 24.5 tall 417's your going to want short rubber Quote Link to comment https://www.bigmacktrucks.com/topic/39005-r-model-ratio-suggestions/#findComment-280297 Share on other sites More sharing options...
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