VaOutlaw Posted October 26, 2016 Report Share Posted October 26, 2016 Looking at a single axle Volvo tractor with a 3.73 axle ratio. What is the average cost to change the ratio to a lower numeric ratio ? Link to comment Share on other sites More sharing options...
Jeff.Sloan Posted October 26, 2016 Report Share Posted October 26, 2016 I really want to do this on mine as well. I have the 3.73 rear end currently. I'd like to find a rear axle with a lower ratio and a locker. Very interested in what I should budget for a project like this. I have an Eaton 10 speed and already I'm in 8th gear at 35 MPH. Would like to drop to the low 3's or even high 2's (2.64 anyone? lol). 2004 Volvo 630, Cummins ISX, Eaton 10 speed (air assist clutch), 3.71 3.07 rear locker, ET jr, 200" WB, GearMaster 2017 Forest River Sierra 372LOK Full time June 2017 DW, 2 kids, and 2 dogs Link to comment Share on other sites More sharing options...
Sculptor Posted October 26, 2016 Report Share Posted October 26, 2016 I asked this question at the rally, and (I think Gregg?) replied it could be as much as $5000. So there must be more to it than just replacing some differential parts. Don't take my word for it though, I'm sure you will get a more knowledgeable answer from others. Kevin and June 2013 Volvo VNL 730 D13 Eco-Torque @ 425 Ratio 2.47 2014 DRV 36TKSB3 Link to comment Share on other sites More sharing options...
forxlr8n Posted October 26, 2016 Report Share Posted October 26, 2016 Local salvage job quoted me $2k to install an air rear and axle in my truck. "If you can not measure it, you can not improve it." Lord Kelvin Link to comment Share on other sites More sharing options...
GlennWest Posted October 26, 2016 Report Share Posted October 26, 2016 Trying to save fuel? Mine 3:40ish. At 45-50 in 9th. I have ultrashift 10 speed. 2003 Teton Grand Freedom towed with 2006 Freightliner Century 120 across the beautiful USA welding pipe.https://photos.app.goo.gl/O32ZjgzSzgK7LAyt1 Link to comment Share on other sites More sharing options...
SIBERNUT Posted October 26, 2016 Report Share Posted October 26, 2016 You may be mechanical like I am. I traded pumpkins with my yard for $200, replaced it myself. I went to 3.07's, in retrospect maybe too high. (Figure your target speed at www.roadranger.com). Hardest part was lifting the dang thing up into the banjo by myself. If'n I had to do it again, I'd trade my 3.73 whole tandem for a factory single in the ratio you want, heavier rear & brakes, much easier to do. 2000 Volvo 635 A/S, N-14 Cummins"The Phoenix"'03 KA 38KSWB http://s918.photobucket.com/user/sibernut/library/?sort=6&page=1Furkids- Sibe's CH. Sedona & Tseika Link to comment Share on other sites More sharing options...
GlennWest Posted October 26, 2016 Report Share Posted October 26, 2016 What speed does yours go in 10th with that 3:07 gear? 2003 Teton Grand Freedom towed with 2006 Freightliner Century 120 across the beautiful USA welding pipe.https://photos.app.goo.gl/O32ZjgzSzgK7LAyt1 Link to comment Share on other sites More sharing options...
SIBERNUT Posted October 26, 2016 Report Share Posted October 26, 2016 I have an AS, .74 OD & 22" tires. I've had it up to 85 with the coach on back, had a few R's left. What's really cool is that it will do 65 at the top of 9th. Pull up next to a MOHO on a hill, and when you get even w/it, hit 10th 2000 Volvo 635 A/S, N-14 Cummins"The Phoenix"'03 KA 38KSWB http://s918.photobucket.com/user/sibernut/library/?sort=6&page=1Furkids- Sibe's CH. Sedona & Tseika Link to comment Share on other sites More sharing options...
Alie&Jim's Carrilite Posted October 26, 2016 Report Share Posted October 26, 2016 I started a topic about this last summer. http://www.rvnetwork.com/index.php?showtopic=122956&hl= Currently, we have 2.93 at the rear with a Rockwell 10 sp. Pulls great and rarely needs to downshift running thru mountains, but we are out of gears at 80ish mph. I've made several trips into Montana this summer and I can't keep up much less actually speed! Where we were before in eastern NC, there was a truck salvage yard that had a 2.7? rear assembly for $600 but I had to pull it. Never had time to do it. Funny thing to me is, even bobtail at 79mph the truck gets 11mpg.... until the Montana head wind hits.... Alie & Jim + 8 paws 2017 DRV Memphis BART- 1998 Volvo 610 Lil'ole 6cyl Cummins Link to comment Share on other sites More sharing options...
Jeff.Sloan Posted October 27, 2016 Report Share Posted October 27, 2016 How do I figure out the gear ratios of my transmission? The more I read about this, the more I want to do it. Is it a bolt in type conversion (straight axle swap) or is fabrication needed (on a truck that is already singled)? 2004 Volvo 630, Cummins ISX, Eaton 10 speed (air assist clutch), 3.71 3.07 rear locker, ET jr, 200" WB, GearMaster 2017 Forest River Sierra 372LOK Full time June 2017 DW, 2 kids, and 2 dogs Link to comment Share on other sites More sharing options...
Pat & Pete Posted October 27, 2016 Report Share Posted October 27, 2016 Don't know about HDTs , but on just about every vehicle I've been under , there's a tag attached to the pumpkin with information stamped into it . Goes around , comes around . Link to comment Share on other sites More sharing options...
MrSeas Posted October 27, 2016 Report Share Posted October 27, 2016 Jeff, The model of transmission installed in your truck should be listed on the "door tag" on the drivers side door pillar. From there you could get the info on the gear ratios. Link to comment Share on other sites More sharing options...
Wrknrvr Posted October 27, 2016 Report Share Posted October 27, 2016 Maybe change tire and wheel size. Especially if you need new tires. Or swap tires and wheel with someone with the size you want just for a test . Just a thought, Vern Link to comment Share on other sites More sharing options...
Brad & Jacolyn Posted October 27, 2016 Report Share Posted October 27, 2016 At the rally Greg said that for the price of the swap you can buy a lot of diesel. Just something else to consider. Brad and Jacolyn Tucker the Wonder dog and Brynn the Norfolk Terrier 2009 Smart "Joy" 2004 VNL630 "Vonda the Volvo" 2008 Hitch Hiker 35 CK Champagne Edition VED12 465 HP, Freedomline, 3.73 ratio, WB 218" Fulltiming and loving it. Link to comment Share on other sites More sharing options...
porky69 Posted October 27, 2016 Report Share Posted October 27, 2016 I started a topic about this last summer. http://www.rvnetwork.com/index.php?showtopic=122956&hl= Currently, we have 2.93 at the rear with a Rockwell 10 sp. Pulls great and rarely needs to downshift running thru mountains, but we are out of gears at 80ish mph. I've made several trips into Montana this summer and I can't keep up much less actually speed! Where we were before in eastern NC, there was a truck salvage yard that had a 2.7? rear assembly for $600 but I had to pull it. Never had time to do it. Funny thing to me is, even bobtail at 79mph the truck gets 11mpg.... until the Montana head wind hits.... Don't take this as me condemning what you are doing, I am no angel myself, I just have second hand experience with the scenario I will relate...... At 80mph you should be out of gears...commercial truck tires (tires on your fiver as well) are only rated at 75mph. I know you are running light and highly unlikely to have issues but if you catch the wrong law enforcement officer on a bad hair day you could be up for making a special donation to the highway fund. Exceeding the speed rating on a tire can get you a ticket! I have a couple of livestock hauler buddies that were doing one of their traditional high speed, middle of the night cow hauls at speeds significantly over 75mph (which is enough to deserve the special attention they got on its own) and the officer that stopped them wrote them up for exceeding the posted speed limit (he give them a break on the speed) and in order to make up the difference he wrote them up for exceeding the speed rating on their tires (can't remember the exact wording). As far as the OP's question unless you put on a LOT of miles or can do the re-gear for virtually nothing you will only be masking your savings. That is to say, undoubtedly you will can/will get better fuel mileage, measurable tank to tank, but over the life of your truck you will still be money behind(cost of gears/center chunk/lubes/gaskets/etc plus labor..even if you do it yourself will be more than the fuel savings). Even when i was long haul trucking, putting 100,000+ miles per year on each truck, it was rarely economical enough warrant changing your gearing. Link to comment Share on other sites More sharing options...
Jeff.Sloan Posted October 27, 2016 Report Share Posted October 27, 2016 I also want to do the swap for the locker. We plan to boondock a lot and I worry about getting the rig stuck in the dirt somewhere. I don't drive fast, not in a rush - so it's not about increasing top speed for me. It's for the locker and to increase MPGs. Rear axle on door tag says: "RT40-145 / 3.73 AVA03233299" Truck has an Eaton Fuller 10-Speed. Door tag says "FRO-1621OC, 10 SPEE P0022298" Is that enough info to determine gear ratios? 2004 Volvo 630, Cummins ISX, Eaton 10 speed (air assist clutch), 3.71 3.07 rear locker, ET jr, 200" WB, GearMaster 2017 Forest River Sierra 372LOK Full time June 2017 DW, 2 kids, and 2 dogs Link to comment Share on other sites More sharing options...
MrSeas Posted October 27, 2016 Report Share Posted October 27, 2016 http://www.roadranger.com/ecm/groups/public/@pub/@eaton/@roadranger/documents/content/ct_196763.pdf Link to comment Share on other sites More sharing options...
Jeff.Sloan Posted October 27, 2016 Report Share Posted October 27, 2016 http://www.roadranger.com/ecm/groups/public/@pub/@eaton/@roadranger/documents/content/ct_196763.pdf Thanks! Found this as well, which has the ratios: http://www.roadranger.com/ecm/groups/public/@pub/@eaton/@roadranger/documents/content/rr_trsl-0261.pdf So 9th is DD and 10th is 0.73 OD. Using the handy calculator from the other thread (thanks guys!) with my 3.73 RE, at 70MPH in 10th my ISX will spin at 1620 RPMs. If I drop to a 3.08 rear end, it'll spin at 1340 RPMs. If I drop to a 2.93 rear end, it'll spin at 1270 RPMs at 70MPH. That's tempting. How do I find the 'sweet spot' RPM fuel economy wise for my cummins ISX? The green band on the tack is 900-1700 RPMs, much too wide of a range to mean anything. Door tag says "500HP&2000RPM" if that makes a difference. This RS23160 looks like it'd be a perfect for me. (spendy though; likely $2k by the time it gets to me) https://www.vanderhaags.com/detailview.php?part=24470005 Any tricks to putting these rear diff's in? I've done plenty of 4 wheeler trans rebuilds, this can't be that different - right? ;-) 2004 Volvo 630, Cummins ISX, Eaton 10 speed (air assist clutch), 3.71 3.07 rear locker, ET jr, 200" WB, GearMaster 2017 Forest River Sierra 372LOK Full time June 2017 DW, 2 kids, and 2 dogs Link to comment Share on other sites More sharing options...
MrSeas Posted October 27, 2016 Report Share Posted October 27, 2016 The ISX will not be your friend if you plan to "lug" it. It's not as low RPM friendly as the other green colored motors. You will have to find your trucks sweet spot concerning best MPG. Link to comment Share on other sites More sharing options...
Jeff.Sloan Posted October 27, 2016 Report Share Posted October 27, 2016 The ISX will not be your friend if you plan to "lug" it. It's not as low RPM friendly as the other green colored motors. You will have to find your trucks sweet spot concerning best MPG. Fair point. I still do not know the 'sweet spot' for this engine model. I need versatility from this truck. We will be full timing for at least 2-3 years and this will be the only family car while we are on the road. I expect we'll be doing a lot of bobtailing and every bit of increased MPGs will help. I don't mind downshifting when needed to get better MPGs the rest of the time. 2004 Volvo 630, Cummins ISX, Eaton 10 speed (air assist clutch), 3.71 3.07 rear locker, ET jr, 200" WB, GearMaster 2017 Forest River Sierra 372LOK Full time June 2017 DW, 2 kids, and 2 dogs Link to comment Share on other sites More sharing options...
NoDirectionHome Posted October 28, 2016 Report Share Posted October 28, 2016 Pulling a 15-16K lb. trailer, it's going to be hard (impossible) to lug your tractor "There are No Experts, Do the Math!" 2014 Freightliner Cascadia DD16 600hp 1850ft-lb 18spd 3.31 260"wb SpaceCraft S-470 SKP #131740 Link to comment Share on other sites More sharing options...
Alie&Jim's Carrilite Posted October 28, 2016 Report Share Posted October 28, 2016 Most Cummins like the 1400-1600 RPM range. Don't quote me on this, but everything I have read about or talked with Cummins engineers about their engines, They usually say that the "Sweet Spot" is in that range. Alie & Jim + 8 paws 2017 DRV Memphis BART- 1998 Volvo 610 Lil'ole 6cyl Cummins Link to comment Share on other sites More sharing options...
GeorgiaHybrid Posted October 28, 2016 Report Share Posted October 28, 2016 Jeff, The 3.08 will be your best bet. Cummins claims the sweet spot for an ISX is 1400 rpm. On mine with that gear set, 75 is right at 1400 rpm and Kenworth even puts two little green lights on the tach face that the needle will center when turning 1400. Gears in the 2.94 or lower range will be hard to back slower and you will have issues finding the right gear on a hill. I had mine set up to run roughly 1400 rpm to get 55 in 11th, 65 in 12th and 75 in 13th. 2017 Kenworth T6802015 DRV 38RSSA Elite Suites2016 Smart Prime Link to comment Share on other sites More sharing options...
Scrap Posted October 28, 2016 Report Share Posted October 28, 2016 CM870 is 1400-1600. That said, toward the very end and starting with CM871 they let on highway linehaul under 80K go to 1350. So that is a possibility - especially if you have an Ultrashift DM as the pavement is all your trans is allowed to do anyways. It is a tough choice, however, because one shift to 9th that the higher gears caused (ie: that you wouldn't have had to do at the lower gearing) will wipe out 100's of miles of fuel savings you would have gained. You also have to do some deep soul searching to gear at your top speed as well. If you have a dedicated run that is 70 or you have a route that requires you to go 70 in order to get it done under 11hrs then sure you would gear to 70. But otherwise you are pushing 100 sq ft of semi through the wind and at 70 you know that you are driving to get it done and not driving for fuel economy. So you gear to your economy speed and your engine speed at 70 it is what it is. The hope is that the savings gotten at the bulk of the economy speed is more than the 70 jaunts. Also note that 70 is pretty fast in a bobtail tractor that doesn't stop for chit. So as a daily driver I'm not sure how much time it would actually be going 70? It just needs a carrier change and a couple of inner hub seals to regear. To go to a locker you need to make the clearance cut in the housing to fit the shift fork and add one new axle shaft with the longer splines. Then, of course, it needs to be plumbed and the dash reprogrammed for the interlock speeds, if equipped. Link to comment Share on other sites More sharing options...
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