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68RFE+3.73= gearing too tall??

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I've been debating purchase of a 6,7 with the 68RFE. I see from the Klenger gear calculator that this transmission with 3. 73 gears is really tall in overall gearing in 6th OD. I expect to use 33-34 inch tires on this vehicle and am concerned the end result would be the opposite of peoples experiance with the G56 overall top gear ratio. Too tall and always in 5th. I would be interested in owners impressions of this espesially if you are running a larger tire. I can find numerous 3. 73 trucks that would suit me but am thinking I should hold out for a 4. 10 truck. It would be great if a 3. 73 truck would work as there are lots of them and the deals are good right now. My use is mixed 50% empty 30% pop-up camper 20% camper and boat at around 9000lb. Can you guys enlighten me? Oh yeah I live in Colorado and we have a few hills around here.
 
Remember, this is a true 4 speed with two overdrive gears, as compared to the 48RE which was a 3 speed w/OD 4th. Fifth gear is the first OD, and sixth is the second, and 5th is just a bit slower than the 6th on the first G56s (AD models). In other words, in 5th gear on 3. 73s it's like having 4. 10s. We had the same thing on AD model G56s. If you compare the G56 (AD or AE) to the 68 RFE, there's not a lot of difference in the gears. The manual gives you a granny low, but you get a torque convertor to take care of that in the 68RFE. Chances are, if you're towing, you SHOULD be in 5th to protect the transmission. I wouldn't hold out for a 4. 10 for a 9000 lb tow with a 68RFE, even in Colorado. On 3. 73s It'll do 70 in 5th at 2100 RPM on 34 inch tires. That's about the same RPMs as the AD model G56 in 6th gear, and the AE model (07 and later) G56 will turn 70 on 34s at 1900 RPMs in 6th gear.
 
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i run a gv od behind a nv4500 4. 10's and bfg 35 tires which are really 34" tall



it is really tall in 5th over (1800 rpm = passin just about everyone)



here is a chart for your truck with that combo: (shows speed in mph)



Axle Ratio 3. 73



Tire Specs

Size 315. 00

Profile 70. 00

Rim 17. 00

Dia 34. 36

Cir 108



68RFE

Gear 1 2 3 4 5 6

RPM 3. 231 1. 837 1. 410 1. 000 0. 816 0. 625

1000 8 15 19 27 34 44

1100 9 16 21 30 37 48

1200 10 18 23 33 40 53

1300 11 19 25 36 44 57

1400 12 21 27 38 47 61

1500 13 22 29 41 50 66

1600 14 24 31 44 54 70

1700 14 25 33 47 57 75

1800 15 27 35 49 60 79

1900 16 28 37 52 64 83

2000 17 30 39 55 67 88

2100 18 31 41 58 71 92

2200 19 33 43 60 74 96

2300 20 34 45 63 77 101

2400 20 36 47 66 81 105

2500 21 37 49 69 84 110

2600 22 39 51 71 87 114

2700 23 40 52 74 91 118

2800 24 42 54 77 94 123

2900 25 43 56 79 97 127

3000 25 45 58 82 101 132

3100 26 46 60 85 104 136

3200 27 48 62 88 107 140

3300 28 49 64 90 111 145





hope this helps



don
 
Your table sorta makes my point. With 3. 73s I'd be tuning 1700RPM at 75mph with 4. 10s it would be just about 1900rpm the way I figure it. Given what the guys with g56 trannys complain about - 2200rpm at 75mph or even 2000rpm at 75 with the AE and 35" tires. I just wonder if the 4. 10 might be a happy medium given my use. At some point the overall gearing would get too low for all but a downhill run. Just don't know where that point is. How usable is that top gear with 3. 73s and 34 inch tires. I realize for towing the boat I'd likely not use 6th at all. How about empty or with just the pop-up -1100lbs??
 
When I was running the numbers for the gear ratio spreadsheet, I noticed that the 68RE with 4. 10's is geared almost the same as my NV-5600 with 3. 73's in 6th gear. Put 3. 73's and over sized tires behind the 68RE and I suspect that you'd be back to a 5 speed for all practical purposes.
 
When I was running the numbers for the gear ratio spreadsheet, I noticed that the 68RE with 4. 10's is geared almost the same as my NV-5600 with 3. 73's in 6th gear. Put 3. 73's and over sized tires behind the 68RE and I suspect that you'd be back to a 5 speed for all practical purposes.



True, but only when heavy. If you're only heavy 50% of the time, and 3. 73s in 5th will do the job without overspeeding the engine, I'd stick to 3. 73s. If anything, it should make it easier to power up a steep hill in 5th w/3. 73s versus 6th with 4. 10s.



I've got 33s on my G56 AD 3. 73, and it needs 3. 42s for empty driving. I think it would thrive on it. With 3. 73s, it screams 2300 plus at 77 MPH. With the 6. 7L and a 68RFE, I don't see why he would need to run in 6th towing a 9000 lb. boat. 2100 RPM (my speed at 70 in 6th on 33s/his in 5th [OD 1] on 34s w/3. 73s) is not screaming, and say what you will, but no one should be driving over 70 in the mountains with a tow. For comparison, my 33s on an AE G56 would put 70 just a shade under 2000 RPM.
 
The 4. 10 is the best gear with stock tires and if you have any plan to go to a little taller tire the 4. 10 is it.
 
Your table sorta makes my point. With 3. 73s I'd be tuning 1700RPM at 75mph with 4. 10s it would be just about 1900rpm the way I figure it. Given what the guys with g56 trannys complain about - 2200rpm at 75mph or even 2000rpm at 75 with the AE and 35" tires. I just wonder if the 4. 10 might be a happy medium given my use... .



it is a live table



i dont remember where i found it but i have it saved to excel



a 'live' table means you can change the factors and it re-calculates the speeds for you



don
 
Axle Ratio 3. 73 Enter the axle ratio here Axle Ratio 4. 10 Enter the axle ratio here Axle Ratio 3. 73 Enter the axle ratio here Axle Ratio 3. 73 Enter the axle ratio here Axle Ratio 3. 73 Enter the axle ratio here Axle Ratio 4. 10 Enter the axle ratio here Axle Ratio 3. 73 Enter the axle ratio here Axle Ratio 4. 10 Enter the axle ratio here Axle Ratio 4. 11 Enter the axle ratio here Axle Ratio 4. 10 Enter the axle ratio here Axle Ratio 3. 73 Enter the axle ratio here Axle Ratio 4. 10 Enter the axle ratio here

Tire Specs Tire Specs Tire Specs Tire Specs Tire Specs Tire Specs Tire Specs Tire Specs Tire Specs Tire Specs Tire Specs Tire Specs

Size 265. 00 Enter metric tire size in MM here Size 265. 00 Enter metric tire size in MM here Size 265. 00 Enter metric tire size in MM here Size 265. 00 Enter metric tire size in MM here Size 265. 00 Enter metric tire size in MM here Size 265. 00 Enter metric tire size in MM here Size 265. 00 Enter metric tire size in MM here Size 265. 00 Enter metric tire size in MM here Size 0. 00 Enter metric tire size in MM here Size 0. 00 Enter metric tire size in MM here Size 265. 00 Enter metric tire size in MM here Size 265. 00 Enter metric tire size in MM here

Profile 70. 00 Enter metric tire profile % here Profile 70. 00 Enter metric tire profile % here Profile 70. 00 Enter metric tire profile % here Profile 70. 00 Enter metric tire profile % here Profile 70. 00 Enter metric tire profile % here Profile 70. 00 Enter metric tire profile % here Profile 70. 00 Enter metric tire profile % here Profile 70. 00 Enter metric tire profile % here Profile 0. 00 Enter metric tire profile % here Profile 0. 00 Enter metric tire profile % here Profile 70. 00 Enter metric tire profile % here Profile 70. 00 Enter metric tire profile % here

Rim 17. 00 Enter rim diameter in inches here Rim 17. 00 Enter rim diameter in inches here Rim 17. 00 Enter rim diameter in inches here Rim 17. 00 Enter rim diameter in inches here Rim 17. 00 Enter rim diameter in inches here Rim 17. 00 Enter rim diameter in inches here Rim 17. 00 Enter rim diameter in inches here Rim 17. 00 Enter rim diameter in inches here Rim 0. 00 Enter rim diameter in inches here Rim 0. 00 Enter rim diameter in inches here Rim 17. 00 Enter rim diameter in inches here Rim 17. 00 Enter rim diameter in inches here

Dia 31. 61 Optionally enter to manually override with Mfg tire specs Dia 34. 50 Optionally enter to manually override with Mfg tire specs Dia 31. 61 Optionally enter to manually override with Mfg tire specs Dia 31. 61 Optionally enter to manually override with Mfg tire specs Dia 31. 61 Optionally enter to manually override with Mfg tire specs Dia 31. 61 Optionally enter to manually override with Mfg tire specs Dia 31. 61 Optionally enter to manually override with Mfg tire specs Dia 31. 61 Optionally enter to manually override with Mfg tire specs Dia 34. 00 Optionally enter to manually override with Mfg tire specs Dia 37. 50 Optionally enter to manually override with Mfg tire specs Dia 31. 61 Optionally enter to manually override with Mfg tire specs Dia 31. 61 Optionally enter to manually override with Mfg tire specs

Cir 99. 29 Calculated circumference in inches Cir 108. 38 Calculated circumference in inches Cir 99. 29 Calculated circumference in inches Cir 99. 29 Calculated circumference in inches Cir 99. 29 Calculated circumference in inches Cir 99. 29 Calculated circumference in inches Cir 99. 29 Calculated circumference in inches Cir 99. 29 Calculated circumference in inches Cir 106. 81 Calculated circumference in inches Cir 117. 81 Calculated circumference in inches Cir 99. 29 Calculated circumference in inches Cir 99. 29 Calculated circumference in inches

Revs/Mi 638. 10 Optionally enter to manually override with Mfg tire specs Revs/Mi 584. 58 Optionally enter to manually override with Mfg tire specs Revs/Mi 638. 10 Optionally enter to manually override with Mfg tire specs Revs/Mi 638. 10 Optionally enter to manually override with Mfg tire specs Revs/Mi 638. 10 Optionally enter to manually override with Mfg tire specs Revs/Mi 638. 10 Optionally enter to manually override with Mfg tire specs Revs/Mi 638. 10 Optionally enter to manually override with Mfg tire specs Revs/Mi 638. 10 Optionally enter to manually override with Mfg tire specs Revs/Mi 593. 18 Optionally enter to manually override with Mfg tire specs Revs/Mi 537. 82 Optionally enter to manually override with Mfg tire specs Revs/Mi 638. 10 Optionally enter to manually override with Mfg tire specs Revs/Mi 638. 10 Optionally enter to manually override with Mfg tire specs

K 0. 025 Calculated Mi / Drive Shaft Rev. * 60 K 0. 025 Calculated Mi / Drive Shaft Rev. * 60 K 0. 025 Calculated Mi / Drive Shaft Rev. * 60 K 0. 025 Calculated Mi / Drive Shaft Rev. * 60 K 0. 025 Calculated Mi / Drive Shaft Rev. * 60 K 0. 023 Calculated Mi / Drive Shaft Rev. * 60 K 0. 025 Calculated Mi / Drive Shaft Rev. * 60 K 0. 023 Calculated Mi / Drive Shaft Rev. * 60 K 0. 025 Calculated Mi / Drive Shaft Rev. * 60 K 0. 027 Calculated Mi / Drive Shaft Rev. * 60 K 0. 025 Calculated Mi / Drive Shaft Rev. * 60 K 0. 023 Calculated Mi / Drive Shaft Rev. * 60

NV5600 6 Speed Manual NV5600 6 Speed Manual G56 6 Speed Manual (AD 2005-2006) G56 6 Speed Manual (AE 2007+) 68RFE 68RFE Aisin AS68RC Aisin AS68RC NV4500 5 Speed Manual NV4500 5 Speed Manual 47RE/48RE 4 Speed Automatic 47RE/48RE 4 Speed Automatic

Gear 1 2 3 4 5 6 Gear 1 2 3 4 5 6 Gear 1 2 3 4 5 6 Gear 1 2 3 4 5 6 Gear 1 2 3 4 5 6 Gear 1 2 3 4 5 6 Gear 1 2 3 4 5 6 Gear 1 2 3 4 5 6 Gear 1 2 3 4 5 Gear 1 2 3 4 5 Gear 1 2 3 4 Gear 1 2 3 4

RPM 5. 630 3. 380 2. 040 1. 390 1. 000 0. 730 RPM 5. 630 3. 380 2. 040 1. 390 1. 000 0. 730 RPM 6. 290 3. 480 2. 100 1. 380 1. 000 0. 790 RPM 5. 940 3. 280 1. 980 1. 310 1. 000 0. 740 RPM 3. 231 1. 837 1. 410 1. 000 0. 816 0. 625 RPM 3. 231 1. 837 1. 410 1. 000 0. 816 0. 625 RPM 3. 740 1. 960 1. 340 1. 000 0. 770 0. 630 RPM 3. 740 1. 960 1. 340 1. 000 0. 770 0. 630 RPM 5. 610 3. 040 1. 670 1. 000 0. 750 RPM 5. 610 3. 040 1. 670 1. 000 0. 750 RPM 2. 450 1. 450 1. 000 0. 690 RPM 2. 450 1. 450 1. 000 0. 690

1000 4 7 12 18 25 35 1000 4 7 12 18 25 34 1000 4 7 12 18 25 32 1000 4 8 13 19 25 34 1000 8 14 18 25 31 40 1000 7 12 16 23 28 37 1000 7 13 19 25 33 40 1000 6 12 17 23 30 36 1000 4 8 15 25 33 1000 5 9 16 27 36 1000 10 17 25 37 1000 9 16 23 33

1100 5 8 14 20 28 38 1100 5 8 13 20 28 38 1100 4 8 13 20 28 35 1100 5 8 14 21 28 37 1100 9 15 20 28 34 44 1100 8 14 18 25 31 40 1100 7 14 21 28 36 44 1100 7 13 19 25 33 40 1100 5 9 16 27 36 1100 5 10 18 30 40 1100 11 19 28 40 1100 10 17 25 37

1200 5 9 15 22 30 41 1200 5 9 15 22 30 41 1200 5 9 14 22 30 38 1200 5 9 15 23 30 41 1200 9 16 21 30 37 48 1200 9 15 20 28 34 44 1200 8 15 23 30 39 48 1200 7 14 21 28 36 44 1200 5 10 18 30 39 1200 6 11 20 33 44 1200 12 21 30 44 1200 11 19 28 40

1300 6 10 16 24 33 45 1300 6 10 16 23 33 45 1300 5 9 16 24 33 41 1300 6 10 17 25 33 44 1300 10 18 23 33 40 52 1300 9 16 21 30 37 48 1300 9 17 24 33 43 52 1300 8 15 22 30 39 47 1300 6 11 19 32 43 1300 6 12 21 35 47 1300 13 23 33 47 1300 12 21 30 43

1400 6 10 17 25 35 48 1400 6 10 17 25 35 48 1400 6 10 17 26 35 45 1400 6 11 18 27 35 48 1400 11 19 25 35 43 56 1400 10 17 23 32 39 51 1400 9 18 26 35 46 56 1400 9 16 24 32 42 51 1400 6 11 21 34 46 1400 7 13 23 38 51 1400 14 24 35 51 1400 13 22 32 47

1500 7 11 19 27 38 52 1500 7 11 18 27 38 51 1500 6 11 18 27 38 48 1500 6 12 19 29 38 51 1500 12 21 27 38 46 61 1500 11 19 24 34 42 55 1500 10 19 28 38 49 60 1500 9 18 26 34 45 55 1500 7 12 22 37 49 1500 7 13 24 41 54 1500 15 26 38 55 1500 14 24 34 50

1600 7 12 20 29 40 55 1600 7 12 20 29 40 55 1600 6 12 19 29 40 51 1600 7 12 20 31 40 55 1600 12 22 29 40 49 65 1600 11 20 26 37 45 59 1600 11 21 30 40 52 64 1600 10 19 27 37 48 58 1600 7 13 24 39 53 1600 8 14 26 44 58 1600 16 28 40 58 1600 15 25 37 53

1700 8 13 21 31 43 59 1700 8 13 21 31 43 58 1700 7 12 20 31 43 54 1700 7 13 22 33 43 58 1700 13 23 30 43 53 69 1700 12 21 28 39 48 62 1700 11 22 32 43 56 68 1700 10 20 29 39 51 62 1700 7 14 25 42 56 1700 8 15 28 46 62 1700 17 30 43 62 1700 16 27 39 57

1800 8 13 22 33 45 62 1800 8 13 22 32 45 62 1800 7 13 22 33 45 57 1800 8 14 23 35 45 61 1800 14 25 32 45 56 73 1800 13 22 29 41 51 66 1800 12 23 34 45 59 72 1800 11 21 31 41 54 66 1800 8 15 27 44 59 1800 9 16 29 49 65 1800 19 31 45 66 1800 17 28 41 60

1900 9 14 23 34 48 66 1900 8 14 23 34 48 65 1900 8 14 23 35 48 61 1900 8 15 24 37 48 65 1900 15 26 34 48 59 77 1900 13 24 31 44 53 70 1900 13 24 36 48 62 76 1900 12 22 33 44 57 69 1900 8 15 28 47 62 1900 9 17 31 52 69 1900 20 33 48 69 1900 18 30 44 63

2000 9 15 25 36 50 69 2000 9 15 25 36 50 69 2000 8 14 24 37 50 64 2000 8 15 25 38 50 68 2000 16 27 36 50 62 81 2000 14 25 33 46 56 73 2000 13 26 38 50 65 80 2000 12 23 34 46 60 73 2000 9 16 29 49 66 2000 10 18 33 54 73 2000 21 35 50 73 2000 19 32 46 66

2100 9 16 26 38 53 73 2100 9 16 26 38 53 72 2100 8 15 25 38 53 67 2100 9 16 27 40 53 72 2100 16 29 38 53 65 85 2100 15 26 34 48 59 77 2100 14 27 40 53 69 84 2100 13 25 36 48 63 76 2100 9 17 31 52 69 2100 10 19 34 57 76 2100 22 37 53 77 2100 20 33 48 70

2200 10 16 27 40 55 76 2200 10 16 27 40 55 75 2200 9 16 26 40 55 70 2200 9 17 28 42 55 75 2200 17 30 39 55 68 89 2200 16 27 36 50 62 81 2200 15 28 41 55 72 88 2200 13 26 38 50 66 80
 
that is part of it copied and pasted



but even if you can figure it out you can not change the factors (such as tire size or gear ratio)



i have the live tables for the following transmission's:



NV5600 6 Speed Manual NV5600 6 Speed Manual G56 6 Speed Manual (AD 2005-2006) G56 6 Speed Manual (AE 2007+) 68RFE 68RFE Aisin AS68RC Aisin AS68RC NV4500 5 Speed Manual NV4500 5 Speed Manual 47RE/48RE 4 Speed Automatic 47RE/48RE 4 Speed Automatic
 
just go to klenger.net and find the dodge link. Inside that link, on the lower right column is the gear speed calculator in xls and pdf formats.
 
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