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bump
Dodge Dakota
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9/15/2009
18:39:36
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 Subject: RE: gears in semi truck?
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dodgedakotas.com ROCKS!!!!!!!
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STS
Dodge Dakota
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9/19/2009
16:39:32
|  RE: gears in semi truck?
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Bump has the same IQ as psst. Any wonder?
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joe nanson
Dodge Dakota
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11/14/2009
21:02:29
| RE: gears in semi truck?
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It depends the type and size. 500 hp = 10-18. 300 hp = 5-9. 180 hp = 3-5.
For example, a Peterbilt might have an 18-speed, but my dad's 213 hp Nissan has 5 speeds (including overdrive).
Plus, it depends the purpose. If you have a truck made for flat ground, you might need 10 gears. If you need a truck for a 15% grade, it'll probably have 18 gears. This is because more gears create smaller shifts; therefore less power loss per shift.
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biscuit
Dodge Dakota
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11/17/2009
19:07:11
| RE: gears in semi truck?
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It all depends on what you intend to do with the truck. The average joe trucker hauling up to 80,000 lbs has 350-450hp, 9 or 10 speed tranny, and 3.55 rears. Same weight in mountainous areas run 3.70 – 4.10 rears and normally upgrade to 13 or 18 speed trannys. Loggers, dump trucks, and other off road trucks usually run 15 (or 18, depending on gearing of tranny and rears). Most local delivery trucks (UPS, bread, and lightweight expediter straight trucks) run 5-7 speeds.
Engine: Size is all based on the performance. With larger horsepower and torque comes ease of less shifting on hills and it will reach top speed faster and stay there longer. It is all performance. I say this because technically a person could pull an Australian road train with a lawn mower if it’s geared correctly, but it might take a year to go 2 feet.
Transmissions: There are two basic generations of shifters. Old school is 2 sticks. New is one stick (thanks to pneumatics). There are also two basic types of gearing – direct and overdrive.
A typical 2 stick is 5/4 (20 gear ratios). This is shifted 1/1, 2/1, 3/1, 4/1, 5/1, 1/2, 2/2, 3/2, 4/2, 5/2, 1/3, and so on until top gear of 5/4. The trick was shifting from 5/2 to 1/3 because when shifting the “4” box, both sticks have to move at the same time. Some trucks had a third stick for an auxiliary box. “Look ma, no hands on the wheel!”
The newer pneumatic (air) shifter is a breeze to learn.
Here’s the 10 speed H pattern.
Low High Low High
R 2 4 R 7 9 or R 2 5 R 7 10
1 3 5 6 8 10 1 3 4 6 8 9
There is a paddle on the front of the shifter to change ranges. Down is low, and up is high. I use my middle and ring finger for the switch. Some H patterns are designed so that 4/5 and 9/10 are reversed.
Here’s the 9 speed H pattern. X being no gear
Low High
R 2 4 R 6 8
1 3 5 X 7 9
On the 13, 18, and sometimes the 15 (I’ll explain later) is a slider on the left side of the shifter (thumb). This is for the auxiliary box (splitter, ½ gear, brownie, or whatever else it’s been called). The 13 and the 18 speed trannys are shifted similarly to the 9 speed H pattern. The difference is the aux box. With a 13, only the high range can be “split” and with the 18, both ranges, or all 9 gears can be “split.”
The “split” is due to the size difference between the gears and ratios inside the tranny. There really is no split. As shown below, the 13 and 18 speeds are based on the 9 speed. There is a 4000rpm gap between gears on a 9 speed. So you’re pulling a hill in 9th gear at 1750 rpm. The incline increases and the engine drops to 1300rpm. Time to shift. So you rev the engine up to 1700 and shift into 8th gear. Same scenario, but with a 13 speed. Climbing a hill in 13th gear (9th on a 9speed). You could let it drop to 1300rpm and shift into 11th gear (8th on a 9speed) OR only let the rpm’s drop to 1500 and shift to 12th aka the split.
These are NOT the exact ratios, but it will give you the general idea of how it works. The typical transmission has a low gear ratio of 17.00 and a high ratio of 1.00. Any number less than 0 is an overdrive ie 0.73. All the gear sizes in between are dependent on the number of gears in the transmission. So, a 3 speed ratio might look like 18.00, 9.00, 1.00. Sort of extreme, but possible. A 9 speed has nine evenly spaced ratios from low to high. So ratios might look like: 17, 15, 13, 11, 9, (change range) 7, 5, 3, 1 (17 being low or 1st gear and 1 being 9th gear). A 13 speed would look like: 17, 15, 13, 11, 9, (change range) 8, 7, 6, 5, 4, 3, 2, 1. An 18 speed would be 17, 16, 15, 14, 13, 12, 11, 10, 9, 8,(change range) 7, 6, 5, 4, 3, 2, 1, 0.82 (0.82 is overdrive).
13 speed H pattern
Low High
R1 2 4 R2/R3 6/7 10/11
1 3 5 X/X 8/9 12/13
Low range cannot be split and the Aux box (thumb) must be in the rearward position. High range thumb is forward/rearwards (6/7).
18 speed H pattern
Low High
R1/R2 3/4 7/8 R3/R4 11/12 15/16
1/2 5/6 9/10 X/X 13/14 17/18
The 15 speed transmission is the “off road” favorite. It is based on the 10 speed, but and additional 5 deep reduction gears are added. So you’ve got 10 forward for the highway, and 5 large (powerful and slow) forward for heavy payloads up and down hills on loose gravel or dirt. The deep reduction aux box can be activated by a switch on the dash (most common) or by the thumb slide on the shifter. Here’s the 15 speed H pattern:
Dash Switch
Deep Low High
R 2 4 R 2 4 R 7 9
1 3 5 1 3 5 6 8 10
OR
Shifter Switch
Deep Low High
R 2 4 R 7 9 R 12 14
1 3 5 6 8 10 11 13 15
Remember, shift it like a 10 speed and only use the deep reduction when heavily loaded going up or down very steep hill at a VERY SLOW pace. Deep reduction is NOT a road gear.
Rear ends: The lower the number (3.06) the faster the truck will run. It will also require more shifting to climb a steep hill. When the number is higher (5.03), less shifting is involved to climb a steep hill, but slows the overall speed of the truck. A universal gear ratio is 3.55. This allows a truck to run comfortably at 75mph, average pull up hill, and ease of starting from stop on an incline.
Here’s where overdrive is a beautiful thing. An 18 speed direct drive (top ratio being 1) paired with 3.55 rears will run 65mph @ 1500rpm. An 18 speed single overdrive (top ratio being 0.84) paired with 3.70 rears with run 65mph @ 1500rpm. An 18 speed double overdrive (top ratio being 0.73) paired with 3.90 rears will run 65mph @ 1500rpm.
The advantage of overdrive is having larger rear ends (pulling a hill better) and on flat ground having a lower rpm.
There are a few different directions people go when choosing rear ends. Some choose 3.06 or 3.12 rears paired with double overdrive and a big engine giving them a VERY FAST truck (120+ mph). Most choose 3.36 to 3.70 for an overall normal speed and great pull power.
Then there’s my field of work: the heavy haulers. I have two speed rears. You know what they say… two speeds are better than one. Boo…Two speeds rears are constructed with orbital gears and planetary gears. When in low range (5.03) the main shaft drives the planetary gear. These planetary gears rotate inside the orbital gear creating a reduced revolution of the orbital. When in high range (3.90) the main drive connects with orbital gears performing as a standard rear end. Although two speed rears add a lot of weight to a truck, they are the perfect solution for getting 250,000 pounds moving from a dead stop on an incline, pulling a hill at a descent speed, and (high range) getting better fuel mileage when deadheading (traveling with empty trailer) at high speeds.
This is my setup: 1998 Kenworth W900L, C15 @ 600horse, 18speed double over with a 4 speed auxiliary box (deep reduction), 3.90/5.03 rears, 24.5 rubber, double frame, Neway suspension, 20k steer, 46k drives with 20k drop axle, 75 ton fifth wheel, 3 axle jeep, 3 axle lowboy, and a 3 axle stinger (complete with Tonka dump truck strapped to back)
Hope this helps solve the question about gears, gearing, rears, and other stuff.
Biscuit
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biscuit
Dodge Dakota
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11/17/2009
19:21:25
| RE: gears in semi truck?
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sorry... it took out my spacing on the H patterns. Now it looks all confusing.
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STS
Dodge Dakota
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11/19/2009
13:16:00
|  RE: gears in semi truck?
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No! Actually you did well in explaining the gear pattern thoughly.
I'm like the super 10 of all the rest of them.
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