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Question on singling a truck


GeorgiaHybrid

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The DW and I are starting to investigate the possibility of swapping over to a HDT and having a smart car bed built for it. So far, a Kenworth T680 is the top truck in the running with a Freightliner Cascadia Evolution in close second. I know that some have noted how hard it is to single a Kenworth but looking at them today, I can understand the AG400 8 bag being just about impossible to single but it looks like (to me) the AG400L 4 bag shouldn't be too hard to single up. Has anyone here ever singled up one of these?

 

The Freightliner looked fairly straightforward to single as well and I like the combination of a DD13 or DD15 with a DT12 tranny. I'm still not too sure about the Paccar engine combined with a Ultrashift in the Kenworth but they seem to be a good combo. I do like the shift controls that integrate the Jake brake and shift controls on the Freightliner steering column but the dash and seating position on that T680 is "just right".

 

This is going to be a lot harder than I thought deciding which way to go...... We will be in Hutch this year to look at bed designs and to take a LOT of pictures to figure out what to do there but you need a truck to put the bed on. First things first.

 

And yes, to the Volvo guys out there, the 780 is in third place but that is like offering a Ford guy a Mopar, it will get him where he needs to go but offers no food for his soul....

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Hi GeorgiaHybrid - a T680 should be a Kenworth :). It will have it's mirrors mounted on the cowl not on the doors, fully integral sleeper (no "roof" on the cab) etc. The sleeper is fully integral with lots of headroom between the seats. You may find one with air conditioned and heated seats, and swivel passenger seat that turns to face the swing out table in the sleeper.

 

The easiest suspensions to single would be an AG380 or an AG400L as you mentioned. Both makes use these.

 

If you want to single an AG400 or AG460 you could leave the suspension where it is, and remove the lead drive axle, leaving the tandem rear axle in the trailing position which is how a single AG230 functions. To alter the location of the suspension trunnion is lots of work.

 

A nice option to find in a T680 would be air front suspension AG130.

 

Strong dealer support network.

 

Kenworth has something like 50,000 MX engines in service now.

 

Edited to correct a typo

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noteven... That's what I get for making a post before waking up good in the morning.....Two places I called it a Pete, Once a KW....It's fixed now.

 

The sleeper has a ton of storage on the T680 and I do like the swivel table. Thanks for the heads up on the AG130 front suspension! I hope I can find an owner/operator spec truck that has been kept up with low mileage. I did notice that they have an extended warranty on a new truck with a MX that didn't cost a ton and warrantied everything out to a million miles.

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The T680 is a pretty sweet truck. It will work well in RV service. You might even consider keeping it tandem if you ever consider a very heavy trailer. I can tell you that with my setup tandem would be better....but I have a 7K lb pin weight. Your DRV will not be near that, but if you ever go to a New Horizon or Forks, or Spacecraft you will be pushing things with a car on deck and "lots of stuff" in the truck. Just something to be aware of.

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Singling an AG400 is no longer the dealbreaker that it once was. With the introduction of the AG230 -- a "factory singled' AG400, if you will -- a few years back, the parts are available off the shelf to convert the tandem suspension into a properly functioning single axle suspension. The parts can even be had to upgrade an AG200 to AG400 components, then single what's left to an AG230.

 

The T680 is an impressive truck. If you find what you're looking for in a T680, go for it!

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I agree with several of the above posts.

 

First off I have to say that I have been a devout Kenworth and Peterbilt (Ford) guy for years and have owned several of each. When looking at the various candidates, on paper, I thought the Volvos were more in the Freightliner category, an affordable throwaway.......lol. But not something you bought if you wanted a long lasting rattle free truck. Then I went down and started crawling over and under some trucks and have to say That I was very impressed. If you want to get a good idea just how good a vehicle is, go look at the older rode hard, put up wet ones, not the shiny bright new ones. For me, the 780 pushed the Peterbilt 387 to the side.

 

On the subject of singling, I am right with Jack on that one. With the number of miles that anyone may put on any of these fun-trucks I just can't see how the cost savings of tire and brakes could overcome the safety of additional tires and brakes, especially with a heavier trailer. I do realize that there are other reasons why people single, such as insurance or ease in licensing, however, those are seldom deal-breakers, just require more legwork and red tape scissors. If you talk to anyone who has had a blow out on a single axle dual wheel class 8, compared to someone who had a blowout with tandems, the tandem guy's stories are usually more boring...lol. And don't buy into the talk that most of these trucks don't have anywhere near the weight of what they were built for, that is theorist talk.

 

Anyway, good luck on your hunt for a new truck.

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One reason to single, if you are not a fulltimer, could be local gubment rules regarding "commercial" trucks parked overnight in neighborhoods. A tandem truck could fit in my driveway, but it is not allowed. The same truck, singled, is allowed. 4 tires make a difference to some politicians.

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On the subject of singling, I am right with Jack on that one. With the number of miles that anyone may put on any of these fun-trucks I just can't see how the cost savings of tire and brakes could overcome the safety of additional tires and brakes, especially with a heavier trailer. I do realize that there are other reasons why people single, such as insurance or ease in licensing, however, those are seldom deal-breakers, just require more legwork and red tape scissors. If you talk to anyone who has had a blow out on a single axle dual wheel class 8, compared to someone who had a blowout with tandems, the tandem guy's stories are usually more boring...lol. And don't buy into the talk that most of these trucks don't have anywhere near the weight of what they were built for, that is theorist talk.

 

 

At least in theory, adding axles (with brakes) doesn't change ANYTHING with respect to the stopping power/distance of the BRAKES. The only place it'd make a difference would be slowing power of the Jake/compression brakes IF the additional drive axles meant that you ACTUALLY put more weight on the drivers (i.e. increase the proportion of weight on the drive tires vs. weight on non-drive tires).

 

In practice, I suspect some folks single their trucks for an improvement in ride by getting the air bags into a better pressure range for a smoother ride. I'm pondering the benefits of adding a specific air tank (plumbed to the air bags) to act as an accumulator: essentially increase the compressible volume of air beyond that which is in the air bags. This should create a more progressive spring rate for those lower-pressure situations, or in other words a 1" deflection (compression) of the air bag results in a smaller dynamic pressure change, resulting in a softer impact. I just fear that it'll require relatively large tubing to get any real benefit.

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Peety3,

 

You may want to rethink that one. By adding a second dual wheeled axle you have essentially multiplied the tire to roadway surface contact by 75 percent, as well as the braking surface. Even though you have reduced the weight on the single rear axle, you have increased coefficient friction and braking ability substantially. Those result in increased braking and lateral traction.

 

As to the ride, if you want to make a single axle truck ride smoother, the best solution is to add a second drive axle......lol. Not sure where you got that single drive trucks rode better than tandems. I have owned both and never found that to be even close.

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Don't take my comment on singling vs tandem wrong. I'm a big proponent of singling. There is virtually no downside in RV application other than cost. But be aware that even in an RV application you can push the limits of the rear axle.

Jack,

 

I think it would be best for us to agree that the term "virtually no downside" is similar to "beauty is in the eye of the beholder".

 

While I would agree that if you started with a single drive axle truck, it would probably never warrant the cost to convert it to tandem. The troubling part is when I see people paying to have a second axle removed and the only reason is because of the status quo, without any intelligent rationale behind it.

 

Please don't get me wrong, if someone wants to buy a KW and convert it to a VW drivetrain, I could care less. I make these points for the people who have never owned or driven a Class 8 truck.

 

My main overall point in all of this topic is that if you find yourself going down a steep wet mountain road and have a blowout on an outside rear tire, or while driving on a flat roadway and have someone pull out in front of you from a side road, it doesn't matter whether you are driving commercially or full time RVing it. At that very moment, more is better!

 

John

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You may want to rethink that one. By adding a second dual wheeled axle you have essentially multiplied the tire to roadway surface contact by 75 percent, as well as the braking surface. Even though you have reduced the weight on the single rear axle, you have increased coefficient friction and braking ability substantially. Those result in increased braking and lateral traction.

 

As to the ride, if you want to make a single axle truck ride smoother, the best solution is to add a second drive axle......lol. Not sure where you got that single drive trucks rode better than tandems. I have owned both and never found that to be even close.

Let's use some SWAG numbers for a moment:

 

17,500 pound singled tractor. Six tires all inflated to 100 psi. There will be 175 square inches of contact area total across the six tires. If the tires offer a coefficient of braking (not sliding) friction of mu=0.3, the truck can create a braking force of 5250 pounds (theoretical: this assumes that the brake pedal has been mashed to the floor, and the ABS is controlling the brakes to the very edge of braking friction without crossing the line to sliding).

 

18,000 pound tandem tractor. Ten tires all inflated to 100 psi. There will be 180 square inches of contact area across the ten tires. If the tires offer a coefficient of braking (not sliding) friction of mu=0.3, the truck can create a braking force of 5400 pounds (theoretical as explained above).

 

Yes there are 5 more square inches of contact area, which represents a 2.8% gain. However, there are 500 more pounds to stop, which represents a 2.8% gain, so it's an absolute net wash: zip, zilch, nada difference.

 

Gregg from RV Haulers and lots of other folks on this forum claim that singled RV haulers ride better than tandem RV haulers. I suspect the basis for that is typical RV hauler weights. Lots of people claim that their truck rides a lot better after adding an RV hauler "bed". I suspect it's a byproduct of how the air springs react under light pressure vs. higher pressure. A singled truck would have 7.5k (in the example above) on a 20k axle, so the bags would be at 37.5psi assuming they're designed for 100psi under rated load. A tandem truck would have 8k on a 34k axle pair, so the bags would be at 23.5psi everything else equal, putting the tandemed truck a lot closer to mandatory minimum of 10psi for most air-ride systems.

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I ain't gots a college degree in math, but if a single axle truck has 175 sq/in of contact patch, it should follow that a tandem would have a lot more than 180. (175/6=29.16*10=291.6) Plus, that second drive axle brings a lot more than 500# to the party. Plus if 100 psi is correct for your steers then it's way over inflation for the tandem drives(thus bigger contact patch). Plus.....

 

I think the number one reason for singling would be to shorten the overall length of the tow vehicle. This will increase maneuverability, increase "chucking" a little, and decrease stability in general because of the shorter wheelbase. There's a lot of weight out front, and more weight, further back, is helpful, especially when bob tailing. Additional thoughts: For full timers, likely the biggest reason to single would be gained storage space. This might over ride any disadvantages, not the least of which is cost.

 

So, I always thought a SWAG was short for "Sophisticated Wild Ass Guess", not "Pulling Random Numbers Out of the Air".

 

It's really not that much harder to use real numbers and thus arrive at a meaningful conclusion. ;)

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Jack,

 

I looked at keeping the truck a tandem as the DRV we have has a GVRW of 21K with basically (2) 8K axles (MorRyde IS) My pin weight is already well north of 5,000 pounds as is. Every KW that I have looked at so far had a 13.2K front axle that should help in the front weight bias singling mid or a little long for the ride improvement without having to worry about overloading the front axle. I also like having the ability to add a bigger storage box in the bed with one less axle as I will have a Thermo King or similar installed on the truck if it doesn't have one to start which will take up one "box". The problem with keeping the tandems include the extra weight (which can be helped if I can find a 6x2 configuration), the cost of the extra tires, brakes, shocks, etc for the other axle and a stiffer suspension.

 

I understand the thought process behind the 780 and it is a nice truck but a Volvo just never caught my eye and I just flat out like the looks of the T680. Unlike a LOT of pros out there, I detest a long nose Pete or KW as the cab is too narrow, not enough ceiling height over the seat and having a bolt on sleeper just never appealed to me. The reason I didn't look at a Pete was the low ceiling height over the driver.

 

Don't get me wrong, if I find a good Volvo with a nice interior and low miles for a good price, I will buy it but I might get a little stupid if I see a nice KW and pay the tariff on it... If I find a nice Cascadia Evo, It might come home as well. I actually like the engine and tranny combo in them and I have to admit that the shifter location and operation are far superior to anything else I have seen (gear select for RND, paddle shifter for up/dn shifts, man or auto selector and the Jake brake off/1/2/3 all in one very intuitive stalk and I can add a driver lounge interior to it (similar to the dinette in the Volvo but the table folds up).

 

So far the BIGGEST problem is FINDING one..... This could take a year of more....

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GeorgiaHybrid;

 

Go with your gut, don't drink the "Volvo" koolaid!

 

Their smoother and quieter, but as you see here their more expensive to work on and when they don't want to run you better be an electrical engineer!

 

My 2 cents

 

Curt

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If you want all of the neutral coast, GPS cruise, driver attaboy, etc, that stuff just came out and isn't retrofittable so it'll have to be a new truck. If you want a 2013 (common rail) MX and all the fancy trans programming for that it can be a year or two old T680, but I suspect that you'll come out even with a new custom spec'd one by the time you pay for a year old used truck to be rigged up - especially since you guys don't do FET. But maybe they don't compare price-wise, I'm not sure. MHC Joplin does have a few of CFI's early 6x2 680's for sale but they are MX10's and manuals so that probably doesn't help. When you've got the pencil sharpened, old truck sold or whatever, and are ready to pull the trigger look me up and we'll get some good ones not in the Truckpaper.

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I ain't gots a college degree in math, but if a single axle truck has 175 sq/in of contact patch, it should follow that a tandem would have a lot more than 180. (175/6=29.16*10=291.6) Plus, that second drive axle brings a lot more than 500# to the party. Plus if 100 psi is correct for your steers then it's way over inflation for the tandem drives(thus bigger contact patch). Plus.....

 

I think the number one reason for singling would be to shorten the overall length of the tow vehicle. This will increase maneuverability, increase "chucking" a little, and decrease stability in general because of the shorter wheelbase. There's a lot of weight out front, and more weight, further back, is helpful, especially when bob tailing.

 

So, I always thought a SWAG was short for "Sophisticated Wild Ass Guess", not "Pulling Random Numbers Out of the Air".

 

It's really not that much harder to use real numbers and thus arrive at a meaningful conclusion. ;)

Agreed completely. I run 70psi on my tandem drives to get a better contact patch. The truck is more stable. With lockers all around it will go almost anywhere. Better ride than a single, but not as smooth as a Tri.

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I agree with several of the above posts.

 

First off I have to say that I have been a devout Kenworth and Peterbilt (Ford) guy for years and have owned several of each. When looking at the various candidates, on paper, I thought the Volvos were more in the Freightliner category, an affordable throwaway.......lol. But not something you bought if you wanted a long lasting rattle free truck. Then I went down and started crawling over and under some trucks and have to say That I was very impressed. If you want to get a good idea just how good a vehicle is, go look at the older rode hard, put up wet ones, not the shiny bright new ones. For me, the 780 pushed the Peterbilt 387 to the side.

 

On the subject of singling, I am right with Jack on that one. With the number of miles that anyone may put on any of these fun-trucks I just can't see how the cost savings of tire and brakes could overcome the safety of additional tires and brakes, especially with a heavier trailer. I do realize that there are other reasons why people single, such as insurance or ease in licensing, however, those are seldom deal-breakers, just require more legwork and red tape scissors. If you talk to anyone who has had a blow out on a single axle dual wheel class 8, compared to someone who had a blowout with tandems, the tandem guy's stories are usually more boring...lol. And don't buy into the talk that most of these trucks don't have anywhere near the weight of what they were built for, that is theorist talk.

 

Anyway, good luck on your hunt for a new truck.

"Freightliner category, an affordable throwaway.......lol"

 

Good thing "Grumps" is dead.......IF he knew that those old Freightshakers were supposed to be thrown-away after only a Million miles or so..... Those "throw-aways" were still making $$$$$ after +2,000,000........

 

Here is the deal......Freightliners ARE throw-aways becaus a LOT of folks Run and Run and Run without just enough patch-ups to get buy......until they get...........you got it....... a slightly newer Freightshaker to abuse all over again (of course some folks go broke because of too cheap of patch-ups......)

 

We ran a "Mixed" fleet Autocars, KW, Mack, Petes, Freightliners Osh, Cornbinder.......and they ALL did well IF you keep them up, fix the little thing before they get to big things.

 

Don't want rattles........don't drive 200 miles of logging roads 6 days a week or drive Highway 99 in central California that will shake the doors of any truck.....period.

 

Used trucks are USED........sure there are cream-puff-non-smokers-bare-foot-rattle-free-trucks but if you follow the forum you soon find these "gems" are fairly rare and demand good prices.

 

As far as rattle-free trucks......don't bet too much on the brand......it depend on what the unit did in it's "previous-life" there are plenty of lessor-cared for trucks of all makes.......

 

"Grumps" maybe ran his trucks too long and with too many miles but they kept the beans on the table........he would be amazed that these days most bean-counters consider the life of a HDT near it's end at 750K to 1,000K .........

 

I will agree as more and more electronics and complex systems are utilized in HDT's they tend to "time-out" likely due to lack of system support and hardware phase-out.........these indeed will be "Throw-Away" trucks.........

 

Ponder on......

 

Drive on..........(sometimes rattles means your still moving......)

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For the anti-narrow cab crowd ( I quit sleeping across the seats in 1981 I think it was, used the 7 ft long sleeper beds ever since :lol: ) don't rule out well maintained Kenworth T700... for sheer cubic space of junk capacity :lol: ...

 

Dollytrolley posted whilst I was composing my latest bit of genius insight... so on the subject of "older, fixable, and rebuildable" I had to link this:

 

Beware safety alert! It is a single drive, it doesn't have ABS, and Ecoroll is manual....

 

http://www.rvnetwork.com/index.php?showtopic=116281&hl=w900

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