New single axel truck- engine, trans, axel ratio questions

Discussion in 'Heavy Equipment & Pavement' started by Hayman, Mar 1, 2007.

  1. Hayman

    Hayman LawnSite Member
    from AB
    Messages: 8

    Hi I'm ordering a little peterbilt 335 for my farm. I pretty much looked at all brands in this class 33KGVW and they seem to come standard with some make of engine rated at 260hp/2400rpm and 620 lbs of torque. Of course you can up grade drastically depending on company. Peterbilt offers thier Paccar PX-6 ( the new 6.7 cummins ISB) or the PX-8 ( the 8.3 cummins ISC) in the 335's.

    I went with the 6.7 cummins rated at 300HP/2600 rpm and 620lbs of torque@1600rpm. They suggested I go with the 6 fuller speed manual trans and an axel ratio of 4.11. I wanted to be sure I'm not reved out too high on the highway like my old truck. So then they suggest I go with the 6 speed fuller overdrive tranny and a 4.88 rear axel ratio. With this trans and axel combo this truck is suppost to cruise at 62mph @ 2000rpm down the highway. This seems to make sense as then I'd have a lower 1st and reverse gear with the 4.88 axel compared to the 4.11 or 3.90.

    The truck will not be carring its limit in wieght ever but it will have to buck a lot of wind when loaded as the load sits high and is 10ft wide. Of course I have no way of test driving this truck as they don't have the exact one on the lot and it wouldn't have my hay mover rig set up on it anyway. But I guess it would be similar to a box truck for wind drag etc.

    The present truck I'm using is a F700 ford with the 370 gas engine in it. I don't even know the hp, I imagine around 190-200hp?? The engine is underpowered for the job. On flat ground with no wind it can pull the load fine but I have my foot into it. It has the typical older truck low gearing so its just screaming (like 3000-3500 rpm)on the highway to get to 60mph. If there is any kind of head wind I have to pretty much stay home!

    I'm hoping some of you guys have single axel trucks with similar gear ratios.

    Do the specs the dealer has recomended sound about right?

    They also tell me I should expect to double my fuel milage from 5mpg to about 10mpg.
  2. ksss

    ksss LawnSite Fanatic
    Messages: 7,157

    I have similiar speced truck. I have an L-10 powered IH with a nine speed. 33GVW single axle. I am not that familiar with that particular 6 speed transmission. I will say that the setup I have, power is not a problem, no matter what I put behind it. The truck pulls it. I really like the 9 speed for this size of truck. I am not sure what the gear ratio is in mine. I guess I would favor more gears in a truck like your specing. It is much easier to find the right one when you have some options. A 6 speed is not offering much of a choice. You do have the hp to carry a 6 speed but you might get better economy with more gear selection. I guess you are somewhat at their mercy. Hopefully the sales guy knows what he is talking about. I don't know why you would push a 6 speed tranny in a 33K truck. However, I am not a Pete sales guy either.
  3. RockSet N' Grade

    RockSet N' Grade LawnSite Silver Member
    Messages: 2,454

    Hayman.....I have a DT466 4900 with a 250 hp Navistar with fuller 6 speed. Can't remember the rear end ratio (will look it up and repost later), but with the 6 speed I am always hunting for more gear. I have thought about a two-speed rear end, different trans,....something. It always seems there is just not enough and the gears seem to be too far apart.If I do it again, I will opt for more gears and probably go with a 300 hp instead of the 250, even though the 250 is adaquate. The standard 190 hp just wont cut it (had one in this truck and swaped it out) unless you just drive around empty....then its fine. If they offer a jake brake as an option, I believe it would be worth it. What size axles? Is it a double frame? Air ride seat or bench? Air plumbed to the back or just electric?
  4. Hayman

    Hayman LawnSite Member
    from AB
    Messages: 8

    I have a 2 speed rear end now and I hardly use it other than when in 1st sometimes or backing into places. When on the road the 5 speed seems to work other than I could use another gear etc.

    It's comes with air brakes, air seat, air ride cab, but no air ride suspension. I was just not sure how the air ride suspesnsion would be for stablity with the top heavy load I carrry and the places I have to get into.

    Half the time the truck will be running empty back to the farm to get another stack to deliver.

    I wanted a easy shifting standard so thats why I went with the six speed. Peterbilt doesn't offer the 7 speed but they do offer a 8 speed. I'm not sure if its a split high low or what like the 10 speed.

    Ford offered a 7 speed spicer trans in their F750 I looked at. But I found best bang for your buck was the peterbuilt for what you all got. Ford was a little bit cheaper but the cab/seat was not as nice etc.
  5. Hayman

    Hayman LawnSite Member
    from AB
    Messages: 8

    Most of the companies seem to bring these little single axels in with the auto trans or a 6 speed manual. I haven't noticed any with a 9/10 speed other than if it was special ordered that way.

    I'm no expert on these trucks so I really don't know how they should be speced other than what he sales guys tell me. I really should take a single axel box truck out for a drive if someone has one on the lot. That would be the best test I think as it would be pushing a lot of wind above the cab like my unit has to.
  6. Gravel Rat

    Gravel Rat LawnSite Fanatic
    Messages: 9,544

    You made a big big mistake your going to HATE the truck get the ISC Cummins quit fooling around with that little engine that isn't designed for the truck you have. I'am not joking your NEVER going to get any resale out of the truck with a underpowered engine.

    You had the salesmen talk you into something that is gov't spec'ed the salesman should be kicked right in the gonads. For a 33,000lb gvw truck you should have speced the truck with 8.3 Cummins power and 9spd. It may have cost more but when it comes to selling the truck its not going to loose 10 grand in price. NO owner operator will buy a underpowered truck like you ordered your stuck with that truck for life.

    You put a load on that truck like max it out to 33,000lbs the truck is going to be so slow you will need a tractor triangle on the truck. I hate to be going down any hills with the truck you will burn out the brakes so quick because the engine doesn't have enough retarding power even with a exhaust brake.

    The 8.3 Cummins is tried and true its used all over and its a dependable medium duty engine. I would rather have a ISL in a medium duty but the ISC will do the job.

    Good Luck I would be canceling that order your throwing money out the window.
  7. Hayman

    Hayman LawnSite Member
    from AB
    Messages: 8

    Well I can still change the specs on the truck I believe in the next few days.

    So you figure the 8.3 is the way to what HP??? I wondered about going to the bigger displacement engine. But it seems all the trucks in this class come with the either the 3126 -7.2 cat, the 6.4 mercedesMBE 900 or the ICB 6.7 cummins.

    As for load I'll never have it at 33GVW with what I haul. The F700 I have now is only rated at 25,000GVW. I think the new truck specs out at 10,000lbs, my stack retriever bed the mounts on the truck is about say 4000lbs and the stacks of hay would wiegh in at a max of 11,000 but typically there around 9000-10,000lbs. So the total GVW would be on average 24-25,000 GVW.

    The thing is I "got by" for 9 years with the little 370 gas pot I have now. I just figured going to this 6.7 would be a big step up in HP and torque compared to it. Plus I'm gaining a gear with the 6 speed. I only had a 5 speed before and the problem was no high gear so the engine was screaming running back to the farm empty. Actually I just put the 370 back together again, it cracked a piston skirt but didn't score up the cyl. wall. So I'm going to retire it to a grain truck.

    I know guys who have older IH DT466 engines and run a rig like I do and say they have enough power. I'm not sure though what their 466's are speced out at though. I'll look into more.
  8. 2109 Stang

    2109 Stang LawnSite Member
    Messages: 136

    Four years a go my friend was going to the same thing you are now , I commended a T300 KW with an ISC they wanted to givem an ISC with 240hp and 6 speed and can't remember the rear ratio , but he didn't wanted a dog so we ask what would be the difference on a 315 hp, it was only $700 but they still wante to spec a tranny that would put this truck at 2000rpm @60 mph I'd said why would you want to do that your wasting your money on the extra hp we went to a 10 speed and 390 rears ,the dealer said it will be to much ,they were very wrong that , thing does 60 at 1400 rpm and when you step on it goes like a bat out of hell and that is with a 590 super M with extendahoe four way bucket a/c cab, gross weight of 40,000 # that truck empty will out run any stock truck any time fuel mileage on stop and go trafic its about 8.5 to 9 mpg ,You cant go wrong with the ISC 260 to 315 and good tranny and rear combo ,its hard when you dont know ,becuase the sales man does'nt know either and I got a stinking feeling that they want to sale a package that gives them more commision but thats only my gut feeling .
  9. NateV

    NateV LawnSite Senior Member
    Messages: 340

    The truck might be speced for what you need, but if you ever go to sell it you will have a harder time trying to find someone to buy it.
  10. snoope

    snoope LawnSite Member
    Messages: 47


    Nice choice in the "Petercar"...But try to push that salesman to "Give a little"...the ISC Cummins or a small Cat....And that 6 speed is tried and true BUT the allison auto and the Fuller 8LL are worth looking at....this leads to the rear-end gear choice...I have 4:88's w/my 8LL but my sister truck w/allison has 5:29's.....Like I said "Push" that salesman for details....he can run specs thru the computer for each option,even where the splits hit....

    One of our major home heating oil companies specs the 335 only ,both propane and oil delivery..12 trucks strong ..replacing the 6 speeds with autos and the bigger motor...only complaint was these things take the driver in some places they should not be:laugh: :laugh: they spec "Auto-chains" with them too:)

    A few of the excavation contractors are up grading to the 335 w/cat 300 and that 8LL......Fully loaded w/ a machine in tow and no problems....

    Only drawback is trying to polish them up so they look new all the time:walking: :laugh:

    Snoope back quiet

Share This Page