Old gears: Transmission info of yesteryear.

Discussion in 'Trucks [ Eighteen Wheelers ]' started by PackRatTDI, Dec 27, 2006.

  1. blackw900

    blackw900 The Grandfather of Flatbed

    5,817
    7,675
    Jul 12, 2009
    A.W.O.L
    0

    There're not too many of us left out here that even remember those old boxes...Thank's for checkin' in!:biggrin_25514:
     
  2. Truckers Report Jobs

    Trucking Jobs in 30 seconds

    Every month 400 people find a job with the help of TruckersReport.

  3. 7mouths2feed

    7mouths2feed "Family Man"

    1,186
    464
    Nov 29, 2007
    Jacksonville, AR
    0
    Curious about possibly putting a 13 spd in my truck and wondering about the consequenses of running in 11 or 12th gear?
    Heres my situation. DD12.7 Pre-EGR, 2.79 gears, direct 10spd. Truck is obviously set up to run 62mph for best fuel milage 1450 RPM's.

    I want to take advantage of higher speed limits (especially out west) but retain lower RPM's for fuel milage. If I put a 13spd in it then at 70mph in 12th my RPM's would be 1410. That being said I would most likely never need 13th gear. Would this hurt the trans to run 11th or 12th the majority of the time? Thanks Any other trans suggestions more than welcome.
     
  4. country29

    country29 Medium Load Member

    518
    156
    Feb 27, 2010
    Arkansas
    0
    i havent really studied it, but the trans manufacturers will tell you yes it will, because it builds up too much internal heat in the trans. is this true, i dont know, but it is very possible.
     
  5. black_dog106

    black_dog106 Road Train Member

    1,786
    1,664
    Mar 29, 2009
    MA
    0
    Excellent thread Packrat! See the modern stuff every day of the week. Nice to read on the old stuff. Then hopefully the other "old timers" will add to it...:biggrin_25519:
     
  6. 7mouths2feed

    7mouths2feed "Family Man"

    1,186
    464
    Nov 29, 2007
    Jacksonville, AR
    0
    Your not the first to tell me that. I wonder if a superflo pump to a good size trans cooler would eliviate that issue.
     
  7. Sportster2000

    Sportster2000 Road Train Member

    1,480
    885
    Jan 5, 2008
    Indiana
    0
    Had a newer KW (2008 model year) that was setup to run 1350 rpm at 75mph. That truck loved CO and the southwestern states. It has a 18 speed and a ISX in it.
     
  8. 7mouths2feed

    7mouths2feed "Family Man"

    1,186
    464
    Nov 29, 2007
    Jacksonville, AR
    0
    Anyone know what the optimum RPM for a Pre-EGR 12.7 DD is? From past experience my "guess" would be about 1450, but thats just a guess....I am basing that on the fact that the Century(12.7 pre, 10od, 3.70 gears) I drove got better fuel milage at 66-67mph than 64mph but it had tall 22.5's on it which put it at 1425-1450 rpm. 64mph ran it just below 1400rpm and milage suffered.:biggrin_25511:
     
  9. eighteenspdjammer

    eighteenspdjammer Bobtail Member

    19
    7
    Feb 23, 2008
    western pennsylvania
    0
    Think of a 13- or 18 speed as two transmissions, a 9-speed married to a two speed. The top two lever positions in the 9-speed are 1.00:1 (direct) and 0.74:1 (overdrive). The two speed splitter in the married back box has two gears 1.18:1 (underdrive) and 1.00:1 (direct).

    10Th: Direct in the front, underdrive in the back 1.00 x 1.18 = 1.18
    11Th: Direct in the front, direct in the back 1.00 x 1.00 = 1.00
    12Th: Overdrive in the front, underdrive in the back 0.74 x 1.18 = 0.87
    13Th: Overdrive in the front, direct in the back 0.74x1.00 = 0.74

    So any time you are in direct the power goes straight through on the mainshaft and it don't make any friction so there is no wasted heat.
    If you run the power through the gears you lose about 1.5% heat in each set of gears due to friction.

    10th is underdrive-underdrive: too slow to run here under power for very long

    11th direct-direct: the most efficint gear in the transmission. There is no friction on the gear teeth because the power just runs straight thru on the mainshaft and doesn't run through the gearteeth. This is where your truck runs now with the direct 10 speed in it and 2.79

    12th overdrive-underdrive: slowing it down in the front just to speed it back up some in the back. You are making double friction and wasting heat. It won't burn up your transmission but it will burn up your fuel somewhat faster.

    13Th overdrive-direct: it is designed to run all the time here and that is why there is an oil cooler

    The answer to your question is that 11th (direct) is the best gear to run from a heat standpoint.

    If you dropped in an overdrive box with that 2.79 axle ratio there might be some cruising speeds where either 11Th or 12Th would feel right and some higher speeds where either 12Th or 13Th would feel right. i would try to avoid 12Th for prolonged periods. You wouldn't burn it up if you did cruise in 12th all the time but you would be putting more heat into the cooler and you will be paying for it.

    Not to mention that the higher mph would cost some too!:biggrin_25523:
     
    Blue jeans, Hammer166 and 7mouths2feed Thank this.
  10. Les2

    Les2 Road Train Member

    5,150
    2,288
    Jul 25, 2008
    kicked back in my lazyboy...
    0
    No it won't hurt it. Remember its a standard trans, you can run it in any gear for however long you want. Its not like an automatic.

    I guess I was lucky, I had the chance to learn how to drive a 5x4 when I was 18/19 yrs old. It was in a 1960 something Mack.
     
  11. OldHasBeen

    OldHasBeen Road Train Member

    1,269
    923
    Dec 16, 2010
    0
    Your welcome and thank y'all for the memories brought back while reading through all of thse post about yesterday years. And your right, not many of us left, I know several that have passed on.

    Back in that day our company had several trucks with boxes, one with the 4 X 4 married, some 5 X 4's. I read else where people complaining how noisy they were. All the ones I drove where much quieter that the 13 overs, especially the 13 overs after they had several miles and have been to the repair shop.

    My 1st experience was driving a mixer truck. I applied for the job having never drove a truck, he hired me, them the next morning he sends me out with a load of ready mix in a truck that had 2 gear shift leavers. I happen to know one hand that worked there pretty good and was able to asked him to explain the transmission. By noon I had made about 10 trips across town to a big pour and I had it down pat, of course that 1st load had many mishaps. I will confess, at 1st I thought it was to much shifting, yet as I got a few miles under my belt I begin to understand them and like them.

    But things were so much different in that day, you did not lug a diesel engine down to 12 to 14 hundred, if you did that engine was a goner and you may well be without a job.
     
  • Truckers Report Jobs

    Trucking Jobs in 30 seconds

    Every month 400 people find a job with the help of TruckersReport.