New to me Freightliner cabover...DD 60 tire size and governor questions

Discussion in 'Trucks [ Eighteen Wheelers ]' started by tinhunter, Dec 3, 2021.

  1. tinhunter

    tinhunter Bobtail Member

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    Hi all,
    I've been lurking here for a while and finally bought an FLA104 high roof cabover with a Detroit 11.1, EFI 9 speed and, according to the spec tag, 3.36 rears. Previous owner said it's governed at 65mph. Tires are 295/75R22.5. It will be a hobby truck running a gooseneck equipment trailer, or pulling an enclosed car trailer.

    On the trip home I ran an indicated 63-65mph at 1800 rpm, but was getting passed by everything on the road. Wife was following behind and said my actual speed was 58-60.

    When I plug the current specs into a calculator, 3.36 gears and 22.5 rubber should run 65 at 1800 RPM. Maybe it's been swapped to 3.55's or lower?

    Is the governor based on RPM or MPH? If I change to 24.5 tires will I be able to increase speed without reprogramming the ECM? (it's a DDEC II)
     
    Pamela1990 and austinmike Thank this.
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  3. BoxCarKidd

    BoxCarKidd Road Train Member

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    It is set both ways in a way. Max RPM and road speed are programable.
     
    Rideandrepair and Oxbow Thank this.
  4. Rideandrepair

    Rideandrepair Road Train Member

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    You can switch the tires from lo pro to tall R-11 22.5’s and get more top speed at the same RPMs. Maybe that’s what the Truck originally had. You can get even more top speed by going to 11/R24.5s, but would need new rims. Lo pro 24.5’s and Tall 22.5s are almost identical height. Play around with Spicers or Wellers calculators, to get a good idea. The speedometer can be calibrated by flipping the dip switches on the backside. Different settings for different drive lines combos. The settings can be found online. You should have a Ametek brand speedometer.
     
  5. Rideandrepair

    Rideandrepair Road Train Member

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    I checked the calculator. Looks like each tire size gets you about 2-3 mph more. The trans must be a 9 spd direct. Might be better to convert it to a 13spd. if it can be converted. If so, I think you’ll run about 65 mph at 1400 RPMs. With the same tires. As long as you’re hauling light, that would be ideal IMO. You could swap to a 9 OD. But a 13 would be nice, giving you more top gear choices. Those 11.1 get great fuel economy. Better than the 12.7s. Never saw one with a 13spd. Looks like 1800 RPMs would put you over 80 mph!! Lol. Looks like the directs serial # ends in A, and .73 final ratio 9 spd. OD ends with a B. I had a 9 OD with 390s. I loved it. I honestly don’t know much about it all. Just interesting to me. Others on here can help with numbers and ideas more than myself.
     
    tinhunter Thanks this.
  6. tinhunter

    tinhunter Bobtail Member

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    You brought up another interesting point - the spec label shows my trans should be a 12609A (direct drive, as you said), but there's no shift pattern label in the truck. The fuller catalog lists a label that shows the shift pattern as
    1 4
    2 3

    but the trans in the truck is definitely
    1 3
    2 4

    I'll have to look for a trans tag next time I have the cab up. I do like the idea of the Fuller bolt on 13 speed kits if that's possible.
     
    Rideandrepair Thanks this.
  7. Rideandrepair

    Rideandrepair Road Train Member

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    I don’t know, mine was a simple double H pattern. That makes me wonder if you can have the top two gears swapped out, and have OD by using the goofy shift pattern. Some of the old transmissions were modified that way.
     
  8. Rideandrepair

    Rideandrepair Road Train Member

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  9. wore out

    wore out Numbered Classic

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    Is it an RTO or RT?

    the RTO 9 speeds were horseshoe pattern the RT were H
     
    Rideandrepair Thanks this.
  10. tinhunter

    tinhunter Bobtail Member

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    The label in the truck cab says RT-12609A, but it shifts in an H-pattern. Must've been swapped at some point?
     
    Rideandrepair Thanks this.
  11. wore out

    wore out Numbered Classic

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    Your gonna have to look at the model tag on the transmission itself
     
    Rideandrepair Thanks this.
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