13spd to 18spd

Discussion in 'Heavy Duty Diesel Truck Mechanics Forum' started by truckerbangin, Apr 1, 2020.

  1. truckerbangin

    truckerbangin Light Load Member

    Jan 22, 2013
    Good day is it possible to use 16913a housing and rebuild it as 18918b? If it is possible what parts would need to change
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  3. Mountaintrucker4302

    Mountaintrucker4302 Light Load Member

    Sep 21, 2015
    Switching from a 13 speed to a 18 speed is not a good idea if the truck wasnt built for it. Its gonna cost you a lot more in the long run than outright buying the 18 speed straight. you would have to change the fitting on the slave valve from the top to the center air line which is the main supply and then dismantle the roadranger valve and grind the interlock to allow the splitter to be used on the low side but splitting the 13 on the low side is where the problem begins The 18 speed uses a bearing in the hub of the splitter gear and a thick round washer to retain the gear and bearing to the output shaft of the transmission, the 13 speed doesnt. the splitter on the 13 speed doesnt see use until the trans is on the high side. The splitter on an 18 speed will see use in both the high and low side of the trans which is what the bearing is for. This means the splitter must be able to handle the torque being amplified in the low side of the trans. the splitter gear is tied directly to the output shaft so there is no difference in speed between the gear and shaft on the 18 speed when in high range. The difference in speed between the splitter gear and the output shaft when split on the low side of a 13 will damage your transmission overtime And then you gonna need a new truck. Lol.
    Rideandrepair and HoneyBadger67 Thank this.
  4. AModelCat

    AModelCat Road Train Member

    Jul 7, 2015
    Easiest would be to swap the whole deal for an 18.

    Eaton puts most of their parts books online. Download the one for yours and the one you want to build. If the cases have the same P/N's you've got a good start. The costly part will be you will probably have to change most, if not all the gears in the main box as the "A" and "B" models use different ratios IIRC.

    The back box is the main issue. The 13 speed auxillary box isn't designed to be run in high split while in low range. It'll grenade pretty quick. You may be able to convert the guts over to an 18 if the cases are the same.

    Just buy the 18 already built. Less headache and cheaper.
    HoneyBadger67, lwlevens, swaan and 2 others Thank this.
  5. Bean Jr.

    Bean Jr. Road Train Member

    Mar 30, 2014
    If I'm not mistaken, there is also the ratio differences. 1st direct is lower than 1st direct in a 13 speed.
  6. little cat 500

    little cat 500 Road Train Member

    Jan 17, 2010
    Abbottstown PA
    I know a guy that cut the little tab off the red button many years ago still working today not saying its a great idea
  7. truckerbangin

    truckerbangin Light Load Member

    Jan 22, 2013
    Ordered a 18spd but was sent a 13. Been running as a 18 from the day I put it in and just found out its was a 13spd all along and no issues except for the stripped 3rd gear and synchro the bushing that the 13has is in perfect condition
    little cat 500 Thanks this.
  8. w9l

    w9l Light Load Member

    Oct 12, 2013
    Should be able to trade up to the 18 for a fair bit less than trying to rebuild the 13 into an 18 and do it right.
  9. x1Heavy

    x1Heavy Road Train Member

    Mar 5, 2016
    White County, Arkansas
    I just as soon buy a 18 outright. Particularly around a truck that comes with it.

    I love my 13's but I don't dare try to add more to them. And I am not as smart as some of the others talking sense here.
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