18 speed grinds while cruise is set

Discussion in 'Trucks [ Eighteen Wheelers ]' started by greasehorn, Feb 19, 2020.

  1. greasehorn

    greasehorn Bobtail Member

    6
    1
    Feb 6, 2020
    0
    a truck i maintain is a 389 peterbuilt c 15 with an 18 speed in it, all is well until you have had the cruise set at 60-70 on flat ground for a few min, then it starts making an aweful grinding noise,(17/18 gear) at first you could just pump the clutch and it would quit, now sometimes it makes it seem like its sticking in gear, oh btw when the grinding starts the RPMs go up, we initally thought it was a clutch (even tho clutches dont make this grinding noise) and put a clutch in it, we have checked rear ends everything we can think of, im reaching out to yall because in 2 weeks the warranty runs out on this transmission, and i would like to solve the issue before that day comes.....thanks in advance
     
  2. Dave1837

    Dave1837 Light Load Member

    245
    485
    Nov 16, 2019
    Pennsylvania
    0
    Try adjusting the suspension. If it's too high (or maybe too low I'm not sure) it will rattle at highway speeds and sound like the trans is going to come apart. Happened to my dad's just this past fall so he wrote it up as the transmission but all they did was adjust the suspension height and it went away, hasn't done it since
     
  3. greasehorn

    greasehorn Bobtail Member

    6
    1
    Feb 6, 2020
    0
    ill try it, at first we thought it was leaf spring bushings clear out of it and had the rear end sideways, we tried about everything we can think of
     
    Rideandrepair Thanks this.
  4. Dave1837

    Dave1837 Light Load Member

    245
    485
    Nov 16, 2019
    Pennsylvania
    0
    Let me know if it works
     
    Rideandrepair Thanks this.
  5. Mid-May Trucker

    Mid-May Trucker Heavy Load Member

    715
    1,237
    Oct 23, 2018
    0
    Maybe go faster seems like you should be going 80 to 90 in 18th gear.
     
    Rideandrepair and Bakerman Thank this.
  6. Judge

    Judge Road Train Member

    1,095
    3,052
    Mar 19, 2014
    Newport, Ar
    0
    Could be different, as I have a 13, but mine started doing the exact same, ended up being a broken spring inside the transmission.
     
    Rideandrepair Thanks this.
  7. Rideandrepair

    Rideandrepair Road Train Member

    5,428
    6,691
    Aug 8, 2015
    0
    Noise on acceleration- too high, coasting- too low.
     
  8. booley

    booley Medium Load Member

    608
    2,086
    Feb 16, 2008
    0
    I had an 18 spd that started clunking in high gear. Put it into the shop and they replaced the suspension leveling valve and told me it was fixed. Picked the truck up, and it was still clunking in high gear. Went back and took the mechanic for a ride, he says, "Oh". They rebuilt the transmission (still under warranty)
    Said it was something that was installed wrong during initial assembly...no charge
     
    SAR and Rideandrepair Thank this.
  9. Powder Joints

    Powder Joints Subjective Prognosticator

    6,244
    5,055
    Sep 25, 2007
    Rosamond, SoCal
    0
    Sounds like the T/O bearing
     
    Rideandrepair Thanks this.
  10. AModelCat

    AModelCat Road Train Member

    15,022
    60,206
    Jul 7, 2015
    The North
    0
    Only thing I can think of internally that could make the RPM race and cause a grinding sound is if the teeth on the splitter dog clutch are worn/damaged and its being thrown out under torque. Once you let off the throttle, air pressure on the piston puts it back into engagement because its not fighting the torque trying to pop it out.
     
    magoo68 and Rideandrepair Thank this.
  • Draft saved Draft deleted