Rebuilt 1986 Velvet drive slipping in forward

Discussion in 'Sport Cruisers' started by dmdmd, Jun 17, 2018.

  1. dmdmd

    dmdmd New Member

    Jun 17, 2018
    1986 Express Cruiser 340
    454 straight shafts (2)
    I have a 1986 340 Express Cruiser. Port transmission overheated and blew dipstick and sensor plug resulting in a small flash fire. Only charred some wires.
    Velvet model #10-18-004 1.52 was rebuilt and a damaged ring gear was replaced.
    When it was started (after rebuild) it still had a significant "cluncking" sound in reverse. This was corrected when throttling up and finally by increasing the idle speed by a few hundred rpms. Still had a slight rotation when in forward (it has done since I've owned the boat..3yrs).
    Test run seemed to go very well. Next day I was pulling out of dock and noticed port didn't seem to engage in forward, then seemed ok for a short time but then was definitely slipping around 2000-3000 rpm. Returned to dock to take a look....still pretty quiet in idle reverse, noted that there was no rotation when in neutral (for the first time ever). Without changing throttle the rotation speed in reverse was probably 2-3x the rotation speed in forward. Fluids were well monitored during the test the previous day (but didn't check day 2). No apparent leaks.
    Does anyone have any ideas what could be happening if this is not a fluid problem?
    Thanks for any help!
  2. fwebster

    fwebster Well-Known Member TECHNICAL Contributor PLATINUM Sponsor

    Oct 6, 2006
    Middle Tennessee ; Panama City Beach, FL
    1996 450DA
    3116 Caterpillars
    Worn or damaged hydraulic pump not holding the clutch plates and iiiallowing them to slip.....?

    When the transmission was rebuilt did you just replace the obviously worn parts or was the case vatted and cleaned and all new bearings, shims, thrust washers pump, etc. installed. All to often a rebuilder just replaces the clutch pack in order to keep the rebuild cost low. If a transmission has has a bearing or other parts failure, it is very difficult to get all the metal filings out of the transmission case and those filings can damage the pump when the rebuilt transmission is put into use.

    I'm not pointing fingers or accusing anybody of anything......... just hoping to give you a direction to look.
  3. dmdmd

    dmdmd New Member

    Jun 17, 2018
    1986 Express Cruiser 340
    454 straight shafts (2)
    Thank you, will check with him. He did say everything inside looked "extremely clean"
  4. LG111

    LG111 Active Member

    Jan 4, 2015
    How about proper fluid level? The trany may have an air pocket giving a false full fluid reading after install. You ran the boat and the air releases and now the fluid is to low to do its job on the clutch plates. Hence slipping.
  5. dmdmd

    dmdmd New Member

    Jun 17, 2018
    1986 Express Cruiser 340
    454 straight shafts (2)
  6. dmdmd

    dmdmd New Member

    Jun 17, 2018
    1986 Express Cruiser 340
    454 straight shafts (2)
    That would be the best possible news. Will check soon. Thank you
  7. ttmott

    ttmott MS/PhD in OCD GOLD Sponsor

    Apr 3, 2012
    Space Coast Florida
    2006 52 Sedan Bridge
    Cummins QSM11
    Important also is to ensure the gear shift mechanism is being fully articulated to their engage positions when the shift levers on the helm are actuated. If they are not then full hydraulic pressure will not be available to the clutch packs.
    LG111 likes this.
  8. PlayDate

    PlayDate Well-Known Member

    Dec 25, 2006
    Washington DC
    1994 370 Express Cruiser
    454 Mercruisers
    What caused the transmission to overheat? Did the cooler fail?

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