wacatak Posted April 2, 2014 Share Posted April 2, 2014 i have a 1991 688 dump truck with a 400hp and 12spd, ive just had the truck for about a yr and dont use it eveyday. My issue is i can shift the truck fine running through the gears but when it comes time to shift down ill shift from 5 h to 5L it wants to grind for a bit going in. Im looking for any advice or info that would be helpful. Thanks Quote Link to comment Share on other sites More sharing options...
gearhead204 Posted April 3, 2014 Share Posted April 3, 2014 try another 50 rpm on the throttle Quote Link to comment Share on other sites More sharing options...
brutus998 Posted April 3, 2014 Share Posted April 3, 2014 I agree, never had that trouble. The only thing I have found tricky on the 12 speed is going from 4h to 5L when Im upshifting almost always grinds there. I usually go 4h to 5h and then downshift real quick to 5L. I have two trucks with 12 speeds they both are E9's Quote Link to comment Share on other sites More sharing options...
RFCDrum Posted April 3, 2014 Share Posted April 3, 2014 It always seems to grind from 4th high to 5th low. Rob Quote Link to comment Share on other sites More sharing options...
leversole Posted April 4, 2014 Share Posted April 4, 2014 I agree, never had that trouble. The only thing I have found tricky on the 12 speed is going from 4h to 5L when Im upshifting almost always grinds there. I usually go 4h to 5h and then downshift real quick to 5L. I have two trucks with 12 speeds they both are E9'sThats the same on mine (4H to 5L)...on the downshift I kinda give the throttle a little blip (to unload to geartrain) just as I am flipping the switch..then qucikly increase the RPM to match and it goes right in to 5L with no issues...Might work on unloading the drivetrain with the throttle to help get it to (thru) nuetral quicker...or like others said, you might be downshifting early (higher speed) and jsut need more RPM to get it in...PS...I LOVE my 12-speed! Quote Link to comment Share on other sites More sharing options...
Timothy Maikshilo Posted April 4, 2014 Share Posted April 4, 2014 Best darn tranny ever made period! Quote Link to comment Share on other sites More sharing options...
brutus998 Posted April 4, 2014 Share Posted April 4, 2014 Best darn tranny ever made period!Agreed! Everyone is so afraid of them. 1 Quote Link to comment Share on other sites More sharing options...
blackdog2 Posted April 4, 2014 Share Posted April 4, 2014 Great tranny switch to a synthetic oil seems to shift a lot better in cold weather and change the air filter for moisture and check for air leaks. Quote Ed Link to comment Share on other sites More sharing options...
theakerstwo Posted April 5, 2014 Share Posted April 5, 2014 One thing about the 12 speed is you don't have that problem with the range snychros that the 9 speed has. Quote glenn akers Link to comment Share on other sites More sharing options...
Td713001033 Posted April 5, 2014 Share Posted April 5, 2014 wacatak are you using the clutch or float shifting. also are you having trouble when downshifting for more power like going up hill or when trying to slow down . Quote Link to comment Share on other sites More sharing options...
mrsmackpaul Posted April 5, 2014 Share Posted April 5, 2014 well the 12 speed is the best tranny I have ever driven had trouble splitting into low once crap built up inside the gears on the low range side takes a bit to pull it all apart but cleaned it all out ran as good as new if it is only in one gear I have no answer if it is on all gears maybe the air ram on the box lid or the regulator is out of adjustment and not enough pressure ?? Paulps I never use the clutch for splitting gears didnt no I was meant to Quote Link to comment Share on other sites More sharing options...
terry Posted April 5, 2014 Share Posted April 5, 2014 Best darn tranny ever made period!I can second that, had one in a DM dump, with 4.17'sand the pump set for 2300 RPM's, it was a real runner. Terry Quote Link to comment Share on other sites More sharing options...
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