raindog Posted December 2, 2013 Share Posted December 2, 2013 I've got a 94 Mack RD688 log truck that I purchased this spring. Since the weather got cold, the splitter selector won't work when it's cold. By won't work, I mean it won't put the transmission into underdrive when the splitter button is in the down position. All that happens is I hear air escaping out of what I presume is an air relief hose...Once I've run a few miles (10 minutes or so) with the splitter in normal drive (over drive?) and I presume things are all warmed up, when I split a gear, I hear no sound of air escaping, and the transmission splits just fine. On a hunch, I pulled up the floor and put a space heater on what I presume to be a control valve unit on the top of the transmission (this has 2 small air lines coming from the splitter selector and 2 large air lines going to what I presume is the actual splitter unit on the rear of the transmission). After about an hour, it warmed up and splitter seemed to worked ok again.My question is--does this sound like something as simple as water from the compressor system in the air line and freezing? or does this sound like something wrong with the control valve unit? I'm running air brake antifreeze in my air system...is there a way to ensure this antifreeze gets to the control valve unit to keep this from freezing up?Any help would be greatly appreciated... Quote Link to comment Share on other sites More sharing options...
2stacksuperdog Posted December 2, 2013 Share Posted December 2, 2013 Sounds like any air transmission. Our 8LL in our RD does it, our 12 speed in our RW does it. The good ole 2 stick 6 speed dont! Once both transmissions warm up they are fine the rest of the day, only happens when you first start out on a cold morning. Quote Matt Link to comment Share on other sites More sharing options...
RFCDrum Posted December 2, 2013 Share Posted December 2, 2013 Run the truck in direct and just straight stick it until she warms up just what 2 stack said. All the Mack trannies would do this in the cold weather. Rob Quote Link to comment Share on other sites More sharing options...
raindog Posted December 2, 2013 Author Share Posted December 2, 2013 Hey thanks. Glad I asked before I pulled it apart any further. Only thing I've lost is the time spent pulling up the floor panel. Quote Link to comment Share on other sites More sharing options...
fullfuel01 Posted December 2, 2013 Share Posted December 2, 2013 It did the same on my superliner. It got worst and worst. I had to change the small rectangular valve bolted on the tranny. Quote Link to comment Share on other sites More sharing options...
David Posted December 2, 2013 Share Posted December 2, 2013 Easy to take apart. Clean everything and replace the O rings. There is a small filter that is the same as the fuel filter at the carburetor on 80's GM's. Quote Link to comment Share on other sites More sharing options...
Superdog Posted December 2, 2013 Share Posted December 2, 2013 does yours have the neutral switch on the dash? In cold weather I used to flip that switch and put trans in gear while truck was warming up,that way trans. was warmed up too. Quote Link to comment Share on other sites More sharing options...
boyd Posted December 19, 2013 Share Posted December 19, 2013 the problem is, after time, the compressors start pumping some oil throughout the air system, when this happens this sludge sits in lines valves and all and causes issues like this. drain air tanks and see if you have oil and water coming out or just water. when you warm your truck up it makes the sludge free up where it will actually let air pass by. if oil in air system i would suggest air compressor, and if water make sure you have your air dryer hooked up, they generally ran AD-9 part number 065225 bendix air dryers on them, you may need to replace. Quote Link to comment Share on other sites More sharing options...
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