xdudebrahx Posted December 18, 2015 Share Posted December 18, 2015 My truck went to Mack a few weeks ago for some stuff and they "fixed" the Jake brake that had never worked before. Lo works fine but Hi doesn't work at all. Is this an external issue with some wiring or maybe the switch, or is it an internal adjustment issue? Kinda wanna avoid it being sent back out. I'd rather have it fixed in house. It's an 88 RD688S. Quote Link to comment https://www.bigmacktrucks.com/topic/43168-two-stage-jake-problem/ Share on other sites More sharing options...
Underdog Posted December 18, 2015 Share Posted December 18, 2015 I would check the wire to each cylinder head sounds like maybe one didn't get plugged in or a loose plug Sent from my XT1254 using Tapatalk Quote Link to comment https://www.bigmacktrucks.com/topic/43168-two-stage-jake-problem/#findComment-316274 Share on other sites More sharing options...
b61mack Posted December 18, 2015 Share Posted December 18, 2015 Check the wire under the valve cover too. Quote Link to comment https://www.bigmacktrucks.com/topic/43168-two-stage-jake-problem/#findComment-316277 Share on other sites More sharing options...
xdudebrahx Posted December 18, 2015 Author Share Posted December 18, 2015 Wires are both plugged in and look good all the way up to the switch. I guess it's something under the valve cover. For whatever reason we won't pull a valve cover in house so it'll have to get fixed the next time it goes in for a major service Quote Link to comment https://www.bigmacktrucks.com/topic/43168-two-stage-jake-problem/#findComment-316279 Share on other sites More sharing options...
felicello122 Posted December 20, 2015 Share Posted December 20, 2015 The solenoid under the cover could be bad, run a wire from the battery and touch the prong, it should click, engine off of course Quote Link to comment https://www.bigmacktrucks.com/topic/43168-two-stage-jake-problem/#findComment-316619 Share on other sites More sharing options...
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