Kreager Posted Monday at 11:31 PM Share Posted Monday at 11:31 PM Hi, I’m having issues with my newer to me 1998 CL715 (E7 with T2180 18-speed) grain truck and shifting into low range. I haven’t put more than 500 miles on the truck since buying it, and the truck shifted fine when I picked it up a few months ago. Recently the transmission will only switch into low range when air pressure in the tanks is at about 65 pounds. At this PSI the transmission will shift into low range upon selection (I can hear the range forks move), but will immediately switch back into high range without selection. Anything higher than 65 PSI and the transmission stays in high range. I took apart and cleaned the range shift valve on top of the transmission. It was pretty dirty inside but not scored. Put it back together and it seems to work ok. I also removed the cover of the range shift cylinder on the back of the transmission. When doing so I discovered that the high range supply line was applying air pressure at the same time as the low range supply. I guessing that’s not normal. I’m also guessing that the high range supply to the cylinder is overriding the low range supply (except momentarily at around 65 PSI) which is causing the transmission to stay in high range. The cylinder does move easily into low range, and hold there, with the cylinder cover off (no possible way high range air pressure can be applied). My questions are: What would cause there to be positive air pressure on both the low and high side of the range shift cylinder at the same time? Is my range selector valve failing and creating blow by to both low and high supply lines to the range shift cylinder Does anyone have a part number for the range shift valve for my truck (see attached photo taken before I cleaned and removed it)? Any help would be appreciated. I do have the T2180 service manual. Thank you, Kreager Quote Link to comment https://www.bigmacktrucks.com/topic/75611-t2180-won%E2%80%99t-stay-in-low-range/ Share on other sites More sharing options...
Joey Mack Posted yesterday at 09:37 AM Share Posted yesterday at 09:37 AM Is the shift knob failing? Quote Link to comment https://www.bigmacktrucks.com/topic/75611-t2180-won%E2%80%99t-stay-in-low-range/#findComment-576891 Share on other sites More sharing options...
fjh Posted yesterday at 12:33 PM Share Posted yesterday at 12:33 PM 2 hours ago, Joey Mack said: Is the shift knob failing? where is the Heinz when you need him! ?? 😅 Quote Link to comment https://www.bigmacktrucks.com/topic/75611-t2180-won%E2%80%99t-stay-in-low-range/#findComment-576904 Share on other sites More sharing options...
Geoff Weeks Posted yesterday at 01:46 PM Share Posted yesterday at 01:46 PM 14 hours ago, Kreager said: My questions are: What would cause there to be positive air pressure on both the low and high side of the range shift cylinder at the same time? Is my range selector valve failing and creating blow by to both low and high supply lines to the range shift cylinder Does anyone have a part number for the range shift valve for my truck (see attached photo taken before I cleaned and removed it)? Kreager 1st let me state, I have no experience on the Mack transmission in question, however I can answer your 1st question. Yes it can be normal to have pressure to both sides of a piston, Eaton does this on theirs. Because the rod takes up some area on the rod side, that "working" area is smaller than the other side, so when pressure to both, the piston moves to the rod side direction, when the back is vented the piston move the other way. Quote Link to comment https://www.bigmacktrucks.com/topic/75611-t2180-won%E2%80%99t-stay-in-low-range/#findComment-576907 Share on other sites More sharing options...
Kreager Posted yesterday at 02:11 PM Author Share Posted yesterday at 02:11 PM 8 minutes ago, Geoff Weeks said: 1st let me state, I have no experience on the Mack transmission in question, however I can answer your 1st question. Yes it can be normal to have pressure to both sides of a piston, Eaton does this on theirs. Because the rod takes up some area on the rod side, that "working" area is smaller than the other side, so when pressure to both, the piston moves to the rod side direction, when the back is vented the piston move the other way. Ok, thank you for the reply. On the T2180 the 'rod side' of the range shift cylinder (at the back of the transmission) is towards low range and won't hold in place when selected. The transmission keeps shifting itself back to high range. I don't remember seeing/hearing any venting on the rear plate that is covers the high range side of the cylinder. If it's normal to have pressure on both sides of the cylinder, despite what is being selected, then I must be losing air pressure somewhere on the low side causing the high side to take over? Quote Link to comment https://www.bigmacktrucks.com/topic/75611-t2180-won%E2%80%99t-stay-in-low-range/#findComment-576910 Share on other sites More sharing options...
Geoff Weeks Posted yesterday at 02:19 PM Share Posted yesterday at 02:19 PM 2 minutes ago, Kreager said: If it's normal to have pressure on both sides of the cylinder, despite what is being selected, then I must be losing air pressure somewhere on the low side causing the high side to take over? I have no idea on Mack if it is normal, I was just saying it can be. In any position does the non-rod side not have air? The rod side can have air at all times in some applications, but the non rod side must be vented in one selection at least. The only way the piston will move out is when the rod side has air and the non rod side does not. The rod side has to be at a higher pressure than the non rod side to move the piston away from the trans case. Quote Link to comment https://www.bigmacktrucks.com/topic/75611-t2180-won%E2%80%99t-stay-in-low-range/#findComment-576911 Share on other sites More sharing options...
The Heinz Posted yesterday at 02:26 PM Share Posted yesterday at 02:26 PM 1 hour ago, fjh said: where is the Heinz when you need him! ?? 😅 I'm here, usually. Lurking in the shadows... The part number for the valve off a '98 T2180 is 25501019, Mack has them in stock. Quote Link to comment https://www.bigmacktrucks.com/topic/75611-t2180-won%E2%80%99t-stay-in-low-range/#findComment-576912 Share on other sites More sharing options...
Kreager Posted 22 hours ago Author Share Posted 22 hours ago (edited) 2 hours ago, Geoff Weeks said: I have no idea on Mack if it is normal, I was just saying it can be. In any position does the non-rod side not have air? The rod side can have air at all times in some applications, but the non rod side must be vented in one selection at least. The only way the piston will move out is when the rod side has air and the non rod side does not. The rod side has to be at a higher pressure than the non rod side to move the piston away from the trans case. I agree. I think that's why I might have a problem with blowby somewhere, or an issue in the range selector valve. I'm also not sure if the range selector valve is supposed to vent the high side (non-rod side). Regardless, high side venting is not happening right now. Edited 22 hours ago by Kreager Quote Link to comment https://www.bigmacktrucks.com/topic/75611-t2180-won%E2%80%99t-stay-in-low-range/#findComment-576921 Share on other sites More sharing options...
Joey Mack Posted 20 hours ago Share Posted 20 hours ago air is exhausted during both range shifts. 1 Quote Link to comment https://www.bigmacktrucks.com/topic/75611-t2180-won%E2%80%99t-stay-in-low-range/#findComment-576930 Share on other sites More sharing options...
Kreager Posted 16 hours ago Author Share Posted 16 hours ago 8 hours ago, The Heinz said: I'm here, usually. Lurking in the shadows... The part number for the valve off a '98 T2180 is 25501019, Mack has them in stock. Thank you, I have a feeling the range valve is my issue. 1 1 Quote Link to comment https://www.bigmacktrucks.com/topic/75611-t2180-won%E2%80%99t-stay-in-low-range/#findComment-576952 Share on other sites More sharing options...
fjh Posted 15 hours ago Share Posted 15 hours ago 59 minutes ago, Kreager said: Thank you, I have a feeling the range valve is my issue. Yup 1 Quote Link to comment https://www.bigmacktrucks.com/topic/75611-t2180-won%E2%80%99t-stay-in-low-range/#findComment-576958 Share on other sites More sharing options...
Joey Mack Posted 15 hours ago Share Posted 15 hours ago Can you pressure wash the top of the tranny? Pay attention to the piston when you pull the range shuttle. Inspect it for wear, likely its good. Quote Link to comment https://www.bigmacktrucks.com/topic/75611-t2180-won%E2%80%99t-stay-in-low-range/#findComment-576959 Share on other sites More sharing options...
Joey Mack Posted 15 hours ago Share Posted 15 hours ago I just saw that you say you have the book..so you can see the interlock pin.. Quote Link to comment https://www.bigmacktrucks.com/topic/75611-t2180-won%E2%80%99t-stay-in-low-range/#findComment-576960 Share on other sites More sharing options...
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