Pipelayer Posted June 26, 2021 Share Posted June 26, 2021 The transmission will not shift gears when in low side. No matter which gear you have it in, when you let up to shift it goes to neutral. I put a gauge in the air line that goes to the valve that shifts it. The pressure stays the same even when the transmission goes to neutral. What am I looking at to get it fixed? Quote Link to comment https://www.bigmacktrucks.com/topic/67153-2180-transmission-low-side/ Share on other sites More sharing options...
Joey Mack Posted June 26, 2021 Share Posted June 26, 2021 Pull the shift cover and inspect the rails, and the silver set bolts in the forks for looseness and any slop... What is the history on this tranny. The poppet balls in the shift cover control rail position, which controls the forks... jojo Quote Link to comment https://www.bigmacktrucks.com/topic/67153-2180-transmission-low-side/#findComment-475885 Share on other sites More sharing options...
Joey Mack Posted June 26, 2021 Share Posted June 26, 2021 I am also curious about the back half . Syncro.... they will act stupid if the snap rings inside the synchro assembly go bad or were left out by a newbie when they synchro was replaced. It's like a motorcycle clutch just bigger and has 2 sets of thrust plates and friction plates... Anyway, there will be more info from others to help you. I have the book on this tranny and can send pics if needed.. Jojo Quote Link to comment https://www.bigmacktrucks.com/topic/67153-2180-transmission-low-side/#findComment-475886 Share on other sites More sharing options...
fjh Posted June 28, 2021 Share Posted June 28, 2021 On 6/26/2021 at 3:07 PM, Pipelayer said: The transmission will not shift gears when in low side. No matter which gear you have it in, when you let up to shift it goes to neutral. I put a gauge in the air line that goes to the valve that shifts it. The pressure stays the same even when the transmission goes to neutral. What am I looking at to get it fixed? which air line are you measuring pressure at the two lines at the rear cyl run the range the two that go to the lid run the split which can be operated any stick position! Quote Link to comment https://www.bigmacktrucks.com/topic/67153-2180-transmission-low-side/#findComment-475972 Share on other sites More sharing options...
Macktech20 Posted July 2, 2021 Share Posted July 2, 2021 On 6/26/2021 at 5:07 PM, Pipelayer said: The transmission will not shift gears when in low side. No matter which gear you have it in, when you let up to shift it goes to neutral. I put a gauge in the air line that goes to the valve that shifts it. The pressure stays the same even when the transmission goes to neutral. What am I looking at to get it fixed? Sadly 99% of the time if a Mack trans does not complete the range shift it has something to do with the syncro and not air pressure. A few things you can do to check is remove the rear cover and remove the range cylinder and fork. Look for any Galding on the cylinder shaft and the fork should have a good amount of wear on the side closest to the rear of the trans. This would indicate that the syncro is not locking in and it was being held for in the low range position by the cylinder and range fork before the syncro went out. Another thing to look at is when the cover is off check the spacing of the steel and fiber disks in the syncro make sure they're not broke its easiest to use a flat head screw driver and push the disks side to side. Also make sure the intermediate plate that sits against the high range gear (small gear) is relatively tight. Its not going to be soild but make sure it has. No more than 3/8 of an inch of movement side to side. Another thing to look at is the 311 spigot bearing in the input shaft make sure it hasn't failed that bearing supports the front of the main shaft and can cause difficult shifting. Another thing I have came across is a broken counter shaft in the back box. Is usually caused by the 538 bearing in the high range gear when it fails it causes one of the 3 to break. But it causes difficult shifting in any range and no coumpound shifts. You can check it by pushing up on the yoke on the trans and see if it the main shaft clunks around. 1 Quote Link to comment https://www.bigmacktrucks.com/topic/67153-2180-transmission-low-side/#findComment-476241 Share on other sites More sharing options...
Hayseed Posted July 2, 2021 Share Posted July 2, 2021 9 hours ago, Macktech20 said: Sadly 99% of the time if a Mack trans does not complete the range shift it has something to do with the syncro and not air pressure. Very True.. 1 Quote "Be who you are and say what you feel...Because those that matter...don't mind...And those that mind....don't matter." - Link to comment https://www.bigmacktrucks.com/topic/67153-2180-transmission-low-side/#findComment-476251 Share on other sites More sharing options...
Dirtymilkman Posted July 3, 2021 Share Posted July 3, 2021 On 6/26/2021 at 5:07 PM, Pipelayer said: The transmission will not shift gears when in low side. No matter which gear you have it in, when you let up to shift it goes to neutral. I put a gauge in the air line that goes to the valve that shifts it. The pressure stays the same even when the transmission goes to neutral. What am I looking at to get it fixed? Mine did this once. I replaced the shift knob/range selector. Fixed it. 1 Quote Link to comment https://www.bigmacktrucks.com/topic/67153-2180-transmission-low-side/#findComment-476320 Share on other sites More sharing options...
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