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lost 4th and 5th gear


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Im fairly sure there is something there to let those rails slide out enough but been a while since I have had one apart and have done what your about to try just make sure you get all the selector fork bits out

Paul

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That was on the 12 speed. I think the main box is the same isn't it?

Yes.

The 4th/5th fork rail is about 10" long. Its the only fork on the rail. I THINK the rail sticks out of front of the trans with a seal, like the compound rail on a 12 speed. Remove the detain ball and spring and try sliding it which ever way you get the needed room to remove the fork. Like mrsmackpaul says, its been awhile since Ive done it too. Definitely worth a shot.

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If memory serves me right, the soft plug in the back of the trans for the shift rail needs to come out. When you slide the rail out the front, the rail hits the clutch before there is enough room to install the new fork. The old one may come out because it is in pieces. Also when you are in there make sure you check the main shaft to make sure it did not sheer in 2 because this happened to me. When the shaft broke, it caused the fork to brake. I put the new fork in and the truck still had no 4th and 5th. because those 2 gears run through the main shaft. I had a hard time seeing the shaft was broke because of the way it broke. It almost looked like it was cut with a saw.

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Live every day like it's your last, because one of these days, it will be.

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why dont you fix the transmission the Mack 12 speed is pretty simple to work on if I can work on them anyone can !!!!!!!! they are fairly cheap to fix and everything will still line up eg Tail shaft mounts air lines ect ect I feel it would be a lot cheaper in the short and long run

Paul

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I only have a 6 speed. The shift fork is only available after market. It's $500. The main shafts is $1300. I can buy the 13speed single over drive for $1300. I would love to have a mack 12 speed but they are getting hard to come by. The other reason is lack of time to tear it down. I need to get back on the road. We started hauling Ag lime this week.

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I had a shaft break on a 5 speed and had no idea it happened until I tried to go into 4th and all I found was what felt like a "sideways neutral" between 4th and 5th. I would've expected some sort of "crash, boom, bang" at the very least.

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Jim

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