pmolitor Posted September 24, 2015 Share Posted September 24, 2015 I lost 4th and 5th gear on my mack 6speed today. Driver got shifter stuck in 3rd gear so I removed cover and got it back to where it belongs. Now I don't have 4th or 5th. Any ideas. It is the 2 stick 6 speed. Gears 1,2,and 3 shift fine. Quote Link to comment Share on other sites More sharing options...
David Posted September 24, 2015 Share Posted September 24, 2015 Forth and fifth are on the same fork. May be the fork or the rail it is connected to. 1 Quote Link to comment Share on other sites More sharing options...
Challenger Posted September 24, 2015 Share Posted September 24, 2015 The fork may have missed the sliding clutch when installing the topcover. Try removing and reinstalling the top cover. 1 Quote Link to comment Share on other sites More sharing options...
pmolitor Posted September 25, 2015 Author Share Posted September 25, 2015 Thanks for the replys. I can't get back to it till this weekend. But I'll let everyone know what I find. Quote Link to comment Share on other sites More sharing options...
pmolitor Posted September 26, 2015 Author Share Posted September 26, 2015 Took the shift cover off today, near as I can tell the shift fork for 4th and 5th is shattered. How does that happen? Quote Link to comment Share on other sites More sharing options...
Challenger Posted September 26, 2015 Share Posted September 26, 2015 Forks usually break off clean towards the top and fall down in the trans. Maybe it broke, and the gears chewed/broke it up more? Quote Link to comment Share on other sites More sharing options...
pmolitor Posted September 26, 2015 Author Share Posted September 26, 2015 I've done some searching on this site. Found a couple post on the forks being replaced without removing the transmission. It said there are plugs in the back housing for the rails to slide out. Does that sound right? Quote Link to comment Share on other sites More sharing options...
pmolitor Posted September 26, 2015 Author Share Posted September 26, 2015 That was on the 12 speed. I think the main box is the same isn't it? Quote Link to comment Share on other sites More sharing options...
mrsmackpaul Posted September 27, 2015 Share Posted September 27, 2015 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 1 Quote Link to comment Share on other sites More sharing options...
Challenger Posted September 27, 2015 Share Posted September 27, 2015 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. Quote Link to comment Share on other sites More sharing options...
MACKTRUCKS4 Posted September 27, 2015 Share Posted September 27, 2015 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. 1 Quote Live every day like it's your last, because one of these days, it will be. Link to comment Share on other sites More sharing options...
pmolitor Posted September 29, 2015 Author Share Posted September 29, 2015 Shaft is broken. Looks like it's time to find an overdrive Trans for the truck. Thinking an 8ll or a 13speed. Don't know what would work best with the 3.87 rears. Quote Link to comment Share on other sites More sharing options...
David Posted October 1, 2015 Share Posted October 1, 2015 8LL or RR13. Mack 13 is too fast for 3.87 Quote Link to comment Share on other sites More sharing options...
mrsmackpaul Posted October 1, 2015 Share Posted October 1, 2015 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 runPaul 1 Quote Link to comment Share on other sites More sharing options...
pmolitor Posted October 1, 2015 Author Share Posted October 1, 2015 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. Quote Link to comment Share on other sites More sharing options...
Green Dash Posted October 3, 2015 Share Posted October 3, 2015 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. 1 Quote Jim Link to comment Share on other sites More sharing options...
pmolitor Posted October 3, 2015 Author Share Posted October 3, 2015 Found a RR13 single over for $1200. Comes with air shift pto. Quote Link to comment Share on other sites More sharing options...
pmolitor Posted October 3, 2015 Author Share Posted October 3, 2015 Driver said he heard nothing. Just Hamed in 4th gear. He tried to put the second stick in reverse to get it out but it was locked up. 1 Quote Link to comment Share on other sites More sharing options...
MACKTRUCKS4 Posted October 3, 2015 Share Posted October 3, 2015 When mine broke, the driver said the same thing, heard nothing, felt nothing. Pulled out from a stop, first , second, third, and nothing 1 Quote Live every day like it's your last, because one of these days, it will be. Link to comment Share on other sites More sharing options...
Green Dash Posted October 3, 2015 Share Posted October 3, 2015 When mine broke, the driver said the same thing, heard nothing, felt nothing. Pulled out from a stop, first , second, third, and nothingThat's exactly how it happened with me. Quote Jim Link to comment Share on other sites More sharing options...
pmolitor Posted October 3, 2015 Author Share Posted October 3, 2015 I figured he was beating on it. Now I have to apologize. 1 Quote Link to comment Share on other sites More sharing options...
Recommended Posts
Join the conversation
You can post now and register later. If you have an account, sign in now to post with your account.