NLC Posted January 14, 2020 Share Posted January 14, 2020 My Triplex transmission will not go into lo. It shifts from direct to high ok. Any information would be appreciated. Quote Link to comment https://www.bigmacktrucks.com/topic/60547-triplex-transmission/ Share on other sites More sharing options...
fjh Posted January 14, 2020 Share Posted January 14, 2020 (edited) 13 minutes ago, NLC said: My Tri plex transmission will not go into lo. It shifts from direct to high ok. Any information would be appreciated. You may have to be in 1st gear to get low! a few Mack Trans were like this! Edited January 14, 2020 by fjh Quote Link to comment https://www.bigmacktrucks.com/topic/60547-triplex-transmission/#findComment-440322 Share on other sites More sharing options...
Rob Posted January 14, 2020 Share Posted January 14, 2020 Not really a lot of information in the original post? Mechanically will not slip into the Low position, or does the shifter handle move but a fork or gear selection doesn't? Never have seen an interlocked triplex myself so I could still be wet between the ears too. Quote Plodding along with no job nor practical application for my existence, but still trying to fix what's broke. Link to comment https://www.bigmacktrucks.com/topic/60547-triplex-transmission/#findComment-440325 Share on other sites More sharing options...
terry Posted January 14, 2020 Share Posted January 14, 2020 4 hours ago, Rob said: Not really a lot of information in the original post? Mechanically will not slip into the Low position, or does the shifter handle move but a fork or gear selection doesn't? Never have seen an interlocked triplex myself so I could still be wet between the ears too. no interlock on the single countershaft transmissions, they started on the triple countershaft trans. terry Quote Link to comment https://www.bigmacktrucks.com/topic/60547-triplex-transmission/#findComment-440335 Share on other sites More sharing options...
Rob Posted January 14, 2020 Share Posted January 14, 2020 Just now, terry said: no interlock on the single countershaft transmissions, they started on the triple countershaft trans. terry I agree. Did the term "triplex" carry over? I've never heard any later triple countershaft trans referenced as such. Quote Plodding along with no job nor practical application for my existence, but still trying to fix what's broke. Link to comment https://www.bigmacktrucks.com/topic/60547-triplex-transmission/#findComment-440336 Share on other sites More sharing options...
terry Posted January 14, 2020 Share Posted January 14, 2020 1 minute ago, Rob said: I agree. Did the term "triplex" carry over? I've never heard any later triple countershaft trans referenced as such. Unless they are confusing triplex and triple countershaft, of course then you have the 12 spd. three transmissions bolted together. terry 1 Quote Link to comment https://www.bigmacktrucks.com/topic/60547-triplex-transmission/#findComment-440337 Share on other sites More sharing options...
Rob Posted January 14, 2020 Share Posted January 14, 2020 1 minute ago, terry said: Unless they are confusing triplex and triple countershaft, of course then you have the 12 spd. three transmissions bolted together. terry Couldn't agree more. The 12 speed as I remember had to be in low gear to go into low range due to the interlock. However the old triplex reference kinda got me out of kilter. 1 Quote Plodding along with no job nor practical application for my existence, but still trying to fix what's broke. Link to comment https://www.bigmacktrucks.com/topic/60547-triplex-transmission/#findComment-440338 Share on other sites More sharing options...
NLC Posted January 14, 2020 Author Share Posted January 14, 2020 It’s the old tri plex in a B61. The shifter will not move when you pull it over to low. The shifter works fine in direct and hi. Quote Link to comment https://www.bigmacktrucks.com/topic/60547-triplex-transmission/#findComment-440342 Share on other sites More sharing options...
Rob Posted January 14, 2020 Share Posted January 14, 2020 5 minutes ago, NLC said: It’s the old tri plex in a B61. The shifter will not move when you pull it over to low. The shifter works fine in direct and hi. Thanks for the update. Does the shifter handle readily move through the neutral gate to where you would pull it back to slide into gear? Does the shifter handle attempt to move into the low gear position? There is a gate apparatus on the top of the transmission that can be rusted precluding it's operation and they also can get packed with mud dependent upon the truck's usage. This gate apparatus is designed to be greased but much of the time neglected for years. Remove your floor pan and it will be readily visible having the two rods which should slide easily for shifting the compound. Quote Plodding along with no job nor practical application for my existence, but still trying to fix what's broke. Link to comment https://www.bigmacktrucks.com/topic/60547-triplex-transmission/#findComment-440343 Share on other sites More sharing options...
Freightrain Posted January 14, 2020 Share Posted January 14, 2020 Agree, the back box has external shift rails and go to the side of the back box. If not lubed i can see it not wanting to go into low. I just had my rods out of mine last winter replacing the clevises to tighten things up. It could be the detents jammed up also in the top of the box. Or even the shifter itself? It is exposed and if not lubed could rust up. Quote Larry 1959 B61 Liv'n Large...................... Charter member of the "MACK PACK" Link to comment https://www.bigmacktrucks.com/topic/60547-triplex-transmission/#findComment-440351 Share on other sites More sharing options...
NLC Posted January 14, 2020 Author Share Posted January 14, 2020 We loosened up the rods and now have the top of the back box off seems that the shift collar on the bottom shaft is the problem. It will move about 1/16 of an inch back and forth. Will check further tomorrow. Quote Link to comment https://www.bigmacktrucks.com/topic/60547-triplex-transmission/#findComment-440353 Share on other sites More sharing options...
NLC Posted January 16, 2020 Author Share Posted January 16, 2020 I found out what is wrong with my triplex transmission. I need a 741KBA 1152A gear assembly, a 747KB 347 gear , a 320KB 251 clutch and 3 of a 3AX 839 screws. Does anyone know where I might locate these parts? I have not called Mack yet. They maybe obsolete. Quote Link to comment https://www.bigmacktrucks.com/topic/60547-triplex-transmission/#findComment-440464 Share on other sites More sharing options...
Rob Posted January 16, 2020 Share Posted January 16, 2020 They are probably obsolete. Last I checked it was getting hard to get anything two stick except some quadraplex parts. PAI shows nothing for a triplex any longer. Quote Plodding along with no job nor practical application for my existence, but still trying to fix what's broke. Link to comment https://www.bigmacktrucks.com/topic/60547-triplex-transmission/#findComment-440465 Share on other sites More sharing options...
Brian L Blaylock Posted January 16, 2020 Share Posted January 16, 2020 I have a complete back box for a tri plex if that will help Quote Link to comment https://www.bigmacktrucks.com/topic/60547-triplex-transmission/#findComment-440484 Share on other sites More sharing options...
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