Triplex Question

[gvam]

I am new to this site (but having a great time). Have a general tranny question

If you have a triplex transmission, but you are not allowed to use direct and Lo split in 5th speed, how do you come up with 15 speeds.

I was looking at a truck listing on eBay and saw this on the shift pattern tag.

Pardon my "newbie" question

[theakerstwo]

I am new to this site (but having a great time). Have a general tranny question

If you have a triplex transmission, but you are not allowed to use direct and Lo split in 5th speed, how do you come up with 15 speeds.

I was looking at a truck listing on eBay and saw this on the shift pattern tag.

Pardon my "newbie" question

You do have 15 gears but some ratios are the same so mack tells you to not use certain ratios. The ratios may not be the same but will be so close to each other that there would be no gain in going into a gear that you may be only 100 rpm different than the one you came from. Some 15 speads do have 15 true and even rpm splits i think that would be a direct drive in hi gear. glenn

[vanscottbuilders]

You do have 15 gears but some ratios are the same so mack tells you to not use certain ratios. The ratios may not be the same but will be so close to each other that there would be no gain in going into a gear that you may be only 100 rpm different than the one you came from. Some 15 speads do have 15 true and even rpm splits i think that would be a direct drive in hi gear. glenn

Glenn is right - by the nature of a duplex, triplex or quadraplex Mack transmission, there are actually two separate transmissions mated in one case. Hence two sticks. The gear ratios do overlap in some instances, especially when there may be an overgear in each of the transmissions like a TRT-7220. You still have, as Glenn said, all 15 gears, but you may only use 12 or 13 of them on a regular basis.

Confusing, I know. But - If it were easy anyone could do it!

Good question,

Paul Van Scott

[Freightrain]

Sounds like maybe a double over Triplex? Where 4th over and 5th under is same, just like the double over Quadbox. It would actually be a downshift instead of upshift, thus you don't use it. Ya, it's not a true 15 spd, but not a big deal.

My single over you can use ALL 15 gears in progression.

[Packer]

My double over Quad box has only 15 useful gears.

13 or 14 would be closer.

Deep under in 1st gear and no where else. Plus a skip (or two) in 1st and your down to about 13.

The shift plate calls it an 18 speed.

Packer

[Joe Ditchkus]

That is what is called a 13 speed triplex, there is also a 18 speed quadbox and a 9 speed duplex.Mack also made a tri-plex with a very deep first gear about the same as a quadbox in first gear it was avaible in vocational B Models as the B-53. You would use lolo in the back box in first or second gear only for starting out. I do not know if all but the quadboxes we had when you shifted out of lolo it could only be put back in lolo in first or reverse gear, it was designed that way from factory.

[Joe Ditchkus]

That is what is called a 13 speed triplex, there is also a 18 speed quadbox and a 9 speed duplex.Mack also made a tri-plex with a very deep first gear about the same as a quadbox in first gear it was avaible in vocational B Models as the B-53. You would use lolo in the back box in first or second gear only for starting out. I do not know if all but the quadboxes we had when you shifted out of lolo it could only be put back in lolo in first or reverse gear, it was designed that way from factory.

[gvam]

Thanks for all the replies.

I am still learning, but I am anxious to take a crack at it. I kind of figured it had to do with the gear overlap and how the transmission is set up