13 Speed?

[Warpman89]

Is there a 2 stick mack 13 speed that came in r models? for some reason i seem to remember hearing about a transmission that had a five gear box and a low, direct, and high box, but for fifth gear you only used high. does this tranny exist or am i losing it?

on this subject, other than the 6 speed, what other 2 sticks trannys did mack have for the r model?

[Packer]

The 18 speed is like that - - - double overdrive but with a Lo-Lo, Lo, Direct, and Hi Quadraplex

A Triplex is Lo, Direct, and Hi.

Go to the oldmacksrus link.

Tom has listed all the Mack trannys!!!

And there is a bunch!!

Packer

[terry]

You are talking about an overdrive triplex, you can use the under, direct and over in the back box with first to fourth in the main, then when you are in fourth in the main box and over in the back box, you just shift the main box to fifth, which is overdrive in the main box. it really gets confusing to try and explain the difference between a trt 72 and a trt 720 In both tranny's the back box is a underdrive a direct and a overdrive. Hope this is not to confusing ! Terry

[other dog]

sorta-kinda-simpler,if 5th is overdrive in the main,it's a 13 speed tri-plex,if 5th is direct in the main you can use all 15 speeds.

[Mack Doctor Jr.]

We have a 2 stick in our R600. Rev and 1-5 on one stick and direct ond overdrive on the other. This tranny sure gets her right down the road with those 4:17.

[vanscottbuilders]

If you check out oldmacksrus.com, Tom Gannaway

has done a great job of detailing all of the older transmission

gear ratios. This might give you a better understanding of why

an overdrive triplex gearbox is used as a 13 spd. vs. a 15 spd.

I don't think that the triplex TRT-720 was ever available with a

Maxidyne engine, so the R-600 must be a fairly early production truck.

I could be wrong about that little factoid - but I'm certain that

someone will correct me if I am.

I do know that a lot of guys use them behind their Maxidynes,

even though the gearbox isn't torque rated as high as the engine.

One good line I heard was "You just have to shift it like you own it!"

In terms of use-ability, the TRT-720 is one of the best older transmissions

for use as a "play truck". Good road speed and good pulling power with

the older, low torque/low horsepower engines and generally low final drives.

Yet it doesn't have the weight of the bigger quadraplex boxes.

Paul Van Scott