splitting 6 speed low hole

[mackr1989]

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we have a 1988 r690 with a 6 speed low hole and a 250 mack motor. not sure what the gear ratio is but its about a 65 mph truck. i was told that you are not supposed to split the gears and that the transmission wouldnt let you regardless. in this truck you can. you can go from low to direct in all of the gears and direct to low without over revving or bogging the engine. ive told people the truck can do this and they didnt believe me and said it shouldnt be able to do that but it does so does that mean i can without damaging anything?

[Bigdogtrucker]

Sure it's not a 12 speed?

[mackr1989]

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yes it has 5 gears on the main stick and reverse, low and direct on the compound stick.

[Bigdogtrucker]

Thought they were air shift by then?(when did the twin stick end?)

[mackr1989]

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i dont know when the change was made but i like being able to shift this transmission the way im describing.

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[nasty51ford]

_{Okay, you can split each gear with a LOW HOLE, BUT !! If you are in 5th gear in the main box for example, and the back box is in high, then you pull it into low, what you are doing, is putting the transmission in the same RPM range as if you left the back box in high, and put the main box into 4th, so if you understand this, you will understand that you still only have 5 speeds with the back box providing a double LOW. Where as with a ten speed, for example, if you take off in first gear, wind it out, then pull the back box into high range, you wind that out, then, shift to second on the main, slide the back box back into low, your RPM's will drop and you will have to wind that gear out, then pull the back box into high gear, for the next shift, and so on through the gears. That's the best way I can explain it. So, while you have the capability to split each gear with the back box, when you do, it's the same as if you had shifted the main box, the 6 speed LOW HOLE trans gear ratios are spaced too close to allow progressive shifting with the back box. I hope I made sense! Lol !}

[mackr1989]

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yea i understand lol..youre right..being in 5 high then going to 5 low is like being in 4th but not quite the same. the engine speed is more compatible with road speed with splitting then just going into 4th like i said and you would have to race the engine to get to 4th whereas just going to 5 low gets you that half gear feeling. i hope im the one making sense now..i guess you would have to drive it and is it ok to do this?

[mrsmackpaul]

With a Maxi torque box deep reduction is in front of the main box not behind it the box behind is range change ie high low split there is a reason that you are not suppose to split the gears with the deep reduction box and I think it may have something to do with the weight and speed that the shafts are spinning because the whole gear box is trying to change not just three gears at the end but I could be wrong

There is meant to be a mechanical inter lock Im pretty sure it is under the main lid and I seem to remember that that if the shifter rod is put in 180degrees around the wrong way it then disables it I think the notch is the on the wrong side of the shaft its been a few years since I have had one of these boxes apart

Paul

[mackr1989]

It has an econodyne. Does that matter?

[Bigdogtrucker]

Shouldn't be an Econodyne with a 6 speed.

[MACKTRUCKS4]

The reason you shouldn't use low in any gear but first is the speed the shafts turn. When it's in low, there is a bearing the low shaft uses that is NOT designed to spin at higher rpm's. When you use it in higher gears, there is a good chance of knocking the bearing out. It will shift in any gear, but that does not mean you should use it.

[mackr1989]

Ok that answers my question then. Why should it not have a 6 speed matched with an econodyne

[2stacksuperdog]

Shouldn't be an Econodyne with a 6 speed.

Our 84 is a econodyne. 300 6 speed. Now has a 350

[jackb61sx]

Our 86 we used to have was also a 300 with the 2 sticks 6 speed and an econodine, but we never shifted from hi to low range or as asked split gears on it. Yes we could shift in reverse to a higher gear on a long back ( did that just to annoy my father)

Jack

[Bigdogtrucker]

Econodynes have a much more narrow power band than a Maxidyne,they'd fall on there face with a 5/6 speed.2stack you sure the old 300 wasn't a Maxidyne?

[2stacksuperdog]

Econodynes have a much more narrow power band than a Maxidyne,they'd fall on there face with a 5/6 speed.2stack you sure the old 300 wasn't a Maxidyne?

Positive. Has a inter cooler on it. Says econodyne on the side of the hood. I believe the build sheet say it too. Ill have to check.

[2stacksuperdog]

Says it has a M6-300. M for maxidyne? instead of E. Either way it has a 350 in it now. Still runs the same and still out pulls the big Cats on the hills.

[Bigdogtrucker]

Hood may have been changed.

[cstaples]

There were many Econodyne 2100 RPM motors with 6 speeds built. Got nothing to do with hoods.

[mrsmackpaul]

I dont think it makes a whole heap of difference with a 6 or 12 speed because most people I know who drive these dont split the lower 1,2,3&4 gears just split into high range in fifth so unless you are hauling big heaps of tons I reckon it would be fine just a bit slow getting to top speed with a big load on

Paul

[MACKS]

As far as I know the five and six speed were designed to be used with a maxi torque engine,never ever heard of anyone trying to split the upper gears in a six speed,the low hole is just that,a low low range.i mean how fast can the truck even go in fifth low,to go from fourth direct to fifth low would be impossible in my opinion..

[Bigdogtrucker]

Every 5/6 speed I've seen in person had a Maxidyne in front of it.Using LO in anything other than 1st or second is a waste of time,and could do some damage as others have said.

[Red Horse]

My two cents on this, the TRXL 107 had a direct (1st) ratio of 8.59 and a a low hole ratio of 14.10. The TRXL 1071 had the same first reduction of 8.59 but the low hole ratio was 23.08. This made it very difficult to start out in the hole and progressively shift and maintain road speed.

One alternative with the 1071 if you are off road or want to start a heavy load and progressively shift is to start in 2nd with the splitter in "low" then shift to first direct. Somehow I came upwith the formula that 23.08/8.59= 2.686. Or 8.59 x 2.686 = 23.07

So as 2nd in that trans has a ratio of 4.99 direct, if you take off with the splitter in low you have an effective ratio of 4.99 x 2.686 or 13.37

therefore going from 2nd low (13.37) to 1st direct gives you a nice prgressive jump from 13.37 to 8.59.

I can tell you, driving a 1071 this way works in terms of a nice easy no strain start. I have asked many "experts" if driving the 1071 this way woud be harmful and can't get a straight answer. In terms of splitting higher gears, no clue but driving it this way makes it an effective 6 speed with a Maxidyne/Econodyne. IMO

[blackdog2]

Red horse 87 88 r models at CF gulf had 2060 couldn't get through the drivers that you could only split 1 st gear had to test the old CF drivers because it was a big jump from 5 to 6 speed tranny.

[Red Horse]

Red horse 87 88 r models at CF gulf had 2060 couldn't get through the drivers that you could only split 1 st gear had to test the old CF drivers because it was a big jump from 5 to 6 speed tranny.

EJ-never understood that trans choice. Big George or Ed W?