Low gear in high range

It is there, But I was told not to use it, as it runs off the back side of reverse or something, anyway I quit using it. Now most of our trucks have automatics so it is not an issue.

 

Page 8, third bullet point from bottom
https://www.eaton.com/content/dam/e...le-transmissions/rt-18/TRDR0800EN-US_0614.pdf

• Never move the shift lever to the LO speed gear position while oper-
ating in HI range.

 

Your right Don379. Learned that lesson the hard way 35 yrs ago. And roughly $6000.00 dollars later. Had a problem taking advice from the million milers or more at that time. One of the reasons that trucking came harder for me.

 

Well someone discovered a secret.

see a lot of misinformation is thrown out there but here is the truth from Eaton.

While you can use the high range lo gear, what it does, no matter the load is, is stress the auxiliary unit to the point it breaks the unit.

the auxiliary unit isn’t designed for the load that a 12 or 14 to 1 ratio that the lo gear is, which with 1400 ft lbs of torque from the engine can do a lot of damage to a unit that should be seeing something from a 8.5 to 1 ratio.

 

Full disclosure my auto hauling trucking business that brings me to this forum is only a part time part of my business I started in 2006 to get me temporarily out of the shop from the constant telephone ringing and the overwhelming pull of customer relations.
My main claim to fame is a transmission builder and shop owner of more than thirty years.
I am not sure of the reasoning why Eaton doesn’t recommend using low in high range but I do know the low range gear spins the same rpm in low range as it does in high range because the INPUT rpm to that gear is the same no matter what range the back half of the transmission is in.

 

Not even almost. Never went to truck driving school either

 

someone will correct me because I know I know I’m about to screw this up, but I believe where low gear is in the front box can’t handle to torque of high range going through the back box, as well as not having the ratios line up you have a better chance of chipping teeth, then the actual size of the actual gear as well as the bearings that makes it 14:1 cannot handle the torque of being 2-4:1 or whatever ratio it comes out to

8LL also has that gear, the performance 9 speed is pretty much shifted like a 10 iirc just don’t use one of the holes by the passenger seat on the low side

 

My understanding is the contact patten from counter shaft to main shaft is to little in that position for HP/TQ in high range. Plus possibility of gear clash with reverse.


Limited contact pattern. I dont do it, some do.

 

The rear overdrive in a 13 is supported in a bushing, 18 speed has a bearing.

 

The perplexing problem for me is the thirteen speed and the 10 speed for the most part have the same or pretty close to the same low gear ratio.
The ten speed ####s the low gear on the high side every time through the gears yet the thirteen speed does not?
One thing I do notice is 6th gear in the ten speed and 5th direct in the thirteen are a comparable gear ratio.
With that being said it leads me to believe for 95 percent of the time using low gear on the high side on a thirteen the gear ratio would be to low for the engine torque and road speed.