LMTV FMTV Exhaust Brake Questions?

[Ronmar]

Here is the link…

 

[GeneralDisorder]

Agree with Ron. Wouldn't mess with the Allison programming. There's no reason and redline under decel with no fueling is hurting nothing. Higher RPM increases hydrodynamic film strength in the main and rod bearings and with no fuel there's also no load. There's no benefit to not using the lowest (numerical) gear that results in maximum engine braking within the RPM envelope of the engine - and the closer to redline the better as that results in higher oil pressure and film strength as well and in a zero-fuel condition so there's no trade-off - the result is simply less service brake wear with zero drawbacks.

 

[Ronmar]

Also what RPM are you calling “Redline”… i doubt the engine is ever pushed over max governed RPM as the trans controller will not allow it… also of note is that the marine variants of these engines have a max governed RPM typically several hundred RPM higher than the road variants…

 

[GCecchetto]

Agree with Ron. Wouldn't mess with the Allison programming. There's no reason and redline under decel with no fueling is hurting nothing. Higher RPM increases hydrodynamic film strength in the main and rod bearings and with no fuel there's also no load. There's no benefit to not using the lowest (numerical) gear that results in maximum engine braking within the RPM envelope of the engine - and the closer to redline the better as that results in higher oil pressure and film strength as well and in a zero-fuel condition so there's no trade-off - the result is simply less service brake wear with zero drawbacks.

Guess we’ll have to agree to disagree. On an interstate in the mountains I want to be able to use the exhaust brake to manage speed on the down grades and in a truck easily capable of moving along with traffic, I don’t want to be in the slow lane with my flashers on going 35mph. I can always manually shift down into third when conditions warrant it, but I can’t prevent the aggressive downshifts to 3rd as currently programmed when I don’t want or need that.

 

[GeneralDisorder]

Wait till you have more weight. That will likely make it less harsh. I don't notice anything untoward with the downshifting down grades. Have a steep one from the grocery store to my house that I travel regularly.

 

[GCecchetto]

Wait till you have more weight. That will likely make it less harsh. I don't notice anything untoward with the downshifting down grades. Have a steep one from the grocery store to my house that I travel regularly.

But is it an interstate with a 75mph speed limit where you are driving 60-65mph? I live in the hills as well, every direction from my house is downhill on steep winding roads. Speed limits range from 25 to 40mph and on the hills that are 40mph, 3rd gear is lower than I want to be in in most cases. In 4th I could comfortably coast down the hill with the exhaust break on.

If it turns out the current programing is better, I can always go back to the current profile. To me this isn't any different than removing the springs in the front on A1R's. It's a design parameter implemented for a different use case that isn't how the vehicle is being used by me.