Jake Brake Programming

[davidbrady]

I've found that turning the fan override on is another way to fine tune the jake brake stopping power. The fan on the LXi can sink another 40 HP of stopping power in addition to the 350 HP of stopping power offered by the jake. In some cases I find that 4th slows me down too much and 5th not enough, while 5th with the fan override on is just right.

Chuck, my LXI works as you describe. If the rpm's are too high for the pre-selected 4th gear to be used, the jake will use 5th and it will operate at speeds above 65 mph. But, when the transmission decides that rpm's are sufficiently low for 4th gear to be engaged the downshift causes the engine to over-rev to 2350 rpm. For this reason I had my transmission programmed to pre-select 5th.

With the new programming the transmission uses a new set of rpm setpoints when downshifting; the chosen rpm setpoints are well below max braking power for each gear. The solution is to manually push the down arrow to select lower gears at rpm's that provide full braking power. The challenge then is remembering to hit the up arrow to allow use of all 6 gears when on the flats. A short cut to depressing the up arrow multiple times is to hit 'D' once - this has the effect of instantly selecting 6th as the max allowable gear.