Re: [A/S] Light Truck Diesel Engine Exhaust Brakes

["Harvey Barlow" <harveybarlow@xxxxxxxxxxxxxxxx>]

Jim,

I'm guessing that when you gas it under load, two things happen.  The torque
converter is unlocked and the transmission downshifts from overdrive to
third direct or possibly to second gear.  After this occurs, if you maintain
a steady foot on the gas pedal, most modern automatics will then allow the
torque converter to lock again in whatever gear it has selected.  At a
steady road speed, the tach should remain steady.  My Ford with E4OD
transmission, forerunner to the current transmission in use, was able to
lock the torque converter in 2nd, 3rd, and OD.  I assume yours does also.

You can test my answer by manually downshifting.  The tach should jump to an
increased but steady rpm at a given roadspeed.  Then, if you gas it, if the
tach jumps again it is probably because the torque converter is unlocking
each time you gas it.

What engine does your truck have?  5.4 liter, 4.6 liter?  It is a little
harder to understand what an engine transmission combination is doing in
modern gas-engined trucks because the engine and transmission are totally
controlled by the engine computer and the transmissions are much more
sophisticated.  The transmissions can shift up or down almost seamlessly and
the engines are so much quieter.  It is sometimes a little difficult to
determine what is happening.

Harvey