Quote:
Originally Posted by mokibrabrant
Thanks Cadillac....that explains the thread I was reading where the guy had changed out the rear axle ratio:. In what he explained to be a mechanical drive train (but obviously wasn't) and was having problems with shift points. And having done rear gear ratios on virtually every Schoolie I ever owned as the first order of business I had never encountered any problems whatsoever. So I couldn't figure it out. Then the discussion went to this modulator and I was completely lost I have avoided intentionally all the years that have any electronics, ECM sensors etc....and international seems to have started like in 1995. Whereas Thomas and Bluebird seemed to run to 2000 with all mechanicals. Think I see the 12 valve up until 99 and then we start getting into electronic 24 valves Cummins. So thanks for setting me clear about this modulator..
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the allison electric modulators are a joke.. they took it from being a modulator to being a kickdown..
in my mechanical DTA360 with the cable modulator to the allison transmission, my shift points are very much a "rheostat".. meaning if i press a little harder on the pedal I get a little later shift.. floor it and the trans shifts at the max RPM..
it works great.. there is a cable connected from my foot pedal down to a unirt on the ide of the transmission which progressivel;y moves a piston in and out to modulate the transmission line pressure..
when navistar (and others did it to) went to throttle by wire, Navistar did it earlier. than the likes of cummins, CAT, GMC.. (1994 the T444E was released).. instead of finding a way to connect the cable to the Fly-by-wire pedal. the electrified it.. in doing so insdtead of using a servo they used a solenoid..
a solenoid is an on / off.. so you either get shifts at the Lowest point (ie foot completely off the pedal in a mechanical).. or oyur shifts are at the highest point (foot floored on a mechanical).. there is no in between..
the foot pedal on a navistar / CAT HEUI engine is nothing more than an RPM setpoint.. even in neutral if I push my pedal down halfway, my engine will only rev up to a certain point.. unlike your gasoline car that in neutral barely pressing the pedal revs it way up. yet when driving it would be light throttle.
Navistar electronic diesel will do whatever it can to reach that RPM.. it will pull hard to do it.. the computer generates an "engine load factor" which approximates how hard the engine is working.. if the engine is working "hard" then the ECM will call for the transmission to downshift or to remain in downshift mode.. once your vehicle speeds up and the RPM gets closer to the "setpoint" your foot givesd it, the load factor reduces and the ECM releases the modulator and the shiftpoint is lowered..
on paper it sounds great.. in practice it was rubbish.. a lot of uo-down-up-down. or your transmission never shifting unless you let off.. or it stayed in high gear too long.. etc
the electric modulators were prone to failing.. and then your trans operated in low-line-pressure mode even under heavy load.. and esp with the AT545 you usually ended up ruining the transmission when the modulator died..
now as for me and electronics?
I can say that im lucky to have the best of both worlds.. my fully mechanical bus with its mechanical transmission works great.. other than blowing up an AT545 (which everyone does).. the drivetrain has been fantastic.. it isnt fast but it works and driveability is good..
on the other hand my Electronic bus (T-444E) with an electronic transmission (allison 1000) works fantastic.. both parts being electronic allows for a fantastic experience.. the 6 speed double OD is nice for having plenty of power around town and yet able to get good MPG on the highway and have niceties like Cruise control, advanced gauges and ability to choose my gear without a cumbersome clutch..
its thaty middle place that sucks.. electronic transmission on a mechanical engine or a mechanical transmission on an electronic engine... (other than a stick..if you like shifting then the mechanical manual trans on an electronic engine is a good fit it works great).. my red bus was originally an AT545 with (a bad) electric modulator that wasted my trans.. so I upgraded
Linear Mode
