Allison HT740 temperatures

[tomhamrick]

The temperature guage for my HT740 has never worked and since I am still converting and not used the coach a lot I have not paid it much attention. Now that I am begining to use the coach more I looked to see if a wire was loose or the sensor on the transmission was bad. In the hole where the sensor is supposed to be is a plug. Guess that's why it does not work. Until I can get the proper part# and order a sensor, what causes the temperature to go up in the HT740    Is there a certain way I can drive or something I need to be aware of to keep temps down?
Thanks for helping a dummy

[edroelle]

If you have a production installed 740, the trans cooler is part of the engine oil cooler.  I found that my transmission temperature followed my engine coolant temperature.  So, watch your engine temperature and don't let it get too high when climbing hills..

Ed Roelle
Flint, MI

[TomC]

The main culprit of heat production in an Allison is the Torque Converter.  While in converter mode, lots of heat is produced.  This is especially evident in stop and go traffic, or around town driving.  Once the converter has locked up, the trans produces small amounts of heat.  It is realitively easy to detect when the transmission goes into converter.  The operation of the HT740 is 1st converter, 2nd converter, 2nd locked up, 3rd locked up, 4th locked up.  So the 3rd bump you feel when accelerating is actually the torque converter locking up-which usually is a short time before shifting again into 3rd.  You can also get earlier lockup by only using about half throttle.  On my V730 (like a 740 without first) I can get lockup as low as 20mph, or as high as 42mph.  If I pull the shifter down to 1st, I can get lockup in first with about 3/4 accelerator pedal (full pedal will keep it in converter no matter the speed-just in 1st).  So when I slow down on a hill to the point that the transmission slips back into torque converter operation in 2nd, I then pull the transmission down to 1st and let up about an inch and the transmission goes back into torque converter lockup in 1st gear, where I pull a hill to keep the heat down, and the engine revs up (this around 35mph).  This little bit of driving the automatic has kept my transmission from overheating.  Hence, last month when I changed my transmission fluid for the first time since buying the bus (12 years ago, but only about 15,000 miles), the old fluid was still red and didn't smell.  You can just let the transmission do its' own thing, but it'll create alot of heat.  With a little intervention and keeping the engine heat below 200, your equipment should last for many faithful years.  Good Luck, TomC

[Kristinsgrandpa]

Tom C. Thanks for the info, I assume this applies to my HT 748 also.

Thanks, Ed.

[tomhamrick]

Thanks for the replys! I can always find help here!!!
Heading out tomorrow for a camping weekend with my 10 year old grandson. I will be hurting Monday from riding bicycles, fishing and playing putt-putt, but it is well worth it!!!   

[TomC]

HT740 is the original mechanical 4 speed.  HT748 is the heavier duty transit coach (with hardened input shaft, heavier duty clutches on 2nd and 3rd).  HT741 is electronic.  Otherwise, all the same inside.  Good Luck, TomC