Model- HT 740 Serial # - 2510101263 23019260 86D0 I am repowering a truck and have part of the wiring harness, but no schematics. Can some tell me what activates the 2 external solenoids at the back of the transmission? It also has a cable driven electric tach drive with no wiring. And was wondering if it maybe rpm activated? The truck has Jake brakes. It came from an '86 Model and having trouble finding out information. Any help would be appreciated.
Well I know a decent amount about the 740/750s and I didn't know there's an electronic solenoid at the back of the transmission. Far as I know there's a neutral light and a reverse light and a mechanical speedometer cable and that's it. Is also a shift modulator that's usually cable driven or electronically driven in the middle of the transmission by the shifter.
I have a little more back story on this. The motor and transmission came out of a fire truck. I do not know if this will help identify the solenoids. There are 2 small lines running to each solenoid and back to the case. Since you are familiar with these transmissions did they have any kind of braking assistance on these non electronic transmissions?
I just found a diagram that said it was a preheat circuit. And since it was a fire truck I guess it makes since. Thanks for the help.
They can have a retarded, its a big mass of valve body on the pass side. They can lock the torque converter and help with braking without a retarder but it's not that great in my experience because of when it does it, I also have a plugged modulator valve and a truck that goes only 44 mph. The trucks I drove that went 67 mph probably didn't have a plugged modulator and only offered engine braking when you went slow and shifted the selector in 2 or 3 gears (1 or 2 in a 740)
Sounds like you are describing the Skinner valves. They are electrically actuated and you when shift the fire truck into pump mode and into Drive, it forces the transmission into 4th (direct) gear and locks up the torque converter. At the same time a transfer case has disconnected the drive shaft from the wheels and connected it to the fire pump. So the engine is directly coupled to the pump. If you have no use for them they can be left alone, or disconnected, but I don't really know the details on it. Look up Skinner valve on the internet and you should find something, however when the internet came along in a big way they were already becoming obsolete with electronic transmissions being around so it might take some digging.
On a 740 I think 3rd is direct and 4th is something like .78, or im thinking of the 4460 Would be cool if there's a skinner valve for one, we put dual modes on them to lock it into gear but that's around $6000 and not made anymore
640 and 740 series are direct drive. Overdrive came with the World series which were originally nomenclatured MD3060 and HD4060 or something close to that, but now they have all kinds of silly names for them. 4th gear direct, 6th gear 0.65 OD
Thanks for all the information and help. We got it figured out now.