Neep help figuring out what they are!

[Hank]

I need help in identifying some parts on my bus. On the driver's side (LH) side of my HT740D mechanical transmission were two pressure switches made by Nason. They were installed off of two NPT ports on the side of the transmission housing just above the oil pan. There were two wires to each switch wired to the normally closed terminals (I think). Both of the housing seals on these switches had failed and they were leaking a lot of transmission fluid. Neither my parts manual, service manual, Luke or the local bus garage mechanic could tell me what these did. Luke and the guy at the bus garage thought they may have been installed by the previous owner for some reason.

Here's what I know so far: with both of these switches removed, ports plugged off and wires disconnected, there is no change in the function of the bus. It won't start in gear, the reverse lights work and the transmission operates as per usual. There are no tell tale lights that come on. However, when I touch the two leads to the rear most switch together, the solenoid in one of the Skinner valves is energized and clicks. It's the middle Skinner valve of the three that are on the rear bulkhead of the engine compartment right behind the turbo-my parts manual doesn't specify what this one does. I didn't try this with the engine running. When the two wires from the other switch are touched together, nothing happens. I'm not even sure that there's voltage present on that circuit.

I'm going to do some more investigation but was wondering if anyone could set me on the right track!
Thanks,
Hank
1985 96A3 6V-92TA/HT740

[skipn]

Hope this helps


   Quote from redwrench in WA.

"The "D" in HT-740d indicates that it is a "Fire truck special". In most special vocational designs it has been beefed up in the nessecary areas to better handle the specific strains caused by the vocation. Fire truck specials usually have a different converter stall torque ratio and have a provision for fourth range lockup used during pump operations or where a constant PTO speed is required.
"

Hope this helps could be the other lockup switch.

    Skip

[makemineatwostroke]

Hank, call United at 1-800-527-1637 a Allison dealer and he can answer your question because I have never saw a 740 with 2 ports on the side but some 750s will have 2 ports, if it came from the bottom on a 740 it would be a lock up  good luck