sending unit #

Link

Link

cut and paste to address for web site.

I was surprised not to see that figure on the Honeywell/Hobbs site.

Where did you get the 2-12 PSI figure? If this is correct, I believe my interpretation is correct... the switch needs 12 PSI to initally "open, then will stay "OPEN" until the pressure drops to 2PSI.

Without at least SOME "differential", the light would flicker continuously when the pressure was near the switch's "setpoint", arcing the contacts.

I will look in the Standard catalogs tomorrow, and see what they have in that range..

Search on Stewart Warner Hobbs. Pull up one of the sites the has Stewart Warner with a header that says catalog index-click on that - then find pressures switches that are titled "Standard and Series 5000 Pressures Switches" On the first page you will find "Single Circut/1 terminal- Series 5000 switches (top) and you will see 78149 with a factory set point of 2 psi Normally closed.

I had to print out this page and take it to NAPA to get them to order the right one. They kept insisting it was an M4001- which the catalog shows as a 4psi Normally closed.

If his information is correct, what is YOUR "take" on what the 12 PSI part means?

The transmission pump feeds a series of valves. The oil first is regulated by a system relief valve set to open at 175psi, then the oil can go to the PTO Regulator valve set to maintan 150 psi (with handle half way out)and also goes to the Trans Regulator valve(inching pedal) also set to 150 psi (with the pedal down) also the oil path goes to the lubrication circuit valve which will open at 43 psi. When the PTO is Halfway open or the inch pedal is depressed the pressure at the lube relief valve drops below 43# (to zero I think if the other valves are correctly set to 150psi) Once that valve closes the lube sending switch goes to zero and the red light comes on .So as long as the pump can put out 175 psi, and you don't lose it through internal leaks including the indirect PTO circuit to the point where you don't have 43 psi to open the final lube circuit you will get oil into the lube circuit. Think of it as series hookup with higher pressure at the start near the pump and the downstream relief valves and the lube openings result in a lower and lower pressure until the lube pressure switch which is the tail end receives only 2 to 12 psi from a start of 175.

Now what happens in the lube circuit is that at specfic points along the mainshaft some oil is bled off to lube the transmission and this reduces the pressure and the sender switch is at the very end so as long as you get any pressure at all at the end you are getting lube to the transmission. The 12 psi reference is in later service manuals and the IT manual as the normal range is 2 to 12. This at 800 RPM and 120 degree oil. So at that speed and temp if you have more 12 you should adjust the lube circuit relief valve to drop the pressure to below 12. I haven't seen one that way and what is normal is that the red light stays on and the Mech would adjust relief valves ahead of the lube circuit to 175 and 150 and then adjust lube circuit to get more oil into the lube curcuit. Don't know if this makes much sense - it has been about three years since I did a bunch of work and experimentation with the valve units- Don laugh I even took out the springs behind the spool valves and replace them with a solid piece to try and increase lube circuit pressure- didn't work but system pressure went to 250 psi when I sped the engine up- good pump but failed experiment (one of many). I have 5 SOS running well, so I haven't got around to really taking a spare trans apart to completely overhaul and go to school on. I also have a pretty complete set of Ford 1960 to 62 original service bulletins with a number of them refering to the SOS, but I do get into memory problems sometimes.

Hobbs Factory Phone number on my box is 217 753 7773

From what I have seen there, here is what the 2 - pound ratings of your switch mean...

The oil pressure has to RISE to 12 PSI to OPEN the switch, which will then REMAIN OPEN until the pressure falls to 2 PSI.

One switch, Deere part # AT85174, has the thread you need, but the "spec's" are a little "off".

It OPENS at 10.5 PSI, and will close again at 5.5 PSI, probably too high for your use. (Too bad, it's only about $14.00.

I am trying to locate the "spec's" for another Deere lube pressure switch, # AH76862 ($7.00), but it is not on the webpage. I MAY have a manual with that information.

Also, I have Standard Ignition catalogs that list senders by appliction, as well as a section listing them by "spec's". I'll take a look there, too.