Hey all,

Going to be getting a 518 non-lockup ready to go into my '81 D-250. The trans is out of a '90 1/2 ton Club Cab longbox so I've got all the crossmembers and driveshafts, and I know it will fit.

What I need is the basics for running pressure switches and vacuum switches for the OD on/off. I dont really feel like toggling a switch at every single stoplight to kick the OD in and out. I will have one however that will kick it out when I'm towing loads.

Anyway I need specifics on what to wire to where, part numbers for the vacuum switches, and I think I read somewhere on here about an A/C cutoff switch for kicking the OD in and out at a specific speed. something like a 44 PSI switch works out at 44 mph if my speedo is right (its only off a small amount, fast by about a mile or two).

I'd like to get this info now, because I'm looking at doing it in the spring and I want to have it and everything I need on hand so I can go to work on it when the time comes. Maybe we should stick this thread in the tech archives for others to see when its done.

If anyone wants a how-to I'll use my truck as a guinea pig.

I'm doing it now with a lockup trans in my 74 D100 and it's been done a number of times before by guys here. Nothing new. PATC transmissions has the instructions. The pressure switch comes from chevy 250 & 350 transmissions and cost about $5 at the trans supply. It's the thrid gear clutch switch. I think the part # is A44416AA. The letters at the end are the code for the pressure. That # comes in everything from 55 to 40psi depending on the last letter or letters.Drive shaft will need to be 3.5" shorter also. If you aren't using a lock up then you just need a toggle switch for on and off and a pressure switch for in and out of OD.