'nornal' O/D & cruise without the PCM?

[cerberusiam]

Is the Hobbs pressure switch adjustable? Also can you adjust the cutout pressure? Part number? What happens when your foot is off the throttle going down hill having only a front trans pump without a rear pump to supply 48psi?

Having a 727 and not a 518, what controls the kick down on a normal 518?

Governor pressure should be pretty steady on a RH unit so shift should be fairly predictable. Gov pressure is speed dependent and the pressure is a function of rpm to the input shaft for pressure. Even though you lift the pressure should ramp down with the speed.



The one caveat to this system is if you mod the VB the wrong way it will try to shift to OD in 1st and 2nd. May be good or bad depending on what one is trying to accomplish.



Here is the cute little bugger that will do the job:



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["Mad Max"]

Overdrive is working and the 'plan' works fantastic, posted in 2 parts.



Part 1:



Here's the schymatic:



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Here's the step-by-step:



First, on the 518 unbolt the transfer case shifter and linkage (if so equipped). The shifter linkage and bracketry is 100% smack in the way of the port . I had to hack the shifter bracket like so:



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Any 518 governor port will function the same. The 618's will not because of the lock-up converter - the pressure varies. Locate this pressure port on the transmission.



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Call up Summit Racing and order up this nice adjustable Hobbs switch (from the Holley NOS lineup no less). It is adjustable from 25-50 psi . $45 bucks later it's in the mail.



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Then grab a 90* 1/8 pipe tee, some teflon thread tape, and make it all look like this:



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Pt II on next post...

 

["Mad Max"]

Pt 2:



Okay, next is controlling the thing. I wanted the O/D to engage/disengage automatically, and also have a manual override. At governor pressure 'x' (proportional to vehicle speed), the hobbs switch closes and, in this case, completes the ground circuit that closes the O/D switch on the transmission (see schymatic), and engages the O/D. But, I wanted manual control of the ground circuit up in the cab at the shifter. Found some great switches and decided to do some surgery on the Hurst tee handle :-laf -



Had to make a big honkin' 3/4" hole for the switch



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Plug in the two wires and press in the switch...



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... but then of course the diff locker got jealous and needed its very own switch too



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Thread the wires through.....



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and here's what it looks like - two switches, ready to go, nice and neat



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Installed...



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Took it out for a spin, got it adjusted, and it's locked in to engage right at 40 mph and it hits every time. I've no idea what the corresponding psi is that equalls 40 mph, but with 3. 54 gears and 36" tires it's diff'rnt than most others' will be. Slow down below 40 and it disengages, speed up and it hits again, then hit the shifter button and it disengages clean. Works great, and for the few miles I've driven it it has worked perfectly, and, I can adjust the engagement psi/speed . Very cool, I like it. PCM... not required.



A big thanks to all of you that have helped figure out the tech side of this conversion. I really appreciate your inputs and thoughts. Thanks fellas.



- Sam

 

[Flexiheep]

Great job Sam, glad to see it done here. I like the adjustable switch instead of having to buy several different set ones to test out..... I need to print this out and file it away for use some day. Maybe it will be of use if I get the crewcab going some day. .