oliver foster

I have had an old RC that is registered as a '79 but was an early production build and has a '78 grille, so I refer to it as a '78.
I bought it just after I bought my '89 from Phoenix, that I call the Gauntlet.
I had looked at and tried to buy the '78 before going to AZ but the guy decided he wanted to keep it. Right after I got back from a 12 day road trip picking up the '89 from AZ, he contacted me and told me the '78 was for sale again, so I just HAD to buy it. It is originally from TX and is completely rust free other than the driver side floor pan.
It has patiently been waiting for its turn for almost 4 years. I am brainstorming the build in my head right now, hoping I have time to work on it this winter.
I plan on a warmed up 12V VE pumped motor making some power with a 47 RH 2wd unit behind it. I plan on it being a fun to drive topless hod rod style truck.
My biggest question I don't have the answer for is the auto transmission and what I will need to make OD and lock up work. I have been a manual transmission guy forever so this is pretty different for me. I have read a bunch of old treads on the subject, but still have questions.
I have a 47 RH 2wd with billet input shaft and internals with a Suncoast triple disk TC that was build 10,000 miles ago. It is still in a complete '94 truck that I plan on using the sheetmetal, which is nice, on my 4x4 5 speed 2nd gen to keep it alive. The transmission shifts great in the complete truck, but I don't want to use the PCM or the 2nd gen wire harness in this build.
I plan to use as much of the '78 RC wires and dash as possible.

So there is the back ground on the rig. I have almost all the parts here to do the swap.
I just need the time and some insight on the wiring of the autos OD and lock up.
Any comments are welcome.

And so another major build thread begins.

NJTman

Ollies rc

thrashingcows

I will be watching the response to your tranny questions Oliver since I plan on a 46RH in Sno-Ball when I do the cummins conversion.....no lock up but the OD has me wondering too.

I think doing away with the TPS and adding the switch, reo-stat(??), on the dash will allow the OD to be fine tuned and engaged. And a 2nd Gen auto lever with the OD on/off switch in it should be able to be mounted on the column, even if it is a couple decades newer. As for the lock up.....not sure on that one...Hobs switch on one of the Hyd lines?

NJTman

Angry Johnny might have the answer to this one....



Nice ride, BTW....

oliver foster

I like the idea of adjusting the OD from a dash mounted gauge.
I was thinking the O/D switch on then column from a later 24V truck might be a slick option, but have not yet checked that the spline count and size is the same for the end.
I have heard the Hobbs switch mention in cougar's 47RH swap saga here at DTR, but am unsure what and how a Hobbs switch is or does.

I too was hoping Angry Johnny would chime in as he seems to know these autos really well.

Thanks guys!

oliver foster

Okay a quick search of "Hobbs switch" showed me a bunch of pictures and descriptions of them.
It is a switch that reacts to changes in pressure, basically. I assume it screws into a port in the transmission line somewhere and does it thing when the pressure changes.

If anyone can enlighten me as to what pressure levels I am looking at, a model # or style that would be great.

Also do I need to splice it in on one of the lines, or is there a factory port I can screw it into?

sooty

been a long time I did one and the switch was adjustable from 25-50 psi I think, and the governor pressure test port is where it installed, im digging around for the wiring diagram and install location in my favorites

oliver foster

That is the kind of info. that is very helpful.
Thanks sooty.

sooty

pm sent

BHD

I wanted to use a Hobbs style switch in the 518 in my Diesel RamCharger. However, I purchased the tranny from a fellow truck puller who had some kind of fancy VooDoo parts installed. My pressure in the test port at 55 mph was well over 100 psi, and I couldn't source a Hobbs switch that would be stay open to those pressures. I'll be watching this build!!!

Angry Johnny

There are several different ways to do this. If you want to use the factory shifter mounted OD on/off switch you will have to use a PCM as it is just a momentary switch. You will probably also need the little box that controls it. I'm not sure if the 2nd gens incorporated that into the PCM or not.

If you want to use a hobbs switch you will need at least two of them. One lower pressure to kick it off and one higher pressure to kick it in and a relay. Otherwise you will get a chattering or hunting at the set point.

I used two hobbs switches, and a relay for my lockup control and ran the whole mess through the ground at the PCM for the OD. This way I only get lockup when the trans is in OD. I will try and find the schematic I used to wire it up but what it basically does is when the high pressure switch closes it also closes the relay. The low pressure switch then keeps the relay closed after the high pressure switch opens and then when the low pressure switch opens the relay clicks off.

I used the governor port which is on the right rear of the trans case where the tailshaft bolts on. The diesel transmissions run a higher governor pressure than the gassers do because of the low RPMs the diesel turns. Mine was about 90 psi at 60 MPH.

Now finding the correct hobbs switches and getting them adjusted is another story altogether. When and if I ever get some time I will try to get you the info on what I used.

Angry Johnny

This is the basic schematic I used. I have a better drawing somewhere I just don't know where right now.

PapeCAT

I used the Compushift mini stand alone controller for controlling my OD in the '73 D200 with A518. It also has logic to control the 47RH and TC lock-up event. It is almost infinitely tuneable to your preference (for shift and lock points / unlock point.)

Spendy but worth it imo for this application.

https://www.hgmelectronics.com/produ...s/csm-chrysler

oliver foster

I am liking the look for the Compushift mini kit. Thanks PapeCat!
I like the plug and play and also the adjustability of it. I am not afraid to spend a few bucks to get it how I want.
I want it to shift hard like my old '70 727 shifted big block Challenger did. You couldn't get that Mopar to NOT chirp the tires when it shifted into 2nd gear.
This will be a fun only, hot rod style build. It doesn't need to haul, it doesn't need to tow, it needs to make me smile when I drive it. I am trying to see why people like autos...

Shelby/Dakota

out of curiosity, why an auto? Just something different or had one on hand type deal? Regardless this should be pretty bad *** when done.