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Author Topic: 12v Cummins Swap/'73 GMC 2500  (Read 4949 times)

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Offline America.Mike

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Re: 12v Cummins Swap/'73 GMC 2500
« Reply #100 on: January 12, 2020, 04:41:20 PM »
Looking good man! If compression is good run it!


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Offline KensAuto

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Re: 12v Cummins Swap/'73 GMC 2500
« Reply #101 on: January 12, 2020, 09:00:52 PM »
Looking good man! If compression is good run it!


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Thank you sir.
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Offline KensAuto

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Re: 12v Cummins Swap/'73 GMC 2500
« Reply #102 on: January 13, 2020, 01:37:43 PM »
Got some pieces welded in.
Yeah I know, the guy that did the welding gets worse with every passing year.
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Offline JR

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Re: 12v Cummins Swap/'73 GMC 2500
« Reply #103 on: January 13, 2020, 02:23:10 PM »
You going to box the whole frame? Nice while you have it apart.

I would address the steering box now while its open. My 77 was so bad I cut the whole area out then welded solid spacers from the box to inside the frame.
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Offline stlaser

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Re: 12v Cummins Swap/'73 GMC 2500
« Reply #104 on: January 13, 2020, 09:36:30 PM »
Welding isn’t terrible Ken, it appears to be getting good penetration which is most important.
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Offline KensAuto

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Re: 12v Cummins Swap/'73 GMC 2500
« Reply #105 on: January 14, 2020, 12:13:44 AM »
You going to box the whole frame? Nice while you have it apart.

I would address the steering box now while its open. My 77 was so bad I cut the whole area out then welded solid spacers from the box to inside the frame.
Weird that mine never cracked there considering what this truck has been through. Gonna box it rearward to the spring hangers. Probably weld a plate on the outside of the frame for the gearbox... would be easier.

Thanks Shawn. Even with a cheater lens I can barely see what I'm welding nowadays.
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Offline stlaser

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Re: 12v Cummins Swap/'73 GMC 2500
« Reply #106 on: January 14, 2020, 08:12:23 AM »
Ken, my neighbor Chuck is in his 69’s and builds hot rods (for himself, been in all the magazines, big sheet metal guy) and is now having cataracts lasered. He’s been using two sets of cheater lenses inside his hood. So I get it....
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Offline KensAuto

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Re: 12v Cummins Swap/'73 GMC 2500
« Reply #107 on: January 18, 2020, 02:49:52 PM »
Finished plating the frame. Added extra to the sides of the mount pedestals, then slotted the holes for more mount adjustability. I know, boring, but necessary tasks.
Next up, I need to swap clutch pedal assemblies and make a place for a hydraulic master cylinder before reinstalling the engine.
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Offline KensAuto

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Re: 12v Cummins Swap/'73 GMC 2500
« Reply #108 on: January 18, 2020, 02:53:12 PM »
And carried the plate to beyond the rear hangers...
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Offline JR

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Re: 12v Cummins Swap/'73 GMC 2500
« Reply #109 on: January 18, 2020, 03:16:25 PM »
I was going to suggest looking at or replacing the rear spring hangers. All I have removed were wore all the way to the bushing and cutting into it.

You are doing it about like I did my 77. Leaving the cab on you can still get about 99% of it.
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Offline KensAuto

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Re: 12v Cummins Swap/'73 GMC 2500
« Reply #110 on: January 18, 2020, 04:33:54 PM »
JR, I've rebuilt this truck twice and spring bushings were done both times...and they're bad again!

I'm putting a D60 in after it's back to being driveable. I bought it about 12 years ago to put in this truck so another year won't matter. I'll have to add some lift to the front anyways.
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Offline stlaser

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Re: 12v Cummins Swap/'73 GMC 2500
« Reply #111 on: January 18, 2020, 06:17:34 PM »
Ken when you do that front you should look at DIY B52’s and re spring the front end.....
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Offline JR

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Re: 12v Cummins Swap/'73 GMC 2500
« Reply #112 on: January 18, 2020, 06:53:08 PM »
Went with the 4x4diy hangers on mine, poly bushings and greaseable.
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Offline KensAuto

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Re: 12v Cummins Swap/'73 GMC 2500
« Reply #113 on: January 18, 2020, 08:55:36 PM »
Ken when you do that front you should look at DIY B52’s and re spring the front end.....
Diy b52s? WTH is that? You can build your own bomber? Interesting but I think you posted in the wrong thread. This is a pickup build. ,
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Offline stlaser

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Re: 12v Cummins Swap/'73 GMC 2500
« Reply #114 on: January 18, 2020, 08:59:33 PM »
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Offline KensAuto

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Re: 12v Cummins Swap/'73 GMC 2500
« Reply #115 on: January 18, 2020, 09:12:50 PM »
Interesting. Is that what Don put on his Dodge ?
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Offline stlaser

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Re: 12v Cummins Swap/'73 GMC 2500
« Reply #116 on: January 18, 2020, 11:09:55 PM »
I don’t believe so, someone else builds the dodge stuff
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Offline swbhobie16

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Re: 12v Cummins Swap/'73 GMC 2500
« Reply #117 on: January 19, 2020, 07:13:12 AM »
the duramax swap guy in CA makes a kit for the square bodies that move the shackle hangers to the cab mounts and uses 52” spring. that’s what i’m doing..

Offline JR

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Re: 12v Cummins Swap/'73 GMC 2500
« Reply #118 on: January 19, 2020, 03:04:50 PM »
website?
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Offline KensAuto

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Re: 12v Cummins Swap/'73 GMC 2500
« Reply #119 on: January 19, 2020, 07:35:57 PM »
If, and when I change out the front diff, I'll start a new thread and I'll put this info over there. Leaning towards leaving the leaf springs stock length, but we'll see.
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Offline stlaser

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Re: 12v Cummins Swap/'73 GMC 2500
« Reply #120 on: January 19, 2020, 09:29:27 PM »
It needs an 05 + Superduty 60 front.....
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Offline KensAuto

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Re: 12v Cummins Swap/'73 GMC 2500
« Reply #121 on: January 19, 2020, 10:42:15 PM »
Why? I abused this truck (3 engines and 6 clutches) and never broke the 44. Luckily the front driveline was the weak link.
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Offline JR

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Re: 12v Cummins Swap/'73 GMC 2500
« Reply #122 on: January 20, 2020, 12:21:05 AM »
But was it a 1000 lb cummins up top?

Never broke my 44 either, SBC but lots of universals!
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Offline KensAuto

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Re: 12v Cummins Swap/'73 GMC 2500
« Reply #123 on: January 20, 2020, 08:54:00 AM »
But was it a 1000 lb cummins up top?

Never broke my 44 either, SBC but lots of universals!
Not much more than a loaded down Pontiac tbh.
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Offline stlaser

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Re: 12v Cummins Swap/'73 GMC 2500
« Reply #124 on: January 20, 2020, 07:09:12 PM »
Well, H in the bed is like what 3 Cummins motors?  :tongue:
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Offline Bigdave_185

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Re: 12v Cummins Swap/'73 GMC 2500
« Reply #125 on: January 20, 2020, 10:44:16 PM »
Is hot air a power source for vehicles now?


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Offline stlaser

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Re: 12v Cummins Swap/'73 GMC 2500
« Reply #126 on: January 20, 2020, 10:48:25 PM »
Is hot air a power source for vehicles now?


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Just old dodges......  :popcorn:
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Offline wilsonphil

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Re: 12v Cummins Swap/'73 GMC 2500
« Reply #127 on: January 20, 2020, 11:47:54 PM »
Dont listen to them Ken, the 440CI engines that are in the Dodge series of truck was only 100lbs lighter than the Cummins.  I beat the snot out of many D44 5lug with a 440 and never had a problem.  Tire weight and size is much more of an issue.

Offline swbhobie16

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Re: 12v Cummins Swap/'73 GMC 2500
« Reply #128 on: January 21, 2020, 08:13:36 AM »
website?

https://precisionfabricationplus.com/shop?olsPage=products%2F80-91-gm-k-and-v-series-truck-blazer-and-suburban-52-hd-boomerang-shackle-kit&page=3

it moves the front upper shackle hangers (FUSH) back to under the front cab mount which allows your to run 52” (i actually thing he’s building them 53”) which gives you much better/softer ride with the increase length. i also believe he’s pushing the front axle forward 1” to allow for better steering characteristics. only down side is you’d have to take some of the plating off to get to it now..

Offline stlaser

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Re: 12v Cummins Swap/'73 GMC 2500
« Reply #129 on: January 21, 2020, 10:16:34 AM »
I have a customer scheduled to do the b52’s and rear shackle flip on his 86 Blazer. New springs and shocks. Trying to build him a hd 44 and 14 bolt locked 8 lug.
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Offline KensAuto

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Re: 12v Cummins Swap/'73 GMC 2500
« Reply #130 on: January 21, 2020, 11:35:51 PM »

Working on the clutch hydraulics now.
The donor truck had used the Dodge slave and master. The master was cobbled to the firewall pretty badly so I wanted to do something better.
First I had to swap over the pedal assemblies. Donor truck had hydro pedals, which are different than the'73 mechanical linkage style.

Here they are . Old one on top.
Other pic is of the cobbled twist style adapter for the Dodge master cylinder.

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Offline KensAuto

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Re: 12v Cummins Swap/'73 GMC 2500
« Reply #131 on: January 21, 2020, 11:42:12 PM »
The main difference is that the newer style ('85?), has two separate pivot bolts for the clutch and brake, allowing for 2 struts to bolt on the clutch pedal, that extend to, and through the firewall that the master bolts on to.
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Offline KensAuto

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Re: 12v Cummins Swap/'73 GMC 2500
« Reply #132 on: January 21, 2020, 11:45:57 PM »
The other thing worth mentioning is that the newer one is set up for a hydroboost. It only has 2 booster studs, instead of 4, like the'73.
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Offline KensAuto

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Re: 12v Cummins Swap/'73 GMC 2500
« Reply #133 on: January 22, 2020, 12:07:20 AM »
I wanted to get away from the plastic master, so I spent some time trying to sort that out.

The '85 Chevy version is cast, but only 11/16 bore...but...direct mount and proper rod length and geometry.

The Dodge is 7/8"... not even close. ..no way that smaller bore would work with the Dodge slave. (which is 1" bore )
I'm going to try a cast slave from a 91 Chevy 3500. I'll have to redrill the mounting holes and cut the push rod.
It has a 13/16 bore, for an .85:1 ratio, compared to the Dodge's .875:1 ratio.

With this setup I can get rid of the plastic line and o-ring connections... just hope it works.
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Offline KensAuto

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Re: 12v Cummins Swap/'73 GMC 2500
« Reply #134 on: January 22, 2020, 12:12:19 AM »
Got a pattern off of the donor firewall, drilled, then mounted the pedal assembly, then the master.
And that's as far as I made it today.
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Offline JR

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Re: 12v Cummins Swap/'73 GMC 2500
« Reply #135 on: January 22, 2020, 12:15:53 AM »
Have to see what my pedal setup is.

Any aftermarket for the slave, plastic sounds hokey.
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Offline KensAuto

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Re: 12v Cummins Swap/'73 GMC 2500
« Reply #136 on: January 25, 2020, 09:17:01 PM »
Ordered some AN adapters to fit the cylinders. 12mm x1.0 threads.
I'll wait till the trans is installed before ordering a braided hose.


« Last Edit: January 25, 2020, 09:17:42 PM by KensAuto »
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Offline KensAuto

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Re: 12v Cummins Swap/'73 GMC 2500
« Reply #137 on: January 25, 2020, 09:26:39 PM »
One more issue to deal with. In '73 GM vehicles only used a single fuel line...no return system. Most diesels , and gas vehicles after the late 70s, use a supply and a return.
Since I'm replacing the fuel tanks, I ordered newer style senders, with 2 lines.
The original line was on the passenger side. Cummins gets fed from the left side.
I installed new fuel lines:
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Offline KensAuto

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Re: 12v Cummins Swap/'73 GMC 2500
« Reply #138 on: January 25, 2020, 09:38:27 PM »
The next issue is that the truck has dual tanks. The early square bodys use a simple 3 port switching valve, with one wire. Flip the switch and it sends 12 volts to the valve to switch over to auxillary, or driver's side.
In the late 70s when they went to a return system, they used a similar valve but with 6 ports, so that the return fuel returns to the proper tank... again, a single wire.
That valve is no longer available. The replacements are for the trucks in the 80s, with 6 wires. It can be converted, but I'm too lazy, so I found a used 6 port, single wire to use for now.
^^^^I should really learn to condense my thoughts.

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Offline KensAuto

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Re: 12v Cummins Swap/'73 GMC 2500
« Reply #139 on: January 25, 2020, 09:47:33 PM »
Now moving on to the cooling stack.
There's no way to make room for an intercooler in a '73 without 'ruining' the radiator support, and using a different grill. ..the only body parts still original, and unmolested. The grill recesses inward, etc. and it's staying.
So, I'm going to run a water to air cooler. Her days of working hard are over so it should be fine.

The grill and hood latch support:
« Last Edit: January 25, 2020, 09:48:08 PM by KensAuto »
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Offline KensAuto

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Re: 12v Cummins Swap/'73 GMC 2500
« Reply #140 on: January 25, 2020, 09:52:57 PM »
Pics of the donor truck. They were able to cut around the radiator core support channels, then extended the inlet/outlet on the intercooler because they put the cooler on the outside of the condenser. Then they ran an aftermarket grill. ..but the'73 and 80s core supports are way different.
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Offline KensAuto

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Re: 12v Cummins Swap/'73 GMC 2500
« Reply #141 on: January 25, 2020, 09:57:23 PM »
First the factory condenser was tossed in favor of a small one made for r134a.
The intercooler radiator was mounted to that on the outside so I can access the drain.
The assembly was then mounted in the opening.
I have an 1/8" gap between it and the hood latch support... barely fits but good enough.
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Offline JR

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Re: 12v Cummins Swap/'73 GMC 2500
« Reply #142 on: January 26, 2020, 03:32:04 AM »
Plus they were diff for 2 or 4 headlights in the 80s, 70s all the same.

What intercooler was that Ken? I got a ford SD that everyone said would fit and it turned right into the uprights.

Mine is the lower 80s hood and already have a aftermarket grill.
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Offline swbhobie16

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Re: 12v Cummins Swap/'73 GMC 2500
« Reply #143 on: January 26, 2020, 08:07:39 AM »
so.. i’ve been doing some reading and thinking (mostly thinking) about how to efficiently run dual tanks on the dmax. well.. not just thinking about dual tanks but also a burb tank behind the rear axle too.

i found a manual 6 port brass valve that would make it fool proof to operate (no wires) and has the return going to the appropriate tank as well. pretty slick design. but i’m not sure i want that. other thought is burb tank. pretty straight forward.  just 33 gal behind the axle.

option #3 i’m tossing around is plumbing the 2 tanks together with a single low ~1” line crossing between the 2.. 

now i know this sounds risky, but a quick glance at the truck the other day shows that the tanks dont hang below the frame.  so. thought: drill a hole in the frame close to the bottom of the channel forward on the tanks. weld bungs into said tanks and have them run across and over DS just behind tcase.

tell me i’m wrong and just need to run a burb tank, not worry about being able to carry a full size spare and need to figure out how to fill it. which would be more functional..?

Offline swbhobie16

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Re: 12v Cummins Swap/'73 GMC 2500
« Reply #144 on: January 26, 2020, 08:17:41 AM »
https://www.groco.net/fv-65038

here’s that valve. would be perfect sitting under the driver seat of just on the side towards the door.

Offline KensAuto

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Re: 12v Cummins Swap/'73 GMC 2500
« Reply #145 on: January 26, 2020, 11:47:55 AM »
Yeah I didn't mention the manual valve. Not a fan (lots of long rubber hoses to make it work) but definitely an option.

JR, they used the 2nd gen it looks like.
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Offline stlaser

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Re: 12v Cummins Swap/'73 GMC 2500
« Reply #146 on: January 26, 2020, 12:42:09 PM »
I’m with Ken, those hoses are a drawback however I like the mechanical aspect. I may use that on upcoming build actually.
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Offline KensAuto

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Re: 12v Cummins Swap/'73 GMC 2500
« Reply #147 on: January 26, 2020, 01:35:31 PM »
Just thought of a different option. The 3 port valves are made in 2 different sizes. GM uses 3/8" ports and Ford, and maybe Dodge, used 5/16", single wire.
Use the 3/8 one for supply and 5/16 for return, wired together. If one quits just make sure the switch is on the main tank and keep trucking.

The main reason I don't want to use the 6 wire modern one is that I used to see issues with them quite often. They have a worm gear motor that drives one way or another. Not only do they quit completely, they can also get stuck in any position. This design is supposed to be better because on the old ones, they stay engaged (solenoid style) when on auxillary. Mine made it 30 years by only using aux. when needed so I have more trust in them.
« Last Edit: January 26, 2020, 01:45:16 PM by KensAuto »
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Offline JR

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Re: 12v Cummins Swap/'73 GMC 2500
« Reply #148 on: January 26, 2020, 01:47:22 PM »
Yeah I didn't mention the manual valve. Not a fan (lots of long rubber hoses to make it work) but definitely an option.

JR, they used the 2nd gen it looks like.

2nd gen Dodge?
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Offline KensAuto

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Re: 12v Cummins Swap/'73 GMC 2500
« Reply #149 on: January 26, 2020, 04:21:18 PM »
Yeah
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