6.7 Cummins Suburban Build

[grampsbutler]

The Snag List: Obviously there is a lot still to do on this project. Now that the big stuff is done, I am starting a snag list of all the remaining things that need attention.

- Fuel Tank Breather Line - fabricate and install
- Air intake modification (current set up is too high and won't allow the hood to get installed. I am also concerned about using a non-paper air filter. Need to figure out the best system)
- Cooling system finishing - Seals, thermostat, relays, and coolant overflow tank.
- Hood Install
- Intercooler clearance: Current position won't clear the stock grille.
- Left inner fender install
- Vintage Air install
- Dynamat and Carpet
- New dash pad
- New door hinge pins
- Instrument cluster (probably dakota digital)
- Dual battery install
- Additional gauges - Boost, fuel pressure, egt.

 

[grampsbutler]

Intercooler relocation and grille install:

I had to move the intercooler, because it was interfering with the grille. This was a minor tweak, where I had to move it back by ~3/4" at the bottom only. Even with this movement, there was no room for the stock grille, without witling it to provide clearance for the intercooler ducting. I decided to abandon the stock grille (it was broken any way) because I didn't like the idea of cutting away at an already flimsy grille. Instead I ordered a billet style stainless steel grille.

I had to fabricate a new bracket for the intercooler. It is pretty simple, and attaches to the core support with nutserts. The way that it sits now it has about 3/8 of a gap with the stock ac condenser. It sits parallel to the radiator line.

The new grille was easy to install, I hope that I will get used to the way that it looks.

The new grille cost me $107 from Fleabay, and I reused the emblem from the stock grille.

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[grampsbutler]

Big plans for Thanks Giving weekend: My Vintage air kit arrived this week! I'd like to get the interior started including installing the under dash portion of the Vintage Air system ready to plumb in. I don't want to go camping or skiing this winter without heat. Around here it is pretty mild, but as soon as you get into the mountains or desert it is COLD.

I got a new dash pad and carpet. I plan to use Dynamat on the metal and then a jute underlay. I went with the ACC carpet kit.

I ordered a gauge cluster from Dakota Digital. They are not cheap, but I really like their features. I am going to get most of the sensor readings from their OBDII adapter, which saves me from having to put old chevy sensors into a Cummins block. It also gives me flexibility to see boost, fuel pressure and I will get a tack all from the OBDII data. I got Dakota digital to do a special overlay on the cluster, so that I can have a 4000RPM diesel tach and max speed of 120 on the speedo (standard is 160mph...... this is a lifted 40 year old truck with sketchy steering and brakes......anything over 90 is terrifying). They will do a Diesel Fuel only annotation on the fuel gauge and I should be able to calibrate the fuel gauge to match the Dodge sender unit in the tank, which is way simpler than trying to make the chevy fuel gauge work with the not-chevy sending unit.

That is the good news. The bad news, is that Dakota Digital have a 13 week lead time.....so I am going to have to be patient.

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[grampsbutler]

Electrical Gremlins: I have been having intermittent dead pedal. I am pretty sure that this is not an electrical connection issue because as soon as shut it off and restart I get my pedal back. I had to do this yesterday at 70mph on the freeway....I was able to restart before I got down to 55. I am doing some data logging with EFI Live to try and diagnose the issue. But out of an abundance of attention deficit and hyperactivity disorder.......I am planning to make a new body wiring harness to eliminate all possible electrical gremlins from the used wiring harness which I have been running.

The hardest part about doing this is sourcing the ECU Connector. After days on the web searching and dozens of phone calls, I found a source. Mike of Mikes Power Wire stocks these connectors! I'll report back once I receive the connector, but having spoken to him on the phone, he is very knowledgeable and has what I need. They are not cheap, but if it eliminates the old wiring, and gives me peace of mind it is worth every penny. Total cost on this was ~175 for the connector.

 

[grampsbutler]

Electrical Gremlins - possibly fixed: I think I have resolved the electrical gremlins.....based on advice from another board I cleaned all of my ground connections, and put an additional connection directly from the negative battery terminal to the intake manifold. I have not put a lot of miles on, but from 2 days of doing the school run, so far the dead pedal has not returned. It seems to be running pretty well. I have to go up to LA on Friday, so that will be the real test.

 

[grampsbutler]

Vintage Air, Dynamat and Carpet: Over the long weekend I was able to get the Vintage air system into the vehicle. On the whole the install was pretty straight forward, but there were a few surprises. When removing the old dash pad I broke most of the crappy plastic studs that secure the AC bezels. So that meant I had to order new facia for the new dash pad. I am sure I could have drilled out the old one and used 'actual real' hardware, but my AC vents were not in perfect shape, so I thought it good opportunity to finish the job properly. I also discovered some rust in the passenger side floor pan. It was not so serious to require welding, so I took it back to bare metal, treated with phosphoric acid, and repainted.

Vintage air kit for the square body chevy is well done. The instructions are clear and easy to follow. The electrical connections are simple, and easy to hook up.

Day one: I was able complete the whole disassembly. I removed front and rear seats. Rear seats came all the way out, and the front bench got pushed into the back. I removed all the under-dash stuff from the factory heater, as well as all the shifters.

Day Two: I cleaned everything, treated the rust on the passenger side. I installed the block off plates on the firewall. I started the Dynamat install, but ran out of daylight.

Day three, I finished the Dynamat. I took it all the way from the top of the cowl, down the interior of the firewall. I covered almost 100% on the floor in the front. Then I installed jute insulation and prepared the vintage air unit for the installation. I was not able to complete the unit install, because it requires a 90degree drill for the mounting holes. It is way up in the cowl, and there is no clearance for normal tools......I wish I'd known this ahead of time.

Day four: I got the unit installed, and wired up. The wiring was very easy. I plumbed the heater, but not the air conditioner. I installed front carpet. The carpet took hours to get it to fit rightish.... I reinstalled the shifters and front seats so that it is driving again.

In summary, this is a fairly major undertaking. It is definitely a two day job, if I had not been doing dynamat, treating rust and installing carpet. Technically is is very straight forward requiring only basic skills. Once you have the dash pad removed, there is lots of access to route the ducting. If you are considering a Vintage Air install.....REMOVE the front seat. It makes the access so much easier.

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[Powerhouse Ranch]

Holy hell dude. This is dang impressive in countless manners. For me, to work on the "sister" ISB6.7 in the Freightliner M2s and some Internationals all day and see someone put a 6.7 in a Square is quite the feat. Seeing all the hurtles, craftsmanship and brainpower going into this project makes me feel like not all hope is lost in the world; that if you want to do something, something unheard of, YOU FIGURE OUT A WAY AND DO IT!

This is a hell of a build. Thank you for sharing these moments with us and the wisdom to go along with it. Keep up the excellent work Graham.

 

[CountKrunk]

As said above, simply awesome man.

 

[Big Ray]

You sticking with a 10 bolt!?!?
That is one bad ass truck. Very, VERY impressed!!

 

[grampsbutler]

Hey Big Ray.....the 10 bolt is something I have been pondering recently, and I don't know which direction to go. The 10 bolt has stood up fine so far but I don't want to stick with it long term because 1: the brakes are slightly small for running 37s, 2: I will likely break something in the rear axle at some stage because of the torque and power from the Cummins.

I'd be interested in suggestions for which way to go.

There are 2 options as I see it.

1: I could swap only the rear for a 14 bolt or an AAM 11.5 out of a dodge. I am less worried about breaking the front axle, because I only put power into it when off pavement, and I don't plan on rock crawling. The advantage of this would be lots of axle choices and rear disc brakes. The disadvantage would be that I would end up with 8 lugs on the back and 6 on the front, so I'd either have to carry 2 spares, or use a 6-8 adapter.

2: I go with 1 tons front and rear. The challenge here will be to find a front with a passenger side drop. I'd really appreciate recommendations what would be a good candidate for this. I am not that familiar with GM axles....but I assume a set out of any Squarebody 1 or 3/4 ton should do the job? Were there variations in spring perch width? Anything else I need to consider?

 

[Frankenchevy]

Hey Big Ray.....the 10 bolt is something I have been pondering recently, and I don't know which direction to go. The 10 bolt has stood up fine so far but I don't want to stick with it long term because 1: the brakes are slightly small for running 37s, 2: I will likely break something in the rear axle at some stage because of the torque and power from the Cummins.

I'd be interested in suggestions for which way to go.

There are 2 options as I see it.

1: I could swap only the rear for a 14 bolt or an AAM 11.5 out of a dodge. I am less worried about breaking the front axle, because I only put power into it when off pavement, and I don't plan on rock crawling. The advantage of this would be lots of axle choices and rear disc brakes. The disadvantage would be that I would end up with 8 lugs on the back and 6 on the front, so I'd either have to carry 2 spares, or use a 6-8 adapter.

2: I go with 1 tons front and rear. The challenge here will be to find a front with a passenger side drop. I'd really appreciate recommendations what would be a good candidate for this. I am not that familiar with GM axles....but I assume a set out of any Squarebody 1 or 3/4 ton should do the job? Were there variations in spring perch width? Anything else I need to consider?

Dana 60 front is what you’d be after for a heavier duty front axle.

Awesome build, btw!

 

[grampsbutler]

Cool...do you know what years the Dana 60 were put into the squares? Are they a direct bolt in? Or will be be doing mods? I'll try searching the internet for this, but if anyone has first hand experience it would be cool to hear.

I have a couple of update on the build since my last post. I got the new Dash pad in last Sunday, and am starting work on the sound system.

Sound System: Nothing super fancy....I wanted something close to modern stock, so that my son can sing along to Disney soundtracks (Frozen, Moana.......its good stuff) and I can geek out on podcasts. I actually don't like loud systems, and prefer to be able to hear the engine. I went with the Retro Sound system for the head unit. I am renewing the stock corner dash speakers, and putting a compact amplified speaker under the bench seat.

I got the dash speakers in before the dash install and forgot to take photos..... Dash speakers are JBL 3". That is as far as I got.

I'll get the under seat speak and head unit in this coming weekend.

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[Bextreme04]

just find a junker heavy K20 that someone is selling for cheap. Either the 8600GVW from 73-80 or a C6P optioned one from 81-up will have the heavy 13" rear drum 14BFF and a heavy hub Dana 44 or 10 bolt front. Up here in Oregon you can find a whole set of axles from one for about $300. A Dana 60 front is going to run you about $1500-2000 by itself.

 

[Bextreme04]

Dana 60 was every year squarebody K30. There is a difference between a dually Dana 60 and Non-dually... so keep that in mind too. You can also get passenger drop Dana 60's from some year dodges.

https://www.pirate4x4.com/threads/front-dana-60-axle-tech-page-1.2702793/#post-44988366

 

[Catbox]

I was totally supposed to be working, but I read this whole thread instead.
Very nice work indeed!