6.7 Cummins Suburban Build

Mark Baur said:

Adding a flange and gasket to seal the shroud to the back of the radiator should really help make the fans more effective.

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Never mind, I see you have some sort of seal there in later photos.

Mark Baur said:

Never mind, I see you have some sort of seal there in later photos.

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Good observation. When I first assembled I had not put the shroud seal in, but installed it later when I got to doing final assembly. The seal is epoxied to the shroud and touches the radiator. So far I have had zero overheating issues. The electric fan thermostat is 180 degree on, which is too cool. I have a new switch which is 200 on, that I have not yet installed.

So far I am very happy with the performance of the cooling system. I have lots of highway driving including long steep uphill grades. I've also had my fair share of diabolical Southern California stop and go traffic, and it never gets hot. I am yet to take it off road for an extended period. The off road is the ultimate test for cooling.

Update: I took some time off from working on the truck last month. We went on a 1000 mile trip up to the mountains for a week of winter sports fun. The truck ran very well except for 2 things.

1: Problems cold starting: We had a pretty good storm dump a foot of snow on us and pull temps down to ~10 degrees Fahrenheit (that's -12c). Truck would not start, and I had to get a jump. Lesson learned: These trucks need dual batteries to handle cold weather. I only had a single battery installed. It started on the first turn every time over 20 degrees (grid heater is not connected). Parts for the second battery are on order.

2: Dead Pedal: If you've been following along, you'll know that I have been battling intermittent dead pedal. I thought I had it solved after cleaning my ground connections, rebuilding the body wiring harness and replacing the Accelerator pedal. Truck ran all week with no issues, but on the way home I lost accelerator several times. I ran through the accelerator recalibration procedure when I got home, and it seems to have cured the problem....at least for the time being.

The dead pedal has been the most persistent and frustrating problem with this build. My next step will be to replace the the ECU.

grampsbutler said:

Update: I took some time off from working on the truck last month. We went on a 1000 mile trip up to the mountains for a week of winter sports fun. The truck ran very well except for 2 things.

1: Problems cold starting: We had a pretty good storm dump a foot of snow on us and pull temps down to ~10 degrees Fahrenheit (that's -12c). Truck would not start, and I had to get a jump. Lesson learned: These trucks need dual batteries to handle cold weather. I only had a single battery installed. It started on the first turn every time over 20 degrees (grid heater is not connected). Parts for the second battery are on order.

2: Dead Pedal: If you've been following along, you'll know that I have been battling intermittent dead pedal. I thought I had it solved after cleaning my ground connections, rebuilding the body wiring harness and replacing the Accelerator pedal. Truck ran all week with no issues, but on the way home I lost accelerator several times. I ran through the accelerator recalibration procedure when I got home, and it seems to have cured the problem....at least for the time being.

The dead pedal has been the most persistent and frustrating problem with this build. My next step will be to replace the the ECU.

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Why is the grid heater not hooked up? That really helps too for cold starting.

Front Axle: I put some time in to regearing the front D60. The axle came with 4.10 gears, but the truck is 3.73. I am very happy with the 3.73 ratio. I can run on the highway at 75 mph at approximately 2000 rpms and 1600 at 65mph. I have never felt like it was geared too high.

I got a gearset and master rebuild kit from Motive Gear, and I ordered a new carrier from Ox Locker. I ordered a D60 carrier bearing puller (linked). I went with the Ox locker because I like the simplicity of a mechanical system.

Before I started the teardown, I measured the backlash to be 10 thousandths. I pulled the old bearings and took careful notes of the shim pack measurements. I put the new bearings on the new carrier with the shim packs measuring the same as the original. First time out the gate the gears were binding - Zero backlash. I pulled it all apart and moved shims to move the crown gear away from the pinion. This time I was able to run a gear pattern and found that contact was too far to the tip of the gear. So I increased pinion depth, and adjusted the preload to be approx 25 in lbs. It ran another gear pattern, and it was much improved centering on the tooth, but the backlash was coming in at 18 thousandths. Final adjustment I adjusted shims by 0.018, reassembled and got to 0.006 of backlash. I am happy with this because they are new gears and should wear in to ~0.01".

That is about as far as I got this week next I need to take a look at the U-Joint and see whether I need to replace it to match the front drive shaft. Then it is diff cover and axle reinstallation.

Final Pattern


First pattern

mcarlo86 said:

Why is the grid heater not hooked up? That really helps too for cold starting.

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I just haven't had time to figure out how the grid heater should be wired up and whether it should be controlled by the ECU. The symptom was a dead battery. It wouldn't even turn the engine over, so the grid heater wouldn't have helped me in this case........as soon as I had a jump start it fired right up.

To make sure that this doesn't happen again, I did install a second battery this weekend. I placed it in the cargo area over the rear wheel, and ran heavy cable to the back. I will figure out the grid heater before next winter, but it really will only get used when I go up to elevation. Where I live it never gets below freezing.

Where did you order the wiring blocks for the battery posts? Those are awesome .

1lejohn said:

Where did you order the wiring blocks for the battery posts? Those are awesome .

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I got them on amazon. https://www.amazon.com/dp/B0C69M6T84/

Battery box came from Ruff Stuff Specialties.

grampsbutler said:

I got them on amazon. https://www.amazon.com/dp/B0C69M6T84/

Battery box came from Ruff Stuff Specialties.

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Thanks . added to my favs.

Thrilled to see someone has accomplished what I am in the process of setting out to do, even if you are clear on the other side of the country! Rolling through your posts have answered a few of the questions I had rolling in my head about my own swap, how have you liked the dakota gauges running them on the obd connector? Have you had any thoughts for how you're going to get speed signal to the dash?

Also a thought on your dead pedal situation, the pedal circuit is EXTREMELY sensitive to any breaks or increase in resistance over factory on the common rail cummins, how did you run that wire from the OEM connector to the pedal in the cab? Your ecm may be seeing a variance between apps 1 and apps 2 circuits and assuming there is a failure, hence the dead pedal.

NHsquare said:

Thrilled to see someone has accomplished what I am in the process of setting out to do, even if you are clear on the other side of the country! Rolling through your posts have answered a few of the questions I had rolling in my head about my own swap, how have you liked the dakota gauges running them on the obd connector? Have you had any thoughts for how you're going to get speed signal to the dash?

Also a thought on your dead pedal situation, the pedal circuit is EXTREMELY sensitive to any breaks or increase in resistance over factory on the common rail cummins, how did you run that wire from the OEM connector to the pedal in the cab? Your ecm may be seeing a variance between apps 1 and apps 2 circuits and assuming there is a failure, hence the dead pedal.

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I love the Dakota gauges! They are very responsive, and having a tach is awesome. So far I've had no issues. Fuel gauge works perfectly with the Dodge in-tank sender. Temp gauge is accurate. Voltage also seems to work well.

There are a few downsides I should mention. Oil pressure reading is worthless. The CM2200 ecu calculates oil pressure from RPMs, temp etc rather than having a pressure sensor. The only sensor on the engine that actually measures oil is a low pressure warning signal. I am planning to wire in an oil pressure sensor so that I have actual data.

Speed sensor is easy. Dakota supplies an electronic pulse generator that is driven by the gear in the transfer case. It wires directly to the control module.

It's been a while since I updated this thread....lots of progress and adventures!

I took the truck on a 5 day trip through the white rim road in July. It was HOT. It was a great test for the cooling system, which held up fine. Engine temps stayed under 210 even when climbing out of the canyon going slow on a long up hill. The bad news was that the air conditioning could not keep up. I wasn't able to get enough heat out of the condenser.....probably because it is sitting behind the intercooler. This wasn't an issue on the drive out - on the freeway - where the ram air was able to keep up. Temperature in the Mohave desert was 121 in the shade, air was blowing cold. Temp on the trail on the hottest day was 116 in the shade and it was blowing cooler than ambient, but was still hot (I am guessing it was blowing 105).

Soooo. I am thinking of a few options to fix this.

Choice 1: Run a liquid to air intercooler so that the condenser gets ambient air, rather than preheated air. This would also provide room to run more powerful electric fans in front of the radiator.

Choice 2: Run a heat exchanger for the AC condenser to an auxiliary underbody radiator. Could also provide additional cooling capacity.

I am inclined towards option 2, because it would increase the overall cooling capacity of the truck, and looking at the routing it would avoid having to re-duct the whole air intake system.

Thought on this are welcome. Here are some pictures from the adventure.

Other things that I have done since the last update.

1: Installed the D60 with the OX Locker
2: Installed cross over steering
3: Built a winch bumper for the front
4: Built a bed slide for the cargo area

I still need to fix the air conditioning issue, and to figure out a swing away tire carrier for the rear....but the truck is really coming together now. I will post some more detailed update of the build when I have more time.

Somehow I missed your post about the oil pressure "gauge". That's been a Dodge thing for 20+ years now and I can't stand it, lol. It's really not an oil pressure gauge... it's really just a moving idiot light.

Front Bumper Build: I wasn't originally planning to change bumpers......but.....events have changed my mind.

1: I got stuck on a remote road in the eastern sierras earlier back in September. 40degree side incline in very soft sand.....for a minute I thought I was going to turn the truck over. After spending the night on the trail, and trying every trick in the book to get unstuck, I had to call offroad recovery. So I decided I needed a winch, and associated bumper. I decided (foolishly in retrospect) to purchase a DIY you weld it kit from Move Bumpers. Cost for the kit was ~650 including tax and shipping. Compared to 12-1700 for a built bumper. Build details below.

2: I built a spare tire carrier that folds down for the rear......but, it is extremely inconvenient. The tire is super heavy, and requires tools to release it.....so I also need a new rear bumper, with a swing out tire carrier. I have not yet started on this but I am debating my options. I am considering Baseline overland bumper kit - but I'm finding the price tag a bit rich at ~3000 plus tax and shipping. I am also considering a totally custom build which will be a lot cheaper, but a lot more work. Has anyone on here got the Baseline Overland? I'd love to get feedback thoughts recommendations for the rear. I'm not in a hurry, because I have a system albeit suboptimal.

The move kit arrived about a month ago. On first glance the parts are well made and the design is intuitive (which is lucky because the instructions are very bad). I also bought the 18k lbs winch from Vevor (~250 shipped). I highly recommend getting the actual winch that you are going to use ahead of the build.....because in my case the geometry was totally off, and needed substantial modification to the bumper. The Chevy is a heavy truck, so I really wanted to get a large winch, to be confident about recovery without needing a snatch block.

To accommodate the larger winch I had to space the bumper out by an extra 1.25 inches, and lower it by 1 inch. I also had to extend the mounting plate and move the holes 1inch aft ward. With all these changes it is still a tight fit.....but it does fit!

I tacked the front plate weldment on the bench, but joined it to the mounting brackets using the truck as a fixture. Once I had figured out the spacing, everything fit together pretty well. Once tacked I removed it from the truck and did the finish welding on the welding table. Then I put it back on the truck to fixture and weld the tubular wings and caps. It was a lot of on and off, and a huge amount of welding required.

I got it built over 2 weekends.....but I did put a little time in in the evenings after work. So all together I probably have ~40 hours into it....... The result is GREAT, and the welding is better than any premade bumper....but I am not convinced that it was worth 40 hours of my time to save $600...... although I did enjoy it, and it does fit.

The finishing touch is a stainless laser cut plate for the front (does not come with the kit) I designed and had it made. The Move bumper is not the best looking, so I felt like it needed a visual highlight.

Bumper is at powder coat now, and I'll post again once I have it back and installed. See below pictures of the build.