6.7 Cummins Suburban Build

[Mark Baur]

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

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

 

[grampsbutler]

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

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.

 

[grampsbutler]

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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[mcarlo86]

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.

 

[grampsbutler]

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

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First pattern

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[grampsbutler]

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

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.

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[1lejohn]

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