6.7 Cummins Suburban Build

[grampsbutler]

Do you still have the "Load Sensing" rear brake valve? The one that applies more rear brake pressure when the truck squats more, and less with normal suspension height. It has a linkage from the axle up to the valve underneath the body. I'd check the adjustment on that first.

Also, double check the adjustment on the brake shoes. Assuming you kept the brake shoes, and did not convert it to rear discs.

I think I figured it out.....I have a leak in the left cylinder which I suspect was causing the lock up condition. I am going to do a brake job tomorrow and will report back the results.

I don't think I have the load sensing proportioning valve. I'll know for sure tomorrow after redoing the brakes. In fact I don't know whether they ever put them into Suburbans, I think it was more of a pickup truck K20 thing.

 

[grampsbutler]

I have lots of progress to add, but not time to do it!

INSTRUMENT CLUSTER: I received the Dakota gauges ready to go in this weekend. I'll take some pictures and post once it is done. I also got my fuse panel and relay box installed after rebuilding the wiring harness.

REAR AXLE: The big news! I pulled the trigger on a Dana 60 front. I overpaid (I'm embarrassed to say how much), and it is a 4.10 ratio so I'll have to do a re-gear. These things are REALLY hard to find and SUPER expensive. The one I got is in good shape.

LOCKER RECOMENDATIONS ANYONE? Seeing as I am doing a regear anyway does anyone have recommendations on lockers. I am leaning towards the OX locker, but would love to hear what others have done.

Same question on gear sets: Are there any quality differences or preferences I should know about?

 

[Blackbeard44]

I used an Eaton TruTrac in my Dana 60 front, I am very happy with it, road manners on the ice couldnt be better, I have a standard detroit locker in the rear wich I really dont care for, it works great but you have to be aware at all times its there, like downhill on a twisty road, it engages anytime your on the throttle and the rear walks out easy. but the biggest reason I keep it is that it will engage both tires in reverse, Ive had other LSD unit that wouldnt lock in reverse.

 

[bucket]

I used an Eaton TruTrac in my Dana 60 front, I am very happy with it, road manners on the ice couldnt be better, I have a standard detroit locker in the rear wich I really dont care for, it works great but you have to be aware at all times its there, like downhill on a twisty road, it engages anytime your on the throttle and the rear walks out easy. but the biggest reason I keep it is that it will engage both tires in reverse, Ive had other LSD unit that wouldnt lock in reverse.

That's good to know about the true trac in the front.

For the rear, I have no recommendation lol. People say they don't like the engagement of the Detroit, along with it's popping and banging. But they don't bother me. I even don't mind a welded rear diff, including on the street.

 

[Blackbeard44]

ive heard with manual trans the detroit can be annoying, never had a manual trans in front of one, my LS swapped k20 is an auto, the noises dont bother me, but when theres no weight in the bed and im going downhill on the ice throught the corners I just have to stay aware the rear likes to walk out, I have lots of fun with it in the snow/ice.

 

[grampsbutler]

Rear Brake Lock Up: I pulled my rear brakes apart and sure enough the wheel cylinder seals were bad, and was leaking brake fluid all over the pads. It seems that this also caused the wheel seal to go bad. Wheel seals were replaced at the time of the axle install......so I can only assume that they were damaged by the brake fluid. Pads were totally saturated with a mix of gear oil and brake fluid, and caused the brakes to grab. After rebuilding it stops just fine with no wheel lock up.

I took the opportunity to make the parking brake work. The fix here was to adapt the 14B parking brake bolt in bracket for the more modern push in bracket. I took it apart and welded a washer on the end of the bolt in bracket so that the cable pushes into the bolt in bracket. Pictures below.

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[DoubleDingo]

Rear Brake Lock Up: I pulled my rear brakes apart and sure enough the wheel cylinder seals were bad, and was leaking brake fluid all over the pads. It seems that this also caused the wheel seal to go bad. Wheel seals were replaced at the time of the axle install......so I can only assume that they were damaged by the brake fluid. Pads were totally saturated with a mix of gear oil and brake fluid, and caused the brakes to grab. After rebuilding it stops just fine with no wheel lock up.

I took the opportunity to make the parking brake work. The fix here was to adapt the 14B parking brake bolt in bracket for the more modern push in bracket. I took it apart and welded a washer on the end of the bolt in bracket so that the cable pushes into the bolt in bracket. Pictures below.

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Well done!

 

[grampsbutler]

Turbo Actuator Failure: Back in January the truck started running like crap. Lost power and, would stumble and stall. Upon investigation I found a blown fuse on the ASD circuit. I replaced the fuse and it immediately blew the new fuse. The ASD circuit runs the MAF sensor, Turbo Actuator and intake air temperature sensor. I unplugged the turbo actuator and replaced the fuse........and it didn't blow. I checked the wiring, to make sure it wasn't a wiring short, but couldn't find anything. Time for a new turbo actuator.

After some internet research I decided that the City Diesel actuator was the best option. So I started trying to find a place to purchase it. I initially called and ordered from DDP Motorsports, they were back ordered with a 12 week lead time. I called around and was able to get it direct from City Diesel in under 2 weeks. Sooo I cancelled the order with DDP.....who tried to charge a 5% restocking fee (for an item that was not in stock!). To be fair to them, they did eventually give me a full refund, but not without emails and calls back and forth. These guys are pretty sketchy, and I would not buy from them again.

New actuator installed very easily with new seals. It now cycles at every key on which is good, because it gives me positive confirmation that it is working. Also drives way better now. I highly recommend the City Diesel product. The old actuator had bad seals, and had coolant infiltrated into the circuit board. The board was all burned up as a result.

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[grampsbutler]

Air Conditioning: This past weekend I got around to wiring up the Air Conditioning system (Vintage Air). I had a vacuum pulled and it held vacuum. Then I charged it, and discovered a leak in the stock condenser that I was planning to reuse.... So I got a new condenser and installed.

I have not yet charged it (having this done by a shop). I am slightly concerned about the AC condenser sitting behind the intercooler not getting enough cool air flow to condense properly. If the intercooler sheds too much heat, it might not allow the condenser to function efficiently. Proof will be in usage. I'll report back on the outcome.

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[grampsbutler]

Exhaust modification: After driving for a few months now, I decided I needed to add a muffler to the exhaust. I was not happy with the exhaust drone especially on the highway. It wasn't terrible, but after 8+ hours it did wear on me a little. Sooo I bought a class pack muffler that won't restrict flow and added it into the pipe. The difference is very noticeable, and it now makes the wind noise dominant on the highway.

Wiring Cleanup: I have not yet taken photos, but I have spent a lot of time on wiring recently. This has included new fuse and relay boxes, and re-looming all the wiring in the engine bay. I'll post some pictures later showing the detail.

Front Axle update: I have the Dana 60 and am about to start work on the rebuild and upgrades. I have decided to go with the Ox Locker. It will need a regear to 3.73. Does anyone have a recommendation for a good quality gearset? I have looked at Yukon, but I see many other less expensive options, is it worth the extra for a yukon gearset?

Lastly I am planning for crossover steering. I am trying to decide between the ORD kit and the Ruff Stuff Specialties Kit. Anyone on here have experience with either?

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[Blackbeard44]

I've always ran Richmond gears, not sure if they are any better than any others, they've always worked for me, The cross over steering I think is a good idea, I've never heard bad about ORD, I have ordered some stuff from them and quality was good, never used rough stuff so I cant comment about them.

I gotta say I think you suburban is my favorite build I've read on here, I like they way your going about doing it and you oughta get years of enjoyment from it.

 

[bucket]

The ORD crossover stuff is very good. There's no guesswork involved, just buy the parts that you need.


As for the AC condenser, it will be interesting to see how it does. I can't think of a factory application where the condenser is not in front of the intercooler. I'm not saying there aren't any, just none that I remember dealing with.

 

[Mark Baur]

Radiator choice and set up:

Another weekend and more progress for the books! I got the radiator and core support in the vehicle! It fits but only just.

Radiator choice was something that I made long before the swap. The third gen dodge radiators are huge, 26.5625x32.4375 providing 861.62 square inches. I knew that I was not going to be able to get enough surface area to match the dodge radiator. The standard chevy radiator is 19x28 = is 532 sq inches ---- 38% smaller. The diesel version of the chevy radiator has a larger surface area at 19x34 inches = 646 sq in------ 25% smaller. By going up to a 4 core radiator I am effectively doubling the surface area, but also introducing some inefficiency from going from 2 cores to 4. So in round figures I should get JUST enough cooling with the chevy diesel 4 core aluminium radiator.

The bottom line: the dodge radiator won't fit in the chevy, so the point is a little moot, but it helps me to sleep at night doing some calculations and thinking it through.... The other option would have been to go with the second gen radiator, but that would also have been undersized for the third gen motor, and would have required butchering the radiator core support.

I opted to go with a custom fan shroud with three 12" electric fans. Between the longer engine, and the fatter radiator core there is no room to run the mechanical fan... I only have 1/2 inch to spare with the electrical fans. I am really interested to see how it performs.....My guess is that it will be fine under normal conditions, fine at low speed/power but will start to get hot at higher speeds and long climbs on the freeway.

Back up plan: I can add an additional auxiliary radiator, if heat becomes an issue. I am 75% confident that this won't be necessary, but the plan is there in case I'm wrong.

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

 

[Ricko1966]

Your fans are for low speed and stopped traffic conditions the fans are no longer part of the equation above 25 mph. If your fans are against the radiator a shroud is not needed or beneficial it will be more of a hinderence to air flow at higher speeds.

 

[Frankenchevy]

The driveshaft did not need to be shortened.

Just verify that the suspension can be fully cycled without the yoke bottoming into the TC. My guess is that you are fine(maybe better off) because gm liked to build the driveshafts a bit shorter than standard convention recommends. I actually lengthened my k30’s DS a bit to have ~1-1/4” of stick out at ride height. Before it was more than 2-1/2” iirc…

When this truck is done, it’ll be one of the coolest suburbans that I’ve seen. Nice job on it.