You have that 35-foot stock trailer in tow, loaded down with fattened calves headed for the auction, but a couple long 6% grades stand between the farm and the sale barn. This Ultimate Working Heavy Hauler project has come a long way from its stock days but there are still a few parts needed to really dial this truck in perfectly for the hard task at hand. While it already has the extra power needed thanks to the EFI Live engine and transmission tuning, keeping a heavy load under control on the downhill still creates some concern as the factory brakes have gotten hot a time or two in the past. Since this truck seems to always have a big trailer attached to it, trying to combat high fluid temps in the rear axle and maintaining optimal fuel quality to the Duramax’s injection system are important things that need to be addressed.


To avoid riding the factory service brakes down long, winding mountain passes, the addition of an exhaust brake can not only increase the life of your brake pads and rotors, but bring a little piece of mind when you’re behind the wheel hauling a heavy load. While Tow/Haul mode and the previously installed Tapshifter has helped with towing performance by helping maintain the optimum transmission gear while towing, over-revving the engine on a steep downhill is still possible when all that weight is pushing you from behind.

01 The BD Diesel Exhaust Brake uses exclusive Variable Orifice Technology with an offset solid butterfly for maximum horsepower retardation. With top-of-the-line internals, it’ll withstand the harshest conditions for years of trouble-free use. Installation can be a little labor intensive due to the wiring and some minor welding required on the exhaust system, but the end results will be well worth it for a heavy towing application.
02 BD’s tough cast iron housing uses an exclusive alumibronze bushing, stainless steel shaft, and spring-loaded cylinder to produce the preferred 55psi back pressure needed for optimum hold back power. This butterfly design also helps ensure adequate exhaust flow to not hinder performance when running in the open position.
03 Under the hood, BD supplies a prefabbed stainless bracket to mount the supplied air compressor right on top of the engine. This compressor will supply regulated air pressure to the brake’s piston, which will actuate the butterfly when the 12-volt in-cab switch is activated. If an air tank were to be installed, this compressor could also be used to supply air to it for use with rear airbags or for an on-board air supply system.
04 The most time-consuming part of the brake installation is the required electrical wiring. The exhaust brake will run off an in-cab switch, but is also tied into the Vehicle Speed Sensor, Throttle Position Sensor, and Cruise Control. Obviously, a key-on power and ground will need to be supplied as well. Luckily, BD supplies excellent step-by-step picture instructions and the required wire taps, connectors and wires to make this task as easy as possible.
05 The exhaust brake kit is supplied with two flanged adapters that will be installed into the 4” exhaust already under the truck. Do to the back pressure created in the system when the brake is on, the front flange adapter will need to be welded to the downpipe to ensure a leak-free seal. The back flange will be held in place with a supplied band clamp. The BD brake also has a convenient pressure test port so the back pressure can be checked and fine-tuned with a pressure gauge for optimum braking performance.
06 The BD driver side manifold has been a notable aftermarket “must-have” for years. Since the factory manifold slims down after the third exhaust port and can restrict exhaust flow to the turbo, this high-flow cast replacement piece will improve exhaust velocity for better spool-up and efficiency.
07 Installation of the manifold is straightforward; by removing the driver side inner fender liner, you’ll have ample space to work with. Removing the mounting bolts and the up-pipe hardware is all that’s required. The factory gasket should be able to be reused.
08 Sitting side by side for comparison, you can see how much the stock piece can restrict and disturb the exhaust passage within the casting. The high-flow BD piece comes pre-drilled and tapped for an EGT or driver pressure sensor and will fit perfectly with no other modification required. We did spray some high-temp ceramic coating on ours to help from developing surface rust on the cast iron in this truck’s wintery environment.
09 To avoid injection system issues from fuel contaminates and debris, the BD Flow Max lift pump kit will be installed, which will also improve reliability of the factory CP3 and injectors. Since the LB7 Duramax was not equipped with a low-pressure fuel pump, the CP3 has to do a lot of work to not only create 20,000+ psi for the common rail system, but draw fuel clear from the tank. An aftermarket lift pump is always something you should look in to for better engine efficiency and longevity.
10 For this build, we decided that the Flow Max kit would be most beneficial with the optional fuel filter and water separator to be installed as well. The custom billet blocks bolt directly to the Flow Max pump and will allow the replacement spin-on filters to be easily serviced under the truck. These will also eliminate the need to continue running the expensive and hard-to-access OEM fuel filter on the passenger side of the engine.
11 The supplied aluminum mounting bracket installs easily on the inside driver frame rail directly in front of the fuel tank. The factory fuel feed line (lower line seen in picture) will be cut and tied into with the supplied hoses to route fuel through the new filters and pump.
12 The Flow Max kit does not require the fuel tank to be removed from the truck, which helps in making this a super easy install. The factory fuel feed line running from the tank to the engine will be spliced into by simply cutting it in two places with a basic pipe cutter. Have some rags ready and use caution, as this line will have fuel in it and can make a bit of a mess.
13 The suppled hoses tie into the stock fuel line that was cut and clamped into the Flow Max filter inlet and outlet ports. The supplied wiring harness is run up the frame rail to the engine bay and tapped into a key-on power supply and grounded. The single 150gph pump is more than enough to support up to 600 hp and comes with a 5-year 75,000-mile warranty.
14 In a heavy towing application like this, fighting fluid and engine temperatures is usually the biggest struggle. This onepiece cast differential cover offers a unique design that not only allows more oil capacity and cooling fins, but helps deflect oil directly onto the ring and pinion gears for cooler operating temps.
15 The external and internal cooling fins cast directly into the pan help to keep gear oil temps as cool as possible. The gasketless cover also makes installation easy by using a machined groove to hold a reusable Viton O-ring for an easy leak-free seal.
16 This big 3500 dually is used almost every day around the farm for everything from hauling one-ton hay bales around to towing tractors and equipment from one field to the next. The BD differential cover helps keep that rear differential running cool while offering a little better durability in off-road situation.

The addition of the BD Diesel exhaust brake system can safely cut downhill speeds without you ever having to touch the brake pedal. Maximum braking power can be experienced through the air-actuated, exhaust-mounted butterfl y valve that restricts exhaust fl ow and increases drive pressure within the engine to better maintain a safe engine RPM and vehicle speed. By tapping into the truck’s speed sensor, cruise control and throttle position sensor, the truck can still run and function as it did before adding the brake, but offer great hold-back power when engaged. The brake will automatically disengage at speeds under 15 mph for smooth stopand- go driving. Exclusive variable orifi ce technology and the offset butterfl y creates the best of both worlds with optimum braking when closed and maximum exhaust fl ow when open. Its tough cast iron housing and stainless steel shaft and hardware will also help it hold up to the heaviest abuse and harsh road conditions.


An often-overlooked but worthwhile upgrade for the Duramax power plant is the high fl ow BD Diesel replacement driver side exhaust manifold. The factory exhaust manifold on the LB7 Duramax creates an unneeded restriction in the preturbo exhaust stream, which really affects turbo performance. The stock driver manifold fl ows just 80% of that of the passenger side manifold; this difference causes an imbalance between cylinder heads and creates unneeded heat build-up preturbo. By eliminating the restriction and maintaining a constant internal bore size matching the passenger manifold, a more effi cient exhaust fl ow can be fed to the turbocharger to allow for better control of exhaust gas temperatures and exhaust back pressure, in turn allowing for an increase in power and engine effi ciency.


The LB7 Duramax platform has been plagued with injector failure issues for quite some time, so much so that GM had extended a warranty period for up to 200,000 miles on the injectors. A lot of these issues stem from fuel contamination and debris getting through the injection system. The factory CP3 also must do a lot of work to keep the engine running effi ciently, as it has to pull fuel clear from the tank on its own before pressurizing the fuel to 20,000+ psi for the common rail system. To improve the longevity of the fuel system and hopefully avoid expensive replacement parts and repairs, the BD Max Flow lift pump kit was bolted on to offer additional fi ltering plus a lowpressure fuel supply to feed the stock CP3.

The gerotor design within the pump can fl ow 150 gallons per hour for enough fuel supply to support up to 600 hp. While this truck is most likely around 400 hp in the highest EFI Live tune, power potential wasn’t the real reason for the Max Flow system. The optional 30-micron water separator fi lter and 3-micron high-fl ow spin-on post fi lter will help keep contaminants and debris out of the CP3 and fuel injectors. The ultra-quiet and compact system is easy to install and ties into the stock fuel feed line, so there is no need to drop the fuel tank. An additional advantage to the aftermarket fi ltered system is the expensive and problematic OEM fi lter can be bypassed all together, making fi lter services much less expensive and easier to do.


In heavy towing conditions, the rear axle goes through a lot of strain. With the massive amounts of horsepower and torque that Duramax engine can produce, transferring it all to the tires can generate a lot of heat within the rear axle housing. These metal axles, ring and pinion gears will wear with time and put extremely fine metallic debris in the gear oil, which can affect the longevity of the parts.

The addition of a performance BD Diesel differential cover can kill two birds with one stone: reducing fluid temperatures via its cooling fins and oil deflector to keep oil on the ring and pinion gear, and a magnetic plug that will also trap those small metal particles and keep them from being passed through the gears to reduce wear over time. Increasing fluid capacity and keeping that fluid cooler helps extend fluid life and increasing reliability within the axle, even under the heaviest of loads.


In Part 5 of this build the truck will gain some additional load control with a set of bolt-on Hellwig rear suspension airbags and a massive sway bar kit. The cosmetics will also see some improvements with a new set of Ultra Wheels and General Tires for better on- and off-road performance. Building the Ultimate Working Heavy Hauler may take some work and the perfect list of parts, but the end result will be worth it, we promise.DW


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