Lil Red - Duramax 6600/Allison 1000 Conversion & OBS/NBS Dash Conversion

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I watched a couple of pickup truck related events on Youtube recently. The first photo here was screenshot from the 2023 Hot Rod Powertour video while the tour was in eastern Tennessee and the other was from a video about a Chevy C10 group event that was sponsored by LMC Trucks. I saw a couple of trucks while watching the videos that made me hit the rewind button....





Though Lil Red is now 35 years old (but 20 years in its present form), it seems some of the design elements may have appealed to a couple of other truck builders. I think its cool.

Jim

[JohnC]

Oh, those wheels!

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Oh, those wheels!

Don't hit any potholes!

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The power increases eventually reached the limits of the factory Allison. In working with Kennedy and ATS, we came to the conclusion that the "ATS Extreme" Allison would be a step in the right direction. It has been. While the original factory Allison could be made to slip with 500-hp and a power-brake launch at the strip, the ATS has yet to slip, even with more than 600 hp. The torque converter contains a 5-disk pack that provides for a solid connection once locked.



A note about this image... Originally, I used smoke-tinted covers for both the headlight lenses and turn signal lenses. I would then remove the smoke tinted headlight covers if/when the truck was driven in the evening or at night (very rarely). The covers were employed only during during the daylight hours. Because removing/replacing the covers was a royal PITA, I have since replaced the tinted covers with DOT tinted headlight lenses and tinted turn signal lenses. I did give up a small amount of illumination in exchange for a better match for my patience.

A local friend who also just happens to own a mechanics garage (and is a transmission expert), worked with me to install the new ATS Allison. The lift makes this sort of thing so easy, when compared to a transmission floor jack and jack stands...

Shift quality while using performance programming was pretty "performance oriented", sometimes producing a little "bark" from the rear tires at gear changes while on local highways. Who can resist using a little pedal? But, when toning down the ECM programming to near stock levels, the ATS Allison gets real close to factory Allison shift quality.

I've not had any code setting with this transmission - or any other problem. There's only about 12K miles on it since installation, and the ATF fluid remains nice. The transmission has seen only a couple of dozen 1/4-mile runs and a similar number of dyno runs so far, plus highway driving. But, I do plan to service the transmission this coming spring - new spin-on filter and pan filter, plus a fluid drain/refill. I'll report back once that's been completed... if we find anything unusual. Jim

[a5150nut]

Are you running Kennedy's tune on your truck? Or a custom version of his?

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Are you running Kennedy's tune on your truck? Or a custom version of his?

Currently, the truck has a Kennedy EFI-Live switch-selectable tune - a stock power setting with fuel economy, and a +100 hp setting. Time flies, but this programming was added not all that long ago. Jim

[a5150nut]

How street-able is the 100 hp setting?

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How street-able is the 100 hp setting?

Haven't used it enough to form an opinion. It definitely brings a bit more "sport" to the table than the stock setting. It would be interesting to compare the two current power settings on the dyno. I do know that the race programming from before was a bit too sporty for the street - that is, once I got past the "watch this" phase.

[a5150nut]

I was curious about the 100hp been thinking it might be on my bucket list
I'm sure John removes the speed cap too. My son had a 6.0 built and we were on the way to Winimucka from Carlin NV he dropped back about 5 truck lengths and nailed it. When he got up to me I nailed mine. matched his speed, then started pulling away. Up till I hit 94 and the computer started de-fueling my foot

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I was curious about the 100hp been thinking it might be on my bucket list
I'm sure John removes the speed cap too. My son had a 6.0 built and we were on the way to Winimucka from Carlin NV he dropped back about 5 truck lengths and nailed it. When he got up to me I nailed mine. matched his speed, then started pulling away. Up till I hit 94 and the computer started de-fueling my foot

I haven't pushed things too far with the latest programming. I seem to remember talking with John about the engine rpm and vehicle speed limit settings. I asked for 4000-rpm as the programmed max engine speed, and we talked about removing any sort of programmed vehicle speed limiter. So, with an engine rpm limit currently at 4k, and with 2000-rpm currently producing 80-mph, the theoretical vehicle speed limit is.... a little scary. I've not tested the theoretical. I heard once that "there are old pilots and there are bold pilots. But, there are no old-bold pilots."

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This video was produced some years ago, before diesel performance programming could produce power without smoke and while tires were a bit less expensive than they are now. Mind you, something similar to what's shown here can be seen today on nearly any performance automotive cable program or related Youtube channel. So... Lil Red hasn't produced smoke in years and tires are currently viewed as a more longer term investment...



Except for imagining vvrrrooommm sounds, there is no audio. However, no pedestrians or cute bunnies were harmed in the making of this film.

The following image was shot a few months after the above video was taken, only this time I was using a KennedyDiesel.com EFI-Live program that allowed the truck to dyno 500-rwhp. As you can see, there is no visible smoke shown here at the beginning of a 1/4-mile run.

I was likely using a Van-Aaken performance module when the smokey burnout video was made. I liked that in-line module when used at lower power (no smoke) settings, and I used it for years in my 2001 GMC Duramax crew cab where it could smoothly produce more than 400 rwhp without smoke.



Back in the early days of the Duramax I answered a few emails from young guys who wanted ideas for how to get their truck to produce more smoke... I tried to discourage the idea...

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When beginning a project as complex as a Duramax conversion, it's helpful as you work through the project to use checklists, and then concentrate on one or just a few steps at a time. A person can become bogged-down and discouraged when contemplating the entirety of the project. Again, just concentrating on a few steps at a time helps to keep you focused, and allows you to see and measure progress in real terms.

When Lil Red was still in the planning stages, and later while actually working through the conversion, I created many lists that I used to help keep me focused. Shown below is just one of those lists (yes, I kept them all). Some of the lists, notes and hand-drawn diagrams were later refined and then included the "Duramax Conversion Guide". Aside from helping me as the conversion was taking shape, some of this information could be helpful if a problem appears months/years later. Knowing the details can aid in troubleshooting.



When taken as bite-size chunks, the project becomes more doable for most people. And a list helps to keep you focused....

Jim

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Here's an article I wrote for the 2007 issue of Diesel World magazine (involving Lil Red), which wraps up a discussion we were having at the time about Duramax Diesel performance - performance that didn't require tons of money, was relatively easy to do and didn't involve a lot of modification. The actual dyno performance data is included here too.











Let me know if you have any questions.
Jim Bigley

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Early in Lil Red's history we visited a number of tracks here in the Northwest, from Salt Lake to Abbotsford, BC. The following photo was taken at the Spokane Raceway in (I think) mid summer 2005. That day was more of a shake-down, experimenting with different products as well as trying to find the best way to launch the truck (2WD, 4WD, powerbrake light/hard...). 2WD didn't work well at all... And, I didn't have nitrous on it then. This early period was still pre EFI-Live, and the truck was still running with the original Allison, so the day turned out to be more about learning how to run the truck rather than make any real progress in performance. However, it was still a super fun day and I was able to see how well the truck/Duramax performed when close to stock. Plus, I got to spend time with my son and talk to other enthusiasts at the track.

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Rear Disc Brake Conversion
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for GM's 9-1/2" 14-bolt Semi-Float Rear Axle
Part I

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The new GM 9-½" semi-float rear axle has been installed, and to improve braking ability, we've decided to upgrade to disc brakes. Rear discs help with two important areas - the reduce un-sprung weight and they increase stopping ability. Demands on the braking system increase as vehicle speeds increase. Stopping can be more important than going fast.

All of the brake components used in this conversion are factory GM 1999-2003 model-year K1500 parts bought from either a local GMC dealer or from Spalding Auto Parts in Spokane, WA. The only special items not available from GM are the adapters needed to adapt the original axle flanges to the new disc brake backing plates.

The above photo shows a complete set of parts for one side - rotors, assembled backing plate, caliper, caliper mounting bracket, flex hose and related hardware. Not shown is the backing plate adapter and related bolts. We hope to have the newly fabricated flange adapters ready for part II of this article.



The factory cast-iron vented rotors shown here are about $60 each and are designated for a "Pickup JC5/JH5 - Vacuum" braking system, having a nominal diameter of 325-mm x 20-mm thick (12.8 x .787"). Inside each rotor is a parking brake mini-drum.

Note: You may need to reduce the outside diameter of the axle wheel flange to allow the axle flange to fit flush within the inside face of the rotor. I used an angle grinder with the truck's engine idling in drive. Both rear wheels/tires were off the truck, and the frame was sitting on jack stands. I used an 8x16" concrete block to steady the angle grinder - to get a near perfect reduction in outside diameter of the axle flange. It only needed a very small amount of reduction.



The disc brake backing plate assembly (pn-15206075) came as a fully assembled piece, with the parking brake components already installed. The parking brake shoe is a one-piece affair, with cable actuated and adjustable shoe engagement, to compensate for fit and wear over time.



The above shows the rough working drawing used to fabricate the axle flange adapters. The square plates for each adapter are the same size, but are clocked differently to correctly locate the brake calipers at the front - when viewing both left and right sides. The points of the square end-plate that bolts to each disc brake backing plate are positioned at 12 & 6 o'clock. The square end that bolts to the existing axle flange (welded to the axle housing) should be positioned 5° nose down for both the right and left side of the truck. This means that the adapters for both the right and left sides of the axle are different from one another.

See Part II below...

Jim

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Disc Brake Upgrade - Part II
A rear disc conversion generally offers better braking ability - both when dry and especially when wet, weighs less than most drum brakes, sheds heat faster - more fade resistant, and discs just look way cooler... Our rear disc brake installation is now complete. Read on to find out how they look and stop.

We converted to rear disc brakes primarily because we had upgraded to a stronger rear axle, were using a larger tire/wheel combination, and we needed better rear braking than was provided by the original rear drums. The sum of the new rear disc brake components provided no weight savings when compared to the small 10" drums used on the original 10-bolt rear axle, but in addition to the coolness factor, the rear braking ability has definitely improved - more about that later.

There are a number of companies that offer disc brake conversion kits for 1500/2500/3500 series GM pickup trucks and SUV's currently equipped with rear drums (see list at end of article). A DIY project like this, when using all new GM parts + fabrication, will cost about the same as a commercial kit. I chose to use all new OEM parts for ease of maintenance and when buying future replacement parts. Plus, a functional and effective emergency brake was necessary because this truck will be trailered occasionally. The e-brakes included with most aftermarket disc brake kits I've seen don't inspire a lot of confidence.



Fabricating the offset brackets was the most time consuming portion of the project. I had a local fab shop build these for me, using a drawing I supplied. The ½" steel end plates were cut from sheet using a water jet CNC, and a section of steel pipe was located that fit the OD of the axle tubing.

Once back from the fab shop, I spent some time drilling and tapping the sixteen holes for the 12mm bolts, then squirted on a little black paint.

It should be noted that the dimensions listed on the drawing fit the 1997 model-year 9-½" 14-bolt semi-float axle used in our buildup. If you are installing similar disc brake components on the smaller GM 10-bolt rear axle, you may need to adjust the thickness of the offset brackets to compensate for a different axle flange location. Flange offset bracket thickness is correct when the rotors are centered in the assembled disc brake pad brackets.



The newly fabricated offset bracket has been bolted onto the axle flange using four 12mm bolts, each torqued to 100 ft/lbs using thread locker. Correctly clocking the square ends was important to transfer the correct orientation to the disc brake backing plate.

I drilled out the threaded holes in the original axle flange (using a ½" bit) to allow the 12mm bolts to pass through and then thread into the new brackets.

This bolt-on installation has proven to be plenty secure. A lot depends on the quality of the welds. I had a pro do the welding for me.



The disc brake backing plate has been bolted on using four 12mm bolts, each torqued to 100 ft/lbs using thread locker. The calipers and disc pad brackets are bolted onto the forward-facing side of the backing plate, 9 o'clock on the driver's side and 3 o'clock on the passenger side (passenger side shown).

The axle shafts need to be removed when installing the offset brackets and disc brake backing plates. It's a fairly simple job to remove the differential carrier pin, slide the axle toward the center, then remove the axle-retaining C-clip. The axle will then slide out. Be a little careful not to damage the wheel bearing seal.




The original steel hydraulic brake lines were carefully reshaped by hand to fit the disc brake flex-line mounts. The truck's original e-brake cables can't be modified to work with these GM disc brakes due to the new rear facing e-brake cable anchor (1) and actuation lever (2).



To match the new disc brakes, you'll need a set of e-brake cables made for a similar wheelbase 1500 series truck (i.e. 2000 model-year, models 03, 06, 53 - new style 4x4). These loop over/under the axle, then sweep around to make the connection on each side.

This driver's side photo shows the e-brake cable sweeping around and anchoring to the shock mount, then running under the axle tube, before sweeping up and through the wire loop bolted to the frame.




On the passenger side, the e-brake attaches to the rear facing side of the brake backing plate, loops away and then is anchored to the axle tube, before sweeping up and over the pumpkin. The cable mount shown in this photo that secures the cable to the axle tube is simply a steel strap, but you can weld on a tab if you have access to the right fabrication equipment.

A metal clamp secures the e-brake cable from one bolt on the differential cover. From there, the cables sweep across and forward through the wire loop on the frame.



The forward ends of both e-brake cables mount to a fabricated bracket that is bolted to the frame. I may tinker with it a bit over the next few months.

A 2" long piece of ½" square steel tubing was used to provide an anchor point for both cables that can rotate slightly to accommodate a slight misadjustment between the right & left e-brake shoes. This is similar to how the factory parts operate.

Articles have appeared in various truck magazines that mentioned a few potential complications when converting from drums to discs. First, some recommend a new brake master cylinder designed for a 4-wheel disc system, to either provide more fluid volume for the larger rear disc brake caliper pistons or to modify hydraulic brake pressure. Secondarily, they mention that the front/rear brake proportioning valve may need to be modified or replaced for some installations. I had installed a new brake master cylinder and hydraulic brake booster when the truck was assembled a year ago, and I did not want to buy replacements. After breaking-in the rear rotors/pads and performing a few hard stops, I feel that (for this particular truck and installation) a new master cylinder is not necessary, nor is replacing/modifying the proportioning valve. The current front/rear brake proportioning appears to be nearly ideal for this lightweight truck.

I lucked out, but some of the factors that contribute to correct brake proportioning include the weight of the vehicle - especially over the rear, condition of the brake master cylinder and hydraulic brake booster, wheel & tire combination and type/composition of the disc brake pads themselves (some are more aggressive than others). I installed the NAPA Premium Disc Brake Pads #AE-7662-M, which are asbestos-free and are supplied with new anti-rattle clips.

An alternative to retrofitting discs to your existing rear axle would be to locate a suitable disc brake equipped rear axle that had been installed in a newer vehicle. If you can locate a replacement disc brake equipped rear axle in good shape and with the correct gearing, your total cost could be somewhere in the same general price range as a rear disc brake conversion kit. I considered going that route, but unfortunately, GM didn't produce a six-lug disc brake equipped rear axle with the 9-½" ring & pinion that I needed (all current GM disc brake equipped 9-½" rear axles now have 8-lugs, and are used on GM's light-duty ¾-ton trucks).

If you have a drum brake equipped heavy-duty ¾-ton or 1-ton truck, you'll find a variety of aftermarket disc brake upgrade kits currently available for your rear axle. In addition to the braking advantage, disc brakes would provide a worthwhile weight savings due to the much larger drums used on the HD vehicles. Would I do it again on a ½-ton? Tough call, unless you want/need the extra braking performance or just want more modern binders on the back. They do look cool! TDP

Continued next post...

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1999-03 Pickup JC5/JH5 K1500 OEM Six-Lug Rear Disc Brake Components:

• These parts fit models 03, 06, 53 - new style 4x4
• Aluminum Single Piston Caliper Right: #18040088 List $188.02 Discount $131.61
• Aluminum Single Piston Caliper Left: #18040087 List $193.42 Discount $135.39
• Brake backing plate: #15206075 $54.25 ea (2 required)
• Brake Pad Guide bracket: #18040090 $59.25 ea (2 required)
• Brake Flex-hose Right: #15102334 $24.26
• Brake Flex-hose Left: #15102333 $24.26
• Caliper Guide pin: #12530697 $4.40 ea (4 required)
• Caliper Guide pin grease seal boot: #12530703 $3.68 ea (4 required)
• Bolts: #15007007 $2.85 ea (16 required)
• Bolts: #15012506 $0.99 ea (4 required)
• E-brake Cable Left: #15084208 $22.00
• E-brake Cable Right: #15084209 $29.83
• The new factory cast-iron vented rotors shown here were about $60 each and are designated for a "Pickup JC5/JH5 - Vacuum" braking system, having a nominal diameter of 325-mm x 20-mm thick (12.8" x .787"). These were purchased from Spalding Auto Parts in Spokane, WA - 800/366-2070 www.spaldingautoparts.com.

GM pickup & SUV Aftermarket Disc Brake conversion sources:
AP Racing (aka Brake Pros www.brake-pros.com)
888/266-0696
www.apracingusa.com
Dynatrac
714/596-4461
www.dynatrac.com
Stainless Steel Brakes Corporation
716/759-8666
www.ssbrakes.com
Wilwood Disc Brakes
805/388-1138
www.wilwood.com