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How To Build A Mud Truck

Posted in How To on September 1, 1998
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Let's just start this off on the right foot: We can't tell you how to build a truck for mud. You know why? Because we'll say to do this, try that, and swap this, and then when you don't win races or you get mocked by those fishing you out of the soup, you'll curse us and our immediate family. However, what we can do is toss out a plethora of homegrown ideas and some tried-and-true-for-others tips from people who play in the mud so that you can build the ultimate mud truck.

What's on the following pages can be applied to your truck whether your goal is purse or play. Everyone from a pro-racer with an extreme bogger to a guy who four-wheels and daily-drives his rig-when he's not using it for search and rescue-has provided valuable building tips for this story. Each of these drivers has scored well in his class, and all of 'em are pretty happy with their current setups. And remember, they got to that state of mind after frustration, experimentation, and advice from others. Sound familiar?

Here's the thing-driving through mud is like driving through water, only not as clean. Therefore, it's wise to have your truck and its moisture-sensitive components up and out of the goo, with either a suspension or body lift. You don't need a lot of articulation for mud, but you do need some travel so the suspension can handle bumps without bouncing off the ground, as some mud bogs can be fairly rough when they start to harden.

Waterproofing tips galore can be found on mud trucks. Many drivers wrap duct tape around the perishables, such as air cleaners and hubs, but this owner zip-tied a tarp inside his fenderwells. Also note that his headers are pointing up to keep mud out.

One of the key steps to building a successful mud truck is to trim as much weight as you can from the vehicle. A lightweight vehicle is generally a fast vehicle. When it comes to the suspension, this can mean using a coil-spring setup rather than leaf springs. However, most of the guys we spoke with stuck with leaf springs and added as much as a 12-inch lift.

Jim Bamford of Kearney, Nebraska, owns a '90 Chevy S-10 Extended Cab but didn't lift it at all because he wanted to keep the center of gravity lower for more stability. To fit larger tires, he simply cut the body until the tires cleared. But if you want to fit bigger tires without hacking sheetmetal in the process, you can add a body or suspension lift to your to-do list.

Ted Farmer, from Lakewood, Colorado, has been doing the gumbo for about 17 years and says his '77 Ford F-250 had 4-inch springs on the front, which he re-arched before taking out a leaf from each pack for a softer suspension. The rear has custom-made shackles, and he removed the lift blocks and four of the leaves to improve the ride and gain more travel.

Removing everything you can from the interior will reduce your vehicle's weight. And we mean everything that's not necessary-all those little brackets and pieces of metal add up. Also, two words about safety: harness and rollcage. You need to have a minimum of a six-point rollcage attached to the frame, not to the body, and a five-point harness to hold you in place.

Another key to a successful suspension is having the right shocks. Bamford runs heavy shocks in front for better damping and light ones in back so that when he steps on the gas, the front end will lift while the rear sinks for better traction. Farmer has dual shocks in front and singles at the rear, while Fountain, Colorado's George Gallegos runs double shocks at each corner of his '73 Chevy Blazer.

You want to make a lot of horsepower for mud, but if you have a big engine and small drivetrain components, forget about driving out of a pit under your own power.

If you mount batteries in the bed, make sure they're in a durable, full-perimeter marine box that's attached to the frame with a minimum of 3/8-inch bolts holding the battery to the box-don't ratchet-strap it in place. Also, we've seen fuel stored in beer kegs and water bottles, which is not good-attach a fuel cell to the frame and move the fuel lines out of the way. These brake lines are held to the frame with Adell clamps-a wise idea.

Since most mud-runners run tall tires, they make sure their axles can handle the rubber as well as the work that comes with churning it through thick mud. The heavier duty the axle, the less likely it is to break, but you're adding more weight to the truck.

Ross Early from Eaton, Colorado, has a '77 Blazer with a GM 12-bolt rear and a Dana 44 front mated to his 38s, and Farmer has a Dana 60 front and a Dana 70 rear. Bamford has a fondness for Danas and popped in a 60 rear and a 30 front, which is adequate for the front since its only real job is steering and braking, he says. He also has solid-core U-joints in his driveshafts, while Early uses a larger U-joint than stock so that they'll last longer. Both drivers recommend the nongreasable type-the greasable joints can actually end up being a weak link in your drivetrain because of how they're produced in order to hold lube. Because Farmer's transfer case is divorced, his intermediate shaft has been custom-built with the thickest tubing he could get so the driveshafts wouldn't do the twist, and he runs the biggest U-joints he could find.

When it comes to brakes, discs all around work better in mud than drums. Bamford is the only one of this group we spoke with who has four-wheel discs. Farmer bolted in a master cylinder from an '86 Ford F-350 to gain the largest bore Ford had available for more volume of fluid, equaling quicker brake response.

Since Fords are prone to being drowned out because the distributor is in front, mud-racer Ted Farmer has a Magneto that comes with a rubber boot for waterproofing. Ross Early installed a tiny radiator from a Mazda pickup, just so there's something to circulate the water. Some people move the radiator to the rear for better weight distribution but then forget that all the hoses needed to do the modification can defeat the weight watching.

On the transmission front, both Early and Gallegos have added a high-stall torque converter to theirs-it's important to get your stall speed up so you can get a good launch and have your engine operating at the right rpm immediately. Farmer has lower First and Second gears in his C-6, which allows him to throw his transfer case into low range and run all three gears. He doesn't have a shift-improvement kit but does have a Cobra Jet direct drum that takes six clutches rather than four, and a custom servo applies the band harder and quicker.

When Farmer went from 4.88 gearing to 4.10s, people called him crazy. But his is the truck we referred to in the intro as the all-purpose vehicle. The 4.88s and 40-inch tires didn't quite jive at 75-mph freeway speed, and since his engine was making 500 hp, he decided to go back to 4.10s.

Gallegos staggers his gears, with 5.38s in the front pumpkin and 4.88s in the rear, because he wants the front end to spin faster than the rear to help keep his truck straight in the pits. What you need to do is match up the gearing with the rpm you're spinning and the tire size. Bamford's advice is that you should pick your gear ratio based on your engine type. Because he has a small-block, he runs a much lower gear since the engine can handle the extra rpm. Big-blocks should run higher gears because they have more lug-ability.

Gallegos has a posi front and rear, while Farmer had a locker in front but now runs it open for better steering control. He found that when he was locked in front, the truck got squirrelly, something that robs time when you're competing.

Skinny tires in front are common on mud trucks because they cut right through the mud-running the taller tires in front keeps the front end going faster than the rear, which prevents vehicles from turning sideways in the bog.

Many mud-racing classes require the stock transfer case, but others allow a chaindrive, which eliminates a lot of weight. They just put a sprocket right on the back of their transmission to turn another shaft to the front axle. Bamford's open transfer case is just a set of gears with an open chain on it, which allows him to keep an eye on it in case something goes wrong.

To make sure his steering could handle the bigger tires, Farmer pulled the steering box from a Ford 550, which got him a durable, strong unit and eliminated the hydraulic steering from his '77 Ford. Early has plans to take off the power steering and put on manual since it's lightweight and because the pump robs power from the engine. Manual is also considered better for mud-bog racing because keeping belts on is nearly impossible when you're spinning so many rpm. Something else to consider is that many builders of lightweight mud racers add rack-and-pinion from a Pinto, but it takes a lot of customizing to make it fit.

And now, the $64,000 question: How do you clean your rig after a mud bath? There's always parking it in the river or tossing a sprinkler beneath it. Of course, there's also always many quarters and a coin-op. Most competitions have a high-pressure hose for you to use.

Tires And Wheels
If you walked through the pit at a mud race, you'd be amazed at the rubber combinations. So what works? Who knows! But for these guys, Early runs 38.5x11 Swamper Boggers in front and 16x35x15s in the rear. The 35s sport 6-inch-wide wheels, while the 38s have 10-inchers, which he says keep the back tires running in the same rut as the front. His air pressure of choice? About 2 psi at the rear and 5-10 psi in the front. Gallegos has 38.5-inch Swamper TSLs all around and uses stock rims, but has found that tall, skinny tires bite better with more air pressure, so he runs them at 15-25 psi, depending on the bog conditions.

Bamford prefers a wide tire because he feels he can get on top of the mud. His suggestion is that if you have a light vehicle, go with the wider tire; if it's heavier, go with narrow meats. He thinks the Swampers are best for mud, and when it's really wet, he runs 3 psi at all four corners. When it's harder, he pumps them up to about 5 psi.

Some drivers suggest having guards around the driveshafts so that the shafts will stay in position and not smack the transmission or transfer case if something breaks.

Farmer has two sets of tires. One is 40-inch Ground Hawgs on 12-inch-wide wheels, and the spare set is 9.75x16.5s on regular modular wheels. He has found the Hawgs far superior to the Swampers, since they have directional, open lugs and last a whole lot longer.

To keep his air cleaner water- and mud-free, Farmer made spacers to raise the cleaner and then put a piece of aluminum 180 degrees around it to block out the elements; Gallegos put a foam-type sock over his filter.

You can also add silicone around the bottom of the distributor cap to keep out water, but most of the drivers agree that a good set of spark plug wires, with a dab of silicone before installation, will do the trick. Bamford bought a bottle of Mud Off from a performance shop-he sprays it behind the wheelwells and up under the hood, and the mud just hoses right off.

How To Really Build For Mud
To figure out what you should do to your truck if you want to compete, check out the following class breakdowns for the Petersen U.S. Truck Fests and the 4-Wheel & Off-Road 4xFun Fests so you can build right for your interests. For more information, call PACE Motor Sports at 630/963-4810.

Class A
•Four- to six-cylinder engines
•Any size DOT-approved tire
•Factory-style suspension; lift kits allowed
•Pump gas only
•Naturally aspirated with single carburetor or factory fuel injection
•Working head- and taillights
•Full-bodied vehicles

Class B
•Eight-cylinder engine
•35-inch and under, DOT-approved tires
•Factory-style suspension; lift kits allowed
•Pump gas only
•Naturally aspirated with single carburetor or factory fuel injection
•Working head- and taillights
•Full-bodied vehicles

Class C
•Eight-cylinder engine
•36-inch and taller, dot-approved tires
•Factory-style suspension; lift kits allowed
•Pump gas only
•Naturally aspirated with single carburetor or factory fuel injection
•Working head- and taillights
•Full-bodied vehicles

Class D
•Eight-cylinder engine
•Any size DOT-approved tires up to and including 44 inches
•Four-link suspensions allowed
•Pump gas only
•Naturally aspirated with single or dual carburetors or factory fuel injection
•Open headers allowed
•Full-bodied vehicles

Class E
•Open class
•Any size engine
•Any size tire up to 44 inches; cut tires allowed
•Four-link suspension allowed
•Pump gas or alcohol allowed
•Blowers allowed
•Nitrous allowed
•Fire extinguisher required
•Full-bodied vehicles

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