#Hot Rod Network | itsworn (2024)

Cheap turbo + junkyard LS = big power. The formula has been proven multiple times. However, significant power won’t last long with a junkyard transmission. Thanks to the aftermarket, there are several cheap alternatives to an all-out drag transmission. We rebuilt a junkyard 4L80E to handle 1,000 hp—for $1,000.

The plan was simple: Take a 2003 4L80E and rebuild it, upgrading the common failure points. Parts include a McLeod performance rebuild master kit (PN# 88075K, $618.75); Bowler Transmissions 300M hardened input shaft (PN# TCS HP-4L80E-35, $310); and Sonnax Smart-Tech overrun clutch valve kit (PN# 34200-40K, $118.53). We spent $1,047.28, not including transmission and labor.

OEM Rating

Traditional automatic transmissions, such as the TH350, TH400, and 700R4, generally max out at less than 400 lb-ft. GM strengthened them through their respective generations. In 1982, the TH350 gained a Fourth gear and became the 700R4. In 1990, it became the 4L60E, which incorporated updated technology that improved strength. The same applied to the TH400 which, with the addition of an Overdrive gear, became the 4L80E in 1991. The 4L80E evolved to include more upgrades, including a stronger Overdrive sprag and hardened input shaft around 1997. The even stronger 4L85E, introduced in 2002, is rated for vehicles as heavy as 16,500 pounds.

Today, if you’re building an LS drivetrain with an OEM computer or trans controller, it’s likely backed by a 4L60E or 4L80E. The 4L60E is far more abundant in the junkyard and therefore cheaper. A local transmission shop will rebuild a 4L60E for around $900 to $1,200 and a 4L80E for $1,300 to $1,800, with used units going for about $400 and $600 to $1,000, respectively.

Many forums will tell you the numbers in the name refer to torque rating, but that’s only partially true. The “6” and “8” refer to the torque capacity based on Gross Vehicle Weight (GVW), so the 4L60E is rated to handle a 6,000-pound GVW, and the 4L80E 8,000 pounds. That’ll help when finding the right donor vehicle.

The 4L60E is rated to hold 360 lb-ft, and the 4L80E is good for 440 lb-ft engine torque and up to 885 lb-ft of output torque. Bowler Transmissions believes that an accurate torque rating of a 4L80E’s internals, on a prepped track with grip, is around 550 lb-ft, but that’s with a Sonnax Smart-Tech overrun clutch valve kit. Companies that manufacture drivetrain components (such as transmissions, rear-end housings, and lockers) are often dodgy about setting firm torque-capacity ratings, as many factors contribute to breakage. “We pride ourselves on providing ratings based on a tire hooking up. That’s the biggest determination,” said Mark Bowler, owner of Bowler Transmissions. “An 800hp car with 8-inch-wide street tires, that’s never going to break anything.”

The Components

The McLeod performance kit is suitable for 1,000 lb-ft, and McLeod claims this is the only kit of its kind, a complete master kit with name-brand gaskets and performance discs. The package includes OEM-quality National Oil seals, Farpak gaskets, Teflon-coated rings that produce a tighter seal, and a brass filter that makes for better flow and filtration.

We opted for the upgraded Kolene steel clutch discs for their added performance; it retails for $618.75. The same kit with standard steel replacement discs retails for $493.75.

Kolene is a treatment applied to the steel clutch packs that increases holding capacity as much as 10 percent. “But more importantly, it helps prevent warping in high-stress and high-heat applications,” said Brian Gwin, of McLeod Racing Domestic Sales.

Both kits include Stage 1 Raybestos friction pads, which McLeod says have greater holding capacity, improved durability, and less wear than other red performance plates on the market. “The higher coefficient of friction is ideal for high-output engines,” said Gwin. The plates are simple drop-ins, and they’re the most significant performance improvement in the kit. The clutches will produce a smoother engagement, cut down on operating temperatures, and enhance shift feel.

The Bowler Transmissions 300M hardened shaft is good for 1,000 ft-lb and is included in all of Bowler’s performance transmissions (Stage 2 and up). Finally, the Sonnax Smart-Tech overrun clutch valve kit engages the overrun clutch at all times except in Overdrive (4th gear), reducing the chance of an Overdrive-sprag failure.

Our Build

Our 4L80E came from a friend who couldn’t guarantee its condition. We picked it up for less than core charge at $200. We visited local hot rod builder John Young of Winston-Salem, North Carolina, with our parts in hand.

The McLeod kit includes an intermediate-reverse band, but not a low-reverse band. Whether or not this is a common replacement item is debatable. Ours was peeling, a possible result from accidently washing it. We sourced a remanufactured band from a local transmission shop for $35.

Monster Transmissions also offers a rebuild kit that consists of more hard parts, such as solenoids, a shift improver kit, a manifold switch, a harness, and sprags. It retails for around $880 to $1,050, depending on the size of kit and year range.

Today, there are tons of options in the aftermarket to bump up power ratings on drivetrain components. Here’s the quick rundown of our rebuild.

Brand Item Part Number Price Sonnax Smart-Tech Overrun Clutch Valve Kit PN# 34200-40K Price: $118.53 McLeod Performance Automatic Transmission Rebuild Kit PN# 88075K Price: $618.75 Bowler Transmissions 300M Hardened Input Shaft PN# TCS HP-4L80E-35 Price: $310 Total $1047.28

The 4L80E came from a 2001 Chevrolet 2500-series van. The yellow metal tag states the model year and chassis. Before arriving at John Young’s garage, we disassembled the main components, leaving planetary gears intact, and used a friend’s spray-wash cabinet to clean the parts.

We started by removing the pan, filter, and valve body. It’s a relatively simple process, but it’s extremely important to keep track of all the little pieces. You’ll need one T40 torx bit and a skinny 12-point 10 mm. The center support bolt underneath the valve body, endures some abuse as it keeps the center support from spinning. The McLeod kit features a new replacement bolt.

Our kit included the Stage-1 Raybestos Performance friction plates with the upgraded Kolene steel plates. You don’t always need to replace steel clutch plates in a standard rebuild, but our new Kolene plates resist wear and fatigue between 200 to 500 percent better than stock. They have increased lubrication and feature improved heat retention, too.

Our original clutches (pictured right) are in such good condition that we may reuse them in a future stock rebuild. Still, the improvements from our new Raybestos plates are obvious. The OEM frictions friction plates are smooth to increase surface area, but that doesn’t do much for fluid travel and heat dissipation in a performance application. Our friction plates are grooved and textured for those reasons. The material and design compensate for that lack of surface area by providing a higher coefficient of friction.

John disassembled most everything but left the planetary gears intact. We checked for side play. Luckily, all were tight and didn’t require rebuilding. This is a four-pinion set, and a possible upgrade is a GM five-pinion, which spreads the torque load over a greater area. Bowler Transmissions upgrades to five-pinion (featured in a stock 4L85E) in their performance transmissions.

Steel clutch plates beat against the edges of the Fourth gear clutch housing/basket and cause slight ridges. We knocked down the high spots lightly with a file.

We coated all of our clutches in Redline Oil ATF before assembly. In previous transmission builds, we’ve assembled them dry. Which is the correct procedure? We asked Mark Bowler. “You ask ten transmission builders how to do something, you’ll get ten answers,” he says. Despite this, Bowler suggested you find a trustworthy transmission shop and research what questions to ask before arriving.

Here are some of the weak points in a standard 4L80E. The OEM input shaft is a commonly talked-about failure, as it produces carnage when it breaks. Based on Bowler’s 4L80E testing, the Overdrive sprag (the blue and black plastic ring, pictured right) is good up to 550 lb-ft and the stock input shaft, 600 lb-ft. The standard four-gear planetary is often upgraded to the five-gear unit used on the 4L85E.

The changes in diameter on the OEM shaft create weak points. Bowler’s 300M hardened input shaft features new ridges to spread the load more evenly. These are good for 1,000 lb-ft and are included in all of Bowler’s performance transmissions.

After carefully cleaning off the gasket material on the metal gasket, we took a file and lightly knocked down any ridges or marks. It’s important not to bend this gasket.

The valves in the valve body move under pressure. We did a simple visual check of the valves’ movements with an air gun.

The right way to check the valves’ movements is with a vacuum test, similar to a leak-down test on an engine. Pictured here is a vacuum tester at Bowler Transmissions, where they build four levels of transmissions varying from a stock 550 lb-ft rating to 1,000 lb-ft. Bowler believes the most overlooked way to improve transmission life is a well-serviced valve body. They typically ream and resize all the valves.

GM updated the Overdrive sprag in 1997, pictured left. Bowler upgrades all of their 4L80Es with the early, 1991—1995 sprag, pictured right.

We finished the build with a new brass filter, designed to clean better than a stock replacement. We’ll have to wait to see how it shifts, feels, and launches, but we have the option to go back and install a shift kit without removing the transmission.

Here is is the Sonnax Smart-Tech overrun clutch valve kit. It’s a hydraulic solution to a mechanical problem. The valve manifold (shown), reroutes hydraulic fluid pressure, keeping the overrun clutch applied at all times except in Fourth gear, reinforcing the roller clutch to support heavy loads adequately. You don’t have to remove the transmission to install it.

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