What is a Lightweight Crossmember?

When Weight Matters—Try a G Force Lightweight Crossmember

Before you can fully appreciate a lightweight crossmember, you should understand the purpose of a  crossmember, which starts with knowing a little about a transmission swap.

A Brief Explanation of a Transmission Swap

Essentially, a transmission swap entails replacing the OEM transmission with a different one. Often the preferred transmission was not an option for the vehicle when it was manufactured. Typically, the term swap refers to an automatic to a manual transmission conversion. But swap also can refer to any change for performance advantages, including automatic to automatic, manual to manual, manual to automatic, or automatic to manual. Each combination is valid, and each has its benefits and challenges.

What are the reasons for a swap?

The reasons for a swap are as varied as the people that undertake them. However, some of the most popular goals include—

• Eliminating recognized OEM vulnerabilities
• Increasing fuel efficiency
• Enhancing performance
• Improving handling in heavy load situations
• Getting a vehicle running again
• Completing an engine swap

What a Lightweight Crossmember Does

A crossmember is a steel-reinforced bar that bolts across the width of the vehicle supporting the transmission and is essential to body panel alignment and the proper handling of the car. The crossmember must resist twisting and deflection and be durable enough to withstand the rigors of the road or racetrack.

Because of these demands, a crossmember is heavy, often weighing more than 30 pounds. For a lot of applications, the weight of the crossmember doesn't matter. However, for some, even a few pounds make a difference because weight impacts performance. For example, a lower curb weight lessens braking time while allowing for faster acceleration and better handling. All of which are important, particularly to racers. Learn more about Why Weight Matters in our blog.

G Force Lightweight Crossmembers

The G Force crossmember line has long been established as reliable, durable, and strong. Our engineers chose four of our top-selling crossmembers. They redesigned them to maintain the characteristics our customers have come to expect while making them lighter weight to provide the improvements in braking time, acceleration, and handling the owners need.

Proven Strength

Even though we re-engineered these popular crossmembers to weigh up to 10 pounds less, they meet the same stringent standards applied to our legacy products. Additionally, the lighter weight makes them a practical choice for a broader range of projects.

Next Generation Lightweight Crossmembers Independently Tested

Our next generation of crossmembers underwent the same testing as our legacy products. Independently tested for Load vs. Deflection, G Force crossmembers show a negligible difference in the strength of the newer, lightweight crossmember compared to the legacy product.

For example, compared to the original RCG-700, the RCGNG-700 Next Generation Transmission Crossmember, registered only a slight difference during the Load vs. Deflection test.

Difference Too Small For the Human Eye

At the typical load for an installed transmission, 200 lbs., deflection measured 0.089" (up), 0.111" (down) for the lightweight crossmember compared to 0.075" (up), 0.096" (down) for the Legacy part (see graph below). Similarly, tests of other lightweight crossmembers showed comparable results.

Why Choose a G Force Lightweight Crossmember?

There are many reasons why G Force lightweight crossmembers stand out.

1. All G Force crossmembers are built for an exact fit to the year, make, model, and transmission of your vehicle, including our lightweight versions. Not only is fitment no longer an issue but installing our bolt-to-frame crossmember is more straightforward than other options. Installation does not require adapters, cutting, or welding. And because no adapter is needed, our crossmembers cost less.
2. All crossmembers from G Force have our patented double-hump, dual exhaust design, which allows for extra clearance for the exhaust. Most modified vehicles require larger exhaust pipes than those that come standard with the car, and our unique design leaves plenty of room for their larger diameter.
3. When weight matters, our lightweight crossmembers are 1 to 1.5 pounds lighter than others currently found in the automotive parts aftermarket.
4. Each crossmember is shipped with mounting hardware and installation instructions.
5. A G Force lightweight or legacy crossmember is proudly made in the USA.
6. We offer five-star customer service backed by decades of industry experience.

Recently, Mike Montanari of Fast Monty’s Garage reviewed the G Force RCAE lightweight crossmember (RCAE-NG-BLK). Check out his video review and see what an independent expert had to say about his experience installing it as part of his Pontiac rebuild.

Lightweight Crossmember – The Details

Popular years and body types for our Next Generation Lightweight Crossmember line—

• 1964 – 1967 and 1968 – 1972 A Body – RCAE-NG-BLK, RCAE-NG-BLK-6L80, RCAE-NG-BLK-8L90, RCAE-NG-BLK-T56
• 1984 – 1988, 1978 – 1988, and 1978 – 1983 G Body – RCG-350NG-BLK, RCG-400NG-BLK, RCG-400KNG-BLK,  RCG-400NG-BLK-8L90, RCG-8L90NGK,  RCG-700NG-BLK

They feature—

• Scratch, scrape, rust, and chip resistance due to the durable black-satin and powder-coating finish.
• Large diameter header and exhaust pipe fitment because of the patented double-hump, dual-exhaust design.
• Boxed steel tubing construction with high-strength, robotic welds that withstand the most severe abuse.
• Direct factory replacement that requires no drilling cutting, or welding.
• Installation available with almost any transmission you want into popular GM and Ford vehicles. When needed, our crossmembers are bundled with a transmission mount to ensure a proper fit.

Specific information about Make, Model, Year, Transmission, and more is provided on each product page. Also, you may review our complete guide to Finding the Right Crossmember for even more details.

Numerous engine and transmission combinations will work in GM and Ford vehicles. It is essential that you get the correct crossmember and mount for your application.

Make Your GM or Ford Vehicle Perform Better Than Brand New

As previously mentioned, G Force crossmembers accommodate large-diameter dual exhaust systems. Here is an example. The photo to the left reveals the 1/2" steel plate of the twin exhaust humps, which is 6-7" wide, allowing any size exhaust pipes to be installed effortlessly.

Also, ground clearance issues from the exhaust hanging too low is no longer a worry. All G Force crossmembers sit
higher than stock and closer to the floor
to give you extra space for hanging
your exhaust higher.

Side pipes or lake pipes are not needed, and neither is installing an expensive, custom-made exhaust—you can use either stock-size exhaust or larger exhaust pipes.

As a bonus, each G Force crossmember is built super tough with a heavy-duty boxed steel tubing that can handle any amount of frame-twisting horsepower and torque you can throw at it from your Big-Blocks, Blowers, Twin-Turbos, and Super-Chargers.

Now that we have shown you what makes our crossmembers stronger and have more exhaust clearance let's talk about frame differences.

Convertibles, El Caminos, and High-Performance Models like GS and GTO

Because there is no steel roof to help support the vehicle's chassis in a convertible, the car frame must be very strong, which is why boxed frames are used. In fact, both El Caminos & Convertibles use Boxed Frames to give the vehicle that needed strength. The boxed frame in El Camino models also use a convertibles crossmember.

Place the crossmember between the boxed frame rails on small frame ledges when installing it. Using the ledge means the crossmembers must be shorter to fit between the Convertibles and El Caminos frame. In other words, the width needs to be

shorter because it attaches to the inside of the boxed frame rails on frame ledges for convertibles.

The Boxed Frame shown here is for GM A-Body Convertibles & El Caminos from '64 -'67  and is an example of boxed frame rails with mounting plates welded onto the inside, which creates a mounting ledge for the Transmission Crossmember.

The end flange sits on top of the frame rail ledge for installation. Popular GM early A-Body Platforms that use this configuration include: Malibu, Chevelle,El Camino,Le Mans, Pontiac GTO, Tempest, Custom, Buick Gran Sport, Custom, Skylark, Special, GS, Deluxe, Oldsmobile F85, Cutlass, Cutlass,  Supreme, 442, Hurst Olds, and other 1964-1967 A-body models.

Hardtops, like Sedans, Coupes, Fastbacks, and other early A-Body platforms all used Channel Frames. Only El Caminos and Convertibles used Boxed Frames. (See Comparison below)

Shown below are some early-style GM A Body Channel Frames.

       

Shared Dimensions

Since different transmissions often share certain fitment dimensions, they can also share the same transmission crossmembers. G Force put these transmissions into eight groups as an organizational tool. The transmissions in each group have the same measurement from the front of the bellhousing to the transmission mount location. A complete Transmission Group list is available on the Crossmember Transmission Groups page. The most popular transmissions are listed below.

Most Popular Transmissions by Group

• GM Transmission Group – 1 = TH350, Muncie, Powerglide, BW T10, Saginaw, BW Super T10, TH200, and TH250
• GM Transmission Group – 2 = 700R4, 4L60, 4L60E, 4L75E, Tremec TKO-500 and TKO-600
• GM Transmission Group – 3 = 2004R and TH400 (Short Tail-Shaft Only)  
• GM Transmission Group – 4 = 4L80E, 4L85E
• GM Transmission Group – 5 = 6L80E, Tremec T56, Magnum T56, XL T56, TR6060, and Richmond 6-Speed
• GM Transmission Group – 6 = 6L80E (Slip Yoke), 6L90E (Slip Yoke)
• GM Transmission Group – 7 = 8L90E (Slip Yoke)
• GM Transmission Group – 8 = 700R4 (Tailshaft Mount Trans Mount), 4L60E (Tailshaft Mount Trans Mount)

GM Transmission Information

Automatics vs. Manuals: It seems the Automatics have won the argument over which transmission is preferred in America. In 1995, over 70% of cars on the road were automatics, which left 30%, or almost a third, with manual transmissions. Then a significant decline in popularity began and by 2013, only 4% of all cars sold in the US came off the assembly line with a manual transmission. That is quite a change in only 18 years! Interestingly, in Japan and Europe, 80% of all cars still have a manual transmission.

Automatics with Better Fuel Economy

Developed in 1982 to replace the TH350 transmission, the 700R4 is a four-speed automatic. The purpose of the new design was to create an automatic transmission that got better fuel economy. In 1982, GM primarily used the 700R4 in rear-wheel drive vehicles like the Suburban, Blazer, Camaro, Corvette, Impala, and trucks. Then, in 1990 GM renamed the Turbo HydraMatic 700R4 to the 4L60. An electronically shifted version of the 4L60, the 4L60E, has the same case on the outside and identical internal measurements.

The 700R4 and 4L60E are both progressions of the 3-Speed transmission that superseded the iconic GM TH350. The 4L60E is 1-¾" longer than the Metric 200— 30" versus 28-¼". Therefore, performance enthusiasts should plan on getting a new shortened driveshaft when swapping out these GM transmissions. In addition, both 4L60E and 700R4 are very similar in design, so the shift linkage is interchangeable with most applications.

The TH350, TH250, and TH200 are all 3-Speed automatic transmissions that have oil pans shaped the same. However, stamped on the bottom of the TH200 pan are the words: HYDRA-MATIC DIV. / METRIC.

Popular GM Automatic Transmission Pan Patterns and Ratios

Our Most Popular Crossmembers

In addition to our lightweight crossmembers, here are a few of the most popular crossmembers in our line.

RCG-350, RCG-400, RCG-400K, RCG-700, RCAE, RCAE-4, RCF1-700, RCF1-400, RCMFB, RCM1L

Let G Force help you build your vehicle your way! Whether you have a daily driver, weekend cruiser, show car, collector car, street/strip car, vintage muscle car, or professional racecar, G Force has a crossmember that's right for your project. Our Crossmember product line lets you install the automatic or manual transmission you want into your truck or car.   

Questions?

Live Chat or give us a call at 330-753-5300