I have decided to put together a drivetrain that can withstand 700 hp, be easy to drive, and be reliable. This was a virtually impossible (or very expensive) task 15 years ago but with the current status of the aftermarket industry, it is now very achievable. The easiest way to get large horsepower numbers is through the use of a large-displacement engine. I am starting with the old-school Chevrolet 454 big-block.
The Tremec T-56 Magnum is rated at 700 ft-lbs of torque at the input shaft and is truly a brute of a gearbox. This transmission is an aftermarket version of the Tremec TR-6060 unit that is used in many of today’s most hard-hitting sports cars, meaning that it is not only strong but that it will easily deliver years of reliable performance and super smooth shift performance. This level of refinement cannot be found in any other manual transmission available in the aftermarket, making it a great upgrade, rather than reworking 1960s Muncie technology.
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There are two ratio sets available and I chose the arrangement with the following ratios (first to sixth): 2.66, 1.78, 1.30, 1.0, 0.80, and 0.63:1 rather than a 2.97 first with a .74/.50 double overdrive. This offers the best of all worlds with a reasonably steep first gear and two overdrives that help to reduce the big-block’s fuel consumption, without going too tall on the overdrive. If the overdrive is too tall, then the engine could lug, which means that the engine RPM is too low at highway or cruising speeds.
The Magnum transmission coupled to a 4.11:1 axle ratio with 28-inch-tall tires makes a very streetable combination, offering economy, strength, and durability. For this particular custom car build, a 4.11:1 works best for this combination. Many just assume a 4.11 is what they need, but that is not always the case. The section “Axle Ratio Selection” (page 142) includes information to help you select the correct gear ratio for your application. There are many cars with 4.11s running at much higher RPM just screaming at highway speeds. This is not what you necessarily want for a street car.
The Magnum’s claim to fame is offering all of the quality and refinement of a modern original-equipment transmission in a package that is ideally suited for muscle car and hot rod builds.
The T-56 Magnum is basically a TR-6060 transmission in an aftermarket wrapper. Instead of using an integral bellhousing, it uses a T-56-style mid-plate that allows for adaptation to a variety of engines because the aftermarket offers a wide selection of bellhousings. Additionally, while minor sheet-metal modifications to the floor tunnel may be required due to its size, multiple shift locations and dual speedometer pickups allow for many different configurations.
The TR-6060 is found on the Dodge Challenger SRT-8, Viper SRT-10, C6 Corvette, Camaro SS and ZL1, Cadillac CTS-v, and Mustang Shelby GT500. All of these applications use the same basic transmission with minor variations. The transmission can easily support sustained input torque of 700 ft-lbs and shifts near the 8,000-rpm range.
Tremec has a network of “Elite Distributors” that offer many swap support parts such as cables, adaptors, clutches, release components, and transmission crossmembers for most popular applications.
The flexibility features of the Magnum are lessons learned and applied from the TKO 5-speed transmissions that most of us are familiar with. The main differences between the TKO and the Magnum are that the Magnum is a modern “endloader” style of transmission and the older TKO is a “Toploader” style. The Magnum also features a great deal more refinement, strength, and high-RPM shifting capabilities. The Magnum overdrive gears, specifically fi fth and sixth gears, are completely interchangeable. So it can be configured with the 2.97:1 first gears for low-end grunt and could use either the .74/.50 or .80/.63 double-overdrive gear ratios. However, care needs to be taken with an axle ratio that is too high numerically as the propshaft speed may possibly be too fast for a standard propshaft.
Spring Pocket Kit Installation
The entire reason for putting this powertrain together is to match the needs of a well-built Ford 9-inch axle. It does not make sense to have a bulletproof axle with no real power going through it. Let’s face it: You purchased this book and probably a 9-inch axle because the stock unit is just too weak for all the horsepower your new engine produces. Therefore, it doesn’t make sense to put this all together and try to put the power to the pavement through skinny little tires.
I wanted to tuck in some 13-inch-wide tires and still have the car 2 inches lower than stock all the way around. The only way to achieve that is by installing a spring pocket kit.
Step-1: Inspect Components
Here are the pieces that come in the Williams Classic Chassis Works spring pocket kit. The plan is to move the leaf springs, which are mounted outside the frame rails, into pockets that move them under the frame rails while still maintaining the correct spring mounting heights. The pockets and reinforcement brackets are a little long and require some trimming to fi t perfectly. This universal kit works with both one- and two-piece frames, and that is why some minor trimming is required.
Step-2: Remove Springs and Axle
Remove the old springs and axle (see Chapter 2 for more details). Often the fasteners are rusty, which makes this diffi cult. The original leaf spring sits next to an aftermarket 2-inch-lowered spring. Notice the rear eyelet (at the right) is reversed to achieve the required drop. Also, on this original spring (bottom) the sharp bend of about 4 inches from either end was handled with a torch and basically ruined the springs. You can see that even the center spring is cracked in half and separating from the pack. The old springs are junk at this stage.
Step-3: Mark Perch Alignment (Precision Measurement)
Take measurements and mark where the stock leaf spring perches align with the frame rail for the installation of the spring pocket kit. You can use a homemade plumb bob to measure and mark the location of the rear spring hanger pivot. The marks and measurements serve as a reference point for notching the frame rail later.
This is one of the front spring perches, which needs to be removed from the frame. I have marked the spot welds and arc welds with white chalk, so you can see the welds that need to be drilled and ground off. This is a two-piece frame and the body has been taken off the frame; the frame has been flipped upside down.
Step-4: Remove Perch Rivets
The rear perch was riveted to the side of the frame and a weld was placed along the top. (Don’t forget that the frame is upside down in this photo.) I have marked the two rivets with white chalk (left). You just grind the heads off with an angle grinder and punch the rivets through (right). You could also drill the rivets out of the brackets.
If you have a one-piece frame, you need to temporarily clamp the front spring pocket next to the frame to make some marks to guide the cutting for fitting the pocket in place.
Step-5: Align Front Perches
You can use a 1/2-inch piece of threaded rod through the entire frame to help align the front perches. Here you see the area that needs to be removed (outlined in yellow). The grind marks are from the welds that you removed from the original front spring bracket. Cut just inside the yellow and slowly open up the hole to get the pocket to fi t perfectly. For reference, on two-piece frames, the rectangular hole needs to be as wide as the bottom of the frame. On one-piece frames, the width of the rectangle is narrow, so be careful not to cut the hole too large.
Step-6: Cut Front Pocket Hole
This hole was cut in the one-piece frame. Do not cut the entire bottom surface of the frame all the way to the side of the frame rail. Leave a small portion of the bottom surface in place. If you find mouse carcasses or old nests, as I did in this car, just vacuum them out.
Step-7: Weld In Front Pockets
A single-piece frame with the front pockets in place is ready for welding. One of the pockets has been welded in place on a two-piece frame. On the two-piece frame, I have added a rear shock crossmember (from Williams Classis Chassis Works). This way the frame has more rigidity and the shock loads go into the frame and not into the floor or the trunk. I recommend that an experienced professional perform this “upside down” welding because falling weld spatter is very dangerous. If you are going to do it, here are a couple of items to keep in mind: Use the same heat settings as if you were welding right side up and keep the amount of wire “stick out” as short as possible (within 3/8 inch). The short stick out transfers more heat to the welder tip, so take your time and let the tip cool. Stitch these pockets in to avoid adding too much heat to any single area.
Step-8: Align Rear Perches
For the rear spring perch, the yellow line on the frame matches your earlier marks from the stock location and your measurements. Clamp the new bracket on the top of the frame (remember, it is upside down) with the center of the hole aligned with the yellow line.
Use the measurements from the instructions (from the rear of the frame rail along the fi ller piece) as a template to mark the area that needs to be cut out of the frame. The vertical lines represent the centerline of the spring perch and the rearward edge, where the slant begins. Start with the spring perch center, then the start of the angled portion, carry that angle to the bottom of the frame, and use the filler piece as a template. I recommend marking the frame about 1/4 inch short so you can slowly fine-tune the notch with an angle grinder for a perfect fit.
Step-9: Cut Rear Pocket Hole
Here is the rough cut-out portion. You just need to finish grinding with an angle grinder and metal prep the notch to get it perfect.
Step-10: Weld In Frame Notch Filler
It is paramount to have clean steel surfaces that are free of any rust, paint, or oil prior to welding. All of these things contaminate the weld and compromise the strength. I suggest practicing welder settings on a scrap piece to avoid any mistakes on the real parts. Use a MIG welder to attach the frame notch filler piece on the bottom of the frame rail. (The length of the notch piece accommodates both styles of frames.) It’s best to alternate the weld pattern from side to side and front to back (called stitching) while allowing time for the steel to cool. This helps to avoid any distortion from the heat. The filler piece still needs to be rimmed and metal finished. Then repeat for the other side. You can also refer to the sketch that comes with the kit instructions for the notch geometry and location of the bracket on top of the frame.
Step-11: Weld In Perch Brackets
You can now solidly weld in the perch brackets. If these brackets are welded in place with the body still on the frame, which is possible, you do not have complete access along the length of the brackets. In that situation, you need to fabricate a little rectangular piece to cap off the angle ends of the brackets to provide more support and structure. The new spring arrangement has the spring shackles straddle the frame rail.
Here is a close-up picture of the bracket on top of the frame and notch below the frame. This is much easier to weld in place with the body off the vehicle but it is still possible with the body on. If the body is left on and you cannot get full welds along the plates, you can add filler plates on the angled surfaces that can be welded across the frame for further support.
Step-12: Weld Traction Bars to Frame
While the frame is still upside down weld the brackets for the traction bars to the frame and fit them inside the front portion of the spring pocket plates. Shown here, the leaf spring is in place and the traction bar is just roughly assembled. (Of course, for the final assembly, the axle is installed.) Note that the traction bar is backward, as the threaded adjustment portion should be on the frame side and not the spring side. Traction bars stop the front portion of the leaf spring from winding up during hard launches. This also limits the pinion rotation upward during launches. It is a common misconception that the pinion should be oriented downward so that during hard accelerations, the axle housing rotates upward and the driveline angles all line up. This may be fine for some leaf spring vehicles but it is more often than not incorrect. The pinion should be oriented to be parallel with the transmission angle at ride height. Ideally you want the working angle across each joint to be in the 1- to 3-degree range with a difference from each of about 1/2 degree. This car is set up with the engine down 4 degrees and the axle is built with the pinion up 3 degrees.
Wheel Tub Installation
The spring pocket kit installation moves the springs underneath the frame rails and allows for wider than factory rear wheels and tires. Typically you can get an 8-inchwide tire in place. The real benefitis when you also mini-tub the car. This allows at least a 13-inch-wide tire; some have even squeezed in a 13½-inch-wide tire without clearance problems. In my opinion, the spring pocket kit goes hand in hand with mini-tubs to get the most space for wide tires.
Many different methods can be used. I review using the old wheel tubs and adding a spacer, but using aftermarket wheel tubs can also achieve this. I prefer the look of the factory tub compared to the sharp corners of aftermarket tubs.
Also, to allow for exhaust clearance, I remove the spare tire well from the trunk and use a gas-tank centering bracket kit. This allows me to run the tailpipes inboard of the frame rails; they exit straight out the back of the car. Note that the sparetire patch panel and gas-tank centering bracket kit came from Williams Classic Chassis Works.
Step-1: Measure Trunk Area
This trunk is in its stock configuration. The wheel tubs are about 46½ inches apart. The spare tire well and jack brackets are still in place and the original factory-applied seam sealer is intact. (I have removed a portion of it just behind the jack mount by the spare tire well.) Cut the wheel tubs at the top of the arch for each tub in a straight line from front to back. Then weld in about a 3-inch-wide steel strip to space the tubs inboard, so the vertical surface of the wheel well matches the frame rail.
Step-2: Spot Weld Steel Support
Remove the trunk lid to allow for room while working and to remove the weight from the hinge supports. There is a steel support that is spot welded to the wheel tubs on both sides. Drill out the spot welds and cut the bracket where it meets the trunk hinge support. Save these brackets and just re-weld them to the same location on the wheel tub after it is moved inboard. Butt weld the top portion to the inboard side of the hinge bracket.
Step-3: Mark Cut Lines
Behind the rear seat there is a support structure for the rear of the car. You need to cut it loose and trim it so you can slide the tub inboard. Make a chalk line as a rough mark of the cuts you need to make. Fold the U-shaped portion at the top up and temporarily out of the way. Once the tub is in its new location, you can bend this fl ap back down and weld it back into place.
Step-4: Cut Out Driver-Side Wheel Tub
Remove the driver-side wheel tub and trunk hinge support. Also remove the seam sealer and mark a line for cutting. (The support behind the back seat has already been trimmed.) You can use a flexible magnetic strip and straight edge to lay out the cut line prior to marking. This cut line needs to be straight so the filler piece is easier to install without gaps to fill. The bulge at the back of the driver-side tub is where it meets the trunk floor. This is for the gas tank filler tube and the reason the marked line has a slight jog in it. (A small, rectanglular filler piece will be added later.) For this side, I cut about 2 inches away from the seam; notice the black line. Once the tub has been removed, trim the underside where the tub meets the trunk floor (this is required or else the flange below the floor interferes with the frame rail) and re-weld the pieces together. This then allows you to slide the tub over and then butt weld it.
Step-4: Cut Out Driver-Side Wheel Tub (Continued)
The driver’s side tub has been removed and some of the surrounding steel has been cleaned for welding. The floor still needs to be trimmed to allow for the new tub to slide in place. After further inspection, I discovered that the inner wheel well had rusted through previously. Instead of cutting and patching the hole, someone pushed in body filler and nothing is supporting it. These areas will be patched correctly with the final prep of the trunk. You can also see the undercoating in the inner fender well area. The undersides of the tubs were similarly covered. I removed this with the help of some carefully applied heat and a copper scraper.
Step-5: Cut Out Passenger-Side Wheel Tub
Perform the same process for the passenger’s side, except you do not need to jog the cut for the filler tube bulge. Here, the tub has been cut out but it is still in place. You also need to cut out the spare tire well and patch it with a panel.
Step-6: Inspect Cuts
The passenger-side inner wheel well and trunk fl oor is shown. The hole at the top of the picture is from the missing wheel tub and the hole just beyond the frame rail is from the spare tire well. You can also see how severe the kink was torched in the stock leaf spring.
Step-7: Remove Back Seat Support
After you remove the spare tire well and both wheel tubs, remove the remainder of the back seat support structure. To gain more working space to get grinders and welders in place, you may want to remove the 40 or so spot welds and the bracing.
Step-8: Inspect Spare Tire Well and Wheel Tub Spacers
This is the roughed-in trunk with the spare tire well block-off plate and the wheel tub spacers in place. There is still a fair amount of metal preparation required before you paint.
Step-9: Prep Frame for Mounting Shocks
On page 123, Step 7, I showed the new rear shock crossmember already welded in place. This was pretty straightforward and the crossmember comes with good directions for the measurements. Now you need to use a hole saw to drill a couple of holes in the frame to allow the tube to fit inside, prep the area for welding, and align the tube correctly.
On the left is an undamaged leaf spring plate with the factory shock stud in place, and on the right is the modified plate. The new rear shocks came with studs for replacement. I modified the stud, which is the stud in the foreground, to have a 1/2-inch-diameter shoulder that fits into the 1/2-inch hole that I drilled in the bracket. I left a .100-inch-thick shoulder to simulate the stock stud. I just press the modified stud in the bracket; plug weld the back side solid, and weld the spacer portion as well. After primer and paint, it will look just like the original.
Written by Joe Palazzolo and Republished with Permission of CarTech Inc