Ol’ Cotton: Tremec Swap Parts List

We’re beyond ready to row gears in our RCSB modern muscle truck named Ol’ Cotton, but we’re going to need more than just the transmission from Tremec. There are kits now available from companies like Silver Sport Transmission and American Powertrain that give you the Tremec Magnum and all the parts you need to swap it into your two-wheel-drive 99-06 half-ton GM truck. But, because Ol’ Cotton started life with a manual transmission, we opted to piece our swap together, and we’re here to help you with a Tremec swap parts list.

The Bulletproof 6-speed

Tremec offers different variants of their Magnum 6-speed transmission. The Magnum XL is for those with 2005 and up Mustangs and modern GM cars like the 5th and 6th gen Camaro. The Magnum-F is designed to replace the T56 found in 98-02 F-bodies. The Magnum is the original universal manual 6-speed for swaps and conversions in classic and modern cars, trucks, and any other project you can dream of.

These different variants are also available in different gear ratio sets commonly referred to as close-ratio and wide-ratio. So there is no shortage of choice from Tremec to get us exactly what we need. For Project Ol’ Cotton, Tremec suggested the original Magnum due to the uniqueness of the swap and platform, and we agreed. We opted for the close-ratio Tremec Magnum, which Tremec said they usually wouldn’t suggest for a heavier pickup truck. The wide-ratio gear set is great for heavier, lower-powered builds or those looking for an easy-to-drive gear spacing and stellar overdrive ratios (see chart below). But once they heard what the purpose of our project is, its curb weight, and power goals, Tremec said that the close-ratio would work great.

The Clamping Force

When it comes to the clutch, you have to pick a clutch that will not only fit the application, but also work with the power level. The 5.7-liter LS under the hood of Ol’ Cotton makes roughly 450 lb-ft of torque, which means a good quality OEM replacement single disk clutch will work.

The go-to for this would be the LS7 clutch kit you can get from several online suppliers. But, we happened to snag a great deal on the older, and now discontinued, LS6 clutch kit that came in the C5 Z06s. Ours came directly from Luk and came with flywheel bolts, pressure plate bolts, and a pilot bearing. This will work just fine for anything at our power level or lower, so onto our swap parts list it went. But if we ever plan to make more power, a twin-disc clutch from either McLeod or Monster would be a necessary upgrade.

The Bellhousing

For all intents and purposes, we will be picking a lot of parts for this Tremec swap parts list that are also the proper fitment for the 98-02 F-body Camaro and Firebird that came with the LS1 and T56. This is the benefit of Tremec designing the GM versions of their Magnum transmissions after this application.

This means we will need a bellhousing that is dimensionally the same as the F-body application. You can get bellhousings from different brands that are cast aluminum like OEM or fabricated out of steel. The steel versions are sometimes called a scatter shield, because they can be SFI certified to protect you from a clutch coming apart at the dragstrip. But we choose the cheaper and lighter aluminum bellhousing that will be able to handle our current and future power goals (Tremec: 1386-212-005 or GM: 12453263).

Don’t forget to add the bolts to your swap parts list! It’s the little stuff, like hardware, that are easy to overlook. You will need eight bolts to mount the bellhousing to the engine and eight more to mount the transmission to the bellhousing. All sixteen of these bolts measure M10x1.5×40 (GM: 11515768).

The Hydraulics

A Tremec Magnum swap can be pieced together a lot like Legos, so it’s very important to make sure everything matches each other. There are several different hydraulic slave cylinders that GM made for different applications. A quick order placed online with Tick Performance got us a genuine GM F-body slave cylinder (GM: 24264182) and one of their optional speed-bleeders to make bleeding the clutch for the swap, and future maintenance, a breeze.

We understand that the swap parts list can get pricey going with genuine GM parts when the local parts store or online stores have cheaper brands, but we aren’t willing to risk cheap hydraulics; pulling the trans to change the salve can be a real pain and we don’t want to do it more than we have to.

The Third Pedal

If your truck came with an automatic transmission, you have different options to mount a third pedal and clutch master cylinder to the firewall. You can’t adapt the pedal and clutch master cylinder from an F-body or C5 Corvette to these trucks. Silver Sport Transmission and American Powertrain offer solutions to make this easier for those looking to swap. Or, you can do what we did and utilize the stock GM parts.

This should be no surprise to you, as Ol’ Cotton came from the factory with a third pedal and a clutch master cylinder to actuate the clutch. But what is a surprise to most is that the stock clutch master cylinder and pedal ratio gives us exactly what we need to properly disengage the clutch when shifting.

To mate the F-body slave cylinder to the GM truck master cylinder, you will have to swap the braided lines. This isn’t difficult, and we will cover it in the next articles.

The Shifty One

The Tremec Magnum transmission comes with a good shifter base; it’s hard to miss with its bright red paint. But it doesn’t come with a lever or knob, which changes with application and style, so it’s up to the owner to add it to their swap parts list.

The shifter on the Magnum sits further back than the NV3500 shifter and uses the traditional two-bolt lever attachment instead of the threaded style on the stock lever. We knew the lever would need to be taller than what you usually find in a Camaro, muscle car, or Corvette, but we also didn’t want the super tall levers that look more at home in a semi truck.

We settled on a Hurst Competition lever that is a medium height and is a flat, curved, and chrome design you would find in classics and muscle cars (Hurst: 5387236). To keep with the theme, we topped it with a chrome shift knob from a 1969 floor-shift Camaro (OER: 9793565). We figured you can’t build a modern muscle truck without at least a little classic American muscle car touch, right?

You will also need a shift boot along with the swap, but we decided to hold off for now, since we didn’t know which shifter position we were going to end up using.

The Crossmember

Just like the clutch master and pedal, the stock transmission crossmember in the manual transmission trucks works with T56 and Tremec Magnum swaps. The manual transmission crossmembers are different than the auto crossmembers, so it’s either a trip to your local Pick-N-Pull to find one out of one of these rare trucks, or fabricate one yourself using your auto transmission crossmember as a base.

Other than a new transmission mount (Energy Suspension: 3.1108G), we made zero modifications to the factory crossmember. If you are looking for a bolt-in option that doesn’t involving hunting for a rare stock one in the junkyards, reach out to American Powertrain for a possible solution.

The Driveshaft

The stock driveshaft in the GMT800 trucks is made to just handle work duty below 100 mph. It can’t handle high horsepower and high speed, and are too short to use with a Tremec Magnum swap by over six inches. So plan to add a custom-length driveshaft to your Tremec parts swap list, but you won’t be able to order it until the transmission is mounted in the truck so you can measure exactly the length you need.

The Tremec Swap Part List: Complete

What’s next? It’s time to finally get the clunky tractor-like 5-speed out of our project truck for the very last time (and maybe into the junkayrd… for good measure) Click on the next article to follow along!

TABLE OF CONTENTS:

Episode 1: Our Modern Muscle Truck Project

Episode 2: Tremec Swap Parts List (you’re currently on this page)

Episode 3: COMING SOON!

Episode 4: COMING SOON!

Episode 5: COMING SOON!

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