The Gen V LT-series engine uses three specific transmissions from the factory: the 6-speed automatic, the 8-speed automatic, and the Tremec TR6060 6-speed manual. Thankfully, these factory offerings aren’t the only options. Like the LS platform before it, the Gen V LT-series engine uses the standard SBC bolt pattern for the transmission bellhousing, allowing swappers to use just about any GM SBC-based transmission.
Automatic
It might be tempting to stick with the factory automatic transmission for a swap. Under normal circumstances, this would be a good plan. Unfortunately, there are some serious issues with both the 6- and 8-speed transmissions to know about before attempting to use one of these automatic transmissions in your swap. In one word, don’t.
10L80/10L90
This is the newest transmission to be fitted to the Gen V LT-series engine, and it is a collaborative effort between Ford and General Motors. This 10-speed transmission has been used in GM vehicles since 2018, sporting 650 hp worth of power handling in the 10L90 version and 425 in the 10L80. Shifts are incredibly smooth, much better than the beleaguered 8-speed. There are three overdrive gears: 0.854, 0.689, and 0.636. This can be felt when you are doing 80 and punch the throttle to pass a car; you feel it drop a gear, pull hard, and never really feel the upshift, it is that smooth.
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There are many options when it comes to transmissions for LT swaps, but you should know a few things before selecting which one you want.
The newest GM transmission is the 10LXX series, which was codeveloped with Ford. This 10-speed transmission is very smooth when warm but very clunky in cold weather. It is very large, so fitting it under the body of most muscle cars will require heavy modification. (Photo Courtesy General Motors)
The 8LXX series is an 8-speed unit that has massive internal problems, so much so that there is a class-action lawsuit against General Motors over this transmission. Problems with this transmission include hard clunking, erratic shifting, and heavy vibrations between 50 and 75 mph. If you want a new transmission, stick with the 10LXX or 6LXX. (Photo Courtesy General Motors)
The 6LXX is a good transmission with six speeds and a smaller case than the 8LXX and 10LXX units. These are very finicky in their own right. They must be serviced every 50,000 miles, otherwise wear from the torque converter clutch can clog up the pump, which frags the entire transmission around 120,000 to 150,000 miles. It is cheaper to buy a low-mileage used 6LXX than it is to rebuild one, so keep that in mind. (Photo Courtesy General Motors)
One thing that creates a few issues for swappers is that many of the engines available for swaps come out of trucks, and more trucks are 4WD than ever. The transmission for a 4WD truck won’t work for a rear wheel drive (RWD) vehicle, so you may have to source a separate transmission. This is a 6L90 with 4WD transfer case attached. (Photo Courtesy General Motors)
The simplest option that fits in most applications without floor pan mods and bolts to the engine with ease is the classic 4LXX series. This is a 4-speed transmission that uses a transmission controller for tunable upgrades, and did we mention it fits? There are two main types: SBC-based and LS-based. SBC-based 4LXX transmissions have an integral bellhousing (right), while the LS-based units are longer and have a removable bellhousing. Specific flexplates and torque converters are required for each style.
TCI makes this nice billet steel SFI-approved flexplate for the 4LXX series. They are only for the LS-based units.
Under the 1971 Buick GS, the bellhousing for the 4L65 has adequate clearance of the firewall and transmission tunnel. The 4LXX series case is the same as a 700R4, so it fits most GM cars.
On the left is the new LT bellhousing, and the LS bellhousing is on the right. The only difference we found is the additional bolt hole on the bottom left of the LT, which is actually the top left of the transmission.
The crank of the LT engines requires an adapter ring for older automatic transmissions. This one from ICT Billet fits into the crank and provides the correct spacing and diameter for the torque converter hub.
There is a specific LT bellhousing for these transmissions, although the SBC or LS unit still works. Our crate LT1 package came with the LT bellhousing, so we removed the original from the 4L65.
We installed the new bellhousing using the original bolts and torqued them to 48 to 55 ft-lbs.
An often-overlooked spec is knowing which side of the flexplate goes to the engine side. It will be printed or etched into the steel. Do this wrong and it won’t go together.
Always use new bolts for the flexplate because these are one-time-use torque-to-yield (TTY) bolts. If you upgrade to ARP reusable bolts, then no problem. These should have medium-strength threadlocker on them.
The torque process for the factory TTY bolts is 133 in-lbs on the first pass, then 22 ft-lbs on the second pass, and a 45-degree turn on the final pass.
8L90
The Gen V LT engine is controlled by an ECM, and the transmission requires a separate controller. The two units talk to each other to operate both efficiently. The 8-speed 8L90 SuperMatic was a great idea, but the execution was flawed. The transmission performs so poorly that General Motors has been sued via class action over the horrendous operation of the 8-speed transmission. There are aftermarket companies that offer swap components for the 8-speed, but it is not a good idea.
General Motors has issued no less than 15 tech service bulletins (TSBs) on how to fix the inherent issues with the 8L90, but none of them work. Having personally had one of these transmissions in a 2015 GMC Crew Cab Denali, I am keenly aware of these issues. The transmission will buck wildly at low speeds, have heavy double-clunking in reverse to the point of breaking the rear differential, and shudder when cruising. The 8L90 is simply a really bad idea to use in a swap. Not to mention the fact that is a very large transmission. Avoid this unit at all costs.
6L80/6L90
These transmissions are very stout and will perform well under most conditions, although the cases are quite large and do not fit in most passenger cars with a stock transmission tunnel. The 6L90 can handle up to 555 hp in passenger cars. In a truck, the weight reduces handling to 452, torque limits range from 530 to 550 ft-lbs. Both units are fully electronically controlled and can be tuned with programs such as HP Tuners.
The downside to the 6LXX transmissions is the longevity. These transmissions can last 200,000 or more miles, but they have a really bad habit of destroying themselves around 120,000 to 150,000 miles. This is due to a torque converter issue where the clutch in the converter breaks down, sending shrapnel through the transmission, eventually killing the pump and the transmission. This can be mitigated by changing the fluid before the unit hits 100,000 miles and then every 50,000 miles or so.
Older GM Automatics
The 4LXX transmissions that were built for LS-platform engines will bolt directly to an LT-series engine, provided you have the correct flexplate. The LT-series flexplate uses eight bolts instead of six, so they will not swap over. This is crucial because a special LT-to-LS flexplate is needed to make the connection.
Bolting an older SBC-based transmission to an LT engine requires specialized spacers and flexplates because the Gen V LT-series engine’s bellhousing mounting pad is shorter. If simply bolting an old-style converter to an LT engine without a spacer, there will be major problems after only a few miles of driving. The pump seal would be ruined and begin to leak, causing the pump to fail. This is due to the fact that the converter won’t center on the back of the crank because it does not fit.
To make up for the difference, special conversion flexplates are required. Similar to the LS, the flexplate must be spaced out to accommodate the difference in depth. General Motors and many aftermarket companies offer the spacers and longer bolts over the counter. TCI has conversion flexplates for automatic transmissions and kits that include the spacer and longer bolts. You must use a crankshaft spacer, such as the Hughes Performance, TCI, or GM spacer and bolts, or a custom converter must be made with a longer crank hub.
Adapting the non-electronically controlled 700R4 and 200-4R is very difficult on an LT-series engine because there is no way to adapt the throttle valve (TV) cable. The most important component of these two overdrive transmissions is the TV cable. This crucial system tells the transmission when to shift and determines the amount of pressure sent to the clutches. If this cable is off even the slightest amount, the clutches will not fully engage, causing the transmission to burn up and eventually fail.
Adapting the TV cable to the drive-by-wire throttle body on an LT engine is not possible. The only option is to eliminate the TV cable altogether, which requires a constant pressure valve body. The transmission would be manual shift only without any TV cable at all. The TCI transmission constant pressure valve body removes the pressure regulation from the TV system. This valve body keeps the transmission at full-line pressure all the time, ensuring the clutches won’t burn up from slipping. An electronically controlled automatic transmission is the best bet for an LT swap.
The aftermarket also has a vast number of custom-application GM transmissions that work great for LT swaps. One in particular is the TCI 6X 6-speed automatic. This transmission is based on the 4L80E with new guts to provide six forward gears capable of handling 850 hp. These can be configured in several ways and come with a TCI transmission controller. They can even be set up for paddle shift.
Manual
The 6-speed T56 manual is the most popular manual transmission used in LT engine swaps. Formerly offered on the 1998– 2002 F-Body and GTO, the T56 bellhousing, flywheel, and clutch pack are readily available. The T56 transmission fits into most GM muscle cars and requires only minor modifications, if any, to the transmission tunnel.
There are swap kits available to help make the install easier. American Powertrain offers a kit for first-generation Camaro, Firebird, and Nova. The 1968–1974 Nova requires that the transmission tunnel be enlarged. However, the clutch mechanism definitely requires some modifications. There are several ways to get around the clutch mechanism, such as to use an older-style manual clutch or a modern hydraulic clutch.
The most commonly used manual transmission for any swap is the Tremec T56 6-speed. This is a Magnum T56 that had been rebuilt by American Powertrain. The other 6-speed is the TR606, which has an integral bellhousing.
The T56 requires using a hydraulic clutch bearing. This kit is the Hydramax from American Powertrain. It is the simplest version and works like butter.
Now the tricky part. Using a straightedge and a set of calipers, the spacing from the bellhousing flange on the transmission to the end of the release bearing was measured. We did this three times at three different places (3, 9, and 12 o’clock) and averaged the measurements. This is measurement B.
Next, the release bearing is lubricated with some dot3 brake fluid. This keeps things sliding like they need to.
First, the base slide for the release bearing was installed onto the transmission input shaft. The silver post is the locating pin. The longest one is needed for this application.
Then, we slid the bearing over the locating post and the main slide.
We installed the American Powertrain clutch and pressure plate to the flywheel using some new ARP bolts. Don’t forget to use the required clutch alignment tool. Note the gold spacer on the back of the engine block. It is required, so do not forget it.
Using the straightedge and calipers, we took three more measurements at three different positions on the bellhousing to the fingers of the diaphragm. These were averaged as well.
Next, the QuickTime bellhousing was installed to the block. This is an LS bellhousing, it is not LT specific.
Then, we did the math and determined that we needed six spacers between the bearing and the slider post. Before mating the engine and transmission together for the final time, make sure the feed line and purge line are fully installed on the bearing. It is really difficult to install it once the engine and transmission are together.
The T56 has several electrical connections that are important. On the passenger-side front is the reverse light switch.
Move to the driver’s side, and below the shifter is the reverse lock-out solenoid. This must be connected to make reverse shifts easier. There is a special control box from American Powertrain that makes this safe; otherwise, you could end up hitting reverse by mistake, and that would be bad.
On the passenger-side rear below the shifter is the vehicle speed sensor for the electronic speedometer.
Converting an automatic car to manual requires a new set of pedals. Fortunately, the Camaro was available from the factory with a manual, so the pedals are available as salvage items. We bought these on eBay.
The two versions use different sensors, so switch the sensors from the original brake assembly to the new clutch and brake assembly. Don’t forget the clutch engagement sensor, which prevents the engine from starting without pressing the clutch.
We can’t just install the pedals; they have to be modified to operate the hydraulic clutch master cylinder. The original pedal used a stud, but this doesn’t work for us. The stud is pressed in, so removing it is tricky
Once the pin was suitably weakened, we were able to drive it out, leaving a large hole for the new mount.
The bushing allows the pedal to move freely without binding at all. It isn’t required to use a bushing, but it makes things move more easily.
First, we ground the head flush with the pedal arm, which exposed the actual diameter of the stud. Then we drilled out the stud pin.
This Tech Tip is From the Full Book, HOW TO SWAP GM LT-SERIES ENGINES INTO ALMOST ANYTHING . For a comprehensive guide on this entire subject you can visit this link:
LEARN MORE ABOUT THIS BOOK HERE
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We found this bushing in our parts bin. It fits the hole in the pedal perfectly and the bolt for the new clutch release arm.
Once bolted to the bushing, the rod end has plenty of clearance from the pedal and there is no chance of anything binding or hanging up.
For the sake of easier servicing, it is possible to change out the deep-shouldered bolt for a stud and cotter pin.
The bearing and rod mount to the pedal assembly as shown. This will all be removed so the assembly can be installed to the firewall.
American Powertrain’s Hydramax kit uses a Wilwood master cylinder, which is very compact and easy to work with. Anything larger than this simply will not fit under the brake booster in the third-gen Camaro. The hinged bracket makes it easy to get the clutch master where it needs to go.
We made some marks on the firewall to find the correct plane for the clutch rod. The more severe the angle, the harder the pedal effort will be.
We located the original cutout in the firewall padding for the clutch rod and made a pilot hole. There is a lot of guesswork here; it is important to get really close.
The final space had to allow for the movement of the clutch rod. It was more than we had anticipated—as evidenced by the long slot top and bottom of the mounting location.
Once the master cylinder was installed, we took some measurements from the rod to the clutch pedal mounting point. This gives us the total length of the rod.
Once the master cylinder was installed, we took some measurements from the rod to the clutch pedal mounting point. This gives us the total length of the rod.
Then we installed the rod to the master assembly and put it in the car. Don’t forget the jam nuts, you do not want this to come undone while you are driving.
As a side note, the 1993– 1997 T56s use an external clutch slave cylinder, while the later 1998-and-up units use an internal slave cylinder. The 1998-and-up T56 transmission is better suited for the Gen V LT-series engines with the correct bolt pattern and input shaft, but McLeod offers components that will adapt older T56 transmissions to the Gen V LT-series engines.
Early T56 transmissions (1993– 1999 LT1-compatible units) can be converted to mate to a 2014- and-up Gen V LT-series engine with a different input shaft. The input shaft is fairly simple to change.
While the T56 is traditionally the favored 6-speed manual gearbox, Tremec has replaced it with an updated version. Actually, there are two versions: the Super Magnum T56 (the best option available in the aftermarket and from Chevrolet Performance) and the TR6060.
The Super Magnum T56 is capable of managing 700 ft-lbs of torque. The gearing is set at 2.66, 1.78, 1.3, 1.00, 0.80, and 0.63 dual overdrive. This will hit your wallet pretty hard at more than $4,500 MSRP. However, it is the strongest 6-speed manual.
The TR6060 uses essentially the original T56 case with some beefier internals. Those larger guts take up a lot of room. Because the case stayed the same size, the extra room had to be taken from somewhere. Tremec’s solution was to use smaller synchronizers. The result leaves a little to be desired from the TR6060. The synchronizers are very fragile, and grinding the gears even once can wreck the synchro for that gear. Eventually, the synchro will be completely useless and the gears themselves will start burning up. Because of this, the TR6060 is not the best candidate for an LT swap. It will certainly function, but be aware that these transmissions are prone to failure.
If you select a TR6060 in your swap, make sure to use Redline D4 ATF transmission fluid or Royal Purple SynchroMax. These oils have been reported to reduce cold-shift grinding and provide better overall shifting feel for the TR6060.
There are several options for mounting the hydraulic clutch master cylinder. You can build a piecemeal kit yourself and either fabricate the mount or purchase a kit through American Powertrain, Detroit Speed, and several others. The first component is the firewall master cylinder mount. Then a line is run to the hydraulic clutch bearing. Finally, a fluid reservoir is mounted on the firewall.
On the Camaro built for this book, a hydraulic system from American Powertrain was used. This greatly simplified the installation of the Tremec T56 6-speed into the car. The Hydramax hydraulic bearing uses a stack-up of shims to set the depth of the bearing. This allows for a perfect mesh for the clutch diaphragm. The hydraulics are relatively simple to install. The kit comes with a Wilwood master cylinder and can be bolted directly to the firewall where the stock pushrod comes through. The supplied bracket for the master cylinder is adjustable for angle.
All hydraulic release bearings (HRB) require specific spacing between the bearing and the clutch, so measure for the air gap. This is fairly easy, although it is also really easy to get it wrong. We highly suggest doing this when the engine and transmission are out of the vehicle, because it is much easier that way.
First, install the clutch and diaphragm to the flywheel on the engine. Install the bellhousing and any spacers to the engine as well. Use a straightedge and a caliper (a measuring tape is not accurate enough) to measure the depth of the transmission mounting flange to the diaphragm fingers. Measure in three places (the fingers won’t all be at the same depth—there is a variance), and make a note of the measurements, call it Measurement A. Next, install the HRB and carrier to the transmission, then place the straightedge across the mounting flange on the transmission and measure from the flange to the bearing surface. Make note of this measurement, which we called B.
Then you need to do math. Sorry, there’s no avoiding it. Subtract Measurement B from Measurement A, then subtract an additional 0.150 inch (the air gap), and divide this by 0.090 inch (the thickness of the GM T56 spacers provided by American Powertrain). The result is how many spacers you need.
Measurement A – Measurement B – 0.150 = X / 0.090 = number of shims
A minimum of 0.1 inch and a maximum of 0.2-inch air gap is needed for the proper function of the HRB. We used six spacers on our installation with the 3/8-inch spacer plate for the L83. If you get it wrong, pull everything back out to check your work and measure several times.
If we had the right information and spacer in the beginning, this swap would have been a breeze, we wouldn’t have broken our block, and we would have been done in a couple of days. The most difficult part of the entire job was actually getting the transmission to mate to the L83. Even with a transmission jack and a lift, it was quite difficult because the transmission weighs so much. That is definitely a two- to three-man job with a lift. Doing this on the floor with jack stands would be challenging, so be prepared for a challenge if that is your plan. To bolt the original clutch pedal to the master cylinder pushrod, an adapter tab may be required. This tab must be fabri-cated and welded to the clutch pedal. The placement of this tab is absolutely critical. If the tab is too high, the pushrod will not fully engage. If it is placed too low, then the pedal will be hard to push. Using a piece of 3/16-inch-thick mild plate steel cut to 1 x 3.055 inches, the tab should be Z’d to 0.300 inches, beginning at the 1.712-inch mark. Once bent, the tab is drilled with a 3/8-inch hole, measured from the long side of the tab at 2.629 inches on center. The placement of the tab on the pedal is 1.769 inches from the center of the square hole at the top of the pedal, and it sits at 114 degrees from the pedal side to the top of the tab.
The tab should then be fully welded to the pedal arm. Trim off the small triangular-shaped section of the tab that overhangs the pedal on the underside. The clutch pushrod bolts to the tab via a 3/8-inch bolt and locknut.
Using the stock pushrod linkage hole will increase the pedal effort on the clutch. By raising the pick-up point on the pedal, the effort needed to disengage the clutch will be greatly reduced. This is called pedal ratio, which is the difference in length between the pivot (fulcrum) of the pedal to the pushrod hole (Y) and the fulcrum to the center of the brake pedal (X). A hydraulic master system should be between 5 and 7:1.
Consider this: a master cylinder with a 1-inch bore and a pedal ratio of 6:1 with 100 pounds of pedal pressure yields 600 pounds of pressure at the master cylinder. Cut that pedal ratio to 4:1, and the pressure at the master drops to just 400 pounds. That is a significant difference and increases effort by 33 percent. The stock hole can be used in some stock pedals, but it will most likely be more difficult to operate. Measuring the stock pedal ratio is a good idea; you would be surprised how different they can be from the optimal ratio.
It is possible to adapt the LT engine to use a manual clutch linkage. If you are installing an LT and manual transmission in a GM vehicle originally available with a manual clutch setup, then the linkage, clutch, Z-bar, and related components are needed. The Gen V LT-series blocks are not drilled for the Z-bar, which makes it difficult to adapt the LT engine to a manual linkage. Fabricating a simple bracket that locates off the bellhousing bolts and attaches to the Z-bar is the best solution.
The T56 uses a top-mounted shifter at the rear of the transmission, which creates a little compatibility issue for the stock console or shifter location in GM vehicles. This is easily rectified using a shifter relocator kit. As engine and transmission mounts differ, each shifter must be ordered individually. The T56 relocator shifter can move the shifter 1 to 4.1 inches forward. In addition, the shifter can be centered or offset to the left or right. If choosing to use the stock T56 shifter, it will be placed approximately 4 to 5 inches rearward from the stock location. The Viper T56 uses the forward-mounted shifter position, but this requires adapter plates for LT swaps.
Another popular manual swap is the Tremec TKO 500 or TKO 600. These 5-speed manual transmissions are very popular among the GM muscle builders and offer excellent performance. American Powertrain, as well as others, offers complete kits for installing the TKO (and T56) for most popular makes and models. These kits feature hydraulic clutches, bellhousing, and all the components to make the installation simple and easy. The TKO transmissions use a top-mounted shifter as well. To adapt these shifters to match up to the stock location, a Hurst
Blackjack shifter can reposition the shifter to the ideal location.
The TKO transmission does not fit quite as neatly under the body as the T56 does. The transmission fits some GM vehicles without modifications, but others (such as the very popular 1964–1972 GM A-Body platform) require a large section of the transmission tunnel be removed and replaced with a reshaped panel.
For reasons varying from nostalgia, economy, personal taste, simplicity, or originality, some builders prefer to keep the stock manual gearbox in their muscle car or truck when swapping in a Gen V LT-series engine. These swaps bolt up similar to the automatic transmissions, but they require a few specialized pieces. There are a couple of ways to do this swap as well.
The input shaft is too far from the crank with a stock bellhousing—the same situation as with the manual transmission. There are two ways to remedy this problem. The first and best way is to use a retrofit bellhousing and flywheel package. GM sells these components individually through its Chevrolet Performance dealers such as Pace Performance.
The retrofit bellhousing features thick-wall titanium-aluminum alloy construction, CNC machining including spot faced mounting holes, precision dowel-pin holes, and bores that yield a precise fit. This bellhousing bolts to all GM Gen V LT-series V-8 engines for the installation of the Muncie, T-10, Saginaw, Richmond Gear, Tremec TKO, Tremec T56-011, and other specially built transmissions. This bellhousing works with stock clutch linkage and hydraulic clutch actuators, and it includes a steel inspection cover and mounting hardware. It is designed to use a 168-tooth flywheel and standard GM starter. This bellhousing is lightweight, weighing only 15 pounds, and uses all factory linkage parts, including clutch forks, Z-bar, rubber dust boot, etc.
An original big-block Chevy manual bellhousing can also be used instead of buying a new one. The specific part needed is the 621 BBC bellhousing. This will fit most GM chassis and fit the LT engine without issue. The SBC and truck bellhousings have clearance issues. The flywheel will need to fit the LT and have a standard SBC clutch bolt pattern.
The clutch depends on which transmission is being used. GM transmissions use 10- and 26-spline input shafts, the early manuals (before 1971) typically have 10 splines, and the later units have 26 splines. That said, some other aftermarket manual transmissions have either 10 or 26 splines. The 26-spline shaft is more durable than a 10-spline shaft because it distributes the input load better. Make sure you have the right clutch for your transmission. Beyond that, any SBC clutch will work, provided the flywheel has the SBC clutch pattern.
If using the conversion flywheel, the stock-length (1.25 inches) throwout bearing works great. For stock flywheel and clutch combinations, an extended throwout bearing is required. General Motors offers a 1.75-inch length bearing (part number PT614037) for these applications. This will require using the stock mechanical pushrod clutch linkage.
Aftermarket versions of these parts in complete kit form are available from McLeod and Advance Adapters. These clutch kits are designed to adapt the Gen V LT-series engines to early-style GM manual transmissions, such as the M21/M22, SM420, SM465, and NV4500. Additionally, these kits allow the installation of Richmond Gear manual transmissions, such as the ROD 6-speed.
The Advance Adapter clutch kits typically include a custom flywheel, 11-mm flywheel bolts, an 11-inch Centerforce pressure plate and disc, a pilot bushing spacer, throw-out bearing, collector gasket, 10-mm bellhousing bolts, 10-mm lock washers, and XRP dowel bolts. If you want to assemble your own parts, the key is to match the flywheel and the clutch to the engine while making sure the splines on the clutch disc match the transmission.
Written by Jefferson Bryant and republished with permission of CarTech Inc
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