FAQ: Manual Transmission Conversion

“That crisp, six-speed stick really wakes up the car”

AutoWeek Magazine, May 15, 2017

So you want to convert to a manual transmission, do ya? Well you’ve come to the right spot – within the right place – because this here is our comprehensive FAQ on all the things involved with the conversion.

Converting your vehicle from auto to manual may be easy to do or very difficult to do, but the end result is always astonishingly fun.

We’ve summarized the most popular questions we get – along with our best answers – right here. Our goal is to inform, and if you have additional questions we’d love to hear from you – please contact us here.

Request a Quote

How?

We can convert from an automatic transmission to a manual transmission through some parts swapping – if the parts exist. If they don’t exist, one can attempt to repurpose existing parts or fabricate new from scratch. Generically, the steps included in a manual conversion include:

Removal: Remove auto transmission and related components (bellhousing, torque converter, flywheel). This will require also removing your driveshaft and transmission crossmember.
Installation: Install manual transmission and related components (bellhousing flywheel, clutch, clutch release mechanism). This will require also installing a driveshaft and transmission crossmember. Now before you start thinking this whole job is easy, the driveshaft and transmission crossmember you’re installing are most likely different from the ones you removed. You’ll probably also have to cut a hole in your floor for the new shifter to poke through.
Grow a Third Pedal: Install a clutch pedal, and hook it up / make it work.

Chances are you won’t be done that easily. You may also have to address:

Check Engine Light: Reprogram your Engine Control Module (ECM), or Powertrain Control Module (PCM) if so equipped. If you’ve got a computer in there, it’s not gonna be happy without the automatic transmission reporting for duty. Just how unhappy can be correlated with age: the newer the car, means the newer the computer, means the more unhappy it will be. Older cars with a computer for a brain may just shrug with the auto gone, or maybe the computer will just yawn. But not those new ones, no sir or ma’am. Some of those new ones will even have a body control module (BCM) that’s ticked off or at the very least slightly confused.
Drivability: You may have to change your final drive ratio, aka your rear gear ratio in a RWD vehicle. Whether or not you need to do this depends primarily on the gear ratios in your manual transmission as well as your current final drive ratio; some transmissions, like the Tremec T56, are geared on the taller side, so a “lower” final drive ratio helps to compensate and keep your engine in the power zone throughout normal driving. And normal is a relative term of course; since you’re on our website, normal means fun. For an explanation of taller vs lower see “Final Drive Ratio / Rear Gears” below.
Speedometer: Do something to get your speedometer to read accurately. Your current speedometer, auto trans, and new manual trans are each either electrically or mechanically operated. We’ll save the various potential issues for another time, but in the meantime there are a variety of options to get your speedo accurate and with the advent of GPS speedometers many people simply go that route. Pun intended.

What if Parts “Don’t Exist”?

Well, this is where come in! We planted the seed for Three Pedals back in 1996 when we created a clutch pedal for a 1991 Chevy Caprice cop car with a 1994 Camaro LT1 engine and T56 6 speed, and today we design and manufacture race-ready, street-friendly pedal assemblies that are engineered to fit specific applications for an OEM-quality feel.

If your vehicle was originally available with a manual transmission, the factory parts are generally a good starting point, unless these do not meet your needs.

Now back to our parts – we only have so many pedal designs out there, but we’re always working on more. If you’re looking for one that you can’t find we’d love to hear from you.

Naturally, other companies may have the parts you need, and even more naturally, you and some friends could hot rod up some parts.

Why?

With regards to why to switch from an auto trans to a manual trans, we’re inclined to reply to this question with “Get off our website!” But, we are here to inform, not to judge.

So, get off our website, and go drive a car with a manual transmission. Ask a friend, take a class, just do it.

If you’ve driven a manual and are still asking “Why?,” we can comfortably say that we’ve ticked the box and have informed you, so now please get off our website already before we judge you. You’ll find some kindred spirits over here.

Now factually speaking, holding all other variables constant, changing from an automatic transmission to a manual transmission should reduce what is known as parasitic loss – the power that is lost between your engine and drive wheels. Turning all that stuff takes up some energy. Manual transmission cars generally lose 12-14% of engine power through parasitic loss, whereas automatic transmission cars generally lose 16-18%. So, you can pick up ~4% more power just by going manual — that’s not bad! But that’s not why most people switch from auto to manual.

If you were to query our customers, I think they’d answer the “why?” question with the following, ranked in order of popularity:

It’s so much more fun with a manual
The manual is a much more durable transmission and I’ve already rebuilt my automatic X number of times

With regards to switching from an older manual trans to a modern manual trans, the most common answers to “why?” are:

Add overdrive (see below) for increased fuel economy and overall drivability
Increased strength – modern manual transmissions can generally handle more power than their older counterparts
Improved drivability – modern manual transmissions tend to have much more sporty shifter mechanisms, which translate into a more direct feeling and shorter, more predictable shift lever throws.

Who?

We offer installation on everything we sell, so of course we can turn the wrenches for you. We are honored to have had the opportunity to work on cars that come to us from all over the country, including from about as far away as you can get while staying in the US — California (we’re in Virginia). If you’re not within driving distance, we can help you to arrange transport. Please contact us for a quote.

We design our pedals and conversion kits to be something the average home mechanic can pull off in their home garage, so long as you have certain tools. Certain steps are much easier with a second set of hands, all the more so if they’re an experienced set of hands that are also attached to a friend.

When we ship our parts out, they’re at times installed by a shop closer to the customer. Your favorite mechanic may be willing to install our parts, and we can share our step-by-step instructions to put their minds at ease. Please contact us if you need a local referral.

Is it legal?

So long as your end product has a functioning speedometer and reverse lights, most states don’t pay any attention to whether your car has an automatic or manual transmission. In our 20+ years doing conversions, we have yet to hear of a state that didn’t allow such a conversion.

Changing your engine is a different story, not covered in this FAQ. Request a quote for specific advice on your application.

What’s so Great about Overdrive?

We like overdrive, and most people agree. When making the effort to convert to a manual it makes sense to also go with a transmission that offers overdrive. Overdrive became popular in manual transmissions in the ‘70s, and by the late ‘80s pretty much every automatic and manual available in new cars had overdrive. Overdrive reduces your engine’s RPM at higher vehicle speeds, like on the highway, and therefore overdrive generally helps to increase MPG. In racier setups, for example with a more aggressive final drive ratio, overdrive can make the difference between a livable freeway cruiser and something you wouldn’t ever want to take on a long trip.

Getting a little technical, overdrive means that the revolutions per minute (RPM) of your transmission output shaft are greater than the RPM of your engine. Since your driveshaft is attached to your output shaft (at least on a RWD vehicle), your driveshaft speed = output shaft speed.

From a practical standpoint, overdrive means that if we hold all other variables constant and just add overdrive to an older transmission, at highway speeds (55 MPH+) your engine will now have lower RPMs, which makes highway cruising more fuel efficient and quieter.

To illustrate using a T56 6 speed:

- 1^st through 3^rd gears are non-overdrive, meaning they slow down the engine RPM which has the effect of multiplying torque
- 4^th gear is direct drive, meaning output shaft RPM = engine RPM
- 5^th and 6^th are both overdrive gears, with 6^th being “taller” than 5^th, just like 2^nd gear is taller than 1^st gear.

Does My Engine Have to Change? / What if I Want to Change My Engine?

Many manual conversions are done with the exact same engine as the car had with the automatic transmission. There are a few pieces that attach to the engine that change with a manual conversion, but in most cases there is no need to change the engine itself.

That being said, many people do change the engine at the same time – “drivetrain swap” sums it up. Regardless of what your plan is with your engine, as long as you have a plan we can help you find the right parts to make it work.

Newer transmissions are frequently easier to connect to newer engines, but sometimes it makes no difference. When it comes to connecting things that were never connected by your car manufacturer, we have a wide selection of adapter bellhousings and we can fit a lot of things, and we know who to talk to in order to get a custom bellhousing made up, so hit us up with your needs.a

Which Transmission Do I Use?

Which transmission to choose is a question we deal with quite often. If you’re not sure which way to go, we’d love to start the conversation with you. In the meantime, we summarize our thoughts here.

As with any modifications to your vehicle, we like to start with the overall vision you have, and for this purpose we come at it with two questions: (1) how much power are you making or do you plan to ultimately make, and (2) how are you planning to drive your vehicle – street, drag race, road race, autocross, or a combination of these? From there we can make suggestions and fine-tune as needed based on budget and other considerations.

Things to consider when selecting a transmission:

Power level – generally, manual transmission capacity is rated in terms of torque capacity, for example a new Tremec T56 Magnum is rated to handle an engine putting out 700 lb/ft of torque. We are now touching on the tip of a different iceberg, so more on this in a separate tech article.
Overdrive – see above.
Gearing – need to change final drive ratio or no?
Physical size – will it fit in your car or will the trans tunnel / floorpan need clearancing or patching?
Shifter location – will it clear obstacles and can you reach it? Bench seats can be a challenge, but most combinations can be figured out.
Cost – cost is an ever-present consideration of course. We routinely source new, used, and rebuilt components for customers and we can help you find the best way to achieve your goals within your budget.

Sup With Transmission Crossmembers?

Your transmission crossmember, aka transmission support, is a removable piece that supports the tail-end of your transmission. Manual transmissions tend to be shaped differently than automatic transmissions, hence the frequent need for a different crossmember.

Click here for our transmission crossmember products.

The crossmember must support the weight of a part of the drivetrain and must withstand the forces acting upon it. When you accelerate briskly in a rear-wheel drive car you may notice your shifter rising, which means your manual transmission is lifting into the floor – if so that is either your crossmember flexing and/or the rubber or polyurethane mount deflecting. Ideally your crossmember does not flex – ours don’t! – but many do. Crossmember flex means wasted energy and reduced responsiveness.

Crossmembers are ideally tucked up as high as possible for ground clearance and exhaust clearance, but at the proper height of course to maintain the proper driveline angle.

If you’ve changed your engine it is possible that you’ve also now moved the rear face of the block, which would then impact your transmission crossmember location.

We design and manufacturer our crossmembers for certain applications, and we carry a full line of crossmembers to help you fit just about any manual transmission into just about any vehicle.

Where Do You Find a Clutch Pedal?

The astute among you sense that we’re getting to one of our specialties here.

If your car was available with a manual transmission, then generally speaking it’s easiest to start with that clutch pedal assembly. Cars from the ‘70s/‘80s and earlier (and even some into the ‘00s) usually have a mechanical clutch linkage, so if you want to run hydraulics you’ll need to adapt the hydraulic master cylinder to work with your pedal assembly. See “Hydraulic vs. Mechanical” below.

If your car was never available with a manual transmission, we of course offer some options for you. If our products aren’t what you are looking for, or need something beyond what we offer, you can adapt a universal style pedal from Wilwood or Tilton, or adapt a factory setup designed for a different application. There are some key geometric variables to get right, and beyond that there are ergonomic, structural strength, and hydraulic fluid routing concerns, but all are solvable with some ingenuity, a drill, a welder, some duct tape, and a pinch or heavy dollop of JB Weld. If it takes more than 1 package of JB Weld you should start over.

Now, if you’re starting with a factory clutch pedal from the ~‘80’s or earlier, it probably won’t have all the electronic bells and whistles you’ve come to expect, see “Clutch Pedal Electronics” below.

But What About Them Ergonomics Man?

When you hand your keys to a friend so they can test drive your car, you don’t want to hear yourself saying things like, “remember that, in my car, you have to move your left foot a little to the right and your right foot has to come up a bit.” If you do, then you obviously didn’t use one of our clutch pedals.

Clutch pedal ergonomics are important, and we really sweat these details when designing our parts and retrofitting existing parts. Our clutch pedals are designed to be race-ready and street-friendly. Race-ready means our pedals are durable; precision construction and tested designs that stand up to the rigors of racing. Street-friendly means that your left leg will not be punished on the street, so no need to add leg day to your gym routine.

There are several considerations to getting the ergonomics just right:

Lateral spacing: How far is it from the brake pedal? Measuring center-to-center, modern cars like the latest Chevy Camaro have a clutch-to-brake spacing of approximately 5”.
Fore-aft spacing: Is the clutch pedal higher than the brake pedal or equal? We generally design them to be equal but many cars come from the factory with a higher clutch pedal.
Pedal stroke: The amount the clutch pedal arm needs to travel can be expressed in terms of degrees of rotation – more stroke means your leg needs to travel farther for each gear change. The amount of stroke is related to the pedal leverage ratio and other mechanical details.
Pedal leverage ratio: The length of the clutch pedal arm divided by the distance from the clutch pedal arm pivot to the master cylinder pushrod pivot. With a hydraulic clutch a leverage ratio of 6:1 is the common wisdom for a streetable setup. For example, if the clutch pedal arm is 12” in length, the pivot point for the hydraulic master cylinder would be 2” from the pedal arm pivot point.
- A bigger leverage ratio:
  - Reduces the effort required to press the clutch pedal
  - Requires more pedal travel, or “pedal stroke”
- A smaller leverage ratio:
  - Increases pedal effort
  - Reduces pedal stroke, and if you’re good it makes gear changes faster

Brake pedal: Next up we consider the location of the brake pedal foot pad. We are big fans of using the “heel-and-toe” technique for downshifting, so all of our pedal assemblies are designed to set you up just right for that, whether you have big or small feet. This illustration from GM’s crate engine guide offers specifics for the location of the brake pedal relative to the accelerator pedal. And we assume “tunner” refers to the floor tunnel. We couldn’t make this stuff up, we promise.

What is a Clutch Release Mechanism?

To divide the world of clutch release mechanisms, hydraulic vs. mechanical actuation is a nice line.

We are using this broad term to include clutch forks, slave cylinders, throwout bearings, and hydraulic release bearings, as well as other related devices that we have yet to identify right here. Hydraulic release bearings are also referred to as concentric slave cylinders and hydraulic throwout bearings, but we like HRB.

What’s the Difference Between Hydraulic and Mechanical Clutches?

To get to the punchline, hydraulics are where it’s at.

Modern hydraulic clutch release systems make driving a manual transmission car much more enjoyable – particularly on the street – as compared to mechanical clutch release systems. Note that not all hydraulic systems are well-designed – the benefits we are about to list refer only to the well-designed systems, like the setups we spec with our pedals. We have seen many poorly-designed setups and those don’t count.

All of our pedal designs utilize hydraulic systems only for the following benefits over a mechanical clutch:

Superior clutch pedal feel: Hydraulic circuits are closed, so any feedback from the clutch mechanism is felt in the pedal. Just like with brakes, experienced drivers can detect feedback via the pedal, making engagement and disengagement more predictable. Additionally, any issues are also more readily communicated to the driver.
Reduced Pedal Effort: This is part of superior feel, and in particular, if we hold all other variables constant, just changing from mechanical to hydraulic will usually take less pedal pressure to operate. In other words, your left leg will not be nearly as punished with a well-designed hydraulic system.
No Maintenance: Just like your hydraulic disc brakes, hydraulic clutch systems self-adjust as friction material wears down so there is no maintenance required between clutch changes. With your brakes, the pads are a friction material wear component; with your clutch, the clutch disc friction material wears down. Mechanical clutch systems require periodic adjustment in order to take up the slack that occurs as the friction material wears down.

Now the down sides, or perceived down sides of a hydraulic system as compared to a mechanical system:

Retrofitting Can Be Challenging: There are key geometric relationships that have to be spot-on in order for things to work well over the long haul. If a master cylinder is mounted to something that is not rigid, the repeated cycling of the clutch pedal can prematurely cause master cylinder failure. And we mean way prematurely.
Bleeding Hydraulics: This scares most people. But it shouldn’t. We will be publishing tech articles and videos that will ideally eliminate any fears you have.
Leaks Can Be Tough to Find: Hydraulic clutch systems operate at approximately 1,200 PSI. This is in contrast to an LS fuel injection system which runs at 58 PSI. The required hoses and fittings must be able to withstand this pressure, and the tiniest of leaks will be found by some of those 1,200 PSI. Stainless braided hoses with a PTFE liner, as required for this level of pressure, are easily kinked and perforated. Further, any gunk on an AN fitting flare can prevent the male and female flare cones from properly seating.

Cars from the ‘80s and earlier (and even some into the 00’s) generally have a mechanical clutch linkage, so if you want to run hydraulics you’ll need to adapt the hydraulic master cylinder to work with your pedal assembly.

We are using the term “mechanical” to refer to z-bar setups as well as the cable-actuated setups found on relatively recent Ford Mustangs.

If you want to retain a z-bar setup, you may have issues if you change the engine as the z-bar generally rotates on a stud connected to your engine, so any change there creates a problem to solve.

Cable actuated clutches can be easier to repurpose, but they’re still mechanical, so …

What are the Components of a Hydraulic Clutch System?

Listed below are the components of a hydraulic clutch system.

The table below compares component details between Hydraulic Release Bearing setups and Slave Cylinder and Clutch Fork setups:

Hydraulic Clutch System Primary Components

Clutch Pedals Have Electronics?

Here is a rundown of the key electrical things that a clutch pedal might elicit.

Neutral safety switch: Car won’t start unless you’ve got the clutch pedal depressed
Cruise control cancel switch: If you’ve got cruise control, you want any clutch pedal movement to automatically cancel the cruise control, just as any brake pedal movement does
Clutch position sensor: Newer cars tend to consolidate these two functions into one clutch position sensor switch, which informs the ECU of where in the stroke the clutch pedal is. With that info and some logic, the ECU & BCM can take it from there and cover the above 2 functions in its sleep. The clutch position sensor data can also be analyzed and compared with things like expected and actual transmission rotational speed, so some of these new cars will actually warn drivers to stop riding the clutch pedal. There are some cooler things it can do, but they’re hard to retrofit.

Click here for our clutch pedal electronics products.

For Whom the Bellhousing Tolls?

The bellhousing connects your transmission to your engine and lines up your transmission input shaft with your crankshaft. Fore-aft spacing of the bellhousing must position your transmission close enough for the input shaft to be supported by the pilot bushing or bearing in your crankshaft but not so close as to cause interference.

Click here for our bellhousing products.

We’re never really sure if it’s bellhousing or bell housing, but we go with bellhousing. Back to the important stuff, there are a ton of factory and aftermarket bellhousings out there, so many engine-transmission combinations are figured out already. If you’re trying an unusual combination of transmission and engine, it’s quite possible that one doesn’t exist, and in that case you could make your own or get a custom one built by a specialist company. Contact us if you need help obtaining a custom bellhousing.

When installing a bellhousing, a frequently overlooked step is to ensure that the bellhousing aligns the transmission input shaft perfectly concentric with the crankshaft – this is often referred to as bellhousing runout. A dial indicator on a magnetic base is used to verify concentricity. Offset dowel pins are available to correct relatively minor variances.

We recently helped Car Craft Magazine to document how to measure and remedy bellhousing runout – click here for the article.

The flatness of your bellhousing is very important. By this we mean the two surfaces of the bellhousing must be perfectly parallel to each other. If buying a used bellhousing, if it looks like it was damaged at all, even if it was “repaired”, think twice.

If you want a bomb-proof bellhousing, look for SFI 6.1 certification. These bellhousings utilize a clamshell design and are certified to be able to contain a mini-explosion. Specifically, “A 13 inch (33cm) diameter, 30 pound (13.6kg) or equivalent energy flywheel (steel, cast iron or comparable) with ring gear shall be used. The flywheel shall be modified to explode (in six pieces of approximate equal size) between 8,000 and 9,000 revolutions per minute (rpm)… The bellhousing shall be mounted to the fixture as it would be mounted in service using the proper size and number of fasteners as designated by the certifying manufacturer. The flywheel shall be driven to a speed between 8,000 and 9,000 rpm until it explodes inside the bellhousing.” – SFI 6.1 Specification

Are Flywheels as Fun as They Sound?

They’re fun, but they’re also quite serious. Flywheels must be properly matched to your engine and of course must be compatible with your desired clutch and transmission.

If you’re recycling a used flywheel, it is generally recommended to have the flywheel resurfaced before mating it with a new clutch. The

Flywheels have a flat friction surface that engages with one side of the clutch disc friction material, and this flywheel surface can wear down unevenly through use. Many flywheels can be resurfaced so long as the minimum thickness does not fall below specification. Typically, flywheels are resurfaced via a process known as Blanchard grinding, also known as rotary surface grinding, and a good surface is key for good friction.

Engines can be neutral balanced (aka internally balanced) or externally balanced. This is critical to get right when buying your flywheel. If your engine is neutrally balanced, your flywheel will also be neutrally balanced, like your wheel and tire. If your engine is externally balanced your flywheel will have a counter-weight that is often visible, either as a bolt-in piece of metal or a lump in the casting.

Flywheels are generally made from steel, though aluminum versions are often easy to find. Aluminum flywheels usually have a steel friction surface insert that is replaceable. Aluminum offers lighter weight which allows your engine to rev more freely and quickly. However, for most street cars, the advantages of a lighter weight aluminum flywheel are outweighed by more sluggish acceleration and responsiveness at lower RPMs as the extra weight of a steel flywheel gives the engine additional rotational momentum.

Flywheels frequently include a starter ring gear, so your starter and flywheel must be suitably matched. Small block Chevy engines (’55 – ’97) generally use either a 153 tooth or 168 tooth flywheel, and starters are made for both sizes.

What Parts Are in a Clutch?

The term “clutch play” apparently didn’t come about from manual transmission clutches, but it applies here! Without a good clutch, you’re not even spinning your wheels, and that’s the problem. Your clutch should transmit all of your engine’s rotational energy into rotating your transmission input shaft. Anything less than 100% means your clutch is slipping and that’s not good.

There are a wide variety of clutches available and this FAQ is not meant to detail those. Instead, we’ll keep it focused on the key points when converting to a manual.

And when we say “clutch” we’re referring to the collection of parts that are normally sold as an assembly: pressure plate, clutch disc (or discs), and sometimes a release bearing.

Your clutch must be sized properly for your engine, flywheel, and transmission; clutches are sometimes listed by diameter of the clutch disc. Your flywheel and clutch must also fit inside your bellhousing. The clutch disc generally has a splined hub and both the diameter and spline count must match your transmission’s input shaft. By now you know we prefer hydraulic clutch actuation systems, but in any case, your release mechanism must be considered as well. So please consider all of these parts as a package and not as stand-alone parts.

Dual disc clutches are popular these days, with many new cars coming equipped with twin discs from the factory. However, the choice of single disc, dual disc, or triple disc (or more) is not covered here, but of course we can guide you if you request a quote.

Your engine, transmission, and driving style will guide the options available to you, and in most cases you’ll have many options. For example, a push clutch vs a pull clutch might be one option based on your combination. In general, most clutches we deal with these days are the push style, and with hydraulic actuation systems, this generally means you’ve got a hydraulic release bearing mounted on the front of your transmission. Pull styles must use a clutch fork and are usually actuated by an externally mounted slave cylinder. We don’t come up with these names folks, we just tell it like it is.

Clutch material is another important factor, with popular choices including organic material and semi-metallic material. Organic material tends to be more street friendly with smooth engagement. However, high and frequent heat cycles – like racing – can quickly destroy organic material. For more extreme duty we recommend semi-metallic material, which takes heat much better. However, semi-metallic can be grabbier and may produce chatter on engagement. Some clutches look for the best of both worlds, with one side of the clutch disc organic and the other semi-metallic. Please contact us for specific advice about your application.

What is the Pilot Bushing or Pilot Bearing?

The input shaft of your transmission will nestle inside a bushing or bearing located in the back of your crankshaft, called the pilot bushing or pilot bearing. We’re going to call them all “pilot bushings” here. Remember how we recommended you ensure your bellhousing keeps the input shaft concentric with the crankshaft? Well, this highlights the need to do so. If the parts are not concentric, the input shaft will not neatly fit into the pilot bushing, and let’s just say you’ll have some problems. If it’s close enough to jam the input shaft in, you’ll still have problems so just cause it fits it doesn’t mean you’ll be acquitted of transmission destruction.

When converting from auto to manual, your crankshaft may or may not be machined to accept a pilot bushing; if it is machined, tapping the appropriate one in is generally straight forward. If it is not machined to accept a pilot bushing, you’ll have to remove your crankshaft to have it machined. That gets complicated quickly!

As far as bushing vs. bearing, some applications do offer roller style bearings, and we have heard that these are limited to about 6,000 RPM, so we tend to go with a bronze bushing. Request a quote for specific advice on your application.

What About a Shifter?

Most of you are thinking of a manual swap with a floor shifter, but we can’t assume none of you are dreaming about a column shifted manual transmission. But for now, we’ll stick to covering the floor shifters.

Click here for our shift lever selection.

Your choice of transmission will dictate your shifter options. The location of your shifter and shift lever are definitely something to consider when converting to a manual transmission. If you’ve got a bench seat, be sure to measure carefully, else you may have a shift lever attempting to sprout up through your seat. At times, merely changing shifters and/or shift levers can alleviate concerns like these.

Newer transmissions tend to be bigger and longer due to having more gears. And many newer cars position the driver farther behind the engine and transmission, requiring a longer shifter mechanism in order to put the shift lever at the driver’s hand.

Regardless of where your shifter mechanism is located, the shift lever can generally be located several inches fore or aft and several inches left or right in order to get just the right position. Various shift lever shapes also help to fit many applications. Request a quote for specific recommendations.

The Tremec T56 Magnum offers three different shifter mechanism locations giving you almost 8” of fore/aft movement via shifter location alone. We are using the forward most shifter location with the bench seat in our station wagon, Shaken & Stirred, along with a shift lever we whipped up just for the task.

As far as shifter feel, most factory shifters prioritize minimizing noise, vibration and harshness (“NVH”) over crisp feel, so if you’re on our website, chances are you’re already thinking of a short throw shifter. The shorter throw can be achieved by changing the mechanical ratio of the shift mechanism and/or by changing the length of the shift lever. In any case, aftermarket shifters tend to have a firmer, more direct feel and less sloppiness, sending the NVH guys into fits.

Do I Need to Drill Holes in My Car?

When adding a clutch pedal to your automatic car inevitably you’ll have to pass something or somethings through your firewall, which means making a new hole or holes in your firewall. Our pedals are designed to use an included rubber seal that affixes to the firewall. This allows hoses to pass through the firewall while the seal stretches to allow hose ends to pass through, then snugs up against the hose itself to keep hot air and smells out of your cabin, not to mention moisture.

You’ll also need a hole for your shifter to come into reach. For most cars this means you’ll be cutting a hole in your floor, and of course just where you cut it is important. Bench seats and existing center consoles are some things to consider – ideally before you get all your parts. You’ll also need a boot to seal the cabin from the elements and we offer several different sizes. Please contact us for help in selecting the right parts for your application.

If your car was designed for both manual and automatic transmissions from the factory, there may be a pre-stamped knockout for the floor shifter, it may use the automatic shifter hole, or there may be a separate sheetmetal hump that gets screwed into the floor.

Do I Need to Change My Driveshaft?

Sticking with rear wheel drive vehicles for the moment, your transmission finishes its work by spinning its output shaft, aka main shaft, and handing things off to the driveshaft. When changing to a manual transmission, it may be possible to retain your existing driveshaft, but more often than not you’ll need to change how the driveshaft connects to the transmission and the length of the driveshaft. Further, changing your final drive ratio to a lower gear ratio (a larger number) may also require that your driveshaft be balanced to a higher critical speed in order to avoid vibrations. “Critical speed” is the speed at which a spinning driveshaft will become unstable. If you’ve ever driven a car with a vibrating – and unstable – driveshaft, you know it’s a feeling that makes you want to get out of the car right the f now.

Driveshafts are often assemblies comprised of a section of tube with specific ends welded on; these ends each accept a joint. The joint on the transmission side is generally paired with a yoke that interfaces with your transmission. The joint on the rear axle side interfaces with your rear gears, usually by joining to the pinion yoke.

It’s worth mentioning that driveshafts are important – all your power is transmitted through a tube of metal or carbon fiber. If you’ve got a 0.50 overdrive ratio, in that gear your driveshaft RPM is twice your engine RPM. Problems with your driveshaft will likely make themselves known, but by then it can be too late, so be sure to have your driveshaft professionally inspected if you’re not sure of its condition.

The driveshaft connects to the transmission by one of several methods. A splined slip yoke is very common with solid axle cars, while a constant velocity (“CV”) joint and fixed yoke are common with independent rear suspension. In any case, your transmission will likely dictate how it wants to interact with your driveshaft.

A driveshaft safety loop is always a good idea to add, and we offer many designed for specific applications. A safety loop contains the driveshaft in the event of a tube or joint failure and is required in certain racing classes.

Driveshafts are generally available in steel, aluminum, or carbon fiber. Request a quote for specific advice on your application.

Do I Need Taller or Lower or Shorter or Higher Gears?

When you change your transmission, you are probably changing and/or adding at least one new gear ratio. If you haven’t yet considered your final drive ratio, you will quickly learn that it’s a key component of the whole system.

Sticking with rear wheel drive vehicles, the typical rear gear setup is a matched set of two gears: a pinion gear and a ring gear. The gear ratio is calculated as the number of ring gear teeth divided by the number of pinion gear teeth. For example, a 4.10:1 ratio has a ring gear with 41 teeth and a pinion gear with 10 teeth, so 41 divided by 10 = 4.10 ratio. Note that you should not mix and match ring and pinion gears across sets, as they are matched to each other.

The larger the number, the “lower” the ratio. This is because to figure out your rear wheel RPM, you take your driveshaft RPM and divide by your ratio, for example 4.10. A larger ratio numerically – for example 4.56 – results in lower rear wheel RPM for the same driveshaft RPM, as compared to 4.10 gears. So when people say a gear is lower or taller, usually they’re referring to the resulting wheel speed, so 4.56 is a lower gear ratio than 4.10 but a larger number numerically.

We’ll make a video to better explain all this – one day.

Do I need to Reprogram?

If your engine is controlled by a computer, it may or may not care if you remove your automatic transmission. The newer the computer, the more likely it is to care. In fact, the really new ones will become downright moody without the automatic – unless it’s reprogrammed to forget the past.

Other than telling the computer to stop looking for the automatic – get over it man, it ain’t coming back – there are two things that may be of interest with your new manual transmission, and these are addressed above in a little more detail.

Check engine light
Speedometer accuracy

Last but not least, all else being equal, an engine with a manual transmission can have a slightly more aggressive ignition timing curve which should produce more power. Leave this to the pro’s though.

What Questions Do You Still Have?

We love hearing people’s questions so if we haven’t addressed all of your questions please feel free to contact us.

FAQ: Manual Transmission Conversion

“That crisp, six-speed stick really wakes up the car”

Interesting links

Pages

Categories